Author Topic: What size wire from solar panels to joiner box to charge controller?  (Read 212 times)

steven_ucf

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Hello,

I am so confused about wire size.  I have the classic 150.  I have 9 250 watt solar panels.

I was going to have three series of solar panels all with three panels connected in parallel.  Each panel is 8.30 IMP and 30.1VMP and 37.2 VOC.  So that would be three in series with 111.6VOC and 24.9IMP.  When its all combined it will have 116 Volts and 74.7 Amps.  I need to run this  50' from the solar panels to the charge controller.

Question. 

1) Do I run 6 wires from the solar panels back to the joiner box located by the charge controller.  If so what size wire?  Or do I keep the joiner box located by the solar panels and then run one big wire from the joiner box (located by the solar panels) to the charge controller.  If so, what size wire.

2)  It looks like I can not really put any wire above a 4 gauge wire from the joiner box to the charge controller.  Wont that be too small of a wire for this setup?

3) What size ground wire should i run from the solar panel array - 50' to the charge controller?

Thanks in advance!
« Last Edit: October 26, 2020, 06:00:08 PM by steven_ucf »

steven_ucf

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Re: What size wire from solar panels to joiner box to charge controller?
« Reply #1 on: October 26, 2020, 05:54:47 PM »
btw - it is a 24volt system if that matters? Sorry total newbie here:(

boB

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Re: What size wire from solar panels to joiner box to charge controller?
« Reply #2 on: October 26, 2020, 06:41:38 PM »

Hello Steven...

Sounds like you have the perfect combination for a 24V battery system.  3 strings of 3 panels in series is perfect.

So, 50 feet isn't too far.  They way it usually works is to connect the 3 strings together near the solar panel array with the combiner box and then run just two pus and minus wires back to the charge controller area....

4 AWG should be just fine for this but you probably don't need even that big of wire for 50 feet.

6 AWG is probably good but you can use even larger if you use a transition ferrule or a bus bar or better yet, you will need a disconnect switch or breaker for the PV input right at the charger so you can just use the output side of that to change wire size to 4 or 6 AWG to the PV input.

A fine wire 4 AWG will be difficult to put into the Classic terminal block so I would suggest 6 or maybe 8 AWG for that last foot or two.

The 50 foot run wire size will give a slight bit of loss but only a couple of percent maximum or so.
K7IQ

UpNorthMan

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Re: What size wire from solar panels to joiner box to charge controller?
« Reply #3 on: October 26, 2020, 08:00:54 PM »
Hello Steven,
With your panels wired 3S - 3P you will have closer to 25amps. The voltage is multiplied by 3 (3S). And the amps is also multiplied by 3 (3P). Bigger wire is better, but the it isn't the 75 amp min requirement. I'm not a expert on the recommend size. Others will offer there opionion.
Ed
1000W panels Kid CC 184 ah battery bank @ 48v
Weekend cabin, 250w inverter.
Waiting for the new inverter to be released so I can finish my install!

steven_ucf

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Re: What size wire from solar panels to joiner box to charge controller?
« Reply #4 on: October 27, 2020, 04:02:56 PM »
Thanks; this is perfect.  I will use 4awg.  Thanks so much for all the help.

ClassicCrazy

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Re: What size wire from solar panels to joiner box to charge controller?
« Reply #5 on: October 27, 2020, 08:40:21 PM »
Thanks; this is perfect.  I will use 4awg.  Thanks so much for all the help.

I used Southwire voltage drop calculator for your specs.
Sounds like 6 gauge would be fine and you don't have to mess around trying to make 4 gauge  fit in the Classic .
You can use a 60 amp breaker at the Classic for PV in . All your PV strings  ( 3)  in the combiner would have their own 15 or 20 amp breakers ( usually 15 I think ) 

Voltage Drop
Minimum Conductor Size
2.34%
10 AWG

 
1 conductor per phase utilizing a 10 AWG Copper conductor installed Direct Buried will limit the voltage drop to 2.34% or less when supplying 25 amps for 50.0 feet on a 112 volt 1 phase system.

Engineering information only
30
Amps Rated ampacity of selected conductor
1.1417
Ohms Resistance (Ohms per 1000 feet)
0.05
Ohms Reactance (Ohms per 1000 feet)
0.9
Power Factor
3.3600000000000003
Maximum allowable voltage drop at 3%
2.623
Actual voltage drop loss at 2.34% for the circuit
https://www.southwire.com/calculator-vdrop

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