Help CenterPV Calculations
Surge factor — motor startup current
Calculation2 min readUpdated: 2026-06
An electric motor draws 3–7× its rated current at startup for 0.2 seconds. The "Startup" column is always visible in the appliance table.
P_peak = P_rated × Surge_factorAC unit 900 W × 5 = 4 500 W startup → 5 kVA inverter minimum
| Appliance | Surge Factor |
|---|---|
| LED, TV, PC, box/router | ×1.0 |
| Microwave, fan | ×1.5 |
| Washing machine, tumble dryer | ×2.0 |
| Refrigerator, freezer | ×3.0 |
| AC unit, pump | ×5.0 |
| Large industrial motor | ×7.0 |
SolarDim Pro auto-detects the factor from the appliance name. Correct manually if your equipment has a soft-start (VFD).
Common mistakes
- Sizing the inverter on rated power without accounting for the startup peak
- Applying a generic surge factor when the appliance has a VFD soft-start
- Adding up all surge factors instead of considering sequential appliance startup
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