Running cool box on my car battery

[Lawrie8f]

I’ll be spending 9 days on a French campsite soon (Normandy - 75th anniversary D-Day celebrations) and have bought a good quality Cool Box (12V/220-240V) to run off my car battery. The only information I can glean is that at 12V it runs at 48W, so presumably it is 4 amps? The car battery (Exide, 44Ah) is about 6 months old and in excellent condition, starting the engine (Ford Fiesta) instantly.

I’ll run it on my domestic supply for 24 hours before departure, then drive perhaps 100 miles from the UK to the campsite. The beaches stretch over about 65 miles of coastline and there’ll be no problem whilst driving, but I expect to need to ration usage when stationary - any ideas how much? I have a basic multimeter - what readings would tell me I’m overstretching the car battery?

 

[Harald Kapp]

at 12V it runs at 48W, so presumably it is 4 amps?

Why the question mark . Should be an exclamation mark.

I expect to need to ration usage when stationary - any ideas how much?

According to a table here the battery should not be drained to less than 75 %. My guess is that this is a bit conservative, especially taking into account the battery is relatively new. Personally I'd set the limit at 50 % which translates to 12.25 V according to the same table.
For a 44 Ah battery that means ~20 Ah or 5 hours at 4 A.
But: I guess the cooler will operate intermittently, so it will draw an average current much less than 4 A (e.g. only 1 A_average if it is active only 1/4 of the time. This will extend the operating time from a fully charged car battery to approx. 20 h or 1 day. No way the battery will last the whole 9 days. You should pick a campsite with mains available and possibly take a charger with you to keep the car's battery charged for those times you're not on the campsite but need the cooler.

 

[Lawrie8f]

Thanks, that’s very helpful and gives a detailed picture of the parameters I should work to.

 

[Bluejets]

Why muck around..?? Get a decent one like this.....

http://www.asciimation.co.nz/beer/

 

[Lawrie8f]

Haha - a jet-powered beer cooler - just the job!

You’ve set me on a whole new line of thinking...

 

[dave9]

If it is peltier based it will operate continuously at full load and struggle to do much cooling at all at only 4A, but even that might be some conservative rating.

Personally knowing how little the peltier type cools, I wouldn't leave it on for a moment when the engine is off. Do, do your testing though, throw something cold in, run it a while to get the interior cavity temp down too, and leave the door shut for X # of hours with it running and not to see how much difference it makes.