Did my solar charger get fried randomly?

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vulture asked Mar 29, '21

Did my solar charger get fried randomly?

Earlier today, right before noon, my main solar panel array on SmartSolar 150/100 stopped producing power. My smaller one (100/30) is still working. It was decently windy today, but my panels have survived much worse. I walked the cable and everything appears fine. Open circuit at the panels is 114v, right before the MPPT is 74v after a 150foot aluminum cable run. When I connect it to the MPPT, the panel voltage drops to that of the battery voltage and there is zero amperage. I tried resetting it, disconnecting and reconnecting it, etc. Does anyone know what the problem could be? This has bee working great producing 3k+ watts for the past few months. Here's a screenshot of when the failure occurred - is this a hardware issue?

battery charging MPPT SmartSolar solar

capture.png (337.6 KiB)

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Answer 1 · 2021-03-29T20:03:13Z

wkirby answered · Mar 29, 2021 at 08:03 PM

With 114V open circuit, is the 74V also open circuit measurement?
If there are no problems along the cable, then you would also get 114V at the MPPT end open circuit - i.e. no current is flowing, so the Voltage drop should be very close to 0V.

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Answer 2 · 2021-03-29T20:12:32Z

vulture answered · Mar 29, 2021 at 08:12 PM

Yes, I measure 114v open circuit at the panels and 74v open circuit right before the charger. I guess that makes sense that there shouldn't be voltage drop if there's no current - I suppose an animal could have chewed and made some sort of short where it's buried? Could that explain the voltage drop? It seems a bit implausible that it would chew both cables in the same place, and then they would also be contacting each other, so I just want to rule anything else out before I have to dig up all my cables.

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seb71 commented · Mar 29, 2021 at 08:24 PM

Disconnect the wires at the PV end, too and then check for shorts.

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Answer 3 · 2021-03-29T21:45:52Z

vulture answered · Mar 29, 2021 at 09:45 PM

@WKirby

Okay, I disconnected the PV wires from everything and read 120v open circuit there, so I assume the panels are fine. Then, I did two resistance tests at inside my house for my three cables leading to the panel - one where the lines are all tied together and isolated right before the panel, and one where they are all floating there.

Three lines tied together:

+ cable to - cable: Mohm level resistance

- cable to spare cable: virtually no resistance

+ cable to spare cable: Mohm level resistance

Three lines floating:

+ cable to - cable: 60k ohm resistance

- cable to spare cable: 18k ohm resistance

+ cable to spare cable: 8Mohm resistance

Does any insight about what this means or how my cables could have suddenly turned into resistors if these values are abnormal? Is there a short or is this normal resistance? Could this have something to do with a ground loop or something?

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klim8skeptic ♦ commented · Mar 30, 2021 at 02:42 AM

Your problem is definitely a high resistance joint, or damage of the cable on the pv wiring between the array and mppt.

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