inverters

1500W is one big inverter, sure its not a 150W inverter?

Anyway that doesn't really matter, have look on the back on the device and it will say how many watts it uses eg. something that draws 100w of power ( power = volts x current). You know the the car is 12V and the the device uses 100W so 100/12=8.33A

Cheers
Jeepy

I happen to have a (borrowed) Digitor 300w unit at the moment. It has an efficiency of up 90% and is rated at 300w continous at 13.8 volts. It draws less than 0.7 amps at idle (no load, just turned on) and with a 300w load it draws around 28 amps...so..

If the device(Example) is using 300w @240v(pulling around 1.25 amps) from the inverter, then the inverter is pulling around 28 amps @ 13.8 volts from the battery.

I realise this doesn't really answer your question but it is some food for thought. Atleast using the specs on your inverter you can work our a worst case senario (for me.. fully load the inverter and I suck 28+ amps from my battery)... which is a heap..( leaving your lights turned on draws around 9 to 10 amps and how fast does that kill a battery!) Thankfully this inverter has a low voltage warning plus a 10.5 volt cut out!.