PV Combiner to SCC wire gauge calculator inputs?

[brewmium]

Hi All!

I have found a loss calculator to tell me the AWG i need, but am a bit confused on the current (heck, and maybe even the voltage) aspect leaving the combiner, and making the longer run to the SCC.

So, given that I will have 8 panels, in the form of 2p4s for a 24v system,

The specs for each of the 8 panels is this:

• Max. power voltage(Vmp): 19.01V
• Max. power current(Imp): 8.91A
• Open circuit voltage(Voc): 22.5V
• Short circuit current(Isc): 9.44A

Is it 8.91A times 4, at 19.01V times 2? So... 25.64A and 38.02V that is going into that calculator?

I really appreciate the help i've received this last few days since I joined! You all are great, and I can't wait until I can give something back.

thanks,
-eric

 

[Supervstech]

Nope, it would be 9.44 x two since you are at 2P, and 19.01 x four since you are 4S, however you need to make sure the SCC can handle 22.5x four volts within it’s max limit.

 

[brewmium]

Well now, i totally reversed that. It's 2s4p.

So, sounds like 19.01V x2 and 9.44A x4

So, what i learned was: It's the short circuit Amperage, and the max power Voltage that goes into the AWG calcualtion, thank you.

These are the specs for the controller:
40A MPPT Charge Controller Nominal System Voltage: 12V, 24V
Rated Charge Current: 40A <--- 4 x 9.44A == 37.76A
Rated Load Current: 20A
Max PV Open Circuit Voltage: 150V / 138V <--- 2 x 22.5V == 45V
Max PV Input Power: 520W (12v battery) / 1040W (24v battery). <--- 4panel pairs x 170watts == 680watts & ~24V??

So, at 38.4V @ 37.76 Amps, I'm assume i'm within specs?!?

tyvm,
-eric

 

[Craig]

Yes but you would be better off as originally posted 4s2p. So you get around 18 amps an 90 volts

Either way us within spec but you can. Use smaller wires. And two seperate inputs (4 wires) to your combiner box

 

[brewmium]

Hey @Craig, tyvm for the feedback, but now i'm confused. Will my MPPT do the right thing with that 90V, going into my 24v LFP batteries? I am still struggling to wrap my mind around the current state of the art... vs 35 years ago.

 

[Craig]

Hey @Craig, tyvm for the feedback, but now i'm confused. Will my MPPT do the right thing with that 90V, going into my 24v LFP batteries? I am still struggling to wrap my mind around the current state of the art... vs 35 years ago.

Yes the SCC will take in whatever volts up to its Max V input spec and cut that down for your battery voltage.

 

[brewmium]

That’s great! on a super positive note, I was able to get the whole system kind of hooked up, with 2 panels, and a pair of lead acid batteries, just to test out my hardware (while I’m in Amazon’s return window). Was fun to make electricity today!!! And I even ran my l14” bandsaw off of it for a minute.

 

[Craig]

That’s great! on a super positive note, I was able to get the whole system kind of hooked up, with 2 panels, and a pair of lead acid batteries, just to test out my hardware (while I’m in Amazon’s return window). Was fun to make electricity today!!! And I even ran my l14” bandsaw off of it for a minute.

I built one of my cabins completely off of solar power. It is so satisfying to say no generator needed