# How much current draw from an inverter?

If I have a 12 V car battery and I connect it to a 3 kW 10 A 220 V AC inverter, how much would be the current draw? 250 A?

• 220V 10A is 2.2kW, not 3kW. Is it 2.2kW continuous, and 3kW peak? Or is it marketing speak by someone who made up numbers that looked good on the box? May 9 at 20:27

If I have a 12v car battery and I connect it to a 3kW 10A 220v AC invertor, how much would be the current draw? 250 amps?

It may be more than 250 amps and it could be a lot less depending on how much load power you are taking.

If the inverter is rated at 3 kW this will be the maximum output power it can deliver. Given that an inverter might only be 90% efficient, the input power could be as high as 3.333 kW and then the current from a 12 volt battery would be 278 amps.

Of course, the inverter may have a surge power rating of 4 kW and then the surge current taken from the 12 volt battery might be as high as 370 amps.

But, largely speaking, the input current is determined by the load connected to the output of the inverter.

• Makes sense! So if i connect say a 500w load, what would be the power consumption? May 9 at 12:21
• If the inverter is 90% efficient at full load, the losses will be the difference between 3.333 kW and 3 kW i.e. 333 watts. On no-load, you might expect these losses to reduce to about half. On a 500 watt load, you might expect the losses to be around 200 watts so, just the losses will draw about 17 amps. Add to that the current taken from the 12 volts to supply 500 watts (about 42 amps) and the total current drawn on a 500 watt load might be in the region of 59 amps @SimonSultana May 9 at 12:25

If there were no losses, then 250A. In reality it will be around 20% higher assuming a 80% conversion efficiency.

It would want to be a big car battery methinks. The average car battery is not designed to deliver such high Amps for an extended amount of time.

• Would that be the maximum current output though? Or would it depend on the load connected to it? May 9 at 12:19
• @Simon: Thought experiment: what happens when you plug a 20 W (0.1 A) bulb into your house supply which is capable of 63 A or so? Does it draw 63 A? May 9 at 12:54