Off grid cabin set up

[Lloyds]

Hi all, great forum you have here!

I have some questions about setting up my cabin to be off the grid and run on a 12v battery system.

I have a PowMr 60amp MPPT charge controller its specs are:

Current: 60a
voltage: 12/24/36/48v
Max PV voltage: 150v
Max PV Input power: 720w for 12v

I also have some second hand Canadian solar brand panels and their specs are:

PMAX: 250W
VMP: 30.4V
IMP: 8.22A
VOC: 37.5V
ISC: 8.74A

I was originally thinking I could run 3 of these panels in parallel to the charge controller so it would be getting 750w in perfect conditions. 30w more than recommended on the controller. Is that an issue?

I'm getting confused after reading a few articles online about sizing mppt controllers and thought maybe it would be better to run 2 of the panels in series to the charge controller?

I plan on running this to charge my 12v battery bank. I'm working on a budget so i pieced this "odd ball" gear together and need to make it work in the best way possible.

What would be the best way to set this system up safely? Any help would be greatly appreciated!

Cheers

[Mike90250]

Welcome.

I think you are fine to run the 3 panels in parallel, but to do so safely, you need a combiner box. More than 2 panels in parallel requires a combiner to safely prevent a bad panel from catching fire - being driven by 2 good panels.

Panels seldom produce their full power, 70% - 80% is about all you see under normal conditions. Cold temps below 35F and / or white snow in the foreground reflecting onto the panels is the only time you see actual rated or more than rated power.

[Lloyds]

Thank you very much! I will start looking for a combiner box. Also, my cabin is metal framed I was considering using this as the negative/earth in my 12v set up to make cabling a lot easier (cheaper) Can you see any issues with this? The positive feeds will be fused etc correctly, so it will be like an automotive set up.

[Justin B.]

I have the same controller and finally decided to go 24v. Instead of using a combiner I used an in-line fuse on each parallel string.

[Lloyds]

Can I just fuse each panel going to the charge controller? Will this avoid the need for a combiner box? And if so, what amp rating should I use?

[Justin B.]

I have 9 100 watt panels so I hooked 3 in series and put the positive through a 15A in-line fuse to an "octopus" cable instead of a combiner. I have three of these series strings in parallel, each with it's own fuse. You can see the fuse assembly in this picture...

[Lloyds]

Thanks for the info!

[Mike90250]

f you opt to use an in-line fuse, use the MC4 style fuse holder, not the little rectangular Automotive fuse holders. Automotive fuse holders are not designed to carry high amps for hours of charging and often the holder fails.

On the label on the back of your panel, will be the Series Fuse Rating, likely somewhere about 8 amps. Don't guess, use the rating on the sticker.

I use the breakers, yes it costs more, but the breaker can be used as a switch for troubleshooting. peroidcly I switch my strings to compare that all are working and in balance. Can't do that with fuses, their holders might be "touch safe" but the holder cannot be used to interrupt a live circuit, the contacts are likely to arc and weld.



20160608_120434.jpg

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[Lloyds]

Screenshot_20181128-185444.png Maximum series fuse amperage is 15A according to the sticker on the back of my panels. I agree the circuit breaker is a better choice and I will take your advice!

So just to clarify, I will run a 15A circuit breaker on the positive wire from each individual panel, then connect them in parallel to my charge controller?

[littleharbor]

The fused combiner box will do the parallel connection as well as allow you to transition from PV wire to whatever type of larger gauge wire you chose to (preferably) run in conduit to your charge controller.

[SunEagle]

Hi all, great forum you have here!

I have some questions about setting up my cabin to be off the grid and run on a 12v battery system.

I have a PowMr 60amp MPPT charge controller its specs are:

Current: 60a
voltage: 12/24/36/48v
Max PV voltage: 150v
Max PV Input power: 720w for 12v

I also have some second hand Canadian solar brand panels and their specs are:

PMAX: 250W
VMP: 30.4V
IMP: 8.22A
VOC: 37.5V
ISC: 8.74A

I was originally thinking I could run 3 of these panels in parallel to the charge controller so it would be getting 750w in perfect conditions. 30w more than recommended on the controller. Is that an issue?

I'm getting confused after reading a few articles online about sizing mppt controllers and thought maybe it would be better to run 2 of the panels in series to the charge controller?

I plan on running this to charge my 12v battery bank. I'm working on a budget so i pieced this "odd ball" gear together and need to make it work in the best way possible.

What would be the best way to set this system up safely? Any help would be greatly appreciated!

Cheers

It sounds like that CC can accept 3 of those 250 watt panels wired in series and then you will not have to worry about a combiner box or fusing for each "string".

Remember an MPPT does not need to see high currents at the input. It will convert all of the wattage to charging amps at the battery voltage.

While 750 watts may seem to be over the limit of that 60amp CC you probably will never get more then 90% of the panel wattage rating as charging amps so the 60A CC should handle 750 watts.

[Mike90250]

[.......
So just to clarify, I will run a 15A circuit breaker on the positive wire from each individual panel, then connect them in parallel to my charge controller?

Yep, see in the upper right of my 6 breakers, the silvery thing - that's the "combiner" that attaches to each breaker and has 1 beefy screw for your cable to charge controller.

[Lloyds]

It sounds like that CC can accept 3 of those 250 watt panels wired in series and then you will not have to worry about a combiner box or fusing for each "string".

Remember an MPPT does not need to see high currents at the input. It will convert all of the wattage to charging amps at the battery voltage.

While 750 watts may seem to be over the limit of that 60amp CC you probably will never get more then 90% of the panel wattage rating as charging amps so the 60A CC should handle 750 watts.

This is exactly why I joined the forum, there are obviously many ways to skin a cat.

What would you suggest the easier way to run the set up? 3 panels in series to the charge controller or 3 panels in parallel with a combiner box to the charge controller?

If I run them in series will I need to add a circuit breaker inline before the charge controller? And if so, what amp rating would you suggest? 15A as per the "maximum series fuse rating" stated on the panel?

Thanks again for taking the time to help me out.

[SunEagle]

This is exactly why I joined the forum, there are obviously many ways to skin a cat.

What would you suggest the easier way to run the set up? 3 panels in series to the charge controller or 3 panels in parallel with a combiner box to the charge controller?

If I run them in series will I need to add a circuit breaker inline before the charge controller? And if so, what amp rating would you suggest? 15A as per the "maximum series fuse rating" stated on the panel?

Thanks again for taking the time to help me out.

I would go with 3 in series to avoid the combiner box and larger wire.

While you won't be required to have any over-current protection with a single "string" I would use a fuse to sized protect the wire between the panels and CC. 15A sounds about right for a #12 AWG.

[Lloyds]

Thank you! That is what I will do.

One more quick question, can anyone here see an issue of running the galvanised steel frame of the cabin as the earth/negative of the 12v system to keep wiring costs down?