Testing damaged panel

[chilly]

This isn't really DIY, but if readers of this group can build their own panels, I thought they'd be the ones to ask how to check out a damaged commercial one.

I got a set of two 100W Renogy 12v panels off craigslist (w/a cheap pwm cc). One looks new. One has issues. Average deal if just one works. Great deal if both work. They are identical to the 100W mono panels currently sold by renogy (RNG-100D).

One got blown off it's mount - no panel damage, but connectors/box got ripped off. The owner soldered them back up, so I'm wondering if there's anything I should watch for or check. He was not Mr. Wizard. Don't worry about the RTV in the pic and sealing the box - I can handle making it water tight.

I eyeballed that all the connections looked sound and matched the layout of the good panel (they did). Then I put the two panels next to each other in the sun and measured the unloaded voltage (just a multimeter) and they matched... not far from Vmp and definitely not Voc.

I attached a pic of the junction as is. Any opinions or observations would be greatly appreciated.
junction.JPG

[Mike90250]

Well, it shows nicely how the bypass diodes are heat sunk to the copper ribbons. But what does the panel look like where the ribbons go into the sandwich? That's where water and other damage will start.

And use a neutral cure RTV (electronic grade, $9 small tube) or the fumes sealed in the box will ruin it all.

[bcroe]

Open circuit voltage is a starting point, but the real issue is if they can deliver power.
That means somewhere near the MPP voltage AND current. Lets just say V max power
is 16V and I max power is 6.25A. Connecting a 2.5 ohm 100 watt resistor and measuring
the voltage will demonstrate some power. You probably won't reach those numbers
unless the sun is really good, but 2 good panels should put out similar numbers.
Bruce Roe

[chilly]

Ah, good idea - I see how the resistor would work. I will try that that's an easy one.

I'm guessing the leads/strips got torn up a bit from backing and that's why he has silicon globbed above the junction box. So as long as that stays dry and had a decent connection, I'm thinking it should be OK. Silicon's a decent insulator, and worst case it corrodes down the line and I need to rework that area at some point in the future.

As long as I fuse each panel separately (I'm planning to anyway - with 12v parallel wiring), is there anything particular that could go wrong - beside them not working? I don't mind if it doesn't end up working - I just don't want to burn down my trailer.

Good tip on the RTV, I was not aware of that.

[inetdog]

Easier measurement to make (since great hulking resistor is not needed) is just Voc and Isc. But those two measurements will not detect certain kinds of damage to the individual cells.
Once you are cooking at Imp, you can partially shade the panel in different places to see whether the bypass diodes work. (Voltage should go down, but not below 1/3 of the panel Vmp voltage.)