Short answer: an MPPT controller with a LiFePO4 profile, rated for at least array watts ÷ battery volts × 1.25 amps, and a max PV input voltage above your array's cold-morning open-circuit voltage.
| If you need… | Look for |
|---|---|
| 1–2 panels, small budget | PWM is OK only when panel voltage closely matches the battery (12V-nominal panels) |
| 200–400 W | MPPT, 30–50 A at 12 V |
| 600 W+ or panels in series | MPPT, 60 A+, high PV voltage input (100–150 V) |
| Lithium bank | Selectable LiFePO4 profile, no/low float, low-temp charge cutoff |
| Monitoring from your phone | Bluetooth or a display; pair with a shunt monitor |
Amps = array W ÷ battery V × 1.25. Cold Voc = panel Voc × panels in series × (1 + cold %). 10–15% is a common allowance for freezing mornings; use your panel's temperature coefficient for precision. See also the charge controller calculator and series vs parallel.
Safety: These are general estimates, not a design. Follow your equipment manufacturer's instructions and local electrical code, and consult a qualified electrician for anything connected to shore power, a house, or high-current batteries.
About 400 ÷ 12 × 1.25 ≈ 42 A on a 12 V bank, so a 40–50 A MPPT. On 24 V it is about 21 A.
For most RV systems, yes: MPPT converts excess panel voltage into charge current and lets you wire panels in series with thinner cable.
Many controllers allow more watts than their rating and simply clip output, but never exceed the max PV input voltage. Check the manual.
Yes for LiFePO4: it charges to about 14.2–14.6 V and avoids a high float that ages lithium cells.
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