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Inverter size calculator

Inverter watts and surge for your loads, with the battery current it draws.

Try the circuit in the labBuild it on the simulator's bench and measure it.

How it is worked out

Add up everything that can run at once, then add 25 %: an inverter run flat out all day runs hot. Motors draw several times their running power for a fraction of a second when they start (a fridge compressor about 3×), so the inverter's surge rating must cover the running loads plus that one motor's start. Most inverters surge to about 2× for a few seconds.

Battery current = watts ÷ battery volts ÷ 0.9. A 3,000 W load on 12 V pulls about 280 A: that is why bigger systems use 24 V or 48 V.

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