3 way fridge AH rate.

[mibosa]

Can anyone please advise a formula for calculating the amp hour rate for a three way fridge?  I have a Chescold 3 way fridge and the inside label states 12v DC @ 150 watts.  A formula I have been given is 150 w divided by 12v = 12.5 AH.  Anyone have another manner in which to guesstimate the battery consumption, as in the various forum and magazines etc I have seen people talk about their fridges pulling 4 - 7 AH?  Regards, Bob.

[2up]

Hi Bob, I think you are getting amps and amp hours mixed up. Someone correct me if I'm wrong,and I'm sure someone will, I was to told VAW - volts X amps = watts therefore watts divided by volts equals amps. So if you have a 200 amp/hour battery at 12.5 amps you would idealy get 16hours continuous use. I think that's how it works! Cheers Les

[Aussie]

How old is it? This will also play a part in the final result.

New fridges are efficient and most ive had experience with run on what youve stated above and less. Primus being the most efficient ive seen.

[mibosa]

Thanks Aussie and 2up for your responses. I think 2up has said what I was thinking, but just couldn't word it appropriately. And Aussie, I am not sure how old it is as I haven't really examined all the exterior to find any plate which might indicate the age of the unit. I will conduct some research as I would only be guessing, even though it looks in good condition. My concern was how much it would pull whilst driving and before setting up on gas upon arrival at my destination. Thanks again, Bob.

[gregh]

Hi Mibosa,

The formula you have been given is correct. Watts /volts = amps. Based on 150W, your fridge will draw a constant 12.5amps; there is no thermostat control on 12v. Unlike new 12v only fridges which use compressors and use as little as 2amps, the 3-way fridges use heater elements - use lots of amps. (I know a heater element in a fridge sounds strange but these fridge works on a heat exchange system.)

3-way fridges should only be run on 12v while being towed, then switched to either 240v or gas on arrival at destination. You can run it directly off your car battery or from a dual battery system - you just need to ensure that the wire you use is capable of 2 things.

1/. Handling the amperage draw.
2/. heavy enough to deliver 12v to the caravan - voltage drop will cause fridge to not run well and potentially damage the heat element.

And most importantly, have a circuit breaker or fuse in the wiring.

Cheers
Greg

[mibosa]

Thanks gregh for your detailed response. I fully understand what you have explained and confirms bits and pieces I had put together through various sources.Regards, Bob.