Author Topic: Charge controller + relay for dumping into heating elements  (Read 260 times)

moosemaster

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Charge controller + relay for dumping into heating elements
« on: October 03, 2020, 10:44:11 AM »
Hello all,

I've been working on a fairly novel application of PV... A 12kW roof array would meet our winter electricity needs (Outer Hebrides, Scotland) for lighting and charging small DC devices (I'm considering forgoing conventional AC ring mains). In the summer this will kick out mountains of juice - which I will dump straight into elements for hot water and cooking (think of the cooker as a modified "storage heater" or Rayburn - bricks with a high thermal mass which are heavily insulated).

There are DC Fridge/Freezers on the market (pricey, but efficient) and we're looking at off-grid alternatives to washing machines... may go full Amish! 😉

In the winter we'll probably generate some additional leccy with a few small wind turbines and we can heat water/cook using wood and peat (plenty about, free - dug by hand in an environmentally sensitive manner...).

This is for a new build, essentially I can put the money that would otherwise be spent on roofing materials on some second hand PV. I can cover 100m2 for £4,570 - this includes purpose made weather proof GSE integration fittings.

I had seen someone else using Midnite controllers in a similar application - prioritising charging a NIFE battery bank - then dumping excess into elements:

https://diysolarforum.com/threads/oil-filled-radiator-as-hydro-dump-load-w-midnite-classic-250-pwm-relay-control-solid-state-relay.8612/#post-103758

Can anyone give any pointers as to how I might best achieve my goal using Midnite's products? I will have 56 230W panels total https://www.secondsol.com/en/anzeige/24287/solar-panel/crystalline/poly/ldk-solar/ldk-230p-20

 I've attached an estimate of annual PV output using this handy tool - https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html

ClassicCrazy

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Re: Charge controller + relay for dumping into heating elements
« Reply #1 on: October 04, 2020, 06:33:46 PM »
If you are talking about using AC from an inverter you can use the Aux 2 on the Midnite Classic to PWM a solid state relay controlling a resistance heating load.
But most people though use Aux 2 for Whizbang - Aux one does not have PWM capabilities but can switch things on and off.
If you are going to be using two or more Classics you can use the Aux2 on the second one for PWM .
There is a post on here where someone went into many details in his quest to dump all available extra power into water heating.

The  other option is to put DC directly into resistance heating load and can be efficient if you match the heating coil elements resistance correctly to the PV .
I know someone who is talking about using IGBT transistors to be able to switch high voltage high currrent DC  from PV. 
I have a PV direct water heater now and am using a DC SSR rated to handle the voltage and current .

Larry
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

moosemaster

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Re: Charge controller + relay for dumping into heating elements
« Reply #2 on: October 06, 2020, 11:49:10 AM »
If you are talking about using AC from an inverter you can use the Aux 2 on the Midnite Classic to PWM a solid state relay controlling a resistance heating load.
But most people though use Aux 2 for Whizbang - Aux one does not have PWM capabilities but can switch things on and off.
If you are going to be using two or more Classics you can use the Aux2 on the second one for PWM .
There is a post on here where someone went into many details in his quest to dump all available extra power into water heating.

The  other option is to put DC directly into resistance heating load and can be efficient if you match the heating coil elements resistance correctly to the PV .
I know someone who is talking about using IGBT transistors to be able to switch high voltage high currrent DC  from PV. 
I have a PV direct water heater now and am using a DC SSR rated to handle the voltage and current .

Larry

Thanks Larry!

I had been considering hooking directly up to appropriately rated DC elements for simplicity's sake. Can I find more details on your DC SSR anywhere? Sounds great.

Ta,

Sean

ClassicCrazy

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Re: Charge controller + relay for dumping into heating elements
« Reply #3 on: October 06, 2020, 07:49:35 PM »
If you are talking about using AC from an inverter you can use the Aux 2 on the Midnite Classic to PWM a solid state relay controlling a resistance heating load.
But most people though use Aux 2 for Whizbang - Aux one does not have PWM capabilities but can switch things on and off.
If you are going to be using two or more Classics you can use the Aux2 on the second one for PWM .
There is a post on here where someone went into many details in his quest to dump all available extra power into water heating.

The  other option is to put DC directly into resistance heating load and can be efficient if you match the heating coil elements resistance correctly to the PV .
I know someone who is talking about using IGBT transistors to be able to switch high voltage high currrent DC  from PV. 
I have a PV direct water heater now and am using a DC SSR rated to handle the voltage and current .

Larry

Thanks Larry!

I had been considering hooking directly up to appropriately rated DC elements for simplicity's sake. Can I find more details on your DC SSR anywhere? Sounds great.

Ta,

Sean

I have been using one of these that are rated to 220v DC . Not very expensive but works.  At first I didn't think it was working , then read the note that said the polarity on the output needed to be the right way. So I switched the sides I had the wires connected and then it worked right. I have it mounted on one of their bigger heatsinks .  I have gotten the relays fairly quickly from them.
https://www.aliexpress.com/store/group/Single-DC-To-DC/5105062_515838821.html?spm=a2g0o.detail.0.0.75b667bb81ErSA
I have a thermostat contact in series with the control voltage to the relay to shut off when it gets to temperature .

Larry
« Last Edit: October 06, 2020, 07:53:37 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

moosemaster

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Re: Charge controller + relay for dumping into heating elements
« Reply #4 on: October 12, 2020, 11:24:52 AM »
I have been using one of these that are rated to 220v DC . Not very expensive but works.  At first I didn't think it was working , then read the note that said the polarity on the output needed to be the right way. So I switched the sides I had the wires connected and then it worked right. I have it mounted on one of their bigger heatsinks .  I have gotten the relays fairly quickly from them.
https://www.aliexpress.com/store/group/Single-DC-To-DC/5105062_515838821.html?spm=a2g0o.detail.0.0.75b667bb81ErSA
I have a thermostat contact in series with the control voltage to the relay to shut off when it gets to temperature .

Larry

Amazing, thanks for your help Larry  :)

coniferous

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Re: Charge controller + relay for dumping into heating elements
« Reply #5 on: November 16, 2020, 02:47:10 PM »
I know you are talking about DC loads and the SSR will work well for those, but if you ever decide to hook up an AC load I'm using this with my Midnite Solar and it works *perfectly*. It's very simple.

https://www.adafruit.com/product/2935
Offgrid Trailer
1.4 Kw array, 1000AH of AGM batteries in 12v config
3000 watt main inverter, 300 aux inverter
1 Classic 150 - Plans to supplement with wind.

boB

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Re: Charge controller + relay for dumping into heating elements
« Reply #6 on: November 16, 2020, 04:05:42 PM »
I know you are talking about DC loads and the SSR will work well for those, but if you ever decide to hook up an AC load I'm using this with my Midnite Solar and it works *perfectly*. It's very simple.

https://www.adafruit.com/product/2935

Interesting.  Do you know how you control it with the control input ?  It shows an polarized AC input.  Maybe it can take AC or DC input for on/off.

Too bad it is only rated for 12 amps AC (maybe ?) but I don't think it is listed by UL or ETL or CSA, etc.  Says "QC" on the label though whatever that means.

K7IQ

coniferous

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Re: Charge controller + relay for dumping into heating elements
« Reply #7 on: November 19, 2020, 12:17:19 PM »
I know you are talking about DC loads and the SSR will work well for those, but if you ever decide to hook up an AC load I'm using this with my Midnite Solar and it works *perfectly*. It's very simple.

https://www.adafruit.com/product/2935

Interesting.  Do you know how you control it with the control input ?  It shows an polarized AC input.  Maybe it can take AC or DC input for on/off.

Too bad it is only rated for 12 amps AC (maybe ?) but I don't think it is listed by UL or ETL or CSA, etc.  Says "QC" on the label though whatever that means.

It can take DC input. I have it on my Aux1 right now and I configured the output to be 12v. The writing on the actual device isn't super intuitive, but the datasheet says "Universal control voltage 3-60VDC or 12-120VAC, or connect directly to a 12V, 48VDC, or even 120VAC circuit."

And the 12 amp rating is for the 120 AC relay, it can do 1440 watts. I wouldn't switch it on an off rapidly (traditional relay), but still.
« Last Edit: November 19, 2020, 12:19:33 PM by coniferous »
Offgrid Trailer
1.4 Kw array, 1000AH of AGM batteries in 12v config
3000 watt main inverter, 300 aux inverter
1 Classic 150 - Plans to supplement with wind.

ClassicCrazy

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Re: Charge controller + relay for dumping into heating elements
« Reply #8 on: November 19, 2020, 07:55:11 PM »
I know you are talking about DC loads and the SSR will work well for those, but if you ever decide to hook up an AC load I'm using this with my Midnite Solar and it works *perfectly*. It's very simple.

https://www.adafruit.com/product/2935

Interesting.  Do you know how you control it with the control input ?  It shows an polarized AC input.  Maybe it can take AC or DC input for on/off.

Too bad it is only rated for 12 amps AC (maybe ?) but I don't think it is listed by UL or ETL or CSA, etc.  Says "QC" on the label though whatever that means.

It can take DC input. I have it on my Aux1 right now and I configured the output to be 12v. The writing on the actual device isn't super intuitive, but the datasheet says "Universal control voltage 3-60VDC or 12-120VAC, or connect directly to a 12V, 48VDC, or even 120VAC circuit."

And the 12 amp rating is for the 120 AC relay, it can do 1440 watts. I wouldn't switch it on an off rapidly (traditional relay), but still.

I looked those up after you posted . They look like a nice handy way to control stuff using the classic Aux.  All the associated safety components to make sure the relay coil doesn't get zapped by flyback voltages is built in . So plug and play .
Can't use them for PWM so would still have to go with an SSR for that if PWM wanted.

Larry
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