determining Battery size to run fridge

Rabs. Lots of more info would be needed before you could get a full answer on this topic from the people that know, here is a good link to do a bit of research

http://www.fridge-and-solar.net/info.htm

Cheers Tony

a lot depends on:
ambient temps
lid opening
product temp you may put in
temp it is controlled at
etc etc
how long is a piece of string

but as guide you may get 2-3 days form a fully charged large capacity deep cycle battery..more batteries the longer it will last

Assuming no charging, it is not too hot ( say below 25deg), and you set the fridge to about 3 - 4 degrees, have the food already cold and don't open it often then about a 120 AH should see you through without going below 50% battery capacity ( which kills batteries in a relatively short time). You should average about 1.5A per hour not .85 unless it is colder outside.

Set it to freeze or open it lots and top it up with warm beer and it will last 24 hours with the same battery.

thanks for the replies, and thanks for the link it was a good read.so assuming i got 2 days out of 1 fridge would 2 in parrallel give me around double?

Thanks again

Rabs

rabs,
you ask,
(a) How do i determine size of battery to run fridge with draw of <1 amp per hour ?
(b) How big would the battery need to be to run it over a weekend.'

the fridge uses ~1 AH, so uses ~48 Amps in 48 hours
** - ONLY IF YOUR NUMBERS ARE ACCURATE- **
( I don't think they're realistic in real world usage )

the "web site" nominated gives you the answers and 'reasons' for those answers too.
As posted above you should never allow the battery to get below 50% of battery capacity.

Is a case for 'bigger is better' as you can't have too much battery power :-))

Mainey . . .

>.85 amp per hour

Hmmmmm.... I suspect Waeco are being "economical with the truth". My guess is that for most people using the fridge in a normal camping situation it would be at least 1.25 amps per hour.

So; 1.25 * 24 = 30Ah

Now it's best not to discharge an AGM battery below 70% of capacity in order to maximise its life - regularly discharging one to 50% will reduce it's life to about 500, or fewer, cycles whereas staying at 70%+ will increase life to around 2000 to 3000 cycles.

In light of the above my suggestion is a 100Ah AGM and a $99 GMC generator providing you have space for the gen and its noise is not an issue. Actually you'll need a charger too (the 12V "charger" in the gen won't hack it) so that's about another $150 from Jaycar, maybe $100?

With a 15A charger you'll need to run the gen for about 2 hours per day so a long extension lead would be in order.

If the gen is not an option you could go for 2 x 100Ah batteries (we're talking $600! Expensive beer) which would give you two days of running or three if you're prepared to push the batteries.

Ah the beauty of 3 way fridges :)

Mike Harding

Hi Rabs
Many frig manufacturers put out these mythical figures which realy mean nothing,they are based on the average current used over 24hrs with controlled conditions that do not in any way represent real conditions.
The wattage[ should be on the nameplate somewhere] divided by 12 will give you a much clearer idea of the current draw in amps while the fridge is actually running . How much it runs in any 24hr period & there for how long the bat lasts is totally dependent on your conditions of use.ie ambient temp ,thermo setting ,heat of items going into frig, frequency of opening & length of time opened etc .Depending on these conditions the fridge may run for 20% or up to 100% of the time.
YES running 2 in parallel will give you the combined amp hr output but do not discharge wet lead acid bats beyond 50% capacity if you want long bat life ie 2x100amps hr bats give effective only 100 amp hrs of usable power