If it is the type of fridge that also runs on AC mains, then the wattage quoted is probably the maximum when on mains and may be about 10-20W less on DC 12v.
Also, some fridges have a fixed temperature thermostat so may use less power when cool enough.
Your calculation looks ok to me, except that I do it a different way, calculate the current used first then divide into the A/H which gives the same answer.
If your battery has not been used for a while then it may not still be able to achieve that capacity and I bet the manufacturers quoted the capacity as the maximum obtainable in ideal conditions?
hi bitem,
Another point to consider is when the fridge is down to temperature and the door is kept closed, the fridge will not be powered 100% of the time.
If its well thermally insulated you can get a say, a 50% duty cycle, so the battery could last twice as long, say 15hrs??
Hero999,
Many small portable fridges don't need an inverter as they use a 12v DC Peltier cooler and are actually less efficient when powered by the AC mains option.
Hero999,
Many small portable fridges don't need an inverter as they use a 12v DC Peltier cooler and are actually less efficient when powered by the AC mains option.
Sorry, I obviously didn't read your post properly.
All those smaller fridges seem to be Peltier coolers. I wonder why because compressor fridges are so much more efficient. Perhaps it's because they're cheaper?
I wonder if a mains fridge powered from an inverter works out more efficient than a Peltier cooler.
They're much more physically robust. They're compltley solid state, only moving part is a fan, and even that isn't required depending on the application, a compressor and the coolant lines are much more complex and expensive to make and easy to damage. I'm going to guess (just guess) that a mains fridge is more effcient at the same temperature differential as a peltier can create. Compressor powered friges however are capable of a much higher differential in temperature just by running it longer. It's just the way the basic physics of the two devices work. One pumps heat using electrons, the other uses a gas with a very large compression ability so it can pump heat much better.