Author Topic: Designing an Opportunity/Diversion Load For AUX 1 CTRL using an SSR - AC or DC?  (Read 5791 times)

ClassicCrazy

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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
« Last Edit: May 26, 2018, 11:48:45 PM by ClassicCrazy »
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

Matrix

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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.
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

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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.

system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

Matrix

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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)
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

Vanman

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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.

Vic

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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
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

Vanman

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Thanks Vic, that makes perfect sense.  Battery voltage it is.
Cheers

Vic

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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
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

Matrix

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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 ...
« Last Edit: June 06, 2018, 08:35:14 AM by Matrix »
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

Vanman

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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!


bee88man

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Can you point to or provide a wiring diagram that contains these capacitors and diodes?

TIA

ClassicCrazy

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system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

Vanman

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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

Vanman

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Bee88man— 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.