Inverter amp load questions.

[Gerdo]

I need a little advice on inverters. Correct me if I'm wrong. A 400 watt inverter should draw about 40 amps? I have heard that if you don't use the full capacity of the inverter it will only draw what is used. So if I'm only running 200 watts then my draw will be about 20 amps? And If I'm running 100 watts then my amp draw will be about 10 amps (12 volts DC).

[madjack]

I need a little advice on inverters. Correct me if I'm wrong. A 400 watt inverter should draw about 40 amps? I have heard that if you don't use the full capacity of the inverter it will only draw what is used. So if I'm only running 200 watts then my draw will be about 20 amps? And If I'm running 100 watts then my amp draw will be about 10 amps (12 volts DC).

Gerdo, you are correct, the inverter will only draw the power needed to run the appliance(s) hooked to it(plus some small amount for inefficiencies in the inverter)...in your example, a 400W unit would put out that much 120vac power @ 3.3 amps...given the 10 fold difference between 120VAC and 12VDC, the amperage draw on the DC side would be 33amps...200W/16.5A...100W/8.25...basically what you said.......
madjack

[Gerdo]

That is what I thought. I was shooting high on the amp draw for the inefficiencies in the inverter.

Thanks

[artfd]

I wish I had known all this before I bought a 1500W inverter in the forlorn hope of running a 700W microwave by 12V battery power.
Too late I learned (1) a 700W microwave draws about 1100W of power from a 110VAC line (2) 1100W 110VAC supplied by a voltage inverter turns into a 110A draw from a 12 vdc battery, (3) drawing 110A from a regular 12VDC auto battery for 10 min will kill it in pretty short order (4) cables that will supply 110A for 10 min are expensive & best kept rather short, (5) the best way to supply 110A at 12VDC for 10 minutes is to use one or more expensive deep cycle 12V batteries and finally (6) it would have been cheaper for me to buy a small generator to do the job, which is what I wound up doing.