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rararames avatar image
rararames asked

Low panel voltage MPPT 75/15

Recently replaced a solar panel and charge controller in my Airstream but unable to get the MPPT to charge. The panel is new, and testing shows it is providing 21v (tested at the panel and at the wires where they go into the MPPT). However, the MPPT shows >1v being produced. When I test the wires the voltage is good, however when plugged into the MPPT and I test the terminals, it is showing less than 1v. The MPPT is brand new and I have verified that the fuse is not blown.

Anything else I need to check here? It seems unlikely the MPPT is bad as it is brand new. Thank you.


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MPPT Controllers
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2 Answers
kevgermany avatar image
kevgermany answered ·

If you're getting nothing measured by the MPPT, it can only be fuse, bad connection or MPPT fault. Are the PV cables in the correct terminals? If the MPPT does not have mc4 connectors, did you measure the input voltage on the screws, or cables?

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rararames avatar image rararames commented ·
The polarity was reversed. I don't understand why, but swapping between the positive and negative terminals fixed it and it began charging.
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Justin Cook avatar image
Justin Cook answered ·

PV cables reversed, virtually guarantee. Check your polarity.

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rararames avatar image rararames commented ·
This was the answer. So help me understand...from my solar panel, I connected the green wire to negative and the yellow wire to positive. I then connected the green wire to the MPPT PV negative terminal and the yellow wire to the MPPT PV positive terminal. Why would this result in reversed polarity?
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jetlag avatar image jetlag rararames commented ·
Does the PV Module have MC4 connectors and did you refer to these markings? If yes, this might be misleading... If you extend the wires with the counterpart connectors, then the polarity marking on the connectors does switch around and people get confused.

The best way, and a must anyway, is to check the polarity with a voltagemeter and then connect the MPPT.

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