The formula
DC current (A) = AC watts ÷ (Battery voltage × Efficiency)
Worked example
A 1,000 W kettle on a 12 V system with an 88% efficient inverter draws 1,000 ÷ (12 × 0.88) = 95 A. As the battery voltage sags under load the current rises further, so size the fuse with at least 25% headroom: a 125 A fuse. Many installers size the fuse and cable for the inverter's full continuous rating rather than the expected load.
Quick reference (12 V, 88% efficient)
| AC load | 12 V | 24 V | 48 V |
|---|---|---|---|
| 300 W | 28 A | 14 A | 7 A |
| 1,000 W | 95 A | 47 A | 24 A |
| 2,000 W | 189 A | 95 A | 47 A |
| 3,000 W | 284 A | 142 A | 71 A |
Frequently asked questions
How many amps does a 2000W inverter draw?
About 190 A from a 12 V battery at full load, 95 A at 24 V and 47 A at 48 V.
How many amps does an inverter draw with no load?
Typically 0.5–2 A at 12 V (6–25 W), depending on size and make. Check the 'no-load current' in the specification.