I had a large diesel generator for a back-up genset at my house, started to realize that at 3GPH x $3/gallon, I'm looking at $9/hour in fuel, x 24hours = $216/day. I could stay in a nice hotel room, order room service, and let insurance pay for the lost food.

Anyway, with a stock alternator on a 240D, 45a, which is more like a 1200rpm output, not idle, you're putting out 45v x 13vdc = 585watts. Most of my inverters are high-end sine-wave units, IIRC around 95% efficient, the cheaper ones are typically less (some much less, and if a square-wave it will lose a great deal more efficiency running an inductive motor like a refrigerator). So, lets figure 80% efficiency from the 585watts = 468watts which is 4amps load at 117vac. It will likely have enough surge capacity from what's in your battery to start the load, but unless your total combined loads are less than 4amps continuous/average, you will drain the car battery until the inverter drops out on low voltage. The current drawn will also increase as the voltage drops so that even a 3a or 3.5a load will be greater than the output of your car's alternator, and the alternator will lose output as it heats up, and we're assuming the alternator is capable of its original rated output even though most aren't after some miles/years of use.

A lot of fuel and car use for a little output, but better than nothing I guess.

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Gone to the dark side

- Jeff