Charge controller + relay for dumping into heating elements

[moosemaster]

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]

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

[moosemaster]

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]

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

[moosemaster]

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]

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

[boB]

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.

[coniferous]

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.

[ClassicCrazy]

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

[Mike H]

I have been working on something like this for a while and I would like to attach a picture but it will not let me, any ideas why?

[ClassicCrazy]

I have been working on something like this for a while and I would like to attach a picture but it will not let me, any ideas why?

It won't let you upload large photos. I usually use irfanview and make them into a smaller photo that isn't as large and then it works.

Larry

[ClassicCrazy]

I just did an update video of my PV solar water heater project.
I use both direct DC and also use PWM from Aux 2 .
Here is the link
https://youtu.be/s7trVpHLts4

Larry

[ClassicCrazy]

This guy designed a board that will take excess power from PV system ( at DC source I think ) and dump it into water heater.
I don't understand exactly how it is wired in and other details .
https://youtu.be/yegjGYDMDJg

Larry

[Mike H]

I have been working on something like this for a while and I would like to attach a picture but it will not let me, any ideas why?

It won't let you upload large photos. I usually use irfanview and make them into a smaller photo that isn't as large and then it works.

Larry

Thanks Larry, it's a 40.9kb jpg.  When I hit the attach button it shows the jpg but will not add it to the post.

[Mike H]

lol, it posted.
So question, do I need the 2 CB between the heating ele. and the SSR?