Wierd fault on My solar panel

[sim]

Can anyone help? I have some fault on a solar panel I can't figure out. I have 3 Kyocera KC120 panels connected in parallel which I use do charge a 12v battery bank. 2 of the panels give an acceptable output but i get nothing from the 3rd. Testing the suspect panel I find I get Voc about 19.5v, Isc about 6a in good sunlight (same as other panels). But once I connect the panel to the system I get no current flowing. I have fitted individual ammeters to each panel to confirm my findings, ie. 2 panels are charging the batteries but the 3rd one is not, despite the apparently correct test readings. I'm at a loss what to do next. Anyone got any good ideas would be much appreiciated.

[DamonHD]

Do you have one marginal cell on the 'defective panel' so that when the other two are going full blast the third panel cannot match the voltage of the other two?

In principle it doesn't matter if so because the higher-voltage panels will have their voltage pulled down first by charging the battery allowing the third panel to contribute some charge current all else being equal.

Just a guess, clearly.

Rgds

Damon

[sim]

Hi, Thanks for your thoughts, I had wondered about that so I have in fact connected each panel to the system individually, ie. 1 at a time, and I get, say, 4 or 5 amps out of each of the 2 good panel but nothing out of the 3rd, even when its on its own!

Any more ideas?

Regards

Sim

[Micheal]

First I have to point out I don't have any panel repair experience. What I do have is years of experience soldering on laptops, doing repairs. I could be wrong , but that sounds like a faulty connection. Its pretty common to have a connection break under load that wont under no load. eventually it will not even work under no load. I would check for discoloration on all connections. as far as anything that is inside the panel, at this point I would not recommend anything more than just looking to see if you can see a "hot spot" aka discoloration on the strips that solder the panels together.   reversed polarity would also cause that to happen. double check the blocking diode polarity. and for that matter if your using 3 diodes check them too.

good luck !

[sim]

Yeah, see where your coming from but then wouldn't I get zero current flow under short circuit test; Am I missing something here?

Further to my last msg I have just connected a 12v bulb across the terminals and it lights. To me this suggests it will deliver smal current to a light (no pun intended!) load, but nothing to a larger load, ie, the batteries. But then why full rated current under short circuit test.

Going to take the panel down next and have a closer look for damage as you suggested.

Thanks

[DamonHD]

Intermittent connection?

[DamonHD]

Honestly, intermittent or oxidised connections behave very weirdly and can change with load, day of week, phase of moon, which multimeter you have out, etc.

You could try applying a gentle patented 'engineer's thump' to the edges of the panel to see if that changes anything.  This only works because of oxidised/dry/buggered connections.  It works rather too often for comfort, IMHO.

Whoops, are we allowed to use the word "engineer" here?  B^>

Rgds

Damon

[TomW]

Damon;

Whoops, are we allowed to use the word "engineer" here?



Yes, but "buggered" may offend some.

Cheers.

TomW

[electronbaby]

alot of the KC120's have defects. I know from experience. I have changed out hundreds in the past year. Look through the glass on the front of the module and look for tiny little burn marks at the top of the module (where the solder lands pass under the cells near the center). Sometimes the cell interconnects open up where the lands make 90 degree turns. Sometimes a "burn" mark is visible. If you see this, Kyocera will honor the 25 year warranty and replace it for you with a brand new 130GT (dBlue cells). At least thats what they have done for me. Everytime I get a bad module, I have to remove all the mods and ship back for brand new replacements. Check the lands, it seems like this might be what you see. The problem seems all too familiar.

Beware, if this is the case, the 130GT mods you will get as replacements have only a 20 year warranty.

[ghurd]

Do Not try to fix it!

It may void the warranty.

I have some old Siemens 60W PVs that did that, good Isc, good Voc, near nothing into the battery. Strangest thing is sometimes they work fine for a few minutes and then not a milliamp for a week.  One only works when the temperature is below ~40F, but then it works fine.  Can't find the problems. :-(

G-

[sim]

Thanks everybody for all the ideas.

Guess the panel is going back to Kyocera.

Long way from Guatemala!

Thanks again