The same 3.2 kW array needs a 100 A controller on a 48 V battery but a 200 A controller on 24 V. How the current rating is worked out.
| PV array | 3.2 kW (STC) |
| Controller type | MPPT |
| Battery | 48 V nominal (compared with 24 V) |
| Design margin | 10% on top of the 125% continuous factor |
The controller's maximum PV input voltage must exceed the array's open-circuit voltage at the lowest site temperature, and its PV input current must cover the array short-circuit current. These are separate checks on the controller data sheet.
| Check | Requirement | Actual | Status |
|---|---|---|---|
| 48 V system controller rating | ≥ 91.7 A | 100 A | ✓ PASS |
| 24 V system controller rating | ≥ 183.3 A | 200 A | ✓ PASS |
Key insight: For an MPPT controller the output current is set by array power and battery voltage, not by the array current. Doubling the battery voltage halves the controller size.
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Open Solar Charge Controller Sizing calculator →A PWM controller passes the array current almost directly, so it is sized from array short-circuit current × 1.25 (× margin), with the array voltage matched to the battery.
Many MPPT controllers allow some array oversizing and simply limit output current, but check the manufacturer's maximum array power and input current limits.