Strange panel issue - urgent!

[Jemplayer]

I have a strange problem


I am reinstalling an off grid solar system that was working fine a few weeks ago.

There are four strings of panels made up of x4 200watt panels per string. There are 4 strings total.

One of the string does not have any voltage!? I have tested voltage on the each panel in that string, and all are 100% fine at around 28 Volts (cloudy weather).

I am able to series two and then three together, but the moment I add the fourth panel, voltage drops to zero again.

This is very strange as each panel is 100% .

Anyone have any ideas, again, panels have been test individually and All have the same voltage. I have also put them in sets of two, and they work, but all 4 in one series string does not??!!

[Mike90250]

(Just back from a short vacation)
Quite possibly a bad MC connector. The MC series of connectors are NOT rated for connection / disconnect under load. If your system was powered up, a connector could have arced and ruined itself. A test prod could bypass the bad portion and still show OK. Use a flashlight, and look deep inside the connector for pure, shiny, gold contacts. Any dark spots and you need new connector there. Caution, if there is light, the panel is producing power - don't get shocked.

Less likely is a cracked trace or ribbon on a panel behind the glass, if the panels got manhandled that could do it. reads OK on test, but when loaded and it heats up, breaks the circuit. You can likely see a small burn spot in behind the glass, That means the panel is shot.

[Jemplayer]

(Just back from a short vacation)
Quite possibly a bad MC connector. The MC series of connectors are NOT rated for connection / disconnect under load. If your system was powered up, a connector could have arced and ruined itself. A test prod could bypass the bad portion and still show OK. Use a flashlight, and look deep inside the connector for pure, shiny, gold contacts. Any dark spots and you need new connector there. Caution, if there is light, the panel is producing power - don't get shocked.

Less likely is a cracked trace or ribbon on a panel behind the glass, if the panels got manhandled that could do it. reads OK on test, but when loaded and it heats up, breaks the circuit. You can likely see a small burn spot in behind the glass, That means the panel is shot.

I did inspect the MC connectors and nothing seemed out of order but will check again and look for what you have mentioned. I did test two at a time in series and worked. Then connect the two sets together and did not, so though it was that connector in the middle so cut it of and used a copper Farrell to rejoin the wire, still did not work.

[sensij]

Could the zero on your meter actually be an "O" , indicating "out of range" on a 100 V scale?

[Jemplayer]

Could the zero on your meter actually be an "O" , indicating "out of range" on a 100 V scale?

No, unfortunately not. Meter set correctly.

[Sunking]

Measure each panel Voc individually before connecting.

[Jemplayer]

Measure each panel Voc individually before connecting.

Yes did that. And then connected them together and no voltage. Then re-checked them all again. Still all fine. Then wired them in sets of two, still fine then set of three still fine, then four, NO VOLTAGE

[sensij]

Do you have the ability to measure current? If you short circuit them, do you get Isc appropriate for your conditions?

[Sunking]

Yes did that. And then connected them together and no voltage. Then re-checked them all again. Still all fine. Then wired them in sets of two, still fine then set of three still fine, then four, NO VOLTAGE

Do these two test to find your problem. Lastly make sure Polarity is correct. Would not be the first time a manufacturer got the red and black wires reversed. My color blind brother may work there.

[littleharbor]

Sounds like the 4th panel could be the problem. Have you tried rearranging the order of panels? Take panel #4 and #2 and switch them and try again. Also, as Sunking eluded to, possibly reverse polarity. Be sure your + and - cables are correctly done.

[SunEagle]

Sounds like the 4th panel could be the problem. Have you tried rearranging the order of panels? Take panel #4 and #2 and switch them and try again. Also, as Sunking eluded to, possibly reverse polarity. Be sure your + and - cables are correctly done.

A second question would be, are all the panels the same make & model or at least have the same spec? Sometimes adding a bastard panel to existing ones can be an issue.

[Jemplayer]

All idenatical and same age.

[max2k]

All idenatical and same age.

can you connect the one which 'brings voltage to 0' with just one of any of the remaining 3 and check if the voltage corresponds to 2 panels? Where those panels connected to? I'm just trying to confirm when you stated '4 panels have 0 voltage' they were not connected anywhere else, just 4 of them in series.