What size alternator do you need with a 1000watt inverter with a 1999 ford e-150 4.2 liter?

Answer 1

A quality 1000 watt Inverter could be expected to require about 84 amps at 12V. If we figure that the charging system is going to be operating at about 13.8V this figure could drop to about 75 amps (considering conversion inefficiencies). If we then consider that the truck electrical system will require some current just to keep the truck running, say 25 amps, then we'll need an electrical budget of at least 100 amps. So if you plan to use your inverter for a continuous application then you'll need a 100 amp alternator otherwise you'll slowly discharge your battery. If for example you had a smaller 75 amp alternator then you would be draining the difference (25 amps in this case), from your battery. Since most quality automotive starting batteries have an RC (Reserve Capacity), of less than 120 minutes at a 25 amp draw you'd drain your battery in less than 2 hours. Keep in mind that nearly all alternators do not provide full rated amperage at idle. A 100 amp alternator is likely to be pumping out only 75 amps at idle. For a continuous use inverter application I'd play it safe and install at least a 120 amp alternator minimum.