how can I test for bad cell? or panel?

[SerTiminS]

Hello all,
I'm working with 50 panels divided in to 7 groups. 4 panels in series grouped in 2 parallel (24V output). X 4. 3 panels in series grouped in 2 parallel (12V output). X 3.
Below is data gathered. Apparently #1 and #7 is only outputting half of amps compared to others with same input. How can I test for bad cell or panel. As you can see, the voltage is similar.

#1 58V 11.97A 25.8V total 5.182kwh
#2 60.6V 22.86A 25.89V total 9.787kwh
#3 61.2V 22A 26.14V total ~9kwh <- aprox as picture is bad
#4 58.7V 21.69A 25.88V total 9.116kwh

#5 53.2V 30.38A 13.8V total 7.94kwh
#6 44.9V 30.22A 13.68V total 6.764kwh
#7 54.3V 14.86A 13.80V total 5.193kwh

 

[MisterSandals]

Can you test the voltage of individual panels in string #1 and #7? Be careful connecting/disconnecting if these strings are energized...cover with blanket to reduce electrical shock hazard.

I suspect you will find a faulty panel (low or zero voltage) or connection.
Report back with what you find to further diagnose individual panels.

 

[SerTiminS]

Can you test the voltage of individual panels in string #1 and #7? Be careful connecting/disconnecting if these strings are energized...cover with blanket to reduce electrical shock hazard.

I suspect you will find a faulty panel (low or zero voltage) or connection.
Report back with what you find to further diagnose individual panels.

Thank you for your support MisterSandals,
Every panel has good voltage. I tried to measure current using voltmeter on Amp setting but gives 0.

 

[MisterSandals]

i do not think you can measure amps without a load.

Perhaps with trial and error you can take a panel out of strings 1 and 7 to identify which one(s) are not contributing under load?

A little tedious but you will find the culprit panels. Close inspection of those panels may reveal some broken traces or issues in the plastic junction box (that the panel output wires come out of).

I am sure there are more clever ways to test panel, maybe someone has experience trouble shooting them (all mine work, never had to do that).

 

[jimbo78]

I tried to measure current using voltmeter on Amp setting but gives 0.

This is by design your multimeter does that because you would have created a short across the panel and blown the fuse in your multimeter.

You need to swap the leads on your multimeter, but you also need to setup a load correctly as suggested already so as you don't create a short situation. Your also messing with potentially dangerous voltages so you really need to know what your doing. That is far beyond the scope of this forum.