Fault Diagnosis, Testing and Repair Procedures
Systematic diagnosis
Fault Diagnosis, Testing and Repair Procedures covers finding faults without replacing good parts. Isolate the circuit safely, then work from the array to the load: visual inspection, open-circuit voltage (Voc), short-circuit current or clamp current, insulation resistance and continuity. Compare strings and modules with each other. An I–V curve tracer gives more information than a single multimeter reading. Check inverter error logs and battery voltage before replacing parts.
Common faults
Open circuit: broken connector, blown fuse, cut cable or failed bypass path. Low current with normal voltage: shading, soiling, partial string failure or a faulty module. Low voltage: shorted bypass diode, reversed polarity or a shorted cell. Insulation fault: damaged cable, water ingress or a pinched conductor. Battery faults show as rapid voltage rise on charge or low capacity under load.
Worked example
A two-string array has one string at 350 V and the other at 0 V. The inverter is not necessarily faulty. Isolate, then measure the dead string at the array end. If Voc is 0 V, check the string fuse, MC4 connectors and cable continuity. If Voc is normal but current is zero under load, suspect an open circuit downstream or an inverter input problem.
Traps
Do not measure Isc with the meter set to the wrong range or without checking the meter's DC current rating. Do not replace a module with a different rating in the same string. Do not test insulation resistance on a live circuit.