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Solar butt connection gone bad

solar electrical butt connect

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#1 photohc

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Posted 01 August 2019 - 06:05 PM

Back from a recent trip, I noticed a brown mark on the front of my 2013 Hawk. Thinking it was dirt, I discovered that in fact it was the vinyl discolored due to the solar butt connector at the front heating up. I've had the same solar panels up for the last two years (3x120w) and didn't notice any issues until now. I'm guessing, the connection has gone bad and resulted in a poor connection, thus causing the heat. I cut them out and rewired the connection, this time soldering with heat shrink wrap. It was tough working behind the collapsable panels to gain access to the wires.

 

I'm surprised with couple issues.

1. I did not measure any high resistance from the clipped out butt connections.

2. There were 3 wires coming from the roof. Yellow for fan and lights. Red/Black (hot/ground) from solar panels. The yellow did not have a splice. Why did FWC not have a continuous run instead of making butt connection at the front collapsable panels?

 

At this point, I'm guessing the bad connection was intermittent.  Any feedback would be appreciated.

 

48432416386_b936a63801_c.jpgI

 

48432563252_ac0907a5cb_c.jpg


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#2 Stan@FourWheel

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Posted 01 August 2019 - 09:25 PM

I’ll check when I get back to the office. Four wheel campers does not recommend more than 160 to 200 W on the roof, max. Back then you might only have a 12 gauge wire for solar. 360 watts of roof solar is probably too much power for such a small wire. ☹️
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#3 photohc

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Posted 01 August 2019 - 09:56 PM

Thanks for responding. I have #10 in mine. The most current these panels will produce is 18 amps.Should not be a problem.
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#4 Lineman

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Posted 01 August 2019 - 10:26 PM

A bad connection like that would have to have load on it to measure its resistance. It will always test good without load, i.e. with an ohmmeter. Its resistance would have to be calculated based off the voltage drop across it with load applied.

If the rest of your wire and connections at the panels and the controller look good it was likely just a bad butt splice. I would just keep an eye on it. If any other connections look like they have been hot you are probably overloading the wire. In that case wire your panels in series and use a mppt controller.

I have 300w in series on mine and haven't had any trouble with the factory wiring.
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#5 photohc

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Posted 02 August 2019 - 12:51 AM

A bad connection like that would have to have load on it to measure its resistance. It will always test good without load, i.e. with an ohmmeter. Its resistance would have to be calculated based off the voltage drop across it with load applied.

If the rest of your wire and connections at the panels and the controller look good it was likely just a bad butt splice. I would just keep an eye on it. If any other connections look like they have been hot you are probably overloading the wire. In that case wire your panels in series and use a mppt controller.

I have 300w in series on mine and haven't had any trouble with the factory wiring.

Thanks Lineman for your thoughts. I used an ohm meter but had no load on it. Rest of the wire appears to be okay. I snipped off the butt connection, re-stripped the wire and soldered and shrink wrapped. I'll need to take the camper outside to test before my next trip. 


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#6 ntsqd

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Posted 03 August 2019 - 01:17 PM

For least current drop 10ga. over that likely length is probably not big enough. However I'm guessing at MC4 connectors at the panels, and those limit you to 10ga. max.

 

I'm estimating that the total circuit length is about 25 feet (hot + ground). I calculated amps at 12.0 VDC figuring that is worst case voltage (30A) and for 3% voltage drop this page: http://www.ancorprod...nt-voltage-drop

 calls for 6 ga. for that much power over that length.

 

I would venture that over time condensation also worked it's way into those unsealed connectors, which caused some corrosion and started the cascade. Some light reading (cough, cough) on wire and terminals:

https://marinehowto....re-termination/


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Thom

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#7 photohc

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Posted 03 August 2019 - 06:44 PM

I did an unscientific test and rigged up a load test on the cutoff butt connectors. Based on appearance, it look like the negative butt connector was the problem. Hooked up a 12v source and connected a 12v bulb with a 1.5 amp draw, I measured a voltage drop of 0.15v at the butt. With the 3 panels in parallel and at peak sunny day, that would mean 18 amps x 0.15v = 2.7 watt lost to heat. In reality, the resistance would probably increase as it heated up resulting in even a higher heat lost.

 

Thinking about it, I could have had a fire started if it got hot enough. The circuit breaker would not have helped as the current would not have increased to a point that would trip it. I hope, FWC doesn't make those unnecessary butt connections (especially with the vinyl leaning into the connection) in their current campers. Check your camper as a precaution!


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#8 rando

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Posted 03 August 2019 - 08:31 PM

For least current drop 10ga. over that likely length is probably not big enough. However I'm guessing at MC4 connectors at the panels, and those limit you to 10ga. max.

 

I'm estimating that the total circuit length is about 25 feet (hot + ground). I calculated amps at 12.0 VDC figuring that is worst case voltage (30A) and for 3% voltage drop this page: http://www.ancorprod...nt-voltage-drop

 calls for 6 ga. for that much power over that length.

 

I would venture that over time condensation also worked it's way into those unsealed connectors, which caused some corrosion and started the cascade. Some light reading (cough, cough) on wire and terminals:

https://marinehowto....re-termination/

 

Quick clarification here - the 3% voltage drop suggestion doesn't really apply to solar wiring.   It doesn't really matter if you drop 3% between the panel and the charge controller - if it is a PWM controller it doesn't matter at all as that voltage is lost in the controller anyway, if it is an MPPT you may loose 3% efficiency under peak illumination, but that is not a huge deal.   

 

What does matter is the ampacity rating for the wire - this is the maximum current a wire can carry without excessive self heating.   For 10AWG the limit is 60A, so you are well within the safe limits no need to upgrade the wire:

 

343a.jpg

Source: https://www.jamestow...nt.do?docId=343

 

PS Checking my wiring for dodgy splices!  Thanks for the heads up.


Edited by rando, 03 August 2019 - 08:37 PM.

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#9 Lineman

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Posted 04 August 2019 - 12:37 PM

I did an unscientific test and rigged up a load test on the cutoff butt connectors. Based on appearance, it look like the negative butt connector was the problem. Hooked up a 12v source and connected a 12v bulb with a 1.5 amp draw, I measured a voltage drop of 0.15v at the butt. With the 3 panels in parallel and at peak sunny day, that would mean 18 amps x 0.15v = 2.7 watt lost to heat. In reality, the resistance would probably increase as it heated up resulting in even a higher heat lost.

 

Thinking about it, I could have had a fire started if it got hot enough. The circuit breaker would not have helped as the current would not have increased to a point that would trip it. I hope, FWC doesn't make those unnecessary butt connections (especially with the vinyl leaning into the connection) in their current campers. Check your camper as a precaution!

Nice test.  You are right that the resistance would increase with more load.  More amps causes more heat which causes more resistance, kind of a positive feed back loop.


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#10 ntsqd

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Posted 07 August 2019 - 01:43 PM

if you loose more than 3% in the wiring and then again another 3% in the controller you've lost more than just 3%. So it does too apply. All losses are important no matter where they occur.

Say it is a 100W panel that outputs @ 17 volts. A 5% Voltage Drop in the wiring will consume 15 watts. How is that not important?


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Thom

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