Running a 3 way fridge on 12 volt for short periods

Personally I never run the three way on Battery Power during shortish trips.

Providing you aren't trying to keep frozen goods you can go for 3 or 4 hours without power.

I usually have a couple of large Esky Freezer Blocks in the freezer compartment and they will stay frozen for 5 or 6 hours whilst travelling.

You may get 4 hours out of a fully charged 100AH battery using it on a three way. I think they draw around 12 amps and run full time.

Howdy, We plug ours into 240V 12 hours or so before leaving & switch over to 12v while travelling. Apparently, from what I have been told, they will flatten your battery fairly quickly if the motor is not running. We have had a solenoid fitted under the bonnet so that when the ignition is switched off it cuts the power to the frig. If you don't open the Frig door while stopped for a couple of hours your beer will still stay cold!!
Before we had the solenoid fitted & when we pulled up for an hour or so I used to simply change the switch on the frig to 240V which of course simply stopped it from drawing on the battery, or sometimes we just used to disconnect the plug supplying power to the van.

3 ways on 12v draw about 10A continuos.
So it dosent take long to draw down a battery.
Use that to calculate the size battery you require.

Putting 12v computer fans to blow over the top cooling fins on the rear part of the unit can help alot in heat transfer, and increase the efficiency of the fridge, as too with good sized cables to the fridge, and a good connector to minimise voltage drop.
With these additions we can freeze on 12v under 35deg outside temp.

Cheers

Trains

Ps, with our old borrowed brown 32l chescold, I covered it in 1" packing foam, then put packing tape over the foam to give it abrasion resistance. made a large difference in its keeping its temp down too.

We have an Ultimate, and the way the standard Ultimate wiring works is that it runs the fridge from the car but only when the engine is running. If we only stop for a couple of hours the fridge seems to stay cold (depending on the outside temp of course!), but if in doubt we have to change it over to gas.

The 3 way is so power-hungry that we don't run it on 12volts at any other time, even though we have upgraded the Ultimate's power system (Ours has two 100ah agm batteries).

We have a compressor fridge in our fourby that is much more power efficient. The 3-way is fine, though, when camped - it runs efficiently on gas, even in 35+ weather.

Hope you enjoy your Ulti as much as we do!

Increase the battery capacity to at least 100AH (2 x 80ah even better) and make sure you get AGM Deep Cycle batteries, because they will charge much faster.

Mainey . . .

The Ultimate 3-way fridge, when switched to 12V, never draws power from the Ultimate battery, but may draw power from the vehicle battery. The Ultimate battery is used for all other Ultimate electrics (lighting, water pump and radio) and this battery is charged when you connect to 240V power.
As Gary P has said above, the standard Ultimate vehicle wiring ensures that the fridge is only connected to the vehicle battery when the fridge is switched to 12V and the vehicle ignition circuit is on. This happens via a relay fitted to the Ultimate electrical box and is done to avoid flattening the vehicle battery by inadvertently running the fridge from it.
Hope this helps.

I believe that I have a unique system to run my 3 way Eletrolux when ON THE MOVE.
My caravan has 140 amp hr batteries mounted on the draw bar. These are charged from either the car's alternator or via a smart charger permanently mounted in the caravan of the mains or an alternator (generator)
The cables from the car to the caravan are 4 aswg (18mm2)
When the engine of the car is running the 3 way fridge draws it's power from the batteries on the caravan but of cause these are being charged by the car at the same time.
When the ignition of the car is turned off the 3 way fridge is isolated from the system but there is still power to run all the other accessories in the caravan including an Engel fridge.
I did a check some time ago of the voltage at the 3 way fridge as installed by the caravan manufacturer and found that due to line loss (voltage drop) I had only 10.75 volts so don't trust caravan manufacturers to install adequate weight cables

Hi,

Don't know what 3way you have but the 90L one in my Jayco uses a 175W heating element on 12v (150w on 240v). I would say that it would run full time on 12v to try and keep the fridge cold.

On the fridge (mine was on the back of it) it says what size the heating element is so you should be able to work out how many amps it will pull over a set time and hence calculate how long you can run it off you batteries or how many batteries you need.

I always have my fridge cranked on 240v for about 36-48hrs before I head off so that you could leave it off for about 4 hrs and it would make very little difference to the fridge temp (dependant on outside temp obviously).

Good luck mate.

If you have heavy enough cable from the alternator to the fridge then you should not have to worry about running the fridge off battery during extended lunch stops. In fact a lot of travellers get by not powering their fridges when they are travelling.

On the crossing to Tasmania you can not power your fridge. Batteries will not last long and you are not allowed to run the fridge on gas. We switched the fridge off at 1900 on the night sailing. The fridge was only opened for the quarantine check the following morning. We travelled to Burnie after we got away from the ferry. When we checked the freezer at Burnie the contents were just getting mushy. We were not worried about the safety of the contents as the under certain conditions food can be refrozen. The "you can't refreeze food" applies to food that is removed from the fridge to thaw. If you thaw food properly - ie thaw it in the fridge - then it can be refrozen. Also the food would have only been above the recommended temperatures for a short period. Generally food is not kept in a caravan fridge as long you keep your food at home, which is also a factor in your favour.

Compared with those crossing Bass Straight and surviving, your 3 hour lunch stop is harmless if you have good cables to your alternator. Just don't keep opening the fridge, if you do then run it on gas.

PeterD

was delayed once getting back to van ---battery flat -----ever since when i leave it for over 2 hours i switch to gas thats what its for ----only run on 12volt when travelling

The 3 way fridge in our van is connected to the auxillary battery in our vehicle by an Anderson plug & heavy wire.

As the auxillary battery is isolated from the cranking battery, i have no problems leaving the fridge running for an hour or two whilst stopped.

We also run a 50L Waeco in the back of the tug & we have had no problems with this set up.