Fridge battery consumption.

[Huntsman]

A 12 volt fridge spec sheet says it draws 40 watts. Running from a 110amp/hr battery.

40w/12v=3.3 Amps

110a/hr battery / 3.3 amps = 33.3 hours run time before battery dead.

At 25 deg C ambient the fridge runs at 25% of the time.

33.3 hours/ 25% = 133 hours = 5.5 days

Is that right?

Fridge cuts off when batter gets down to 10.7 volts, that must have a bearing on it.

[annodomini2]

Battery draw is non-linear.

See here for an example ( http://www.digikey.co.uk/en/resources/conversion-c...)

Which reports ~23 hours with your parameters.

@25% duty cycle just under 4 days.

Also there will still be current draw with the Peltier off, to supply the electronics.

[Simpo Two]

Peltier or compressor?

I don't think you'd want your batteries down to 10.7V.

I turn my fridge (Waeco 50) off at night and move a freezing pack from the ice section to the fridge section. That keeps it fine until morning, indeed colder sometimes! - when I switch it on again and put the pack back to freeze.

[Huntsman]

Simpo Two said:

Peltier or compressor?

I don't think you'd want your batteries down to 10.7V.

I turn my fridge (Waeco 50) off at night and move a freezing pack from the ice section to the fridge section. That keeps it fine until morning, indeed colder sometimes! - when I switch it on again and put the pack back to freeze.

Thanks.

Compressor.

[Simpo Two]

Then without trying to do accurate sums just copy me

You probably know all about split diode thingies so the fridge can't leave you stranded. The worst offender is the microwave - 10 minutes of that and the split diode thingy is needed

Do you need to leave the fridge on for 5+ days without the engine running? Shorepower?

[MOTORVATOR]

Just run the Genny up?

[maser_spyder]

Mine has a 70ah battery and runs for about 3 days before the lights start going a bit dim. That runs the lights and other electrics too (phone chargers, 3G router, etc), so your calculation probably isn't far out at 4 days.