? wiring ?

raindog · November 2019

I see that I have what looks like 10awg wire from the controller to the solar panels (wire is not marked). I estimate the length to be 15' or less by a foot or so. The wire from the controller to the inverter is marked 10awg.

Is this ok for the 2, 250w panels I have?

BB. · November 2019

What is the distance, Vmp/Imp of the panels? Are the two panels in series or parallel? What is the battery bank nominal voltage?

-Bill

raindog · November 2019

Hi Bill

, I don't have all that information. The distance is about 12-15' I guesstimate. The panels were already here, on the roof, and are visually different with respect to the frame color. One is a Trina (if I can trust a receipt found among some papers here). I suspect they were purchased at different times and know they were purchased from different suppliers, as another receipt just says "solar panel". Where the wires come into the house and join the wire that goes to the controller, it is black : red. Battery bank is currently 24v, 2 x 104ah, but I am replacing the batteries with 2 x 200ah).

BB. · November 2019

Generally (but not always), These panels are around Vmp~30 volts:

http://www.princetonsolarsystems.com/solarpanels/trinasolar/tsm-250pa05-08/

For a 24 volt battery bank, two of these panels in parallel is not really high enough voltage to properly/quickly recharge a 24 volt lead acid battery bank.

Normally, that would be two of these panels in series driving an MPPT solar charge controller, and 15 feet of 10 AWG cable is fine... The calculations:

Electrical Data @ STC

Peak Power Watts-PMAX (WP)	250
Power Output Tolerance-PMAX (%)	0/+3
Maximum Power Voltage-VMAX (V)	31
Maximum Power Current-IMPP (A)	8.6
Open Circuit Voltage-VOC (V)	37.4
Short Circuit Current-ISC (A)	8.59
Module Efficiency ηm (%)	15.3

So, that would be Vmp-array~62 volts, and Imp-array~8.6 amps... Using a simple voltage drop caculator with 10 AWG and 15 feet (one way run for this calculator), we get:
https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=3.277&voltage=62&phase=dc&noofconductor=1&distance=15&distanceunit=feet&amperes=8.6&x=63&y=13

Voltage drop: 0.26
Voltage drop percentage: 0.42%
Voltage at the end: 61.74

Typically, we use 1% to 3% voltage drop (more than 3%, start to waste some power, less than 1%, not usually worth the cost of copper).

-Bill

PS: I need to add, when you place panels in parallel, you should match Vmp-panel within ~10% or less (i.e., 31 volts +/- 3.1 volts).

And if placing in series, the panels should match Imp-panel within 10% or less).

raindog · November 2019

Hi Bill, I thought I didn't explain the wires to well, so I'm sending some photos just to confirm about parallel vs. series:

Wires come separately from the panels to this point under the eves:

Image: https://us.v-cdn.net/6024911/uploads/editor/bh/uvh3hrd9klgg.jpg

Then, inside the porch, looks like this (not such a good photo: actually red:black on one side, and black:black on the other):

Image: https://us.v-cdn.net/6024911/uploads/editor/31/7b1h9rvimj60.jpg

Then, where they go into the controller, looks like this:

Image: https://us.v-cdn.net/6024911/uploads/editor/wz/odqbujsce8f9.jpg

I know very little about wiring; I apologize and thank you very much for your help.

Estragon · November 2019

Looks to me like parallel wired. In series, the +ive of one panel would normally be connected to the -ive of the other on the roof, and just one +/- pair brought down. The first pic appears to be a 'Y' connector, combining + to +, and - to -.

BB. · November 2019

Also a warning on wiring and sharp metal openings... Long term, is is very possible for the cable insulation to get cut on the unprotected entrance to your controller.

And I agree with Estragon, the present panels look to be connected in parallel. If those are Vmp~30 volt panels, that is too low of voltage to properly recharge your 24 volt battery bank.

-Bill

? wiring ?

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