One of our customers was getting less than 20% of the rated power from his 400-watt solar setup. Using a Victron MPPT controller and two CMPower 120 Ah LiFePO4 batteries, he should have been receiving over 25 amps of charging power. Instead, he was only getting 4 amps. After hours of troubleshooting—charging and discharging the batteries, testing the solar panels, and reprogramming the MPPT controller—nothing changed.
Finally, he sent a picture of his installation and mentioned he was using a 25-foot, 12-gauge wire between the controller and batteries as a temporary setup. I suggested he replace it with a short, 10- or 8-gauge wire. Instantly, the system worked perfectly.
We recreated this setup in our shop and confirmed the same results: inadequate wiring severely limits system performance. Bottom line: always use appropriately sized wires between your controller and battery bank (and between your solar panels and controller) to handle the load. Don’t skimp on wiring—it’s crucial for optimal performance.