> If I have an inverter that providers 1000W @ 120V from a standard automotive
> 12VDC (13.8VDC) system. Can I calculate the amp draw by doing 1000/120= 8.3A
> to see how much of a drain this device will place on the auto system?
The amperage ON THE 120 V SIDE will indeed be 8.3 A, if the load is
resistive. But you wanted to know the current on the 12 V side. The
inverter acts like a transformer. Voltage transforms one way; current
transforms the other way.
1000W out means something greater (in watts) into the inverter. For
purposes of this exercise, let's say the inverter is 90% efficient at
this power level, meaning it draws 1111 watts from the 12V side. The
excess 111 watts goes into heating the inverter.
1111 W / 13.8 V = 80.5 Amps, drawn from the car's electrical system.
If the DC voltage drops, say to 12.0 V, then the current increases to
92.6 A to deliver the same power.
If the inverter's efficiency is less than 90%, the required input
wattage, and amperage, must be greater.