Panel reversed polarity -- now outputs half rated voltage and zero amps

andybaird
andybaird Registered Users Posts: 1 ✭
in Advanced Solar Electric Technical Forum #1
A friend bought a 180W 32V panel. When connected to a Victron controller, it didn't work. Investigation revealed that the leads from the panel had been mislabeled--positive was labeled - and negative was labeled +. When the reversed polarity was corrected by switching the leads, the panel was found to be putting out exactly 16V and 0 amps. 

A replacement panel was shipped by the manufacturer and it works normally, proving that the Victron controller was not damaged. There's no visible damage to the nonworking panel, but its junction box is potted with white stuff--probably silicone rubber--so it's not possible to examine the diodes or measure voltages on the two flat leads from the panel to the j-box. Grrr!

Questions: Is it possible that the panel itself (that is, not the j-box) was damaged by the reverse-polarity incident? Damaged in such a way that it only puts out half its rated voltage? Or is the j-box the culprit?

I have not yet gotten hands and eyes on the panel, but I hope to provide more specifics soon. Meanwhile, if anyone has seen similar behavior after a reverse-polarity incident, I'd like to hear about it. Thanks!
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  • Graham Parkinson
    Graham Parkinson Registered Users Posts: 177 ✭✭✭
    #2
    It wouldn't seem likely that the panel would be damaged by a reversed connection to a MPPT controller, given that panels are safe to short circuit.

    I'm not sure if a Victron MPPT controller actually can put out any significant current/voltage on it's inputs with a reversed panel connected, that's about the only way the controller could damage the panel.   

    MPPT controllers change their input impedance (effective resistance) by boosting and bucking the PV output voltage and current so they are actually working with what comes out of the PV panel.   MPPT controllers do need to be connected to the battery first though - was that done?

    However, there was probably something else wrong with the solar panel's internal connections made during manufacture that resulted in both reversed output polarity and reduced power output.

    Offgrid in cloudy PNW

    Full Schneider system with 18 REC 420W panels, 100A-600V controller, XWPro, Insight Home, six Discover AES Rackmount 5kW batteries, Slimline enclosure, Lynk II, AGS, H650,  H2200, H3000 (Propane conversion on Victron AutoTrans with Gen Line 2 wire AGS on AC1), Kubota 4500, Onan 7500 (on second AGS and AC2).

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,654 admin
    #3
    If the panels was connected "reversed" in parallel with multiple other panels, it is possible that those panels exceeded the reversed panel's reverse current limits... Basically, solar panels are large arrays of reversed biased diodes (solar cells) in series. If you connect the panel "reversed", those diodes are now forward biased and will carry any and all available current.

    Of course, that means there has be an available source of current... The MPPT controller should not output any current, the other panels in parallel will, and of course if you connect backwards to a battery (I.e., a full size battery bank, not just "D" Cells), any of those that can output (at a guess) >>10 amps, can fry the cells in the reversed connected panel.

    If a reversed biased/current panel is damaged--it is not repairable.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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