How long is a piece of string?

These 3 way fridges are in their most inefficient mode running on 12 volt.
How much gas do you think that they use? I know that the old 35 litre Finch fridge use to consume 1/4 ounce an hour.
Maybe if you "take off 5" on your way to the campground you will be able to afford to run your fridge.

Harry,
1. We don't know the size of your battery's.
2. Those 3 ways draw around 15 amps so it will not take long to flatten a battery.
Say you have a deep cycle 100a/h battery in good nice it will flatten it in around 6 hrs.

I think you are better sticking with gas or buy a 12v compressor fridge. The other way is if it is cold enough switch it off at night

Have a good one,
RA.

You don't say how big your fridge is, but even a small portable will draw about 12 amps on 12 volt. Let's allow 15 for a slightly larger fridge.

You don't say what sort of batteries you have, so again, a bit of a guess coming up. Lets say you had 200amp-hours total battery capacity in two dual-purpose batteries. (ie crank/deep-cycle) Now the set-up ypu have is not ideal for looking after batteries, so you probably won't have the maximum capacity. Lets be generous and give you 150 amp-hours.

Simplistically, 150 amp-hours divided by 15 amps gives you 10 hours until the batteries are flat. But it doesn't really work like that because battery capacity is worked out using a lower discharge rate, maybe 5 amps, so your time to flat will probably be less. I'm thinking maybe 6 or 7 hours, but admittedky it's a guess.

Now the batteries are flat - they won't crank an engine. AND your fridge has stopped and the contents are warming up.

You won't get cranking ability after overnight use of the fridge on 12 volt. I don't think you'll get it after 6 or 7 hours. You might get it after 3 or 4.

Use the gas, mate. It's why the fridge is 3 way. 12 volt is only for transit when it has an alternator to supply the power.

Cheers

Frank

How long is a piece of string, try twice the distance from the centre,

I agree with the above replies, my 3 way frig is very gas efficient.

Regards

G'day Harry, I'm at a loss to understand how your 3way is expensive on gas. My 25
year old Finch ran for 5 weeks..15 hrs a day.. & didnt use a 9kg bottle. In fact, that is
why I stick with it...there is no cheaper option to run a fridge when camped. While
I have no beef with the solar/battery brigade..set up is bloody expensive. Many 12v
users have issues because the wiring is inadequate..even new ones have this issue,
but when wired correctly work ok....but gas is the 3ways real advantage.......oldbaz.

Hi harryopal,
You don't say how big your 3 way fridge, I will presume it is a 90ltfridge/freezer. Which will use about between 600-750gms of gas in a 24 hour period depending on you thermostat setting and the weather(humidity and air temp).
This will also depend on the age of the unit and how good the seals are.
These fridges as others have said run better on Gas than 240/12V.
The element for the 12V will be anywhere up to a 150W or there abouts and will flatten a battery very quickly, even two.
If cost is your only concern with running it on gas, I would keep to the gas.
I take it your running the fridge on 12V while traveling as this the right thing to do, I also presume you free camp a bit to be running it on gas.
We have a 3 way 90 lt in our camper and run it on 12V while on the hop, 240V if staying in a park and if free camping run it on gas when stopped.
I would also check a few things if it wasn't running as it should.
Check the flue for blockages, Eg mud wasp nests in the exhaust, or in the vents at the rear. Check seals and the thermostat is working properly. Also clean were the flame is, soot builds up here which reduces it's performance.
Here is a link to aPDF File/Manual for a RM360 , these units are basically the same from model to model.

Hope this is of some help to you.
Cheers

As said previously, you did not state what the fridge is. If it is a small one, your batteries will last about the same as leaving your headlights on. If it is one of the larger ones, you will kill the batteries quicker.

The previous replies are all correct, we are on the road at the moment and our 4.5kg gas bottle has run the 90ltr dometic and cooking for 4 weeks free camping 70% of the time. 12volt by day when travelling, gas by night, you won't find a cheaper way if your fridge works and seals correctly.

A small 240/12v fridge will run about 4 days on 100amp/hr deep cycle which can be topped up on solar but 3 way fridge on 12volt is nearly impossible due to continued current draw due to no thermostat.

Good morning and thank you all so much for your replies.
Have a bonzer weekend.
Yours tropically, Harry