Match your MPPT controller to your array's output current and voltage — size it to the panel wattage at your battery voltage, with the panel string voltage under the controller's max PV input. A common rule: controller amps ≥ (array watts ÷ battery voltage). A 400W array on a 12V battery needs about a 30A MPPT; the same 400W on 24V needs about 20A. This chart pairs typical RV arrays to the right controller so you don't clip output or overspend.
How to size an MPPT controller
Two limits matter:
- Output current (A): array watts ÷ battery voltage = the charge current the controller must handle. Pick a controller rated at or above that.
- Max PV input voltage: your panel string's open-circuit voltage (Voc), cold-adjusted, must stay below the controller's max PV voltage.
Sizing the array first? Start with the solar panel buying guide, then come back here to match the controller.
Array → MPPT pairing chart
| Array size | Battery | Approx. charge current | MPPT controller |
|---|---|---|---|
| 100–200W | 12V | ~8–16A | 15A MPPT |
| 200–400W | 12V | ~16–30A | 30A MPPT |
| 400–600W | 12V | ~30–50A | 50A MPPT |
| 400–800W | 24V | ~16–35A | 35A MPPT |
| 600–1000W | 24V | ~25–45A | 50A MPPT |
Add headroom for cold-weather voltage spikes and future panels. Shop MPPT charge controllers.
Why not just buy the biggest controller?
An oversized MPPT costs more and gains nothing if your array can't produce the current — the controller only passes what the panels make. Conversely, an undersized controller clips output, wasting solar. Match it, with modest headroom for expansion.
Series vs parallel changes the numbers
Wiring panels in series raises voltage and lowers current (smaller battery-side cable, watch the max PV voltage); parallel keeps voltage low but raises current. Either way, the controller's output current is set by total watts ÷ battery voltage. See how to install RV roof solar panels and the cable & fuse sizing chart.
FAQ
What size MPPT do I need for 400W of solar?
About 30A on a 12V battery (400W ÷ 12V ≈ 33A, so a 30–35A controller), or about 20A on 24V. Confirm your panel string voltage is under the controller's max PV input.
Can my MPPT be too big?
It won't harm anything, but you pay for capacity the array can't use. Match the controller to the array with a little headroom instead.
Does series or parallel change the controller size?
The output current (watts ÷ battery voltage) is the same, but series raises PV voltage — keep it under the controller's max PV input, especially in cold weather.
Can I add panels later?
Yes, if the controller has spare current and voltage headroom. Size up one step now if you plan to expand.
Match it right: Shop MPPT controllers — in stock, ships from Upland, CA.