MPPT not detecting panels: 5 causes and step-by-step diagnosis

MPPT shows 0 V PV or 'no panels' with full sun. Before assuming it's broken, check the 5 most common causes in order.

1. Voltage below startup threshold

MPPT needs array Vmp > battery voltage + 5 V to start. Example: 24 V battery → array must deliver 29+ V. With only 1 panel 24 V (Vmp 18 V), it'll never start. Series the panels to sum voltage.

2. Reversed panel polarity

+ cable where - goes and vice versa. Some MPPTs don't protect and burn instantly. Others show '0 V' and just don't start. Multimeter: + of red cable must match + on MPPT.

3. Blown string fuse

With 3+ parallel strings, each usually has a fuse. If one blows, that string is out. Multimeter on continuity. Replace fuse (gPV typical 10-15 A).

4. Loose MC4 connector

Vibration or rushed install leaves an MC4 not fully clicked. Chain breaks. Test: gently tug each MC4. Moves = not locked. Reseat until you feel the click.

5. Reversed blocking diode

If you have blocking diodes between strings and installed reversed, no current flows. Check diode polarity (white band = cathode). Cathode must point toward MPPT.

If nothing works

After ruling everything out: connect panels directly to a 12 V bulb or tester. Panels deliver current and MPPT still shows 0: bad controller, RMA or replace.

If battery won't charge, read battery won't reach 100%.