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Old 27-01-2021, 16:16   #1
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wires burned up with 4 100 watt panels

i have 4 100 watt solar panels wired parallel using 10 gauge on all the panels i have a 20 amp fuse on the red leading to the controller. i am using 10 on the final wire to the controller. the fuse burned pretty bad and i replaced it and i amost had a fire. the fuse melted and there was a lot of smoke. should i use an 8 guage wire for the final wire to the controller ? thought 10 guage was big enough. the final wires. go about 10 ft the panel wires do about the same but some are very short
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Old 27-01-2021, 16:24   #2
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Re: wires burned up with 4 100 watt panels

400 watts / 12.5 volts = 32 amps
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Old 27-01-2021, 16:25   #3
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Re: wires burned up with 4 100 watt panels

The problem is not the wire guage. If you are burning out fuses you have a lot of current going somewhere. You have a major problem in your system design or configuration.

t's not a matter of wire gauge - if the fuse is blowing and the wires aren't melting, the wires are handling the current. (10 guage should be OK up to about 30 A)


Added: As s/v Thea points out. If your 400W is at anything less than 20V, you are exceeding 20A current.


You panels are probably putting out around 14 - 17V making it 25-30A . You need a 30A fuse.
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Old 27-01-2021, 16:37   #4
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Re: wires burned up with 4 100 watt panels

I'm no expert but have been doing a lot of research and studying up so that I can be better prepared to build/maintain my own system. Usually that is an indication of too small gauge wire for the amount of amps you have flowing through the wire.

Anyway, I do watch a lot of videos from a specific Youtube channel that the guy breaks everything down really clearly and covers a lot of aspects of solar and electrical systems. It is not marine specific but non-the-less has great information.

Here is a video where he discusses just the issue you are describing
https://youtu.be/cX4s-bxn4fs?t=260
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Old 27-01-2021, 18:58   #5
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Re: wires burned up with 4 100 watt panels

Wire size also depends on the length of your runs. 8 ga is only acceptable up to 15 feet, one way, (assuming 3% voltage drop and 22amp here; 400w/18amp=22.22222). Higher voltages (and therefore lower amps) can handle the smaller wires more easily.

With those same assumptions 10 gauge wire is stille (barely) undersized for 10' runs.

1% voltage drop needs 6 ga wire after about 6' one way.

I have 380w of solar and about 12', one-way, to my controller. I used 6ga wire. I also used 6ga from the controller to the battery, even though it's only about 3 feet, because I had plenty left on the spool, and the lower voltage from the controller means it pushes more amps through.
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Old 27-01-2021, 19:47   #6
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Re: wires burned up with 4 100 watt panels

"the fuse melted and there was a lot of smoke."


I agree with Stu. You have another electrical issue. A 20amp fuse should not be letting out any smoke much less a "lot of smoke" when it melts.
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Old 28-01-2021, 01:28   #7
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Re: wires burned up with 4 100 watt panels

sounds like you need to disconnect it and hire someone to do it....
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Old 28-01-2021, 01:43   #8
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Re: wires burned up with 4 100 watt panels

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Originally Posted by smac999 View Post
sounds like you need to disconnect it and hire someone to do it....

This!

The saying 'A little knowledge is a dangerous thing' is especially true when you are dealing with electricity.
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Old 28-01-2021, 03:35   #9
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Re: wires burned up with 4 100 watt panels

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Originally Posted by shadowdancer View Post
i have 4 100 watt solar panels wired parallel using 10 gauge on all the panels i have a 20 amp fuse on the red leading to the controller. i am using 10 on the final wire to the controller. the fuse burned pretty bad and i replaced it and i amost had a fire. the fuse melted and there was a lot of smoke. should i use an 8 guage wire for the final wire to the controller ? thought 10 guage was big enough. the final wires. go about 10 ft the panel wires do about the same but some are very short
Something is wrong here. Fuses should not smoke. Generally they fail with a faint click or pop sound.

Sorry to say, I'm going with the view that it's time to bring in a pro. When there is visible smoke there is a very, very serious threat to the boat.
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Old 28-01-2021, 11:00   #10
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Re: wires burned up with 4 100 watt panels

Do the panels have blocking diodes?
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Old 28-01-2021, 11:17   #11
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Re: wires burned up with 4 100 watt panels

I'd question why you have a fuse in that position at all? Solar panels are current-limited sources, there is no way for a solar panel to deliver in excess of its Isc, so there is no need for an overcurrent protection device between the panel(s) and the controller.

With four panels in parallel there is some argument to be made for having a fuse in each panel's line so that if one panel faults (or shades a great deal, or...) and becomes a current sink the other panels can't feed into it. A 10A fuse in the lead for each panel would prevent the other three panels from dumping their 20+A available current into a faulted panel. Diodes can also be used in this position, with their attendant voltage drawbacks.
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Old 28-01-2021, 11:38   #12
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Re: wires burned up with 4 100 watt panels

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Originally Posted by Dsanduril View Post
I'd question why you have a fuse in that position at all? Solar panels are current-limited sources, there is no way for a solar panel to deliver in excess of its Isc, so there is no need for an overcurrent protection device between the panel(s) and the controller.

A current limited source solves ONE fuse, not both. You have, in theory, TWO sources of fault current -- the panels and the battery. The panels can't exceed their Isc, so as long as you size the wire for the Isc, you can't burn the wire. But you can still have a fault fed by the battery, so you still need a fuse (without the current limited exception, you need TWO fuses --one at each end, for instance an ACR that connects two batteries). In this application, the fuse would be where the controller connects to the battery (or ideally, the bus).
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Old 28-01-2021, 11:40   #13
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Re: wires burned up with 4 100 watt panels

Quote:
Originally Posted by shadowdancer View Post
i have 4 100 watt solar panels wired parallel using 10 gauge on all the panels i have a 20 amp fuse on the red leading to the controller. i am using 10 on the final wire to the controller. the fuse burned pretty bad and i replaced it and i amost had a fire. the fuse melted and there was a lot of smoke. should i use an 8 guage wire for the final wire to the controller ? thought 10 guage was big enough. the final wires. go about 10 ft the panel wires do about the same but some are very short
I installed 4x140 panels on my boat in 2015 and have not had a problem.

Each solar panel pair went to a single controller and then connected to a single 8D GEL battery, i.e. 2 panels to one controller to one battery with one fuse. I used 10 AWG cable all the way and a 30W fuse for each battery. All this was provided by the provider, eMarine Systems.

Hope that helps.

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Old 28-01-2021, 11:40   #14
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Re: wires burned up with 4 100 watt panels

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Originally Posted by s/v Thea View Post
400 watts / 12.5 volts = 32 amps
Someone correct me if I'm wrong. My understanding is the panels produce a higher voltage and the controller knocks it down to charging levels. The 10ga. wire would seem more than adequate from the panels of 100W each.
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Old 28-01-2021, 11:44   #15
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Re: wires burned up with 4 100 watt panels

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Originally Posted by sailingharry View Post
A current limited source solves ONE fuse, not both. You have, in theory, TWO sources of fault current -- the panels and the battery. The panels can't exceed their Isc, so as long as you size the wire for the Isc, you can't burn the wire. But you can still have a fault fed by the battery, so you still need a fuse (without the current limited exception, you need TWO fuses --one at each end, for instance an ACR that connects two batteries). In this application, the fuse would be where the controller connects to the battery (or ideally, the bus).
Exactly, there should still be a fuse at the battery-controller connection. That protects against faults that would drain the battery. Many/most controllers won't pass that fault through to the panels, but either way an overcurrent protection device is needed on the battery end of any cable connected to the battery.
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