i just noticed some corrosion on the mounting holes of a MPPT250 70 in a dry area where no corrosion should occur. So i thoungt it could be galvanic corrosion.
The grounding point of the MPPT was not connected (yes i know it should have been, all others are, i dont know why this one was not).
With a multimeter i measured PV voltage (120V) between the grounding point and earth.
When I touch the grounding point with a cable, that is grounded, there are sparks and the MPPT resets.
Am i right thinking this is a defekt in the MPPT or could there be a problem with the PV or the wiring?
With a fault like this, how much current could be going trough the grounding wire? PV short circuit current? Would this be detected?
Ist step is to isolate the PV (both Poles) Measure PV + to Ground, PV- to Ground, also PV+ to PV-and if you have an insulation tester, when the light level is low, short PV+ to PV- and measure the insulation to ground.
This assumes that your PV frame is grounded.
Voltages should be BOTH less than 30 -50V - depending on your Voltmeter impedance. This test to be carried out in full light. If the sum of the PV to ground voltages is the same as the PV +/- voltage, then you have a ground fault in the array. The ratio of PV+/G to PV-/G will tell you about where the fault is.
Also, with the Array disconnected from the MPPT, recheck the ground terminal to battery -ve or ground. this should be close to 0V.
From what you describe, it seems like the battery is not grounded, and also that there is a ground fault in the array.
It is unlikely to be a fault in the MPPT.
When i connect the grounding point to the negative terminal on the battery, there are no sparks and the current through the grounding wire is <1mA. It seems like the sparks only appear with higher PV voltage.
I did the same measurement with a different MPPT and there is no voltage between the negative battery terminal an the grounding point.
