Designing a Diversion Water Heater Load For AUX 1 using an SSR - AC or DC?

[Matrix]

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 Thread

Links to other threads, forums, papers and PDFs discussing SSR usage etc  - Post #38

My original early setup with pics.  The next few comments after discuss settings - Post #40

Final Design and Links to SSR Options and with settings for SOC Hi and discussion following - Post #48

Waste Not Hi turns the Load on/off too much at the end of the day - Post #50

My Current AC Element and  Settings Using Waste Not Hi with better success - Post #68

Other Users Settings - Post #41    Post #69

[ClassicCrazy]

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

[Westbranch]

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...?

[Matrix]

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.

[ClassicCrazy]

Search SSR or Solid State Relay  and you will get a lot of info on how to use the Aux

Larry

[Matrix]

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?

[ClassicCrazy]

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

[Matrix]

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 so far complete with wire diagrams and recommendations.  Pete's PDF article 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 connected to the Charge Controller to Battery +/- bus bar.  This would be 24v nominal
2. a Crydom D1D** 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 ?

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?

[ClassicCrazy]

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

[Matrix]

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.

[SolarMusher]

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).

[Matrix]

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.

[SolarMusher]

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.

[Matrix]

...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)

[Matrix]

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