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groingo
Member
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# Posted: 19 Jul 2025 11:21pm
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I am running 800 watts 40 amp 12 volt solar panels,
what guage cable / wire to run 50 feet?
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Steve_S
Member
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# Posted: 20 Jul 2025 05:55am
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You can stick with the 10 AWG Fine Copper Strand solar wire that's on the panels now... should not be a probem.
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Brettny
Member
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# Posted: 20 Jul 2025 10:34am - Edited by: Brettny
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Theres a chart for this...but are you sure the pannels are putting out only 12v?
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groingo
Member
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# Posted: 20 Jul 2025 11:49am
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On the panel they show 23 volts max but normally they show 15 to 17.
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Steve_S
Member
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# Posted: 20 Jul 2025 01:33pm
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My main array is 2 strings of 4 panels with 2 parallel strings. That brings in just under 200VDC. Both strings are combined @ Rack and use 10-AWG medium stranded NMWU that runs underground for 55' to powerhouse from the array without any losses.
When adding panels in Series (a string) that increases to collective Voltage. In Parallel the arrays increase the Watts/Amps.
hope it helps.
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travellerw
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# Posted: 20 Jul 2025 02:25pm
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As Steve said, you would need to know if you are running the panels in series or parallel. It makes a HUGE difference. I'm going to make some assumptions as I don't have all the data from your panels. The short circuit voltage is what we really need. I'm going to assume 20V for your panels as 20V times 40A is 800W.
Here are the numbers
Parallel
800W/40a = 20V
To carry 40amps @ 20V for 50ft with a 5% loss you would need to run 3awg cable (in open air).
Series
20V X 4 panels = 60V
800W/60V = 13.3A
To carry 14amps @ 60V for 50ft with a 5% loss you need to run 12awg (in open air)!
There are tons of calculators online to figure this stuff out. Here is one I use often
https://solarwiresizecalculator.com/
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Brettny
Member
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# Posted: 20 Jul 2025 06:29pm
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How high of a PV voltage will your charge controller support? Also post a picture of the tag on your pannels.
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groingo
Member
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# Posted: 21 Jul 2025 03:30pm - Edited by: groingo
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Just called Renogy in hopes they could give a straight answer using information off the panel and all I got was well, well, maybe, could be.....
Here is the tag, what do you guys think?
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travellerw
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# Posted: 21 Jul 2025 04:17pm - Edited by: travellerw
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LOL.. I spotted a boo boo in my math.. Lets do this again.
First, we need to know if your solar controller can handle the voltage in series. Since you mentioned Renogy, I'm going to assume you have a Rover. It should be good to 100V
Series
18.2V X 4 panels = 72.8V 10.9A (in series volts go up, but amps remain the same).
To carry 11amps @ 72.8V for 50ft with a 5% loss you need to run 14awg (in open air)!
To carry 11amps @ 72.8V for 50ft with a 2% loss you need to run 10awg (in open air)!
As Steve pointed out in his first posts, you will be fine running 10awg IF you run the panels in series. However, with panels in series you need to be very careful of shade. Do everything you can to minimize shading as it will be killer.
If you run in parallel, you WILL need much bigger wire. MUCH MUCH bigger wire!
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travellerw
Member
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# Posted: 21 Jul 2025 04:22pm
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One last thing.. You don't mention what wire you are running from the MPPT to your batteries.
I'm assuming a 12V system.
728W / 12V = 61A (rounded up)
To carry 61A for 2ft with a 1% loss you would need 6AWG.
Of course I'm assuming copper wire and not Copper Clad Aluminum.
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groingo
Member
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# Posted: 21 Jul 2025 04:39pm - Edited by: groingo
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The wire is solid copper 4 awg.
Panels run in Parallel.
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travellerw
Member
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# Posted: 21 Jul 2025 05:22pm - Edited by: travellerw
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Quoting: groingo The wire is solid copper 4 awg. Panels run in Parallel.
That wire is not big enough to carry that current. You would need 2AWG STRANDED to carry 44A@18.2V for 50ft with a 5% loss (too much in my opinion). Using 4AWG with that current your loss is probably like 9% when in full sun. You also run the risk of overheating the wire and having the insulation fail premature. Worst case = Fire!
This why people no longer run low voltage panels and run panels in series. Otherwise the wire size is not feasible.
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MtnDon
Member
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# Posted: 21 Jul 2025 05:36pm - Edited by: MtnDon
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My calculator indicates 1/0 AWG for 50 feet, 48 amps, 22 volts, and a 3% max voltage drop. (2.66% drop more exactly.) One wire size smaller would likely work unless you have continuous great sun for a few hours.
You should maybe look at doing a 2S2P or all series if there are no shadows at all, ever.
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groingo
Member
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# Posted: 21 Jul 2025 09:10pm
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Funny you mention wire overheating, wire coming into the charge controller from panels has always been room temp, from charger to batteries same thing no temp issues now if I pull a heavy load from the battery cables to the inverter then I had to go with 0 AWG cause they were cooking.
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groingo
Member
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# Posted: 21 Jul 2025 09:13pm
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One issue I have with that is the power outlet ports to the controller and output from the controller can't handle that large of wire.
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travellerw
Member
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# Posted: 21 Jul 2025 09:34pm
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Quoting: groingo Funny you mention wire overheating, wire coming into the charge controller from panels has always been room temp, from charger
Pull the batteries down to 50% SOC the night before a sunny day. Those wires will get hot the next day. There is no way around it, dropping that much current is going to cause heating.
You have 3 options. 1. Move the batteries and solar controller closer to the panels. 2. Switch to series configuration. 3. Sell those panels and buy high voltage panels (panels are so cheap now, I just bought 585W high voltage panels for $200 each brand new).
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travellerw
Member
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# Posted: 21 Jul 2025 09:36pm
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Quoting: groingo I pull a heavy load from the battery cables to the inverter then I had to go with 0 AWG cause they were cooking.
What size is your inverter. I just assumed 800W as that is what you posted. If its bigger, then yes you will need bigger wire.. None of this is rocket science, its all math. You need to do the math to ensure you are building something safe.
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MtnDon
Member
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# Posted: 21 Jul 2025 10:24pm
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Quoting: groingo ports to the controller and output from the controller can't handle that large of wire
Use coupler blocks that will accommodate the different size wires; short pigtails should be okay.
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groingo
Member
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# Posted: 21 Jul 2025 11:21pm - Edited by: groingo
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Inverter is 80 AMP 160 max volts
As far as drawing down battery to 50% or below I do that pretty regular and have not had wire heat issues, then again I have not seen over 20 volts or over 13 AMPS either.
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travellerw
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# Posted: 21 Jul 2025 11:45pm
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Quoting: groingo Inverter is 80 AMP 160 max volts
Quoting: groingo Inverter is 80 AMP 160 max volts
Quoting: groingo As far as drawing down battery to 50% or below I do that pretty regular and have not had wire heat issues, then again I have not seen over 20 volts or over 13 AMPS either.
Wait.. You have never seen more than 13 AMPS at the solar controller on the PV side? or 13 AMPS between the solar controller and the batteries? In either case, that would be a huge problem with something.
You won't see 20V as the MPPT voltage of your panels is 18.2V
At any rate.. I'm going to step out of this thread as I feel like you don't have the basic knowledge to be building a system like this. You seem to not grasp the simple math or concepts (like resistance) for a system. I feel like we might just be giving you enough information to be dangerous. I recommend you do some research or get someone with knowledge to help you out and mentor you!
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Grizzlyman
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# Posted: 22 Jul 2025 09:11am
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One thing that might help if you’re not aware is
Watts=volts x amps.
Using the formula you need to decrease amperage and the way to do that is increase voltage.
Then find the appropriate wire sizing chart online for your voltage and run.
So as previously stated in this thread you need to run the panels in series to increase the voltage and lower amperage. If your controller can’t handle wires that size it’s probably a good sign that it’s meant to be wired in series and at a higher voltage.
As stated more research would be needed.
Hope this helps.
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Brettny
Member
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# Posted: 22 Jul 2025 10:21am
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For PV wireing you really want to run as many pannels in series as your Charge Controller will allow with some buffer. This lets typicaly the longest run of wire in a solar system be smaller/cheaper wire. Higher voltage means smaller amps. Smaller amps means smaller wire. You should really learn how to use the chart and do the simple calculations your self if your building your own system.
Here's another chart for 12v systems withba bit more information on it.
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groingo
Member
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# Posted: 22 Jul 2025 06:47pm
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Been this way for past 13 years, just added 200 watts more juice, nothing over heating, just trying to get what I paid for. Seems to be a ton of variables according to all the conflicting information on the net, from Renogy etc.
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groingo
Member
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# Posted: 22 Jul 2025 06:53pm
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Series is not much of an option as I have a lot of trees and moving shade and series doesn't like that, also looked into 2S2P connection but that requires 2 charge controllers according to Victron.
I appreciate everyones assistance, will just build around what I can get from it or learn to live what I can get from it.
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