Solar Panel Issue - Maybe Faulty Diode?

Talk Electrician Forum

Help Support Talk Electrician Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Marcel Grigore

New member
Joined
Jun 1, 2014
Messages
3
Reaction score
0
Location
Ipswich
Hello everyone.

This is my first experience on a public forum, so please bear with me.

I have recently acquired a solar system which contains 4 x 85w BP solar panels, a STECA charge controller and 2 x 6V 400amh deep cycle batteries. I have the 4 panels connected in series and the 2 batteries linked in parallel. The panels are charging the batteries at 12.5A max in full sunny day, which I thought it is not really enough. I started disconnecting the solar panels one by one, to find out that one of them wasn't producing any Amps. I then opened the black box on the back on the panel, and checked the 2 diodes, the panel is fitted with. When I connect the voltmeter to the negative and positive of each diode, one diode is reading 9.4V and the other only 4.47V. I opened the other panel's boxes and checked the voltage, and every single diode produces around the 9.4-9.7V. 

The questions I have are: Is this particular panel faulty? Is the diode at fault? How can I fix the problem? Could this damage the system?

I think I have described the issue accurate, and I hope that there is an answer to my question?

Many thanks

Marcel

 
Diodes are there to stop backwards flow in the panels, and allow a panel to be by-passed should it be shaded, or defective. The won't affect the panel outputs. 12.5A sounds pretty reasonable for  your panels which output around 4.5A max. If you think a panel is defective, then disconnect one at a time. Or check them with a simple multimeter that can test DC voltages. Disconnect panels from system, point roughly at sun, and test for DC voltage at panel connectors. You'll have to keep an eye for clouds, but basically all 4 panels should give the same voltage output. To check ampage, you will need a 'clamp ammeter'. Join ends of panel connectors together, place clamp around cable to take a reading of ISCC. Compare all 4 to get an idea if one is faulty. ISCC (short circuit ampage) for these panels is around 5.1A

 
hi binky. Much appreciated your email. I managed to get hold of a amp meter, and the panel was working as it should. I might have done something wrong or looked at the wrong thing...

i have another question, if you don't mind: when all the panels are connected, they produce around 17.5A in full sun - according to the amp meter reading, which is connected to the end wires. However the charge controller only shows a max of 13A coming in. Is this how it should be? Sorry, i appreciate it might be a silly question...

 
'stalled' condition versus 'in use' condition. When testing panels it is effectively a short circuit which allows a higher current to flow because there is no load, where as when driving through the charge controller it is under load.  from Ohms law, V=IR assuming voltage remains constant, the resistance R has increased, hence current I decreases.

You are also assuming the charge controller display is accurate, I would think of it as more of an 'indication or performance'.

 
Top