Solar Charge Controller Sizing Guide | PES Supply
Solar Charge Controller Sizing Guide
How to choose and size MPPT and PWM charge controllers for solar systems
MPPT vs PWM: Which to Choose?
| Feature | PWM | MPPT |
|---|---|---|
| Efficiency | 70-80% | 95-99% |
| Cost | $30-$100 | $100-$800 |
| Voltage Matching | Panel V must match battery V | Steps down higher V to battery V |
| Best For | Small/simple systems | Any system, especially higher V arrays |
| Cold Weather | No boost | Extra power from high panel voltage |
| Series Panels | No | Yes (recommended) |
How to Size a Charge Controller
Controller Amps = Array Short-Circuit Current (Isc) × 1.25 (NEC safety) × 1.25 (continuous use)
Example: 4 × 450W panels (Isc = 11.5A each) in parallel = 46A × 1.25 × 1.25 = 71.9A → Use 80A controller
Sizing Chart (450W Panels, 48V Battery)
| Array Size | Config | Total Isc | Controller Size | Recommended |
|---|---|---|---|---|
| 2 panels (900W) | Series | 11.5A | 20A | Victron MPPT 100/20 |
| 4 panels (1.8kW) | Series | 11.5A | 20A | Victron MPPT 150/35 |
| 6 panels (2.7kW) | 2S3P | 34.5A | 50A | MidNite Classic 200 |
| 8 panels (3.6kW) | 4S2P | 23.0A | 40A | Victron MPPT 250/60 |
| 12 panels (5.4kW) | 6S2P | 23.0A | 40A | MidNite Classic 200 |
| 16 panels (7.2kW) | 8S2P | 23.0A | 40A | EG4 6500EX (built-in) |
| 20 panels (9kW) | 10S2P | 23.0A | 40A × 2 | 2× MidNite Classic 200 |
Voltage Matching
MPPT controllers can step down higher array voltage to battery voltage. This allows series wiring for efficiency:
| Battery Voltage | Min Array V | Max Array V | Typical Config |
|---|---|---|---|
| 12V | 17V | 100-150V | 2-6 panels in series |
| 24V | 34V | 100-150V | 2-6 panels in series |
| 48V | 68V | 150-250V | 4-10 panels in series |