MPPT ill effects from bad reverse diode? Shows battery voltage at night

[Thorium]

I have a Victron 150/## MPPT that shows battery voltage level (eg 52V) as PV voltage at night when it should show near zero
Upon researching it appears the most likely reason is a broken reverse diode.

Victron staff commenting on identical issue:
“the charger should switch to off mode during the night and the panel voltage should go down to (almost) zero. If this is not the case, the most obvious cause is that the reverse diode is broken, this causes the battery voltage to remain visible on the panel connectors.” (https://community.victronenergy.com/questions/6134/10020-odd-behavior-at-night.html)

However, I’d been running the MPPT perfectly fine in my 48v system for more than a month before I even noticed. i only realized this was abnormal after I added a second charge controller and saw it’s PV voltage near zero and started asking questions.

Victron is happily replacing the unit (excellent service)…
But what ill effects Could the broken reverse diode cause that I’m not realizing?

They told me to dispose of the faulty unit after I receive replacement, and I’m considering reselling it instead (of course with flaws fully disclosed and no warranty), but I don’t want to do that if theres any safety issue or other unacceptable ill effects from the broken reverse diode that go well beyond just a bad PV voltage reading at night or other very minor negative effects.

 

[RCinFLA]

If you have nearby lighting, like a street lamp, may show some voltage on panels at night. Panels will not produce any significant power but when unloaded they can show voltage with a slight amount of ambient light.

Probably best way to check is to disconnect panels connection to SCC and check with a voltmeter. SCC may need some resistive loading on its PV input to show zero volts as any minor leakage through blocking diode will show voltage on a 10 meg ohm high input impedance DVM.

You can load unconnected SCC PV input with about a 1k ohm resistor to see how much current is coming from SCC input. If less than couple of mA's (<2v across 1k resistor load) I would not worry about it.

 

[Thorium]

I think you misunderstood. The MPPT definitely has an issue where battery voltage is leaking back to PV inputs of MPPT. Most likely this is due to a broken reverse diode in the MPPT that usually prevents this. This MPPT shows 52V on PV inout at night, which is battery voltage. Anothe MPPT on same system will only show 0.02V or something very low (from ambient light).

it’s got this problem for sure, but continues to function fine.

My question is what negative effects does this problem actually cause, since the MPPT has continued to function fine for a month despite this condition.

 

[RCinFLA]

Unless you have blocking diodes on panel output, which I don't recommend, all panels have shunt leakage to some varying degree.

 

[Smokin]

Replace the Diode

 

[Thorium]

victron MPPT are sealed units, Victron has replaced it under warranty. But they don’t want the unit with this fault back.

I’m asking because I difure I’ll resell it (with flaws fully disclosed).

first I wanted to confirm it’s not a safety issue or would otherwise be unethical to resell the faulty unit.

 

[sunshine]

first I wanted to confirm it’s not a safety issue or would otherwise be unethical to resell the faulty unit.

It is unethical not to destroy it as Victron requested!
You sell with the faults noted, The buyer then resells it as in good condition to some other hapless buyer.

 

[RCinFLA]

Again, disconnect panels, load input of SCC with about 1k ohm resistor and see if voltage drops on SCC input. A blocking diode into a high impedance load will show output voltage even in blocking direction.