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[Chance]

Originally Posted by scrubjaysnest

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For 120 volt ac devices divide the wattage by 120 and multiply by 10 to get an approximate DC current. This ignores inverter efficiency.

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For 12-Volt system, a quick estimate one can do in their head is taking wattage and divide by 10, which is the same but makes an allowance for inverter efficiency. That works out to around an 83% inverter efficiency, which is in right ballpark.

As an example, an air conditioner that requires 450 watts, pulls 3.75 at 120 Volts. Then at 12-volts it's 37.5 Amps. Using 83% efficiency batteries have to supply 45 Amps.

Instead of all the math, I can divide 450 watts by 10 in my head to get to the 45 Amps directly.

Obviously that's a rough approximation, and either way ONLY works with 12-Volt systems.

Anyway, we can easily see that running a 1500 watt microwave or coffee maker will require about 150 Amps from 12-volt battery bank, which is a lot even if comming from 2 typical RV batteries.

I think one of the factors that gets overlooked is that many owners do not adjust available battery Amp-hours (rated at a very slow 20-hour discharge rate) to much faster discharge rates that can't even be supported for an hour. Not only is this hard on batteries, it also throws the numbers for energy storage and production off. It may be tedious to estimate, but when using high-power devices (microwave, Keurig, air conditioner) we need to go beyond simply adding up Amp-hours.