Using a Portable Fridge

Thanks for the replies. . .

Its those times when the car will be stopped for a few hours, or we're at a non-powered camp site that I'd like to know about. How do you work out how long you can run the fridge while the car's not running? How long can you leave the fridge switched off at different temps without ltting your food go off?

Much of it is trial and error.

A lot of fridges have a cut out when the voltage drops to a certain level that you can still start the vehicle at.
If your fridge does not have this function ,you can buy an inline gadget that does the same thing.

One tip is to turn the fridge to low temps while you are driving and turn it back up when the engine is off.
On cool nights ,you can even turn the fridge off.
It also helps to put some thought into how your food is packaged.
For example ,vac packed meat uses less power to store than frozen meat.
I keep my salad items in square containers.
A bottle of frozen water can keep it colder if you have room

Sorry for delay - I tried to post this the other day but my internet connection was going too slowly...

Firstly, I would recommend buying the biggest capacity battery you're willing to pay for and willing to carry in the car - if you get something too small, you'll regret it everytime you use it, but you'll be unlikely to ever regret getting one with 'too much' capacity! And it’s much cheaper to go up a size in the initial purchase than to buy another/bigger battery later.

"How do you work out how long you can run the fridge while the car's not running?"
Batteries are rated in Amp hours, that is put simply: generally the number of hours the battery can provide 1 Amp before being 'flat'. Theoretically, most compressor fridges use about 3.5-4.0 Amps while running. If it was to run continuously for an hour, this would equate be 3.5-4.0 Amp Hours. Usually a fridge will switch on and off (by the thermostat) to regulate the temperature. Often this means the fridge is only running for about 1/4 or 1/3 of the time (and of course this can vary significantly depending on the set temp, outside temp, how often you open the fridge, quality/thickness of insulation, etc.) meaning that in any given hour, you would be using approx between 0.9 and 1.3 Amp hours each hour. Assuming you have a healthy (and fully charged) 48 Amp Hour battery, based on the figures above, you could probably expect the battery to last up to 36 to 48 hours depending how much of the time it is 'running'. In practice, I've always found that my portable battery pack never runs my fridge (Waeco) as long as it 'theoretically' should! Remember that a battery might be rated at XX Amp Hours when new, but won't retain this whole capacity for long.

"How long can you leave the fridge switched off at different temps without letting your food go off?"
This will depend on what food you have in it, as well as outside temp, how often you open the fridge, whether the fridge is in the sun, etc. of course, the quality/thickness of insulation, and lastly, how full your fridge is (a full fridge will 'hold' temperature better (due to the higher thermal mass) but will also require more effort ie. running time to restore the required temperature when you switch it back on). This one is going to be a bit of trial and hopefully not too much error! If it is a cool evening in the Vic Alps, there should be no problem leaving it off overnight, but if you are in the tropics you might need to leave it switched on all the time. The best way to get an idea of the inside fridge temp (remember that you let heat in everytime you open the lid) will be to get a digital thermometer (Woolies used to sell cheapies for $10 in the elect section or Jaycar/Dick Smith might have something a little better for $20-30) and watch how quickly/slowly the temperature changes when you switch the fridge off.

I hope all this helps. I'd also recommend you click here for an ExplorOz article on portable fridges. It's a long article but there are headings that deal with power usage, how to get the most out of the fridge (ie. improve efficiency).

Again, I'd recommend getting the biggest battery you are willing to pay for and are willing to carry - I run my fridge off a 60 Amp Hour "Blue Apple" portable battery pack (from "Home of 12v") and I always wish I'd gone the next size up to 75 Amp Hour! I'd also recommend not running the fridge from your vehicle's main battery even if the fridge has a low voltage cut-out - from my experience they don't always cut out when they should!

Good information link


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