I have really been looking at ways to use my extra 900 watts /hour (most of the day) from my solar array. My array is oversized. I knew that when I set it up. But now I dont want be pouring unused power in the dirt, so to speak.
I want to convert my AC water heater tank to a split solar DC on bottom, AC grid connection on top of the 40 gallon tank for quick recovery and having a bit of hot water always, and AC from inverter or DC direct from Array/battery for the bottom as a Diversion Load.
I have looked a lot of threads about Waste Not thru AUX 1 (have a WBJ on Aux 2) .... but it seems complicated and most threads act like it is difficult to program so it works correctly. I read nearly every thread I could google on this site (what ever happened to Chris Olson anyway - seemed to have disappeared around 2015). The "Dummies" thread seemed to end without a final resolution. But from what I could find, to use Aux 1 I would need:
1. a DC 24v Element (found one rated for 900 watts)
2. an SSR (but I never could find any clear diagrams on how to even wire that in to the Classic 150)
3. and how would I control temp? Would I need a DC thermostat? or could I continue to use the existing AC stat? seems there is disagreement here. Some say it will burst into flames or whatever.
4. would the Classic control the volts so I would not be exceeding the 24v limit to the element (I would connect it to the element from the busbar that also connects the Classic to the battery for charging I would assume)
5. but then there is the whole "tension" (??) during the absorb and float stages I have read about when using AUX 1
So was thinking to myself ... I have a SW 4024 inverter that is roughly 1700 watts continuous on L1 and L2 for a total of 3400 watts. I am only using (and would ever use in my present config) about 2400 total on both legs. And my well pump is almost half of that on L2.
So why even bother with going DC to the water heater as a Dump. Just do it thru the inverter on L1 off the inverter to a single 120v 1000 watt lower element still keeping the upper element connected to the AC line for back up and quick nite us.
1. I could still use the existing thermostat
2. I would have to resize the lower element ... but easier as AC elements are available at the local hardware store
3. The Classic would manage needs based on what is going on with the system: ie. charging or dumping and I would not have interruptions and for Absorb and Float
3. Then use a timer to only let the DC element run during the day to avoid it running at nite and discharging the battery too much. (or would a timer not even be need if I could us an SSR on AUX 1 to turn the AC supply off the the element at nite or when no solar power is available - options?? )
4. I con to this idea would be, on cloudy days, even with a timer, the once the thermostat turned on the element, I would be draining the battery ... unless it could be somehow controlled thru AUX 1 (which might lead me back to a DC element anyway)
Please give me your thoughts, Pros and Cons, or a better solution. I need to do something with the 900 watts I am wasting from the array. And yes I have read every thing I could find here and on other site. Nothing is quite clear to me yet. I guess DC is probably the better route thru AUX 1 ... but I do not want to burn the house down or turn my tub into a death trap either. I do not know how to control DC temp thru the day. Nor do I want to have absorb or float bouncing around all the time.
EDIT: May 26, 2018 - Quick Reference Guide to this ThreadLinks to other threads, forums, papers and PDFs discussing SSR usage etc - Post #38 (http://midniteftp.com/forum/index.php?topic=3881.msg37894#msg37894)
My original early setup with pics. The next few comments after discuss settings - Post #40 (http://midniteftp.com/forum/index.php?topic=3881.msg37927#msg37927)
Final Design and Links to SSR Options and with settings for SOC Hi and discussion following - Post #48 (http://midniteftp.com/forum/index.php?topic=3881.msg38025#msg38025)
Waste Not Hi turns the Load on/off too much at the end of the day - Post #50 (http://midniteftp.com/forum/index.php?topic=3881.msg38477#msg38477)
My Current AC Element and Settings Using Waste Not Hi with better success - Post #68 (http://midniteftp.com/forum/index.php?topic=3881.msg39824#msg39824)
Other Users Settings - Post #41 (http://midniteftp.com/forum/index.php?topic=3881.msg37978#msg37978) Post #69 (http://midniteftp.com/forum/index.php?topic=3881.msg39825#msg39825)
AC is certainly the easiest way to do it since then you can use the water heater as is and it's built in thermostat.
But it is not the most efficient way if that matters because you are heating up both the controller and inverter to make power to the heating element.
As far as controlling the AC input to the water heater seems like you could do that fairly well using AUX contact into AC SSR .
The thing you need to know is you have to put diode protection into the proper place - and that was talked about in some of those other discussions you looked up.
Maybe if you don't look at the extra power as lost - it is just not utilized that is a better perspective. It isn't like it is a bucket of water that is overflowing - it is just not filling up.
Seems like the best way to do the water heating is to put up a dedicated string of panels in series and heat the water that way and you don't have to worry about battery issues. You just need a DC control circuit to turn the power off when water gets up to temperature. I haven't tried it myself yet - but yes I have read enough that says the built in thermostats on water heaters are designed for AC and won't take interrupting DC power. So you need to rig up a DC SSR to do that with appropriate diode. They say you don't need diode for resistive loads but then I have read that the wiring makes something of an inductive load so that is why it is better to use them .
I haven't used any of the above schemes myself so am just talking from reading posts on here like you have. This year I heated water simply by replacing bottom heating element with 120v element and manually unplugging it when I didn't want it on. I let the built in thermostat turn it off if water got hot enough . Never got around to controlling it with SSR via Aux contact yet.
Read Pete's article on solar hot water heating with PV
midniteftp.com/forum/index.php?action=dlattach;topic=3457.0;attach=5306
did you read this thread too ?
http://midniteftp.com/forum/index.php?topic=3666.0
Larry
I must be missing something here, so please explain why this would not work. To use AC power not DC, to utilize excess power from array, when batt is i.e. in Absorb
I think that you need to disconnect the power 'link ' between both DHW elements. Then when batt bank reaches target SoC or ? a switch/SSR is closed by Aux1(?) signal (closes contacts) and ~ 900w will flow into the 900W AC DHW element. when the Temp sensor goes Hi, it opens its separate on/off switch and all is happy... Now the question is how to reset Aux 1...?
Thanks for the Suggestions and links. More reading. And more good stuff to go on. As I start to mess with it I will write back.
Oh and Larry, no I did not see either of those. It may have been the HWT abbreviation that kept me from finding it.
Search SSR or Solid State Relay and you will get a lot of info on how to use the Aux
Larry
Larry, tried the links in ur response at the thread u linked here...
http://midniteftp.com/forum/index.php?topic=3666.0
but the links are not working for me. Can u update and repost them here?
Quote from: Matrix on November 02, 2017, 08:37:55 AM
Larry, tried the links in ur response at the thread u linked here...
http://midniteftp.com/forum/index.php?topic=3666.0
but the links are not working for me. Can u update and repost them here?
I fixed those links - they changed the website so if you find any other broken links change beginning to
http://midniteftp.com/forum/******* and then they should work
Larry
Ok so it looks like AC is out for me. (edit: but read on ... I ended up using AC) While it might be a great idea, I dont think my inverter could handle the load even of a 1500 watt element. (which is the lowest I could find). My inverter is a split 240 with L1 and L2 ... but is rated for 1800 watts continuous on each leg. So I best not push that.
All that said, I am back on the DC train. I read several threads about which SSR to use, and back-n-forths on AUX 1 and AUX 2. Most of the threads I read seem to end with no final plan. They just end, with no out come. So I am still stumped as to things like which SSR, Amp ratings, etc.
But tonight I came across an article that might help anyone looking in to the Dump loads and SSR's. This is the best article I have found (https://www.homepower.com/articles/solar-electricity/design-installation/harvesting-surplus-energy-grid/page/0/1?v=print) so far complete with wire diagrams and recommendations. Pete's PDF article (http://midniteftp.com/forum/index.php?action=dlattach;topic=3457.0;attach=5306) that Larry posted above was excellent too. I have written Pete, but have not yet heard from him.
Drawing from these articles, I think I get the basic idea now. Here (from the articles linked above) is what I have in mind (see attachment).
Parts I think I might need. Are these large enough or of the correct amp size?
1. DC 900 watt element (https://smile.amazon.com/dp/B0182BEVJY/_encoding=UTF8?coliid=I1IRLZF7JTGAIA&colid=28GSOAUQ6M2YF) connected to the Charge Controller to Battery +/- bus bar. This would be 24v nominal
2. a Crydom D1D** (https://www.alliedelec.com/crydom-d1d60/70130702/) with heat sink. I was thinking either a 60 amp or 80 amp. But what would my system draw? 900w/24v = 37.5 amps. So I am guessing a 60 would work, an 80 would be better.
But I still have questions:
1. I still need a thermostat to keep the water from over heating if the dump is too hi
- There seems to be fairly good agreement that the AC stat will not work for long on DC. Yet some say if you place it in the 12v DC side of the control (like the attached diagram has it) an AC one will work.
- Does it wire to the 12v side before the SSR or to the higher volt side between the battery and the DHW element?
- I would have thought the later, but the diagram I found shows it going on the 12v side.
- And if so ... that would mean not only running #10 wire the 25 ft to my DHW for the element, but a second smaller gauge wire for the 12v stat. What gauge wire would that be?
- Do I keep the AC stat or Should I just get a DC stat like this one (https://www.ebay.com/itm/Water-Heater-Thermostat-for-DC-Water-Heating-Elements-140-Degrees-Fahrenheit/321900401652?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649) ?
2. I still have not found a good source for explaining the Use of AUX 1. Most threads i find where people use AUX 1 end up using AUX 2 for various reasons. But I have a WBJ so Aux 2 is out. Is it possible to be successful with a DHW dump load on AUX 1 ... or will it give me Bulk / Absorb / Float battery charging issues?
3. What size DC breaker between the battery and the Element? I would assume the same size as the SSR amp rating ... I am looking at 60 amps
4. Do I need a breaker for the positive lead coming off of Aux 1?
5. Do I need Diodes in a PV setting? I keep reading where some people say diodes are needed. I understand them in a Direct PV system with NO CC or in a Wind system, But Where do they go in this configuration WITH a MPPT CC? I do not understand Diodes at all. What will they do?
Any help with my final set up before I purchase anything would be appreciated? Does it look like I am on the right track?
Your schematic looks okay to me but I don't have any real world experience with setting one one up .
For wiring you need to account for current and voltage drop for the wire run. Your breaker is based on the size wire you run , not on the load . So you can oversize the wiring if you need to for voltage drop .
I would consider using a contactor instead of an SSR - at least compare the costs and longevity . Contactors are made to handle large current loads and may have all the low voltage protection built in .
Look up Gigavac website - they have full line of contactors and lots of info http://www.gigavac.com/
Here is an example http://www.evwest.com/catalog/product_info.php?products_id=273&osCsid=v5hp69bh491uj7lp9e8kv7edf4
http://evwest.com/support/gv200.pdf
Larry
Thanks Larry
I will study up on contactors. Don't really understand what they do. I guess like an automated on off switch?
But I'm mostly still stuck on the thermostat. If it goes on the load line or on the low voltage control line? And do I need a dc one or will the AC one work.
You have it on your diagram... ::)
Use 12Vdc from Aux1 to control your existing thermostat.
Use new or used Crydom ssr from Ebay, D1Dxx are mosfet and can be paralleled (2x D1D40=> 1x D1D80).
Quote from: SolarMusher on November 04, 2017, 12:40:24 PM
You have it on your diagram... ::)
Use 12Vdc from Aux1 to control your existing thermostat.
Use new or used Crydom ssr from Ebay, D1Dxx are mosfet and can be paralleled (2x D1D40=> 1x D1D80).
Yes I realize that its in the diagram that way ... but that is not my diagram (found it), and i am trying to avoid running both the load and control wires to the DWH. Trying to avoid having to run the load wire AND the 12v control wire the distance from the load panel / PV battery busbar to the DWH. No big deal. A distance of 25 feet. But what would be an acceptable wire Guage for the 12v run?
Also, if I were to go the DC stat route, could the stat I linked above b used inline on the load positive wire... avoiding running the 12-volt wire the 25-foot to the hot water heater? Or are they just not made for that.
Quote from: Matrix on November 04, 2017, 12:50:43 PM
Quote from: SolarMusher on November 04, 2017, 12:40:24 PM
You have it on your diagram... ::)
Use 12Vdc from Aux1 to control your existing thermostat.
Use new or used Crydom ssr from Ebay, D1Dxx are mosfet and can be paralleled (2x D1D40=> 1x D1D80).
Yes I realize that its in the diagram that way ... but that is not my diagram (found it), and i am trying to avoid running both the load and control wires to the DWH. Trying to avoid having to run the load wire AND the 12v control wire the distance from the load panel / PV battery busbar to the DWH. No big deal. A distance of 25 feet. But what would be an acceptable wire Guage for the 12v run?
Also, if I were to go the DC stat route, could the stat I linked above b used inline on the load positive wire... avoiding running the 12-volt wire the 25-foot to the hot water heater? Or are they just not made for that.
What your classic aux terminal can take, 16awg or a bit smaller should be great to control this existing AC thermostat.
I've never use these ebay DC thermostats and I think that it's safer to use control and relay to supply your load.
Quote from: SolarMusher on November 04, 2017, 01:40:34 PM...and I think that it's safer to use control and relay to supply your load.
I like the idea of safer. That is what drove my Off-Grid solar project costs up in the first place. I started the project with the idea I could use an Ebay/Amazon $225 CC and $300 Inverter ... until I realized neither was UL Listed 1741 (In home wiring grade) and many at that price point had NO certification AT ALL. Can you say "fire hazard". I ended up with all UL 1741 products including $560 worth of CC and $1,450 worth of Inverter.
So safety is a HUGE priority for my system. That and low maintenance. I don't want to have to continuously be testing and replacing things that burn out in 6 months to a year ... every so often ... if possible.
So when you say
"...safer to use control and relay to supply your load." do you mean... that It is safer to control the stat on the low volt side of the SSR Relay? AND that it is safe to use the existing AC Lower DWH thermostat ?
Thanks (I know, probably dumb questions, but its not like we are sitting discussing this over coffee face to face)
I'm guessing these SSR's are not as good as the Crydom's ??
https://www.ebay.com/itm/1pc-KYOTTO-DC-Solid-State-Relay-SSR-KG2075D-5-220VDC-75A-DC-in-to-DC-out/140534723852?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649
Quote from: SolarMusher on November 04, 2017, 12:40:24 PM
Use new or used Crydom ssr from Ebay, D1Dxx are mosfet and can be paralleled (2x D1D40=> 1x D1D80).
So would it be better to a parallel connection with the control wire like this...
Quote from: SolarMusher on November 04, 2017, 12:40:24 PM
Use new or used Crydom ssr from Ebay, D1Dxx are mosfet and can be paralleled (2x D1D40=> 1x D1D80).
Or would it be better to do a parallel connection with the control wire like this...
Quote from: Matrix on November 04, 2017, 02:01:23 PM
Quote from: SolarMusher on November 04, 2017, 01:40:34 PM...and I think that it's safer to use control and relay to supply your load.
I like the idea of safer. That is what drove my Off-Grid solar project costs up in the first place. I started the project with the idea I could use an Ebay/Amazon $225 CC and $300 Inverter ... until I realized neither was UL Listed 1741 (In home wiring grade) and many at that price point had NO certification AT ALL. Can you say "fire hazard". I ended up with all UL 1741 products including $560 worth of CC and $1,450 worth of Inverter.
So safety is a HUGE priority for my system. That and low maintenance. I don't want to have to continuously be testing and replacing things that burn out in 6 months to a year ... every so often ... if possible.
So when you say "...safer to use control and relay to supply your load." do you mean... that It is safer to control the stat on the low volt side of the SSR Relay? AND that it is safe to use the existing AC Lower DWH thermostat ?
Thanks (I know, probably dumb questions, but its not like we are sitting discussing this over coffee face to face)
I mean that it is safer to disconnect your original water heater thermostat with good quality products such Crydom or other ssr/relay/contactors using 12V control than to use directly a cheap made in china thermostat ($15?) to disconnect higher current. You won't have any problems using the AC original thermostat with 12Vdc from aux1.
Try to find 1x Crydom D1d80 first, it will be better/safer than two D1d40 (if one fails, you will have 900W/37A on just one 40A ssr).
Your first picture is ok for ssr parallel connection, you can also find good diagram in Crydom spec sheets (D1d serie).
Sorry, I know nothing about Kyotto ssr.
Chris Olson, AFIK, abandoned his wind & solar, in favor of stacked diesel generators, which he found more reliable in his harsh winters. Perhaps he uses solar in summers.
Another route, is to use an inverter, with a remote Off / Disable control, and feed AC (mod-sine even) to the heating element and control the inverter with the Waste Not.
Contactors are simply Heavy Duty High Current relays
Cool. Thanks folks.
I saw a 100 amp Crydom on ebay NIP with a best offer. Shot a low ball. Waiting to see what comes back?
I ordered the 900 Watt 24v Element (https://smile.amazon.com/gp/product/B0182BEVJY/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1) today. Am I correct that this will pull 37.5 amps (900w / 24v = 37.5), and so it will require AWG 8 wire and a 40 amp breaker?
In a DC set up, is it OK to use NMB #8 that is solid copper?
You need to do the voltage drop of the wire you would be using also when planning .
Also you will need a very good heat sink on your SSR . And the diode as it says in spec sheets.
I think the advantage of a contactor may be that it won't heat up so much like SSR since it is mechanical contacts instead of SSR which is solid state and gets warm when passing high amounts of current.
It wouldn't matter if wire is solid as long as it can fit in whatever terminals it is going to - or put a ring terminal on it that will fit the terminal that it is going to .
Larry
I plan to use ring connectors so that's not a problem, but what do you suggest for diodes I'm clueless
Quote from: Matrix on November 04, 2017, 07:59:24 PM
I plan to use ring connectors so that's not a problem, but what do you suggest for diodes I'm clueless
Here is the info on heat sinks - I will try to find the one on diodes
http://www.crydom.com/en/tech/white-papers/hs_wp_hs.pdf
http://www.crydom.com/en/tech/techlab-videos.shtml
Larry
Quote from: ClassicCrazy on November 04, 2017, 08:16:53 PM
Quote from: Matrix on November 04, 2017, 07:59:24 PM
I plan to use ring connectors so that's not a problem, but what do you suggest for diodes I'm clueless
Here is the info on heat sinks - I will try to find the one on diodes
http://www.crydom.com/en/tech/white-papers/hs_wp_hs.pdf
http://www.crydom.com/en/tech/techlab-videos.shtml
Larry
Follow all that or else just put a really good sized heatsink on it !
Here is the info on diode or resistor protection of coils in SSR . It says resistive loads aren't really a problem but I thought I had read somewhere in past that the some wire runs can present some capacitive load .
http://www.crydom.com/en/tech/newsletters/solid%20statements%20-%20coil%20suppression%20&%20dc%20output%20ssrs.pdf
Larry
Thanks for all the research assistance Larry. This is working out great.
I have a friend who is an electrical circuit and relay type engineer at a large local Natural Gas lift station for the pipe line that runs thru central FL. He is going to be checking my set up before I go live with it. But I really wanna understand what and why I am doing things before that. I plan to be ordering the pieces bit by bit in the next week.
even if you use a Contactor, it has a coil like a relay does, and needs a snubbing diode on the coil.
https://electronics.stackexchange.com/questions/100134/why-is-there-a-diode-connected-in-parallel-to-a-relay-coil
Looking for a diode. I can't find anywhere that suggests exactly which diode I need to purchase and where to purchase it. I can only find that says I need a diode. Where are some links to purchase the diode that I need?
Quote from: mike90045 on November 05, 2017, 01:16:10 AM
even if you use a Contactor, it has a coil like a relay does, and needs a snubbing diode on the coil.
https://electronics.stackexchange.com/questions/100134/why-is-there-a-diode-connected-in-parallel-to-a-relay-coil
Mike - some of the Gigavac contactor models have this note
" Contactors feature internal transorb for coil suppression. No external
diodes should be added across the coil. "
Larry
Quote from: Matrix on November 05, 2017, 04:27:10 PM
Looking for a diode. I can't find anywhere that suggests exactly which diode I need to purchase and where to purchase it. I can only find that says I need a diode. Where are some links to purchase the diode that I need?
Ha ha - yeah I was trying to figure that out also earlier this summer - I believe the info is there in the technical data I linked above.
Larry
most diodes would be ok, I have used 1N4000 although a schottky type diode is better
you can find these on ebay for cents to a couple of dollars.
dgd
Thanks dgd.
This morning I got back on the AC from Inverter Idea instead of DC. I can get a DC control / AC load SSR correct? And then the AC load can still be controlled but the DC control / AC load SSR thru the Aux 1 settings of the Classic? Correct?
If I go AC, I think I can use my existing 4500w 240v element and thermostat, but (if I did the math correctly) ... at 120v the 4500w element would only be 1125watts.
4500 (120v/240v) x (120v/240v) = 1125 w
and the Amps at 1125 watts / 120v = 9.37 amps
Did I do that math correctly?
This would mean:
1. An SSR rated for lower amps
2. Less copper (I could use #12 or #14 wire instead of #8)
3. No replacement parts at all.
4. And I dont even have to take my water heater apart.
Except for inverter inefficiencies ... what am I missing here? If I can control the and AC load just like a DC load off AUX 1 ... this would give me everything I want, and all I need to buy is a 3-35v DC control / 120v AC 25 amp SSR. My inverter could handle 1125 watts no problem.
Quote from: Matrix on November 05, 2017, 04:27:10 PM
Looking for a diode. I can't find anywhere that suggests exactly which diode I need to purchase and where to purchase it. I can only find that says I need a diode. Where are some links to purchase the diode that I need?
the required diode size is a function of the coil voltage, and the size of the inductive "kick" the coil delivers (like an automotive spark coil). once you settle on a relay/contactor, call the engineering support and ask them for sizing a anti-flyback diode.
the link i gave earlier has some guidelines. Installing it properly (correct polarity) is crucial, ask a local hobbyist how to read the markings on the diode to ascertain the proper orientation.
Just found this - best info on SSR I have seen yet
It has easier to understand Selecting a Diode section
http://omronfs.omron.com/en_US/ecb/products/pdf/precautions_ssr.pdf
Larry
Cool thanks everyone.
Well I just found a piece of number 12 wire 27 ft long. And I ran it from my inverter off of L1 to the bottom of my hot water heater through my AC thermostat. The whole thing is AC coming off the inverter. It is a 4500 watt element at 240 volts. But I wired it 120 volts. And it is pulling exactly 1125 Watts and 8.75 amps aa tested by my clamp meter. Working perfectly. The thermostat Cycles on and off no problem. I'm using all of my Excess power. The only problem is I have no automation yet because I have not connected an SSR to the AUX 1 on the classic
So now to find an SSR that works with DC control and AC load. I know that crydom makes them no problem so this should be an easy find. And now it only has to be 25 amps instead of 60 or 100 amps
Yes crydom makes good relays. Thats what im using ,also not sure if you disconected the upper thermostat wiring to the lower element as the house 240 volts upper thermostat has a switch from bottom element to upper element during high water demand , im using a lower a.c element 120 volts 500watts wired to my inverter, with a crydom ssr dc control, a.c. Load relay on the classics aux1 using waste not , left the original a.c. Thermostats in place and it works great ,the upper element is on house a.c 240 volts and is on a timer ( its on after 7 pm until 7 am ) as our hydro rates more then double during the day , you will have to play with the aux 1 setting to suit your system , during a full sunny day all my hot water is produced by solar ( were only two people using it and are conservative ) my system is very small 1320 watts of panels .
Don
Quote from: Taos on November 08, 2017, 05:14:49 AM
Yes crydom makes good relays. Thats what im using ,also not sure if you disconected the upper thermostat wiring to the lower element as the house 240 volts upper thermostat has a switch from bottom element to upper element during high water demand , im using a lower a.c element 120 volts 500watts wired to my inverter, with a crydom ssr dc control, a.c. Load relay on the classics aux1 using waste not , left the original a.c. Thermostats in place and it works great ,the upper element is on house a.c 240 volts and is on a timer ( its on after 7 pm until 7 am ) as our hydro rates more then double during the day , you will have to play with the aux 1 setting to suit your system , during a full sunny day all my hot water is produced by solar ( were only two people using it and are conservative ) my system is very small 1320 watts of panels .
Don
Hi Don.
Yes I have the Upper and lower disconnected from each other.
Upper = 240v AC Line with 4500watt element. No timer ... that that is a really good idea
Lower = 120v AC Solar/Battery at 1,125 watts using the stock Element and lower Thermostat. Element is 4500w, but at 120v it is 1,125w (4500 (120v/240v) x (120v/240v) = 1,125)
Ordered a Crydom D1240 SSR, which is a DC 3-32v control / AC 24-140v Load. should be just right.
Can you give me any starting suggestions on using Waste Not as far as Aux 1 Settings? I really do not under stand how it is suppose to work. I realize the - volt values you enter will not start / stop the Water heater element until those user set points, But I read some where that it controls it for each of the charging stages as well - Bulk / Absorb / Float. How does that work? Does Waste Not wait until there is enough power coming off the array to power the element with out jeopardizing charge?
Some good starter point settings and tips would be helpful.
The links posted in this Thread so far have been very helpful. I know that your time is valuable and most if not all are merely fellow users and not MidNite Solar employees. My questions may at time seem elementary and redundant, But Thanks for your patience and all the input from the Forum participants.
To further help anyone else who may see this thread in the future, and to help make a comprehensive guide to setting up Hot Water Heating as a Diversion for Excess power ... I have compiled a list of what I considered helpful Discussions on this forum that I found, and other links I have found that seemed to be helpful on this subject.
Forum Threads
Basics of Diversion to Hot Water Tank
http://midniteftp.com/forum/index.php?topic=3666.0
Using a Classic with DC heating Element
http://midniteftp.com/forum/index.php?topic=727.0
AUX 1 and AUX 2 Modes in the Classic Explained (complete list)
http://midniteftp.com/forum/index.php?topic=289.msg1667#msg1667
DC wire SSR with Classic
http://midniteftp.com/forum/index.php?topic=3352.0
DC SSR sizing?
http://midniteftp.com/forum/index.php?topic=3595.0
Diversion Load AUX 1 settings
http://midniteftp.com/forum/index.php?topic=3754.0
Off Site Links
Harvesting Surplus Energy
https://www.homepower.com/articles/solar-electricity/design-installation/harvesting-surplus-energy-grid/page/0/1?v=print
Managing Battery Charging Using Diversion Loads
https://www.homepower.com/articles/wind-power/design-installation/managing-battery-charging-using-diversion-loads
Water Heating Controlled by a Classic 150
http://www.fieldlines.com/index.php?topic=147132.0
How to Convert an AC water heater to DC
http://waterheatertimer.org/Convert-AC-water-heater-to-DC-water-heater.html
http://waterheatertimer.org/convert-AC-water-heater-to-DC-using-low-voltage.html
MidNite Solar Classic Papers and Documents
Diversion Load Control with 2 Types of Relays
http://www.midnitesolar.com/pdfs/CLASSIC_DIVERSION_CONTROL_2_RELAYS.pdf
Low Voltage Disconnect with 2 Types of Relays
http://www.midnitesolar.com/pdfs/LVD_2RELAYS.pdf
Other Helpful PDFs
Pete's Diversion for Hot Water Paper
http://midniteftp.com/forum/index.php?action=dlattach;topic=3457.0;attach=5306
Crydom's PDF on Diodes
http://www.crydom.com/en/tech/newsletters/solid%20statements%20-%20coil%20suppression%20&%20dc%20output%20ssrs.pdf
As for my set up so far ... For now I think It will be an AC set up controlled by AUX 1 using an SSR.
- AC seems to be the least expensive and least complicated route if you have a large enough Inverter. But it is not the most efficient.
- due to being able to use already existing parts
- Less copper due to lower amps
I already have the AC system set up. I am presently controlling the On / Off to the element with a breaker and / or the lower AC thermostat of the DWH. Hopefully by the weekend I will have an SSR and will start working with Automation.
So far on hand I have:
- The stock 240v 4500w element already installed in the DWH. Running at 120v 1,125 watts
- Ordered a Crydom D1240 SSR for control off of AUX 1 (should be here friday)
- Got a Heat Sink for the Crydom and the Crydom K100 SSR cover
- Will probably get a 240v 3500 watt element for 875 watts wired 120v
- and a 240v 3000 watt element for 750 watts wired 120v
- A DC 900 watt 24v Element (that I will just keep to try if I go back to DC)
Will get the last 2 AC elements to try if I find I am diverting too much load and the batteries are not getting charged using the stock 4500 watt 240v element. But the lower watt options would also be good choices for people who did not have as much unused power from the inverter as i do. I have a 4000 watt inverter and i never use more than 2200 watts.
After I get the SSR I will post up pictures and diagrams of the set up. Will also update on how it is working and the settings I am trying in the Classic AUX 1.
Any suggestions for initial settings starting out on AUX 1 would be appreciated.
Got the SSR installed and wiring cleaned up last night. Tested from the Local App, and it seems to be working as an on/off switch. Aux 1 is coming on and going off, and when on 118v is passing thru the SSR. But no sun to test and see how it performs during a charge cycle. Today is cloudy in the morning so far, but it is suppose to clear by the afternoon. So I have starting to tinker with the Waste Not Hi settings.
Set up as of now:
- Stock 4500 w element and thermostat in lower portion of DWH disconnected from the top of the DWH.
- Connected to a 12 awg AC line wire at 120v coming from my inverter. At 120v the element runs at 1145 watts and Less than 9 amps when on.
- Crydom Series 1, 3-32vdc / 24-140vac 40 amp, modle D1240
- Mounted to Head sink and set with thermal paste
- Running on Aux 1
Now to try some settings ... I found this thread a very good starting point ...
http://midniteftp.com/forum/index.php?topic=3754.0
But Taos, I do not understand one thing. You Say ...
Quote from: Taos on June 30, 2017, 07:41:55 AM
Update, well (the waste not high) function is the way to go for me , i set the V high setting to -.2 volt and the V low setting to -.4 volt, delay time of 5 seconds and hold time of 10 seconds ...
Don
Trying that ... But in the Local App, If I have my V Low set to -.4, And I try and set my V hi to -.2 ... the V Low goes to 0. It will not let me set it like that. Are the Settings for the V Hi and Low in the Local app measured in tenths? So that -2 in the setting is actually -.2 etc.? Do you mean -2 and -4?
Hi Matrix
Sorry i wasnt checking the forums for a bit , here is how i have mine setup , since my lower tank heating element is a 240 heating element and im running it on 120 volt a.c. Powered by my outback 3600 watt 48 volt inverter , Using the original a.c.thermostat , it draws around 500 watts on the inverter , its a way for me to get some heat in the water tank ,its not the main source of heat but a supplement as my system is small , i have experienced a 100% heat supply from the lower 500 watt element on days in the summer of full sun ,the element is on steady from 10:00 am until 4:00 pm ( and no use of hot water durring that time ) ,before 10:00 am and after 4:00 pm the classic charge controller will try if battery voltages are met according to my settings ,( cycle on and off ) here is what i have for settings im using waste not hi on the classic aux 1 , voltage low -0.4 , volt high -0.2 , and time delay of 5.0 seconds , and a hold time of 2.0 seconds , these are setup on the classics display , not the local app , the way it works is when the battery voltage is at my on setting (just below )my charge voltage settings( for different charge stages ) for my batteries programed in charge settings ( different for different battery types and brands ) once this voltage was met for a delay time of ( my setting 5seconds ) the heating element is powered on ,and if voltage drops( below my aux 1 setting for more then (2 seconds) (my hold time ) the classic turns off the ssr relay ( crydom brand)and power is cut to the lower tank heating element , this cycle repeats itself , and when there is lots of power from my array( ussualy after 10:00 am on a sunny summer day ) and conditions are met the element stays on most of the day , i have found with these settings for my system and house power usage it works good for me and my batteries stay fully charged and i get hot water as a bonus, my kw for the day produced are close to double from not having the waste not water heating set up ! I have found that this maybe isnt the most efficient way of doing hot water heating ( loss from using aux 1 , inverter, ) but found it to be the simplest and i think the safest way , as im using a a.c. Thermostat and heating element thats csa approved( for canada ) and since the wizbang junior is used on aux 2 i didnt want to loose it usefulness ,aux 2 and dc element is more effiencient but for me it worked out the best . Im going to say like most theres not a lot of info on this ,you will have to try different setting in aux 1 and see what works for your system . Matrix you may try setting your v low and v high 0.1 volt lower in aux setting . I think i heard this from bob .
Don
Thanks Don,
Your set up and Mine are nearly exactly alike.
- I cannot use Aux 2 because of the Whiz Bang Jr
- I am using AC for the water heater load as I have plenty of excess inverter power
- Like you I felt this was the easiest and safest method as it would require no changes to the hot water heater
I may swap out my lower thermostat for an upper type thermostat on the tank leaving an upper up top and an upper on the bottom because my lower stat does not have the reset button for thermal over load. it was integrated into the upper stat when they were connected together via 240v... And I have an extra.
Besides that, the only differences in our system are:
1. My array is 2.5Kw charging 4 Trojan L16H-AC 435s that usually get discharged no more than 32% a nite
2. My element is running at 120v 1140 watts .... but even with the larger array at full sun this element is not staying on and cycling off to much to be effective when running on the automation of the SSR
- I tested it last week with out the SSR. As long as it stays on, it is capable of heating my tank to 120* in 3.5 hrs.
- But I cant get it to stay on using the SSR and AUX 1. it cycles about every 20 seconds due to voltage drops below the Low V set point because i such a large load
So I will change that 1125w element out to a 750w element tomorrow which should make things just about perfect.
I will then be able to try your settings (I actually have already but the element is too big to see how it really works) ... but I will try them tomorrow with a smaller element and see if I am golden.
Thanks for the reply
Mike
For what its worth ... here is a link to the final end product of my entire Off-Grid Grid assist solar system.
http://midniteftp.com/forum/index.php?topic=3907.msg37991#msg37991
Hi Mike
I was thinking you had too much load of the water heating element for your system ,since your running off your batteries at night it will not work as good ,as in the morning on a good sunny day you have to get those batteries charged and the lower the state of charge the more the ssr will cycle until your batteries get close to full then your water heating element will stay on constant , i think if you size the heating element around what you stated 800 -900 watts it should work good for you , also you can try lowering the aux 1 ,volt low and volt high and also change the delay to longer time and the same with hold time , i think if you size the lower water heater element corectly it will work for you , im sure using a dc element right from the batteries and aux 2 would work a lot better ( pwm) but theres a trade off as loosing wizbang junior , and finding a safe d.c. Thermostat,and element , i didnt like the way mine worked when i had it set up on aux1 diversion load ,i thought this sucks the way it works ,and also gave up ,but once i got aux1 using waste not high ,things worked so much better and its a keeper , (until theres a safe d.c. Element and thermostat available ! ) Like you i tried without the ssr in the system and worked good and once ssr was hooked up in diversion load it didnt work good until i tried aux1 waste not high ! And played with aux1 settings
Don
Well I just this afternoon got the element switched out to a 720w. So I think this will be OK. At least it will probably stay of if conditions are right thru the day. But It may not heat enough water fast enough. But we will see. Hoping it works out.
If not ... I can always switch it upwards to 900w and see what it does.
Quote from: Taos on November 17, 2017, 05:13:02 PM
Hi Mike
I was thinking you had too much load of the water heating element for your system ,since your running off your batteries at night it will not work as good ,as in the morning on a good sunny day you have to get those batteries charged and the lower the state of charge the more the ssr will cycle until your batteries get close to full then your water heating element will stay on constant , i think if you size the heating element around what you stated 800 -900 watts it should work good for you , also you can try lowering the aux 1 ,volt low and volt high and also change the delay to longer time and the same with hold time , i think if you size the lower water heater element corectly it will work for you , im sure using a dc element right from the batteries and aux 2 would work a lot better ( pwm) but theres a trade off as loosing wizbang junior , and finding a safe d.c. Thermostat,and element , i didnt like the way mine worked when i had it set up on aux1 diversion load ,i thought this sucks the way it works ,and also gave up ,but once i got aux1 using waste not high ,things worked so much better and its a keeper , (until theres a safe d.c. Element and thermostat available ! ) Like you i tried without the ssr in the system and worked good and once ssr was hooked up in diversion load it didnt work good until i tried aux1 waste not high ! And played with aux1 settings
Don
How many amps do you need to switch on DC ?
These Klixon can go up to 7 amps at 30v dc
http://www.sensata.com/klixon/thermostat-precision-4344.htm
Larry
Quote from: ClassicCrazy on November 18, 2017, 02:11:09 AM
How many amps do you need to switch on DC ?
These Klixon can go up to 7 amps at 30v dc
http://www.sensata.com/klixon/thermostat-precision-4344.htm
Larry
Hey thats cool Larry. I had seen the ones from Missouri Wind and Sun ... but was not sure I could trust them. But those look nice. I wrote Wind and Sun and they say they are great and work fine, but in the end it just seemed easier to use AC as my inverter was large enough.
So what is wrong with using AC. I know everyone says "efficiency" , but where does that hurt me? What does that really mean? Not being sarcastic, I really do not know. ( I really don't even under stand in the local app what the input for battery efficiency means or does. I guess I know what it means, but I do not know how I could know that % and what effect it has on my over all system.)
How I Use Excess Power on AUX 1
OK .... for anyone looking to do a Dump Load / Waste Not set up ... if you have read this far you are really trying to discover how to do it. This is what I did, and here are the parts I would recommend
If you are going the AC route. I would get a Crydom SSR. Probably part # D1240 (http://www.crydom.com/en/products/panel-mount/perfect-fit/ac-output/series-1/d1240/) which is 3-32v DC control / 24-140v AC Load and 40 amps. If you needed different specs you could shop around in the Crydom Series 1 SSRs. The D at the beginning indicates DC control (the ones that start with A are for AC control)
- You could connect this SSR to AUX 1 (or I guess AUX 2)
- Diversion load would depend upon the size of your excess array. In my case I seem to have about 600-1100 extra watts, but going to the hi side of available excess seemed to have cause the element to cycle on and off to often and thus not really heating the water.
- Suggested AUX 1 starting point would be: V Hi -0.2 / V Lo -0.4 - Delay 5 / Hold 2. (Thanks Don for the starting set points)
- (UPDATE JAN 2 2018) Or on AUX 1 you can use SOC hi and set it for 98% on and 93% off. Yes it will use some batteries, but only at the end of the day. And this way, it comes on and stays on and does not cycle on and off like Waste Not Hi does. This is the setting I have been using with good success. Or use 99% on and 97% off. Takes longer before it comes on, but does not drain the battery as much at the end of the day.
- Here is a basic wiring diagram (http://www.midnitesolar.com/pdfs/CLASSIC_DIVERSION_CONTROL_2_RELAYS.pdf) to set up diversion load. Load can be either AC or DC depending on how you set it up.
- Here are some suggested links for converting your water heater to use solar. Let me Say Pete (the fellow who wrote the PDF) is very responsive. We corresponded back and forth several times thru the process via email and he was very helpful.
- Pete's PDF paper (http://midniteftp.com/forum/index.php?action=dlattach;topic=3457.0;attach=5306)
- How to convert an AC water heater for Solar (http://waterheatertimer.org/Convert-AC-water-heater-to-DC-water-heater.html). This is a basic idea that you can learn from and adapt to your specific needs
- It is my understanding that you can use the AC parts for DC ... but I was uncomfortable using the AC stat for DC application because of arching. I knew with the SSR the DC load would be switching on and off a good bit. That is one of the reasons I went AC.
If Going DC. I would get a Crydome in the 1-DC Series (http://www.crydom.com/en/products/panel-mount/perfect-fit/dc-output/1-dc-series/). Probably either a D1D60 - 100. They will cost more than using AC ... but you will in most cases by pulling a much higher amp load using DC. That will mean 2 things
- Larger copper wire from the battery to the Water heater. In my case it was going to take #8 awg. With AC I could run #10. With AC I am only pulling 7 amps. DC I would have pulled almost 40.
- Also, I read that you should size your SSR for Double the anticipated amp load. So 40 amps would require an 80 amp SSR
- So with DC cost is going to be another factor. More for the SSR and more for wire.
- with the higher amps and DC volts, you may NOT want to use the AC stat due to arching. So get a DC stat.
- Larry Found these (http://www.sensata.com/klixon/thermostat-precision-4344.htm)
- Or you could get these (http://mwands.com/store/water-heater-thermostat?search=element&description=true)
- DC elements of various sizes can also be found at Missouri Wind and Sun or on Amazon.
And as a final note ... This guy put together the quintessential DIY 14+ part Hot Water Heater Video series (https://www.youtube.com/watch?v=xCvCZVP0AOI). It is Hillarious. You may not learn much ... but you may learn what NOT to do. :D Just the junk in the yard in the first 10 seconds of part 1 is worth the cover charge. But he did get it done and working, and I did learn from him. He has some good ideas. And I talked with him some about his set up. Very helpful guy.
Just watched this good info / tutorial on Solid State Relays - and read the comments about fake vs real Fotek relays
Also shows how to build your own SSR .
https://youtu.be/2UtL2uAYCUA
Larry
Update.
I been have using this set up for a little more than a month now. And I was finding in Waste Not Hi that the systems Aux 1 thru the SSR was turning the water heart on and off about every 15-60 seconds at the end of the day or if conditions were less than optimal. If the conditions were less than ideal, or it was at the end of the day, my element was turning off and on rapidly AND my lights were FLICKERING every time the element came on - presumably not good for the inverter or the household electronics. And Not good for me as I am getting a voltage dip/sag from my inverter every time a large load comes on. I know it is not a connection, as it only occurs thru inverter, and not when the inverter is in bypass mode and/or running off the grid.
So for now, i am using SOC% Hi. Not perfect, but setting at 99% on and 97% off, this allows the element of the hot water heater to come on at float, but the Aux is not voltage dependent, so if there is a drop .... it just keeps on going until the batteries hit 97% and then it turn off. Once on / Once off.
It would be better to have more control over Waste Not Hi as I mentioned here (http://midniteftp.com/forum/index.php?topic=3922.msg38192#msg38192). But that is not likely to happen. So as for now, this SOC% Hi is working pretty well.
I noticed that no one had ever resolved the DC thermostat issue. You could use a insertion temperature switch if you have a spare 1/4" min threaded outlet on your heater.
https://www.automationdirect.com/adc/Shopping/Catalog/Process_Control_-a-_Measurement/Temperature_Sensors_-a-_Transmitters/Temperature_Switches/TSDA25N-0P-0284-H (https://www.automationdirect.com/adc/Shopping/Catalog/Process_Control_-a-_Measurement/Temperature_Sensors_-a-_Transmitters/Temperature_Switches/TSDA25N-0P-0284-H)
Here is a 24v controlled switch with adjustable range. You could wire this in-line with the AUX contact to drive your DC coil on the relay. While I don't see a NSF 61 (Drinking water) certification, it is stainless and ROHS compliant.
Hi All!
Great thread--!
about 5 years ago I used the a DC diversion load approach on a smaller system with great results to make hot water.
Now I'm in onto a bigger set up (House, not cabin) and am trying the AC SSR on a 240 Volt hot water heater.
I should have sufficient inverter power for this (two outback VFX3648 w/ balancing transformer) + plenty of battery depth / solar (~10 KW of total array)
Using the PWM diversion on Aux 2 (as I did with my DC control) gives me a pretty significant light flicker--
I presume this is both stressing the inverters and bad for the rest of my electronics...
I know I can avoid this by moving to DC heating elements and DC SSR, but I'm not nuts about drawing tanks and pulling big wires from the battery bank--
any other options here make sense to use opportunity hi ? Or this load just to large for my inverters. (I can drop to 120 V instead, but I could actually use the full diversion in the summer)
If not, I'll go with Aux 1 w/ high / low voltage set points..
thanks!
Eben
Quote from: ebenbayer on January 15, 2018, 09:01:23 AM
Hi All!
Great thread--!
about 5 years ago I used the a DC diversion load approach on a smaller system with great results to make hot water.
Now I'm in onto a bigger set up (House, not cabin) and am trying the AC SSR on a 240 Volt hot water heater.
I should have sufficient inverter power for this (two outback VFX3648 w/ balancing transformer) + plenty of battery depth / solar (~10 KW of total array)
Using the PWM diversion on Aux 2 (as I did with my DC control) gives me a pretty significant light flicker--
I presume this is both stressing the inverters and bad for the rest of my electronics...
I know I can avoid this by moving to DC heating elements and DC SSR, but I'm not nuts about drawing tanks and pulling big wires from the battery bank--
any other options here make sense to use opportunity hi ? Or this load just to large for my inverters. (I can drop to 120 V instead, but I could actually use the full diversion in the summer)
If not, I'll go with Aux 1 w/ high / low voltage set points..
thanks!
Eben
I don't think you are going to get what you want with any Hi / Low VOLTAGE set point Aux Option. I tried them all, and they all do about the same thing. Using voltage, you are going to have cycling of the Aux on and off (sometimes pretty frequently) unless solar conditions are optimal.
I thought PWMs (which I am unable to use on Aux 1) took up for the fast switching of on and off and helped with the light flickering. Guess not.
But, This was exactly my issue on Aux 1 - Lights Flicker and presumably hard on electronics - and why I asked for some Feature Updates to the Aux 1 / Aux 2 (http://midniteftp.com/forum/index.php?topic=3922.msg38192#msg38192). I do not think we will see the Feature updates any time in the near future. :( Unless perhaps more people asking for them will move things along more quickly.
So in the mean time ... I found it best to use Aux 1 (because that is what I have, Aux 2 is dedicated to the Whiz Bang Jr.), And use the
SOC % Hi option. It is not ideal, but it does allow for the water heater to come on once and only once, and stay on for as long as the sun is out, and then it will draw the battery down to a set % of SOC (about 96-97%) and turn off and stay off if or until the SOC rises back up above the set SOC % Hi on setting (which has to be 99% if you use 96-96% as your off - see below).
Then the lights only Flicker Once a day ... at the one and only Power On of the Aux.Yes it does use some battery with this approach, but for me it was a trade off worth making to stop the flickering.
Here are the Caveats to SOC % Hi:
- You cannot set the On side to come on very early (or at a lower percent) unless you want the Off side to be about 6% lower
- Meaning if you set it to come on at SOC 95% on the way up in charge, it will then turn off at 89% SOC as the battery discharges
- 89% is too low a number to start the evening with for me
- It Would be nice if MidNite would update the AUX settings and Local App to allow an On at say 85% on the way charging up, But then turn OFF at 98% as the discharge starts to take the batteries down (backwards to how it is set up now)
- If the user could set on at 85% and off at 99% ... that would really solve a lot of these issues.
- And if Midnite added a drop down to also select the charge stage (bulk / absorb / float) so it would need 2 condtions (85% and Absorb) we would have a real winner in SOC % Hi IMHO.
- As it is, 99% on is the only percentage that lets you set OFF to the next percent down ... like on at 99% and off at 98%, but if you use 99% as your on, you are losing a lot of diversion power. And the Aux does not really come on until 100%.
- If you use 98% on or lower, then for some STRANGE REASON there is a 5% gap between On and OFF ... like 98% on and 93% off, etc.
But over all, SOC % Hi is the only setting in all the Aux options that will allow the heater element to come on once, and stay on until the Solar conditions or Battery SOC really change dramatically and then turn off. All other settings will have the element cycling on and off, sometimes every few seconds, depending on solar conditions, causing a voltage sag/dip from the inverter, Lights to Flicker and presumably hard on electronics. NOT GOOD.
Hope any of this made sense,
Mike
Mike,
Thanks for the reply!
All good points.
You are right about method. I copied your method using voltage points for now (w/ delay) which cycles every 20-60 seconds.
Had to make a few changes in my wiring as my Whiz Bang was not "seeing" some of my DC inputs (hydro, DC charger, 3 solar arrays with DC interconnect) but now all are on and my primary Whiz Bang can see SOC accurately again.
I'm going to go w/ what you suggest; I don't really mind if I discharge the batteries a bit at eod.
the PWM works brilliantly with DC-DC to the battery; no light flickering and it tracks the charging states. ( I did this for a year or two)
The challenge, is getting large enough DC elements, reliable DC SSR's, and of course, dealing with the wire size needed for a decent DC diversion load (4.4 KW in my set up).
I would think a large capacitor in series with my AC elements would smooth out the pulses but as a mechanical engineer I'm not supposed to speculate on such things.
I'll update back to this thread once I have it sorted out.
Thanks for doing such a nice job documents your work on this, rarely do folks return to report on progress!
best
Eben
Quote from: ebenbayer on January 16, 2018, 07:59:44 PM
the PWM works brilliantly with DC-DC to the battery; no light flickering and it tracks the charging states. ( I did this for a year or two)
The challenge, is getting large enough DC elements, reliable DC SSR's, and of course, dealing with the wire size needed for a decent DC diversion load (4.4 KW in my set up).
I would think a large capacitor in series with my AC elements would smooth out the pulses but as a mechanical engineer I'm not supposed to speculate on such things.
Eben
Eben, I would liked to have tried the PWM method as you did, but for all the DC reasons you listed it was just too much trouble. That is what actually prompted the title of this thread. I had a enough inverter "headroom" and simply decided to go AC out of the inverter. I know not the best given inverter inefficentcies, but definitely the easiest a person has a large enough inverter.
I would like to know more about the idea of a capacitor. It would be nice on the water heater, May even allow for the use of "Waste Not Hi (aka opportunity load) .... And I wounder .... Would that help with smoothing out pulses from an inductive motor like a well pump?
Any suggests would be appreciated.
Sincere thanks to those who contributed to this thread, especially to Matrix, the o.p.
It has been so interesting, enlightening, educational. Just a stellar example of what a forum thread can be.
Hats off!
One question: Isn't the cc's SOC figure notoriously inaccurate, making it somewhat risky (in terms of battery health / DOD) to use for controlling the SSR?
Thanks for the reply, glad it helped someone.
I do not think it is that risky because I have set the ON value so hi (98-99%) and the subsequent OFF value hi as well (no lower than 93%). So even if the SOC number in the CC is off, with values this hi, the danger of over discharge is almost non existent. The whole reason for using SOC % Hi is because any other Aux 1 method will switch the SSR on and off repeatedly when the battery volts drop. And this can happen several times in a few minutes. Not Acceptable in my set up - Which was causing excessive lights flashing from the inductive load of the water heater element cycling on and off.
As long as there is plenty of sun, my water heater will not use battery, it will be using the solar array, once the Aux preset has reached the set SOC value and turned on the SSR. The SSR stays on until the SOC drops to a very hi termination point (93-98% depending on where i have set it - Usually 97%).
Also note, if set at 99% on, the SSR will not come on until the battery hits 100% SOC. And by then it is charged or very nearly charged and so the amps are very low going into the battery so there is very little demand from the battery at the CC so most amps / watts generated by that time are going to the hot water element. Sure there is some loss of array power because I did not turn it ON at say 90% ... but if I did that, I would have to settle for an OFF of 85% as the Aux 1 setting has a 5% spread for anything lower than 99%. At 99% you can set the OFF to 98%. But set the ON to 98% and you are stuck with a 93% OFF - Come on MidNite Solar, this would be easy for you to fix, and even better if you could really tweak the settings per this discussion (http://midniteftp.com/forum/index.php?topic=3922.0) ... :D
Quote from: Matrix on February 03, 2018, 10:23:39 PM
But set the ON to 98% and you are stuck with a 93% OFF - Come on MidNite Solar, this would be easy for you to fix, and even better if you could really tweak the settings per this discussion (http://midniteftp.com/forum/index.php?topic=3922.0) ... :D
Will look into this, Mr. Matrix ! :)
boB
Quote from: boB on February 04, 2018, 02:31:33 AM
Will look into this, Mr. Matrix ! :)
boB
Thanks boB that would be awesome.
And by the way, I meant no disrespect to MidNite in my comment. I was being "tongue-n-cheek". I know Midnite has a lot of other irons in the fire. Just my dry way of saying "Please" as I know no other way to accomplish what I need. I realize what I would like to do (http://midniteftp.com/forum/index.php?topic=3922.0) could possibly be accomplished thru modbus, but I have looked at that and concluded modbus set up would be way over my head. Hope I did not come off snarky.
Mike
Quote from: Matrix on February 05, 2018, 09:00:35 AM
Quote from: boB on February 04, 2018, 02:31:33 AM
Will look into this, Mr. Matrix ! :)
boB
Thanks boB that would be awesome.
And by the way, I meant no disrespect to MidNite in my comment. I was being "tongue-n-cheek". I know Midnite has a lot of other irons in the fire. Just my dry way of saying "Please" as I know no other way to accomplish what I need. I realize what I would like to do (http://midniteftp.com/forum/index.php?topic=3922.0) could possibly be accomplished thru modbus, but I have looked at that and concluded modbus set up would be way over my head. Hope I did not come off snarky.
Mike
Mike - maybe we need to make an Arduino to control Modbus beginners step by step page . I know how to mess around with Arduino's a bit but haven't ever gotten it all together to connect to Classic yet. If I do I will make a new post and document ever step of the way .
You can get Arduino boards on Ebay for a few bucks .
Larry
That would be great Larry. Do you have to write your own control software with that though? I assume the local app would be of no use (or of no more use than it is now thru a LAN)
If you look in the other forum post on Arduino's you will see that others have written code to do various things and shared it. It is possible to modify or use parts of their control codes to do what you want to . So you don't have to start off from scratch if others have already figured it out.
Larry
I don't have any experience with an Arduino device, although it's on the list of things to learn in the future. So I opted for an off the shelf PLC and some ladder logic to implement cpfl's method of tweaking the AUX 2 WasteNot threshold setting. So far it's working well and I'm happy with the results.
Reading one(or a few) registers, comparing them, and then turning on an output is pretty easy to do with a PLC. It may be an option to tighten up the SOC settings for your diversion.
I had some time to test a SOC based PLC program and it works. Screenshots of the ladder logic attached.
The first small program is a simple on/off based on a single SOC value.
The second program turns on at a lower SOC and then turns off when the SOC drops back one percent from it's high. It would also turn back on if the SOC increased again during that charge cycle.
I'm using a Click PLC with an ethernet port, connecting to the Classic over LAN. The program reads once every 5 minutes(adjustable), so the Local App is still able to get a connection in btw those reads.
You program the PLC to do the modbus read of SOC register and then the program you wrote turns external relay on and off ?
Larry
Quote from: ClassicCrazy on February 27, 2018, 08:44:04 PM
You program the PLC to do the modbus read of SOC register and then the program you wrote turns external relay on and off ?
Larry
Yes, that's correct. The PLC output would power the diversion SSR.
Quote from: boB on February 04, 2018, 02:31:33 AM
Quote from: Matrix on February 03, 2018, 10:23:39 PM
But set the ON to 98% and you are stuck with a 93% OFF - Come on MidNite Solar, this would be easy for you to fix, and even better if you could really tweak the settings per this discussion (http://midniteftp.com/forum/index.php?topic=3922.0) ... :D
Will look into this, Mr. Matrix ! :)
boB
@boB ... I have been thinking about that suggestion of having SOC Hi (or whatever) turn the AUX on at a lower % as charge was going up (say as charging reached 90%) and then off as discharge went back down from 100% say to 99% as I was suggesting.
In a perfect world this would be great ... BUT ... I just the other day realized while thinking about it, If the charging system never reached 100% ... the AUX would turn on BUT NEVER TURN OFF. Ummm ... that would be bad, very bad. :-[
So there would have to be other safe guards put into my idea.
My Latest Settings and Setup
As of now I have have pretty much solved the quick light flicking issue with the water heater diversion load coming on and off several times in a short period of time at the end of the day due to low power.
Back a few months ago I installed my latest Hot Water Heater Element. I am now using a 240v AC 1000 Watt element off of my 240v split phase inverter. This helps to balance the load on the inverter much better and lessens the light flicker when the element turns on. I had to order the Element from Grainger (https://www.grainger.com/product/GRAINGER-APPROVED-Screw-In-Style-Water-Heater-2E459), This was the only place I could find such an odd spec element.
I have drifted away from SOC Hi because of the obvious power drain issues on the battery and less control of the SSR.
I have over the past few months been using Waste Not Hi again and the following settings that seem to be working pretty well balancing available power for heating water, Battery charging/discharging and light flickers when the load comes on. Note: I use a hi absorb voltage settings, So the first setting may need to be lower if you use a lower absorb voltage settings.
Relative - (V) = -1.7 (this setting is relative to the absorb volt setting and leaves the AUX on long enough for the CC to settle in to the load. If there is enough solar power, the volts will return to the absorb charge settings)
Relative + (V) = -0.2 (this is the setting that turns on the AUX control relative to the absorb volt setting)
Delay Time = 30 secs (this longer delay keeps they Diversion load from cycling too often)
Hold Time = 10 secs (this keeps the AUX on for 10 secs after the Relative - (V) has dropped below that setting in case of clouds etc)
This has worked pretty well the past few months. I am interested to here what others are having success with.
For now I am using SOC Hi to turn water heater on . It goes on at 96% and off at 94% . So if day is sunny it goes on and will stay on because my load is not so great as to bring back down too fast . I also have a temperature controller in series with the signal from the Classic to the SSR relay which is controlling the heating element in the water heater. So either the water temperature or the temperature controller can shut off the SSR. So far so good. Just using a cheapy ebay Fotec ( most likely fake ) which is mounted on heat sink and cheap $4 temperature controller. Heater element is AC so the built in water heater thermostat is also active . Only using one heating element on bottom of water heater and water heater is not filled up all the way so when water is heated it shuts off.
Larry
"Cool", Thanks Larry
I also just added an update to the bottom of the first post with a quick reference guide (http://midniteftp.com/forum/index.php?topic=3881.msg37786#msg37786) to this thread. If anyone knows of any other info in this thread that might be helpful to others let me know and I will add it to the first post
Quote from: ClassicCrazy on May 26, 2018, 10:10:35 AM
For now I am using SOC Hi to turn water heater on . It goes on at 96% and off at 94% . So if day is sunny it goes on and will stay on because my load is not so great as to bring back down too fast . I also have a temperature controller in series with the signal from the Classic to the SSR relay which is controlling the heating element in the water heater. So either the water temperature or the temperature controller can shut off the SSR. So far so good. Just using a cheapy ebay Fotec ( most likely fake ) which is mounted on heat sink and cheap $4 temperature controller. Heater element is AC so the built in water heater thermostat is also active . Only using one heating element on bottom of water heater and water heater is not filled up all the way so when water is heated it shuts off.
Larry
Larry, re-reading what you wrote, why are you using the temp controller in series with the SSR? For Redundancy? Wouldn't the control on the DHW turn it off when the water reached temp?
Larry, you say that the tank is only half full... is that draining by gravity? Is there air in the tank?
Quote from: Westbranch on May 26, 2018, 11:24:52 AM
Larry, you say that the tank is only half full... is that draining by gravity? Is there air in the tank?
Yes it is an open system in that it is not pressurized. I manually fill it . I have removed the top element and use that hole to recirculate water from the bottom drain hole . I use a small AC electric washing machine pump - this one has never blinked at pumping hot water and does the job of recirculating and also enough to get it up to a shower head .
Regarding the manually fill - I just got pressure switch from a washing machine - those are used to control the solenoid in a washer for low, medium , high water levels - so I am going to use it to either shut the pump off when the water is at high enough level or as a safety to shut the heating element off if the water level gets too low ( so the heater element won't burn out ) .
Larry
Quote from: Matrix on May 26, 2018, 11:18:43 AM
Quote from: ClassicCrazy on May 26, 2018, 10:10:35 AM
For now I am using SOC Hi to turn water heater on . It goes on at 96% and off at 94% . So if day is sunny it goes on and will stay on because my load is not so great as to bring back down too fast . I also have a temperature controller in series with the signal from the Classic to the SSR relay which is controlling the heating element in the water heater. So either the water temperature or the temperature controller can shut off the SSR. So far so good. Just using a cheapy ebay Fotec ( most likely fake ) which is mounted on heat sink and cheap $4 temperature controller. Heater element is AC so the built in water heater thermostat is also active . Only using one heating element on bottom of water heater and water heater is not filled up all the way so when water is heated it shuts off.
Larry
Larry, re-reading what you wrote, why are you using the temp controller in series with the SSR? For Redundancy? Wouldn't the control on the DHW turn it off when the water reached temp?
The digital thermostat is more accurate and is easily adjustable to change temperature settings . Let say I set it for 41 degrees C it will shut off and then not turn back on until it reaches whatever bottom range I set that for - like 38 degrees C . I have the temperature sensor for that stuck between the tank steel and insulation . It is easy to move if I want to try a different location on the heater.
And they are really really inexpensive - a few bucks - I got the one I am using years ago and just finding a use for it.
This is like the one I have.
https://www.ebay.com/itm/DC12V-LED-Display-Digital-Thermostat-Controller-Temperature-Control-Relay-Switch/262326258155?epid=1283191876&hash=item3d13dd09eb:g:H8EAAOSw1DtXHeKV
I also use one of these for refrigerator - it has some more features than one above and is available in different input voltages to power it.
https://www.amazon.com/Inkbird-All-Purpose-Temperature-Controller-Fahrenheit/dp/B00OXPE8U6/ref=sr_1_5?s=hi&ie=UTF8&qid=1527392653&sr=1-5&keywords=temperature+controller&dpID=41qoIapm7VL&preST=_SX342_QL70_&dpSrc=srch
This one wasn't on the market years back - but it looks like a good deal for prewired unit that runs on 110v
https://www.amazon.com/Inkbird-Temperature-Controller-Thermostat-Fermentation/dp/B015E2UFGM/ref=sr_1_8?s=hi&ie=UTF8&qid=1527392653&sr=1-8&keywords=temperature+controller
The factory built in thermostat is not so accurate but serves as a good backup so that is why I leave it wired in.
Larry
How are you safely wiring all that together? Diagram?
My problem would be that my SSR and DC is about 25 ft from the water tank. At the tank all I have is AC, but the idea looks cool.
The wire from the classic aux is low voltage so no problem using long wire - I just used some scrap stuff I had laying around - probably 20 or 30 feet and it has either 20 or 18 gauge wires in it. I had a 12v power cable in the shed already so just pulled it over to my heater to power the temperature controller. The 12v comes from samlex 24 to 12 dc to dc converter. But since it is such low current needed you could probably pull a small cable over with 24v and use one of those $2 small dc to dc converters to drop voltage.
Safety ? Put a fuse on every power cable - little inline fuses work . Fuse anything so if a wire gets shorted it will open up. Usually you fuse for the size wire just like for AC but you can put smaller fuses in if you want .
I took a photo - but keep in mind my setup is an experimental work in progress and I am the only one around who might touch something. So in the photo is to left temp controller , then the SSR on heatsink ( yes 110v hot terminals exposed !) - the outlet is controlled by the SSR and the big plug goes to water heater element ( just a power cord to it ) , the outlet to for right is wired to a hot water differential controller that I picked up somewhere and used last year to control hot water panel pump - it turns pump on and off depending on temp differential . I am only using that now to monitor water temperature for the most part.
(//)
Thanks. Looks like a viable experiment. I do that too. I am trying to figure out a way at this point to install a 3 position switch (not 3 way) to be able to flip the hotwater heater between grid and solar and top and bottom. I think I can do it but at this point it will take 2 of the switches.
https://www.amazon.com/Hubbell-HBL1386I-Toggle-Double-Center/dp/B006L72SUQ
(also know there are cheaper sources for this switch and a 30a version also)
Hello Everyone,
Thanks for the great information. I am trying to follow suit and set up a functioning opportunity load water heating system. I am having a bit of trouble sizing and selecting the appropriate capacitors and diodes to make my system work properly. I was planning on using Aux 2, DC waste not with my midnite cc.
Question one: is it possible to go pull power directly off the PV busbar rather than the batteries? My panels are in series and come into the house at ~135-150v, VOC is 158.8v, 1140w. The reason I'd like to do this is, one for voltage drop over the run from the relay to the element and two, to get the most out of the element. I have a run of about 25' from the relay to my water tank, this I'd use 8-10AWG depending on the voltage. My battery bank voltage is 24v.
I've attached a rough diagram here. I have it set up coming off the PV bus bar, but if that can't be done, just imagine that it's the battery bus bar ;D.
Thanks again for your insight.
Hi Vanman, welcome to the Forum.
One of the several reasons, that those wanting to use Diversion to heat water, use either battery V, or inverter AC output, is, that, when using PV DC into an MPPT CC as the voltage to heat water with resistive elements, the CC (usually) needs to be isolated from the CC input with a large diode. This diode is in series with the PV positive input to the CC. This keeps current from being pulled from the CC input (which could be damaging to the CC).
Another reason that many do not use the PV in DC to the CC as the voltage source, is that this approach can disturb the CC from using a previous Vmp, and may cause very frequent Vmp sweeps, which could reduce power production.
Have not tried to critically look at your diagram ... others will certainly have meaningful comments. FWIW, all just a drive-by opinion. Vic
Thanks Vic, that makes perfect sense. Battery voltage it is.
Cheers
Vanman,
Please let me add, that I am not an expert in this area. Did look at using this very method to heat water, but never did get around to even trying it.
It does look that you have thought quite a lot about using the PV DC approach.
But, again, I am no expert. Others will be able to speak on this subject much better, based on experience. Vic
Quote from: Vanman on June 06, 2018, 12:49:13 AM
Thanks Vic, that makes perfect sense. Battery voltage it is.
Cheers
Dont know if you saw any of these earlier in the thread, and I have not studied your diagram and exactly what you want to do / how you want to do it. But Direct PV DC is possible, but it would involve a smaller separate array and would not need the CC at all. But you might could mode something from these ideas. I had thought about it as it would give me dedicated water heating without ever compromising charging. My array is actually oversized enough I could dedicate 1 full string to this idea and still have enough to charge. But have not done it yet.
http://waterheatertimer.org/convert-AC-water-heater-to-DC-using-low-voltage.html
http://waterheatertimer.org/Convert-AC-water-heater-to-DC-water-heater.html
You could probably use some sort of DC temp sensor and take it to the next level.
And also ...
Thanks Matrix, I have checked all of those links out. I was pretty set on trying to use the waste not function on my CC, as I have a surplus of power in the summer and I heat water with my woodstove in the winter.
What I can't seem to figure out is the appropriate size capacitors and diodes I would need to protect the SSR and make it run properly on the PWM from Aux 2.
I have read pretty much all the information regarding a set up like this, and some members have mentioned capacitors. I understand a capacitor's application here, but I still don't know how to size it properly. Same goes for the diodes.
It seems like the main issues people are having with this sort of project is a buzzing SSR, which would be corrected with a capacitor and a lack of diodes protecting the SSR .
I'd like to avoid those issues if possible.
Thanks again for setting up a link and background post on this topic, chasing all the threads on this topic can be quite the rabbit hole!
Can you point to or provide a wiring diagram that contains these capacitors and diodes?
TIA
Quote from: bee88man on June 07, 2018, 09:51:13 AM
Can you point to or provide a wiring diagram that contains these capacitors and diodes?
TIA
There are formulas on how to size in these documents
https://www.vishay.com/docs/83859/appnote57.pdf
http://www.crydom.com/en/tech/newsletters/solid%20statements%20-%20protecting%20ac%20output%20ssrs%20against%20voltage%20transient%20phenomena.pdf
Larry
Thanks Larry. I'll check that out.
Here's a rudimentary wiring diagram for the design I had in mind....I am certainly not an expert on this, so I'd check my work before you use it as a reference.
http://midniteftp.com/forum/index.php?action=dlattach;topic=3881.0;attach=6627
Bee88manâ€" A side note, as Vic explained, the V+ on the load side of the SSR in the diagram should be the Bat+, not the PV busbar.. In my case that is 24V.
It would be great to see the results of your work.
I am still commissioning a 3kW diversion load system.
It is powered by the battery bus, so uses DC SSRs.
There is a choice to make amongst AC SSRs, which are really TRIACs(as opposed to MOSFET for the DC style.)
You'll see a selection for randomly switched versus zero crossing.
All TRIACS can only cut off at a zero crossing.
It could be tempting to choose the randomly switched AC SSR but these could cause quite a bit of noise thus harming your otherwise clean inverter power.
I actually emailed a design for an AC system with these concerns to MS but got nothing back.
The best part about going AC is high voltage. Over the same #10 wire run that delivers 1kW at DC (48V) could be 5kW at 240VAC at the same current (about 20 Amperes).
Under some PWM algorithm this would be fine. Not sure about MS though; whether the 60 Hertz AC load could send the 500Hz algorithm off. With good averaging it shouldn't be a problem even if there is some sort of ripple. Also having an oversized element will not be a problem since the PWM essentially delivers a continuous amount of power (on average through time).
We need experimental results so I recommend you post your results from this system. I will try to do the same for the DC system that I've designed.
Right now I've discovered that the configuration options of Waste Not Hi mode are trickier and basically undocumented as of the manual 10-001-1REV:H.
I have a system that should work well but have to verify it still. The lack of metric on the Aux 2 PWM out is problematic as well.
The last thing I found out is that setting the first config option to -0.2 is a misnomer; a positive value is needed to engage the PWM in absorption phase. I believe I left the site with it set at +0.5 and did witness it pull power and cut out at the end of the day. I have no idea whether this is a bug in the manual or in the firmware.
- Tim
Tim,
I think you may find Will's project on diversion project interesting - he has done it a different way using an Arduino and has it all well documented.
http://midniteftp.com/forum/index.php?topic=2511.0
I think another approach to what Will has done would be to use a Raspberry Pi and Node Red which I have just started trying to learn.
Using a micro computer instead of the built in Midnite Aux gives a lot more control capabilities and monitoring too.
Larry
I had problems using the AUX 2 PWM that I could not resolve. That is not to say they can't be resolved - just that I couldn't.
1) PWM settings: Under varying conditions the PWM did not turn on when it should have. If one adjusted the offset to always have it turn on then it would not turn off.
2) I was using AC diversion from my inverters. The Classic PWM is very fast and it made my lights flicker like crazy. Also the inverters did not sound happy. I understand now there is a function that permits this PWM frequency to be slowed somewhere in the wind side of the Classic.
3) I really wanted the WBJr which I could not use with the PWM on AUX 2.
So I went to a diversion system using waste not Hi on AUX 1. This system did not work that well for me , particularly on sun / cloud days.
So I went to my own PWM diversion control which I run at 15HZ. Also I dedicate an inverter to diversion and charging. The advantage of this is that you can use a small generator when charging while your house load inverters carry the electrical loads. This system is working very well for me. It is not hard to build and get running the early Arduino UNO version. This system works very well in all conditions.
I wish the Classic was a bit more aggressive with it's algorithm that increases load. I have two Classics each one connected to very similar arrays. I can see that sometimes one array makes quite a bit more power than the other one. Sometimes I turn my stove on to add load for a few moments and to force the Classic to produce more. This works but I cannot figure how to do this automatically. I do consider that the Classic is the best CC on the market and that Midnites support and method of doing business is also the best.
Sometimes I wonder if the new inverter charger will have a diversion system built into it.
Will
Quote from: WillEert on October 12, 2018, 10:22:58 PM
I had problems using the AUX 2 PWM that I could not resolve. That is not to say they can't be resolved - just that I couldn't.
1) PWM settings: Under varying conditions the PWM did not turn on when it should have. If one adjusted the offset to always have it turn on then it would not turn off.
2) I was using AC diversion from my inverters. The Classic PWM is very fast and it made my lights flicker like crazy. Also the inverters did not sound happy. I understand now there is a function that permits this PWM frequency to be slowed somewhere in the wind side of the Classic.
3) I really wanted the WBJr which I could not use with the PWM on AUX 2.
So I went to a diversion system using waste not Hi on AUX 1. This system did not work that well for me , particularly on sun / cloud days.
So I went to my own PWM diversion control which I run at 15HZ. Also I dedicate an inverter to diversion and charging. The advantage of this is that you can use a small generator when charging while your house load inverters carry the electrical loads. This system is working very well for me. It is not hard to build and get running the early Arduino UNO version. This system works very well in all conditions.
I wish the Classic was a bit more aggressive with it's algorithm that increases load. I have two Classics each one connected to very similar arrays. I can see that sometimes one array makes quite a bit more power than the other one. Sometimes I turn my stove on to add load for a few moments and to force the Classic to produce more. This works but I cannot figure how to do this automatically. I do consider that the Classic is the best CC on the market and that Midnites support and method of doing business is also the best.
Sometimes I wonder if the new inverter charger will have a diversion system built into it.
Will
OK Will. I'm going to take your word for it on MS.
The dirty AC power is possibly caused by a randomly switched SSR as opposed to the zero crossing variety. Which did you select?
It surely does get complicated and could depend quite a lot on the inverter too. I'd love to see a clean AC solution.
I use a stand-alone solution for AC diversion on a grid-tied system. Can hold exporting to zero joules.
Arudino based with current direction senseing at main breaker and burst rate cycle to match surplus operates zero-crossing triac or SSR.
Not by my design or code but is a well proven method.
Yes, I have LA battery, but battery is only a back-up, and Classic bulk is set at battery float setting and never switches out of bulk all day everyday.
Also have multi-stage diversion in case early stages become filled diverversion seamlessly shifts to the next line and so on...
I can see where off-grid cannot use this approach, though.
Quote from: bee88man on October 21, 2018, 09:35:56 AM
I use a stand-alone solution for AC diversion on a grid-tied system. Can hold exporting to zero joules.
Arudino based with current direction senseing at main breaker and burst rate cycle to match surplus operates zero-crossing triac or SSR.
Not by my design or code but is a well proven method.
Yes, I have LA battery, but battery is only a back-up, and Classic bulk is set at battery float setting and never switches out of bulk all day everyday.
Also have multi-stage diversion in case early stages become filled diverversion seamlessly shifts to the next line and so on...
I can see where off-grid cannot use this approach, though.
Where you are grid tied I don't think the noise issue will show up as strongly.
Over the course of a second there are 120 zero crossings; each half cycle of the AC voltage signal.
Conceivably an algorithm that syncs to the 60 Hz could be divying up a heavy load to approx. 0.001 of the actual load power as duty cycle in time intervals of one second. So a 4kW heat element could be incrementing at 40 watt increments; plenty good in terms of gradation and I think in terms of time response on a PV system. Thinking of the battery bank as a capacitor it is filtering quite deeply. Still, the electronics should be filtering properly too. Part of the AC problem is having excess inverter headroom to handle both the diversion load and unforeseen house loads. Generally I think when those house loads are running the battery voltage (the metric that determines traditional diversion) should be low, so the diverter will be off anyhow. Inverters have the ability to generate headroom power for short periods of time beyond their steady state output. Given the possibilities of transient overload during inductive loading it could be meaningful to hold off the diverter until the power is clean; beyond its own brownout effect. This problem is lessened in a grid tied system where the grid power is bound to fill the gap.
PV array power versus inverter power becomes a major design issue to this AC style diversion system. With 12 kW of inverter and 7 kW of PV I think the system could work with 7kW of diversion load. With 6kW of inverter and 7kW of panel the system cannot work with 7kW of diversion load; at least not at 100% duty. It is a shame to throw away PV power in an offgrid system and the option to harvest it completely is quite difficult. Still, it is a worthy cause. On a series of sunny days the potential power that is thrown away (given a high days of autonomy system) is substantial. This really argues for diversion load that matches PV power with duty cycle style loading. Also house loads that can be scheduled to work during sun hours can preserve the health of a battery bank. Refrigeration, water pumping, cooking, laundry. It's a tall order, but more practical than not.
In the future the best system will likely tap the high voltage available from the PV array directly, but for now the MPPT algorithms don't like this solution. Well, when they aren't sipping someone else might as well be. The ultimate solution lays within the MPPT algorithm. It knows when there is excess power doesn't it? I've never written one, but this seems terribly logical. To hell with the battery drop style of algorithm. The MPPT can theoretically tell you exactly how much power to consume while keeping the charge controller algorithm spot on.
My grid-tied works well enough to hold the utility metre at a very slight near motionless quiever.
If a off-grid could be made to show current flow attepted as that of grid...the search would be over...
A big thank you to Matrix for posting the summary info about this topic of Diversion Water Heater Load. This is super helpful:
http://midniteftp.com/forum/index.php?topic=3881.msg37894#msg37894
I have been down the rabbit hole on this topic and have done almost nothing else but read this forum for a full week. :o
From what I can tell there doesn't yet seem to be a definitive conclusion to the point about avoiding micro cycling your batteries. Could anyone contribute to help resolve this?
To expand the discussion:
The problem with battery micro cycling is mentioned (with no analysis) here: https://youtu.be/A9Meq8wLbME
TimBandTech has done an amazing job of unpicking some of the related issues here:
http://midniteftp.com/forum/index.php?topic=3881.msg37894#msg37894
But the thread does not conclude with a definitive solution for others to use
Some suggestions are made that perhaps the battery cycling issue can be avoided by configuring the settings appropriately:
http://midniteftp.com/forum/index.php?topic=3457.msg33090#msg33090
So I'm left with a few possible conclusions:
1. Most people are letting their batteries micro cycle and don't know about it, or don't care enough to do anything about it; and
2. A few people with expert knowledge are managing to fine tune the configuration settings on AUX2 on WASTE NOT active high (including the DvrtCnt TWEAKS setting) to successfully avoid micro cycling.
or;
3. Micro cycling cannot be avoided at all.
Could anyone contribute to help form (or point to) a definitive answer on this topic?
Thank you!
Grant