calculating wire size? panel Specs or array Specs?

[Jamie.sanders]

I'm trying to calculate the size wire I need from my panels to the CC. but im not sure
how to calculate or what to calculate?
I know the specs of my panels
VMP 40.99
IMP 9.93
ISC 10.53
VOC 52.6

but do I use this or since my panels are wired 2S3P would I then use those power numbers?
Anticipated array power 2405 watts
VOC 105.2
Rated PV array current 29.79amps
battery charging current at 28.8v 91.7amps

If I should use the array numbers which ones?? or does array wiring not matter?

thanks in advance.

 

[sunshine_eggo]

2S = 2X Voc/Vmp
3P = 3X Isc/Imp

So, 2S3P:

105.2Voc
81.98Vmp
31.59A Isc
29.79 Imp

For wire sizing, plan for Vmp and Isc

Start with Isc to determine the wire size NEEDED
Finish with a voltage drop calculator to determine if the wire size is sufficient for the distance:

10awg would produce a 3.85% voltage drop if your array is 50 feet from the MPPT:

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

3% is considered an acceptable wiring loss in most cases. Lower is better. For extremely long runs, some might consider 10% acceptable vs. spending $1000s on thick wire.

 

[Diysolar123]

wire size is driven by the maximum "current" that will pass thru; it really is that simple.
a 2S configuration outputs the same current as a 1S (which is why you want to put panels in series to keep current low as current is the trouble maker).
your short circuit current is 11amps per "string", you have a 3P setup so thats 3* 11amps or a maximum of 33amps(at 80V) from the panels to the charge controller.

battery charging currents have to do with the charge controller TO the batteries, nothing to do with the panel to CC connections.

use any of the many online wire size calculators to figure out what you want...

Circuit Wizard - Blue Sea Systems

 

[rmaddy]

wire size is driven by the maximum "current" that will pass thru; it really is that simple.

Not quite. You also need to account for voltage drop. Longer runs usually need bigger wires.

use any of the many online wire size calculators to figure out what you want...

That Blue Sea calculator takes into account both current and voltage drop along with a few other factors. It's a good one.

 

[Jamie.sanders]

2S = 2X Voc/Vmp
3P = 3X Isc/Imp

So, 2S3P:

105.2Voc
81.98Vmp
31.59A Isc
29.79 Imp

For wire sizing, plan for Vmp and Isc

Start with Isc to determine the wire size NEEDED
Finish with a voltage drop calculator to determine if the wire size is sufficient for the distance:

10awg would produce a 3.85% voltage drop if your array is 50 feet from the MPPT:

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

3% is considered an acceptable wiring loss in most cases. Lower is better. For extremely long runs, some might consider 10% acceptable vs. spending $1000s on thick wire.

OK, can you check this for me

2S = 2X Voc/Vmp
3P = 3X Isc/Imp

So, 2S3P:

105.2Voc
81.98Vmp
31.59A Isc
29.79 Imp

For wire sizing, plan for Vmp and Isc

Start with Isc to determine the wire size NEEDED
Finish with a voltage drop calculator to determine if the wire size is sufficient for the distance:

10awg would produce a 3.85% voltage drop if your array is 50 feet from the MPPT:

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

3% is considered an acceptable wiring loss in most cases. Lower is better. For extremely long runs, some might consider 10% acceptable vs. spending $1000s on thick wire.

thank you, can you double check my math?
if I wire my panels the other way
3S2P
then it would be
3S = 3X Voc/Vmp
2P = 2X Isc/Imp
or
132.9 VMP
21.06 ISC
for a length of 230 feet in plastic PVC

I plug this into the calculator and it says I can use 6 gauge wire with a 2.89% voltage drop
can you double check that for me? want to make sure before I order wire. but this way will save me around$1,000 vs having to use 2 gauge.

 

[sunshine_eggo]

6awg confirmed.

Confirm that your MPPT controller can handle the input. 3S with those panels will exceed most MPPT Voc limits. You would need a controller with 200V or higher limit.

 

[Jamie.sanders]

6awg confirmed.

Confirm that your MPPT controller can handle the input. 3S with those panels will exceed most MPPT Voc limits. You would need a controller with 200V or higher limit.

Yes, I will be using a midnight 200, I have a 150 but I have already talked to the power store and they are going to let me exchange it
minus a 15% restock fee. after doing the math and counting everything, the restock fee, shipping the new one to me etc I will still save $732.
with will get me over half way to buying 8 more lithium ion cells, then I can go 48 Volt!!!

 

[sunshine_eggo]

Yes, I will be using a midnight 200, I have a 150 but I have already talked to the power store and they are going to let me exchange it
minus a 15% restock fee. after doing the math and counting everything, the restock fee, shipping the new one to me etc I will still save $732.
with will get me over half way to buying 8 more lithium ion cells, then I can go 48 Volt!!!

And a new inverter.

Exercise caution when adding 8 new cells in series with 8 old cells in series to go from 24 to 48V. All cells need to be the same actual capacity, and should be the same age. You want to match everything as close as possible - manufacturer and cell model.

The battery will behave in accordance with the lowest performing cell.

No, things don't have to be perfectly matched, but the farther they are from "perfect," the more problems you will have.

 

[Jamie.sanders]

And a new inverter.

Exercise caution when adding 8 new cells in series with 8 old cells in series to go from 24 to 48V. All cells need to be the same actual capacity, and should be the same age. You want to match everything as close as possible - manufacturer and cell model.

The battery will behave in accordance with the lowest performing cell.

No, things don't have to be perfectly matched, but the farther they are from "perfect," the more problems you will have.

Yes I understand, my 1st battery order has not even arrived,,they are saying within the next 2 weeks.