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Old 20-08-2018, 09:51   #1
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Solar wiring issue

Last year I installed 4 - 100 watt rigid solar panels and a HQST mppt controller on my sailboat.

The setup has worked wonderfully until three weeks ago, when the 10 gauge wire coming from the solar panels and between the circuit breaker and the mppt controller scorched and wouldn't carry the charge.

I then replaced the circuit breaker and upgraded the wire to an 8 gauge wire. Things were working well until this weekend, when this wire was scorched and stopped carrying the current.

Has anyone had this issue? What could be the problem after working perfectly for over a year?
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Old 20-08-2018, 18:24   #2
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Re: Solar wiring issue

My bet would be water in the cable and drove up the resistance and heated the cable.
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Old 20-08-2018, 18:50   #3
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Re: Solar wiring issue

Quote:
Originally Posted by sailscubasurf View Post
Last year I installed 4 - 100 watt rigid solar panels and a HQST mppt controller on my sailboat.

The setup has worked wonderfully until three weeks ago, when the 10 gauge wire coming from the solar panels and between the circuit breaker and the mppt controller scorched and wouldn't carry the charge.

I then replaced the circuit breaker and upgraded the wire to an 8 gauge wire. Things were working well until this weekend, when this wire was scorched and stopped carrying the current.

Has anyone had this issue? What could be the problem after working perfectly for over a year?
You have given us almost nothing to go on. But something is seriously, and dangerously(!), wrong if your wire is hot enough to "scorch"

If you are running a 12 volt system, then 400 watts is about 33 amps... 10 AWG wire would likely be too small. How did you decide that 10AWG was OK? For that matter how did you decide 8AWG was OK? Making some assumptions, I would be looking at a minimum size of 6AWG. But my assumptions could be wrong... so some more questions...


Panel voltage? Series or parallel? 12 or 24 volt system? Lengths of wires?
Can you describe (or photograph) "scorched"? Are we talking about the whole length of the wire, or just the end(s)? Is this name brand boat cable--or something else? Where is the circuit breaker relative to the panels, controller and battery? What size fuse or breaker? How are the wires terminated?
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Old 20-08-2018, 18:54   #4
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Re: Solar wiring issue

Waiting, waiting........
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Old 21-08-2018, 00:03   #5
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Re: Solar wiring issue

The wire gauge I used was determined by tables from both the HQST MPPT controller instructions and the solar panel instructions. It is about 15 feet from solar panels to 50 amp circuit breaker and then 4 inches to MPPT controller.

It is a 12 volt system.

The wire was scorched at the end leading into the MPPT controller.

The MPPT controller is in an area where no water can get to it, and has good ventilation.

As I said in my post, the issue is perplexing because it has worked for over a year with no problems, so it is not the size wire.

The most amps I've seen going into the battery from the controller is 16amps
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Old 21-08-2018, 00:36   #6
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Re: Solar wiring issue

Global warming??

But seriously, still need some info...

Are your panels wired in series or parallel?
What is the actual voltage / current spec for these panels ?

We wired our 3 x 200W panels in series leading to a Victron MPPT, primarily because of cable sizing from the panels to the MPPT.
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Old 21-08-2018, 08:39   #7
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Re: Solar wiring issue

They are wired in parallel.

I will have to pull the specs on the panels to see what they are rated.
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Old 21-08-2018, 08:59   #8
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Re: Solar wiring issue

Your #10 wires are really too small for 400W of paralleled 12V panels, and will give you excessive voltage drop, but they should be capable of carrying that amount of current without burning up. If you had a nick in the insulation and corroded wires, or a bad crimp that could have caused a hot spot with burning, but this can happen with any size wiring.

Still, replace the wires with something heavier. For a 30-ft round-trip run, and a 30A current, #4 wires will give you about a 2% voltage drop.
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Old 12-09-2018, 11:45   #9
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Re: Solar wiring issue

Had marine electrician out.

Problem was loose internal connection in MPPT, which was heating cables. He moved wires from loose connection to spare connection and soldered all connections. No problems with heating or charging since.

According to him, the wiring size was not an issue.
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Old 12-09-2018, 12:30   #10
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Re: Solar wiring issue

Glad you got your controller connections sorted out. But.....

Neither your installation instructions or your electrician know what they are talking about.

The panels are probably running at 17 volts which is usually the mpp, so 400/17 equals 24 amps. 24 amps through 30' round trip of #10 cable results in a voltage drop of about .8 volt. So you are losing some of your solar panel's output to heat produced by that voltage drop.

Good practice is to keep the voltage drop from the panels to the controller down to 0.5V or less and the drop from the controller to the batteries should be no more than a few tenths.

You can probably accomplish the same thing by wiring your panels series/parallel as long as long as they are not subject to individual shading. This will double the voltage to your controller so you have to check to see if its specs can handle it, but it will drop the current in half, thereby cutting the voltage drop in half.

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