Electrics question - inverter amps

Hi, quick question for the electric guys. I have an old inverter in the car (can be run from a cig lighter socket), 500w peak / 300w cont. What will be the max amps drawn on this? I am assuming not too much if it comes with a cig lighter connection. Cheers

I would think the cig lighter wiring/socket/fuse would be your limiting factors.

Hi, going to connect direct to battery, but just wanting to know the max amps it will use if possible. Cheers

I would do it this way:

300W/12V = 25A, without any losses of the inverter. If the efficiency of the inverter is 80% then I would expect 30A. 500W would be 42A.

This would drain a 45Ah battery in theoretical 1.5hours, in reality probably more like 3/4 h and after 1/2hour or less the car might not start anymore.

I hope this answered your question.

In addition I would add a fuse as close to battery as possible and make sure, that the cables from the battery to the inverter a thick enough. If the cable length is 2m then I would go with 16mm2 or 6AWG. Maybe, if the cable is shorter also 10mm2 might be ok but a thicker cable is never bad. This is so that the losses are not too big and the cable do not get too warm.

25A assuming 100% efficiency - which it won't be. 500W peak is approx. 42A.

Now here was my confusion. I got the above answers when looking on Google, but then wondered why these low power inverters come with a lighter plug? Will running an inverter plugged in here not do some damage?