Hello, i recently did my first install of a 300W solar panel in my camper. Linked to a 100 30 MPPT, 300AH lifepo4. Everything went well at first test, even pulling stable 350w. Now I routed the 4mm2 cable through the roof, sealed the entry gland and grommet and connected everything. Now there’s a big voltage drop issue. I turn it on and in full sun it reaches max 220W for a few seconds at 36v and then dips down to as low as 100w and 15v. I measured voltage with multimeter before it reaches the breaker and it confirms the same. The drop only happens when it’s connected to the MPPT. I bypassed the breaker routing directly into the (new) MPPT and removing ferrules incase it was poorly crimped. But no difference.
I put the outside connection in a tight spot I noticed one of the MC4 connectors wasn’t fully plugged in, about 1 mm before it clicked, it sat like this for an afternoon. So I suspect this might have caused an arc that burned the plastic of the mc4 and causes the voltage drop. Visually the inside of the MC4 connectors don’t show any signs of burning. I didn’t screw them apart but just looked into the pins.
Another suspect is that the cable was damaged during install, I bent it and shallow scratches on the insulation. But the bends were not so strong that I feel it could’ve damaged the wire strands. But it could explain the brief 220w followed by voltage drop. If the wire is damaged and the heat increases so does resistance.
I don’t have new MC4 connectors nor a crimping tool. I do have a spare short section of the PV cable with it’s MC4 connectors on it, could I replace the possible damaged ones with this by bud connecting. I also have another solar panel like it which I could Before I rip apart the wiring and start replacing MC4 connectors. Could there be any other cause of the problem? Thank you in advance!
