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

Started by Matrix, November 01, 2017, 03:19:35 PM

Previous topic - Next topic

Matrix

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. 
Grid-Assist Off-Grid
REC TwinPeak 2 285W 3S-3P 2565w-STC 1926w-NMOT Array / Classic 150 / Conext SW 4024 Inverter
Trojan L16H-AC 435Ah bank 4S  with 7' of 4/0 cable
24 volt system /  Need 3200Whs Daily
My System Install

ClassicCrazy

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
system 1
Classic 150 , 5s3p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system 2
 5s 135w Kyocero , 3s3p 270w Kyocera  to Classic 150 ,   8s Kyocera 225w to Hawkes Bay Jakiper 48v 15kwh LiFePO4 , Outback VFX 3648 inverter
system 3
KID / Brat portable

Matrix

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.)
Grid-Assist Off-Grid
REC TwinPeak 2 285W 3S-3P 2565w-STC 1926w-NMOT Array / Classic 150 / Conext SW 4024 Inverter
Trojan L16H-AC 435Ah bank 4S  with 7' of 4/0 cable
24 volt system /  Need 3200Whs Daily
My System Install

Matrix

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 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 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
- How to convert an AC water heater for Solar.  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.  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
- Or you could get these
- 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.  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. 
Grid-Assist Off-Grid
REC TwinPeak 2 285W 3S-3P 2565w-STC 1926w-NMOT Array / Classic 150 / Conext SW 4024 Inverter
Trojan L16H-AC 435Ah bank 4S  with 7' of 4/0 cable
24 volt system /  Need 3200Whs Daily
My System Install

ClassicCrazy

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
system 1
Classic 150 , 5s3p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system 2
 5s 135w Kyocero , 3s3p 270w Kyocera  to Classic 150 ,   8s Kyocera 225w to Hawkes Bay Jakiper 48v 15kwh LiFePO4 , Outback VFX 3648 inverter
system 3
KID / Brat portable

Matrix

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.  But that is not likely to happen.    So as for now,  this SOC% Hi  is working pretty well. 
Grid-Assist Off-Grid
REC TwinPeak 2 285W 3S-3P 2565w-STC 1926w-NMOT Array / Classic 150 / Conext SW 4024 Inverter
Trojan L16H-AC 435Ah bank 4S  with 7' of 4/0 cable
24 volt system /  Need 3200Whs Daily
My System Install

jmccallie

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

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.
Array 1: Talesun 320W 3S - 960W / MidNite Kid / PowerSonic 12-750 4S (48V) / Grundfos 6SQF-3 w/CU-200

Array 2: Talesun 320W 1S - 320W / EPEVER Tracer A 30A / PowerSonic 12-750 2P (RV)

ebenbayer

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

Offgrid;
25KW solar array
MicroHydro @ 150 ft of head w/ adaptive water sensing.
2000 AH 48 V ( Tesla Model S Battery packs in 2s1p format)
240 Gal integrated DHW / pressurized thermal storage

Matrix

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.   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
Grid-Assist Off-Grid
REC TwinPeak 2 285W 3S-3P 2565w-STC 1926w-NMOT Array / Classic 150 / Conext SW 4024 Inverter
Trojan L16H-AC 435Ah bank 4S  with 7' of 4/0 cable
24 volt system /  Need 3200Whs Daily
My System Install

ebenbayer

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
Offgrid;
25KW solar array
MicroHydro @ 150 ft of head w/ adaptive water sensing.
2000 AH 48 V ( Tesla Model S Battery packs in 2s1p format)
240 Gal integrated DHW / pressurized thermal storage

Matrix

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.
Grid-Assist Off-Grid
REC TwinPeak 2 285W 3S-3P 2565w-STC 1926w-NMOT Array / Classic 150 / Conext SW 4024 Inverter
Trojan L16H-AC 435Ah bank 4S  with 7' of 4/0 cable
24 volt system /  Need 3200Whs Daily
My System Install

openplanet

#56
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?
_______________________________________
We are star dust [on a] pale blue dot.
[And yes,] there is grandeur in this view of life.
Joni Mitchell, Carl Sagan, Charles Darwin

https://www.youtube.com/watch?v=cIANk7zQ05w

Matrix

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 ... :D
Grid-Assist Off-Grid
REC TwinPeak 2 285W 3S-3P 2565w-STC 1926w-NMOT Array / Classic 150 / Conext SW 4024 Inverter
Trojan L16H-AC 435Ah bank 4S  with 7' of 4/0 cable
24 volt system /  Need 3200Whs Daily
My System Install

boB

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 ... :D


Will look into this, Mr. Matrix !   :)

boB
K7IQ 🌛  He/She/Me

Matrix

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 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
Grid-Assist Off-Grid
REC TwinPeak 2 285W 3S-3P 2565w-STC 1926w-NMOT Array / Classic 150 / Conext SW 4024 Inverter
Trojan L16H-AC 435Ah bank 4S  with 7' of 4/0 cable
24 volt system /  Need 3200Whs Daily
My System Install