charge current continually changing

Sundancer

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Joined
Jan 2, 2021
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5
I'm helping a friend with a new solar install, He's got two strings of three 330W panels rated at 41 VOC and 10.33 ISC running into a combiner box and then on to an Outback MPPT controller and Outback Inverter. The system is working but charge current is low and always changing. We're testing with a Fluke clamp-on meter and started at the combiner box. Turning on one of the DC breakers at the combiner box, we'll see 10A on the meter for possibly a second before dropping steadily down to between 3 and 4A. Turning that breaker off and testing the other string, we just see between 3 to 4A. Voltage on each string is 123V as expected.

Checking the incoming current at the controller shows a continually changing current ranging up and down between 3A and 7A, Input voltage at the controller is 123V. The lifepo4 batteries in his 24V system are currently in the 26.2 range so they're not full, and the MPPT controller is using the 3 to 4 amps to charge at around 14A in bulk mode. All this was happening with bright blue skies and cold temperatures - no clouds. Panel voltage was checked when the strings were connected but ISC was not.

My first thought was that he had a loose connection somewhere but we checked everything and all is fine. I've never seen charge current varying up and down like this and I'm completely stumped. Any ideas???
 

Sundancer

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Joined
Jan 2, 2021
Messages
5
Thank you so much for the answer. After thinking about it for a while, that has to be the problem. I didn't consider it because I never experienced the problem even with about 100 successful solar installs on RV's under my belt. It's obvious after you pointed it out. Thanks!!
 

Sundancer

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Joined
Jan 2, 2021
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5
I thought I should post a followup in case it might be helpful to someone else. Time2roll's suggestion to check solar Voc and Isc was the obvious solution and one I never considered because I haven't (yet) come across a bad panel. I returned to my friend's house and checked his panels but Voc and Isc were fine. Scratch one more possibility off the troubleshooting list. I went back inside and checked his Mate3 settings for about the 5th time and finally (finally!!) found the problem. I can't remember the specific menu item but I finally (finally!!) noticed an incorrect setting that was limiting the incoming current. A quick change and he was seeing 50A instead of the 14A mppt charge current. I guess the moral of the story is to carefully check and doublecheck all programming settings before you start thinking resistance, loose connections and such. Lesson learned for me.
 
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