Homemade Solar Test Jig Found Bad Panel

[JimD]

Have had 200 watts of solar for a couple of years but it never seemed to do what I had hoped. I recently upgraded the controller to a Renogy MPPT with bluetooth so I could easily see what the panels were doing. I must admit, I love gadgets and gauges.

The new controller showed me that I was only getting half of what I should be getting. Maybe I was expecting too much. I decided to add another 100 watt panel which I bought in February. Then the virus hit. I was isolating from my family so didn't want them to help with the install. By help I mean have my son get up on top and mount it.

So in the meantime I decided to fabricate a simple solar load tester. Basically just some switches and 4 ohm power resistors that could be switched in to load down the panel. All purchased from Amazon of course.

So my tester sat for a couple of months and I finally arranged to drive to my son's house so he could mount my 3rd panel since he did the other 2. In the old days I would have done the work but since I am a rickety 70, I will turn over this kind of thing to the younger generation. Their turn to do for me I guess, although I do insist on paying them.

So, while I was at my controller (with face mask on of course) I disconnected the panel feed so I could load it independent of the controller. Up top I had him connect one panel at a time so I could compare readings. I hooked up a voltmeter across the line, along with my load tester, and also clipped a current meter around one of the wires so I could see what I was pulling.

The first panel tested made me think my tester wasn't working. With a single 4 ohm load my panel voltage dropped to 7.49 volts with a current draw of only .56 amps. Then I hooked up my other panel by itself (all panels are wired in parallel) and tested it. It came back reading 14.54 volts and a current reading of 3.66 amps. This was in the range I was expecting to get with a 4 ohm load because the resistor actually measured 4.5 ohms but may change as it heated. And boy, does it get hot! I was only doing the load for a few seconds at a time.

Tested my brand new panel and received about the same readings as my other good panel. Happy days! I did have a bad panel probably since the beginning so I was never getting the power I had expected.

Right now I have all 3 panels connected (they have blocking diodes in them so the bad panel won't affect the good panels). I did a load test by switching in additional 4 ohm resistors and would see the current I was expecting.

I contacted the panel company and found out it still has a warranty. They want me to perform a diode test which is no big deal. I am just waiting on my son to come and pull the panel for me as the company wants it back for analysis if it fails my test.

They sent me a document on how to test their solar panel which is pretty simple. You take an open circuit voltage and then hook a current meter inline with the 2 wires which gives you a dead shorted maximum current reading. Never considered doing that but who am I to argue.

I have attached their document along with some pictures of my tester plus info in case anyone wants to build one. Can't wait until I have my 300 watts of solar available. Am considering adding a 4th panel just for the heck of it.

[pconroy]

Nice work!!!!!!!!!