Controller upgrade (bad panels?)

garynappi · April 29

Everything "almost" went OK except the current / power being generated was too low at ~5A-8A in bright sun / clouds passing and 3x200W panels connected parallel (12v system) to my Renogy 60A CC.

So I killed breakers one at a time in my combiner and only one (let's say input 3 on the combiner) was putting out the current. So I pulled the two that were showing zero current (but both showed 16 to 19v in the app) and plugged them in turn to the combiner that had the known working panel, same issue.

So, disconnected both panels, and with a DVM connected to the panel connectors I measured:

Volts in sun / clouds passing 15-19 VDC

Switching the DVM probes to read current:

Current in sun / clouds passing 3-4A

So, just in case there could be a connection issue I chopped off the connectors, crimped on two new ones and same problem, the CC shows 15-19VDC and no current.

Can these two panels bought new ~4 years ago be bad and still pass the static DVM voltage / current test???

PS, I installed the known working panel to the other combiner inputs and the CC showed them all as working.

BB. · April 30

Really need to know the specifications for your panels (Voc, Isc, Vmp, Imp, etc.)... Here are some quick charts for solar panel specs (normalized to 100%). Don't see many IV/Temperature Curves on specifications anymore:

https://forum.solar-electric.com/discussion/comment/359660#Comment_359660

Voc of 15-19 volts seems pretty low... Typically for a "12 volt" (Vmp~17.5 yo 18.0 volts), I would be expecting closer to 20-22 volts or so (depending on temperature). Voc--open circuit voltage (no current draw).

While using the circuit breakers in a combiner panel does "work"... I would highly suggest getting some sort of AC+DC Current Clamp DMM (digital multi-meter)... Makes things much easier and you can simply "quickly and safely clip" onto each cable you want to measure current in. You 3x parallel arrays. Just setup in sun with loads/battery bank.

Some examples:

https://www.amazon.com/UNI-T-Digital-Handheld-Resistance-Capacitance/dp/B0188WD1NE (cheaper, works for our needs)
https://www.amazon.com/Auto-Ranging-Resistance-Klein-Tools-CL800/dp/B019CY4FB4 (mid-priced meter, larger Amps, more features).

Note that you want a DC clamp meter (really most are AC+DC clamp meters). An AC only meter works very well, but only for 120/240 VAC house wiring and such. You need a "DC" capable clamp meter for solar.

-Bill

garynappi · May 1

Thanks Bill, my clamp meter only reads AC so I have to rely on my DMM and what wits I have left to sort it out.

I took the two offending panel connections and wired them separately via the MC connectors to my solar powered attic fan and when the breaker to the fan is off they read 19+ volts on the feed side of the breaker and as soon as I throw the breaker the breaker output terminal reads 7 volts. I even tried replacing the MC connectors from the panels with the same results. Testing the other two known good panels connected to my attic fan they work perfectly.

It looks like they just won't produce power under a load. Why they show correct current tested with my DMM? Dunno but clearly whatever Fluke is doing (shunting?) they're not presenting a real load to the panels.

Luckily I have two new lower wattage panels (135W) that I will replace them with for the time being.

BB. · May 1

Solar panels have ~36x 0.50 VDC (Vmp per cell) cells in series. And there are usually 2-3 "bypass diodes" that will send current "around" any bad cells, shaded cells, or broken connections...

So when measuring current flow in full sun with a standard DMM and leads for 10 Amp full scale --The meter is a "dead short" to the array and you can have weak cells/connections and a bypass diodes will send the current around the "bad section". Of course, that drops the "useful Vmp-panel" output voltage by upwards of 9 VDC--And would suggest that you could see Vmp~9 VDC when the panel is connected to a solar charge controller--Which is not going to do any good at getting 15+ volts to a battery bank to charge.

When you measure Voc with a DMM--The meter is drawing milliamps or less current--And even "poor connections" (corroded, fractured cells, etc.) can still supply what appears to be "good Voc" on its leads when connected to your DMM.

Checking for Voc (open circuit array voltage) and Isc (shorted array current) will find about 80%+ of the "bad panels".

To find out if the panels are "really good", they need to be connected to a load--Such as a solar charger, 12 volt light bulb, or even a 12 volt car battery to see if you get rated Imp with the panel connected to an ~12 volt load in full sun.

If you connect your panel(s) directly to a 12 volt car battery--Be very careful that you get panel + to car battery +, etc.... If you connect the panel(s) backwards, they will (usually) be instantly fried by the "reversed battery connection".

Everything you have tested/typed so far--Seems to indicate you have several bad solar panels and they should just be "trashed" (or recycled if you can find somebody to take them). On occasion, even dumps will refuse to take solar panels...

-Bill

Dave Angelini · May 1

The last test I do is cut off the MC connectors and test again. MC's are a huge failure source.

If I troubleshoot an intermittent or worse system the hours really rack-up.
If I remove the MC's with a butt joint connection, the hours are low and often solve the problem.

Controller upgrade (bad panels?)

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