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Old 17-04-2019, 14:42   #1
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Wire size for solar panel to controller

Hi,

Just want a sanity check.

On my boat there is currently 780w of solar from 6 panels wired in series. The problem is that any shade at all kills the output. I'd like to rewire into parallel. However, I want to make sure the wire is safe.

I expect the run to be 20ft from the solar arch to the solar charge controller.

How big of a wire do I need to be safe? I'm guessing 1 or 2 AWG, which seems quite big.

Thanks
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Old 17-04-2019, 14:56   #2
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Re: Wire size for solar panel to controller

6 in parallel? Or 2s 3p? And at what voltage?
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Old 17-04-2019, 14:57   #3
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Re: Wire size for solar panel to controller

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6 in parallel? Or 2s 3p? And at what voltage?
6 in parallel. They are 12v panels, I think they are rated at 17v.
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Old 17-04-2019, 15:10   #4
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Re: Wire size for solar panel to controller

65 Amps @ 12 volt. so 10 gauge from each panel to a splice box then



4 Gauge AWGto the controller will give you 0.32 voltage drop. Less than 3% but ampicity is on the edge. So use 3AWG if you can get it or 2AWG.



You'll probably loose morning and late afternnoon charging capacity with the lower voltage.


You might investigate a 2s 3 p set up if you can get paris that won't be shaded.
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Old 17-04-2019, 15:13   #5
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Re: Wire size for solar panel to controller

Thanks for the info!! I might give the 2s 3p a try, I could go with a smaller run of wire as well.
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Old 18-04-2019, 09:10   #6
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Re: Wire size for solar panel to controller

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Originally Posted by ThereAndBack View Post
Thanks for the info!! I might give the 2s 3p a try, I could go with a smaller run of wire as well.
Smaller is good. But you could also put bypass diodes between each if series has worked for you otherwise.

Actually I'm a bit surprised that 'any' shade kills your output as most panels today would have several diodes in them as well, thereby affecting only the string which has a single (or more) cell COMPLETELY dark.

Shady days shade the entirety. They don't kill my output, but lessen it. Even with my KISS generator on the corner, it doesn't kill even any row, let alone the entire panel.

Whenever you can bring yourself to upgrade, go for the higher voltage panels and let your controller do the heavy lifting. We upgraded from 3 x Kyocera 120 to 2 x Sunpower 360 in essentially the same footprint. During installation, I did a check with the sun at such an angle that my whip antenna shadow would go from one corner to the far corner on one panel.

Multiple up-down cycles proved that there was NO measurable (well, with my analog 50A meter) difference.

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Old 18-04-2019, 09:36   #7
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Re: Wire size for solar panel to controller

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Originally Posted by Wood View Post
>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
So use 3AWG if you can get it or 2AWG.>>>>>>>>>>>>
>>>>>>>>>>>

I have had trouble finding 3 awg. Usually find 2 or 4.
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Old 18-04-2019, 10:07   #8
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Re: Wire size for solar panel to controller

You can also go with multiple charge controllers and multiple wire pairs. Gives some redundancy and maybe you can pair panels intelligently based on your shading scenario... bypass diodes are not a bad idea either.
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Old 18-04-2019, 10:40   #9
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Re: Wire size for solar panel to controller

760 watts. Does that mean 6 panels of 130 watts?

If so, max is only a little over 10 amps on the wire if in parallel to the controller. You could use 14, 12, or 10 gauge wire

I'm using 14 gauge wire on my 20 and 65 watt panels and 10 gauge on my 50 watt panel since it came with that size wire for the MC4 connectors
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Old 18-04-2019, 11:35   #10
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Re: Wire size for solar panel to controller

when I have a question about wire sizing I like to use this calculator:

https://www.calculator.net/voltage-drop-calculator.html
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Old 18-04-2019, 12:12   #11
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Re: Wire size for solar panel to controller

Your calculator can tell me voltage drop but I was more concerned with safety and ampacity of the wire run. For instance, 10g copper at 140F has an ampacity of 30 amps, thus the current wire I have run from the batteries to the solar array cannot carry 780watts at 17v because 780/17 = 45.8 amps.

If I split the panels into series parallel as suggested (2s 3p):
2x130w in series would be 17v x 2 = 34v and 260w -> 260/34 = 7.6 amps per set

7.6 amps x 3 = 23 amps

In theory that should work because the current run from the arch to the controller is 10AWG, and at 34v 23a (max output) it would have a voltage drop of less than 3%. Unless I'm way off.
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Old 18-04-2019, 14:19   #12
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Re: Wire size for solar panel to controller

Quote:
Originally Posted by ThereAndBack View Post
Hi,

Just want a sanity check.

On my boat there is currently 780w of solar from 6 panels wired in series. The problem is that any shade at all kills the output. I'd like to rewire into parallel. However, I want to make sure the wire is safe.

I expect the run to be 20ft from the solar arch to the solar charge controller.

How big of a wire do I need to be safe? I'm guessing 1 or 2 AWG, which seems quite big.

Thanks
You didn't give the panel model or the Isc from the specifications, so there is no way we can help you
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Old 18-04-2019, 14:25   #13
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Re: Wire size for solar panel to controller

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You didn't give the panel model or the Isc from the specifications, so there is no way we can help you

I can check on that later but in the meantime, can you explain why Isc would effect wire sizing?
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Old 18-04-2019, 15:35   #14
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Re: Wire size for solar panel to controller

[QUOTE=ThereAndBack;2872693]Your calculator can tell me voltage drop but I was more concerned with safety and ampacity of the wire run. /QUOTE]

if the voltage drop is low itís a safe run
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Old 20-04-2019, 08:50   #15
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Re: Wire size for solar panel to controller

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Originally Posted by ThereAndBack View Post
I can check on that later but in the meantime, can you explain why Isc would effect wire sizing?
Isc is the maximum current rating so that what you size the conductor for.
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