Hi,
I've searched this forum without success so I'm asking for help diagnosing a problem.
I've got a 100W solar panel connected to a MPPT 75/10 controller which charges a 100Ah LiFeP battery. Last year the system worked flawlessly, but this year it's working intermittently--usually not at all.
The panel checks out fine--short-circuit voltage is 21V with 4.7A of current under bright sun (100W). I measure this both directly at the panel and at the wire feeds connected to the MPPT controller. The entire wire run from the plug on the travel trailer to the MPPT is extremely short, and all the connections are tight . All the wire connections to the MPPT are tight. There are no signs of corrosion anywhere. And, like I just wrote, I'm measuring an PV output of 100W in the wires that are directly entering the MPPT.
However, most of the time the MPPT won't charge and reports a PV voltage equal to the battery voltage, about 13.3V. When I disconnect the panel from the MPPT I measure 21V and 4.7A (various, of course, with sun output). About 20% of the time, however, charging proceeds as normal, though never to completion--it seems to cut out at the equalization stage, when charging current drops back to 0.0W. The state of charge is usually about 90% when this happens.
So I'm stumped! Is it:
(a) user error? I'm using the default LiFeP setting on the MPPT, though it doesn't change anything if I tweak them a little.
(b) A faulty panel? I've talked to the panel manufacturer, and they've told me that it's testing fine--producing 100W as specified.
(c) A faulty MPPT controller?
(d) Something else?
Help!
