solar panel

phum · Veteran Member

solar panel

madaboutled · Guru

You'll need a multimeter that measures both Volts and Amps. Most basic multimeters only measure volts. You need to measure firstly the voltage and then the Amps being generated. Plenty of Utube videos out there if you don't know how. If you don't know what you're doing then best to get it tested by someone who does.

Whenarewethere · Guru

Most multimeters only go to 10 amps. So you should be ok. But a clamp meter is easier, most are AC so make sure you get a DC clamp meter.

Edit: forgot my panels are in series at 3.9 amps. So 7.8 amps for 120 watts. Had 8.0 amps when I cool the panels with water. You will need more than a 10 amp meter. A few go to 20 amps. But to be safe it's a clamp meter.

-- Edited by Whenarewethere on Thursday 21st of February 2019 03:43:22 PM

Jaahn · Guru

Hi phum smile

What are the specs on the back of the panel. 250W is likely to be more than a 12v panel, or if it is the amps are a lot more than 10 A. You can just do the max voltage OK in full sun and if your meter can handle the amps then a short circuit current. But the ultimate test is to do a load test at about the Vmp and see if the current is close to the Amp. But a load for that panel is not easy to find. I have three 12V headlight bulbs I use for loads.

Jaahn

Whenarewethere · Guru

A very crude method, I got a big spark when I accidentally touched the wires together out of my panels.

T1 Terry · Guru

join the plus and minus cable together and read with a clamp meter or through your multimeter when set to high DC amps setting if you don't have a clamp type multimeter. The test will only be short term so they can handle a limited over load. A 12v 250w panel should give a short circuit current of roughly 15 amps in full sun and an open circuit voltage of around 21vdc. If it is a 24v panel the amps will be roughly 7.5 amps and the voltage around 38vdc. If it is roof top grid connect panel the voltage could be anything between 19v to 46v.
If you see the voltage but not the amps or only half or less amps than you should, pop the cover off the back and check to see if the diodes are still in place and have not popped in half. The diodes will pop in half if an accidental reverse connection is made and the battery tries to turn the solar panel into a heater. Check the number on the diode from one that is still in one piece and head down to the local Jay Car stote and buy a replacement for under 50 cents, probably more like 10c or 20c or they will just give it to you.
hope that helps

T1 Terry

Peter_n_Margaret · Guru

T1 Terry wrote:
If it is roof top grid connect panel the voltage could be anything between 19v to 46v.

Or is odd cases even more, like this one in my shed.....

Cheers,

Peter

T1 Terry · Guru

Wow, that is just insane, thanks Peter for putting that example up as a warning. As a precaution before doing any of the things I mentioned above, place a towel or blanket over the solar panel before connecting the cables together or pulling the connection apart. The open circuit voltage would pull quite an arc even at only 1 amp and that would wreck the MC4 pins in the connectors, assuming they are not already the cause of the problem. Yet another thing to check, look inside the MC4 connector and make sure the pin doesn't move if you push/pull the cable, if it does, pull the cable till the pin comes out because the plastic holder is stuffed.
Personally, I never use the plastic holders that are part of the MC4 connector but rather remove the pins from the plugs, slide a length of heat shrink up the cable and push the pins together to ensure a good deep connection. Then I solder the two together just to be sure and slide the heatshrink over the connection. Eliminates this point of a potential problem, yet easy to remove by simply cutting off the heat shrink, heat the connectors with a hot air gun and pulling them apart, now the replacement panel can be connected the same way.

T1 Terry