I have what looks to be a Coleman 100W Solar Panel with a 30 amp Coleman controller in the trailer. It doesn't really charge my batteries, so I checked the open circuit voltage coming off the panel and it's under 13 Volts DC (This is when I remove the leads from the panel to the controller). I can not find a spec for the solar panel open voltage, but most other panels say it should be greater than 20 volts open circuit. Is it a fair guess the panel is shot? The controller rarely shows the indicator light it's charging, but does show the voltage of the battery.

Are you using a digital meter with the panel in full sun? Voc (open circuit) and Isc (short circuit) are 2 basic checks for panel. A 100W 12V panel should have about Voc=18V+ and Isc=3A+.

CA Traveler wrote:Are you using a digital meter with the panel in full sun? Voc (open circuit) and Isc (short circuit) are 2 basic checks for panel. A 100W 12V panel should have about Voc=18V+ and Isc=3A+.Thanks for the response! Yes, i'm using a digital meter (Fluke) and the panel was in full sun. I haven't tried to short it yet and read the current

Might just not be enough sun but I tend to agree you need a new panel.

So just one last question. I just want to confirm that the " Isc (short circuit) " test you put an AMP meter between the positive and negative leads of the panel while it's disconnected from the controller. I wanted to double check because this really is short circuiting the solar panel and i don't want to do a smoke test on it :-)Edit: while it's in full sun

With most DVM's, set the meter to 10 amps and move the lead to the 10 amp position. If you do not you will blow the internal protection fuse for the lower amp readings. Jim.

Question on Coleman 100W Solar Panel "open circuit" voltage

Dirtdaddy
Explorer
Jul 27, 2023
CA Traveler wrote:
Sounds like a short. A shorted bypass diode would not change the amps, assuming multiple diodes.

I'm not sure what the bypass diode(s) function are. I assume they are in the panel, so i'm going to do some googling on the subject. Thanks for the tip to you and Jim.
Dirtdaddy
Explorer
Jul 27, 2023
bigfootford wrote:
Well I have never seen this phenomenon...hahahaaa.
Spec ISC and low Voc.. Like a bypass diode shorted but why is the ISC at spec. Going to have to see if there is an answer from someone else or join the Northern Arizona solar elect forum... I am a member over there. If you get no answer and can not become a member when I get some free time next week I will ask over there.

Jim

https://forum.solar-electric.com/

Thanks for the help! Looks like an interesting forum, I went ahead and signed up
CA_Traveler
Explorer III
Jul 27, 2023
Sounds like a short. A shorted bypass diode would not change the amps, assuming multiple diodes.
CA_Traveler
Explorer III
Jul 27, 2023
Hopefully it's not held down with Z brackets.
bigfootford
Nomad II
Jul 26, 2023
Well I have never seen this phenomenon...hahahaaa.
Spec ISC and low Voc.. Like a bypass diode shorted but why is the ISC at spec. Going to have to see if there is an answer from someone else or join the Northern Arizona solar elect forum... I am a member over there. If you get no answer and can not become a member when I get some free time next week I will ask over there.

Jim

https://forum.solar-electric.com/
Dirtdaddy
Explorer
Jul 26, 2023
bigfootford wrote:
With most DVM's, set the meter to 10 amps and move the lead to the 10 amp position. If you do not you will blow the internal protection fuse for the lower amp readings.

Jim.
Thanks Jim, so I just checked the current using the 10 amp position on the DMM and I read close to 6 Amps (see picture). When I read the open circuit voltage it's 12.8VDC. This is with the panel disconnected from the controller. The current looks fine but the voltage is not high enough to get the controller to charge the battery more than a few milliamps even when the battery is under 12 volts. It's almost like this solar panel has a built-in regulator of its own. I can not see underneath it to read the specifications or brand, so i will have to remove it.
bigfootford
Nomad II
Jul 26, 2023
With most DVM's, set the meter to 10 amps and move the lead to the 10 amp position. If you do not you will blow the internal protection fuse for the lower amp readings.

Jim.
Dirtdaddy
Explorer
Jul 25, 2023
So just one last question. I just want to confirm that the " Isc (short circuit) " test you put an AMP meter between the positive and negative leads of the panel while it's disconnected from the controller. I wanted to double check because this really is short circuiting the solar panel and i don't want to do a smoke test on it :-)

Edit: while it's in full sun
wa8yxm
Explorer III
Jul 25, 2023
Might just not be enough sun but I tend to agree you need a new panel.
Dirtdaddy
Explorer
Jul 25, 2023
CA Traveler wrote:
Are you using a digital meter with the panel in full sun? Voc (open circuit) and Isc (short circuit) are 2 basic checks for panel. A 100W 12V panel should have about Voc=18V+ and Isc=3A+.

Thanks for the response! Yes, i'm using a digital meter (Fluke) and the panel was in full sun. I haven't tried to short it yet and read the current

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