Inverter power calculator
Battery draw of an inverter from its output power and efficiency.
Fill in the fields and the result will appear here automatically.
Calculate steady DC input power and battery current for a stated AC active output power, efficiency and battery terminal voltage. The balance also shows conversion loss. Use efficiency at the relevant load: a datasheet maximum is not constant across the load range. Battery chemistry, start-up peaks, voltage sag and separate idle consumption are not modelled.
How it works
Formula and logic
η=efficiency/100; Pin=Pout/η, Ib=Pin/Ub, Ploss=Pout·(1−η)/η. Power is in W and voltage in V. Pout>0, Ub>0 and 0<efficiency≤100%; 100% is a formal lossless limit.
Example
1000 W, 85% and 12 V give 1176.5 W input, 98.04 A and 176.5 W loss. At the same efficiency and 24 V, current is 49.02 A. At 100% loss is zero; zero-load operation is outside the model because actual idle consumption needs separate information.
Fields and units
- Active output power — W
- Efficiency at stated load — %
- Battery terminal voltage — V
How to use
- — Enter active output power in W, not apparent power in VA.
- — Use documented efficiency at the relevant load and conditions.
- — Use loaded terminal voltage when known.
- — The result does not size cables, fuses, battery capacity or start-up capability.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- Victron Sun: maximum efficiency and separate idle consumption — specified product
- Limitation
- Steady power balance at entered efficiency; no start-up surge, battery model or wiring design.
FAQ
Why is efficiency above 100 percent rejected?
It would mean the inverter produces more energy than it consumes. That is not a rounding issue but an impossible figure, so it is refused rather than calculated.
Does this include start-up surge?
No. Some motors and compressors need more than their rated power during start-up. The peak and duration depend on the load and lie outside this steady calculation.
Where do I find the efficiency?
On the inverter datasheet. It usually varies with load, so the figure at your typical load is the one worth entering.
Is battery chemistry taken into account?
No. The calculation is purely electrical; how the battery behaves under that current is a separate question.