Dometic fridge on 12 volts

briche · Guru

Dometic fridge on 12 volts

rockylizard · Guru

Gday...

confuse duplicate post ?

There are answers in General Forum

cheers - John

Stratman77 · Senior Member

My Avan has a 90 litre Dometic 3 way fridge and it works brilliantly in all 3 modes. I have to ask if the motion detector - I haven't come across these before, but I'm still learning - switches the fridge off every time you come to a stop, as this would be hard on the switch contacts as frequent switching of 20 - 30 amps would be hard work. I have a RedArc VSR to do the job so the fridge supply is on only when the motor is running, but then I don't have an aux battery.

briche · Guru

I Stratman, thanks for your comments. The fridge draws about 15 amps with the motion switch contacts rated at 30 amps. To ensure of the ability to cope with the current drawn by the fridge I use a 50 amp headlight relay to actually do the switching. I run the fridge from the aux battery in the tug so that the starter battery is not loaded and the two are isolated with a redarc unit. Comments I have had suggest that the fridge will cope on 12 volts provided that it is cold already therefore on 12 volts it will maintain It's temp.

As we are intending to travel thruout WA next the days will be long on the road so should be ok.

Just to let you know, I am an electrician so I am aware of the wiring/supply issues but what I was not sure of is how well the fridge works on 12 volts.

Thanks for your comments

briche

-- Edited by briche on Thursday 4th of December 2014 10:04:19 PM

Stratman77 · Senior Member

Hi, Briche! Thanks for the info. It sounds like you have done all the right things and your relay contacts should handle the load with no problems. I know my fridge draws around 20 amps (probably an older model) but it works well - as long as the fridge is cold to start with. I once started a trip with the fridge at room temperature and found that after 3 hours of driving, it was quite cool but the freezer was nowhere near a freezing temperature. I hope you have a great trip - it sounds great.

PeterD · Guru

briche wrote:
I run the fridge from the aux battery in the tug so that the starter battery is not loaded and the two are isolated with a redarc unit. Comments I have had suggest that the fridge will cope on 12 volts provided that it is cold already therefore on 12 volts it will maintain It's temp.

Ideally an absorption fridge should have its power supplied from the alternator and not storage batteries. The use of ignition switched relays and fridge switches is to get close to achieving that goal. The picture below is taken from the handbook of my fridge. The circuit diagram is diagrammatic but people smart enough to be competent enough to wire their own vehicle will be able to nut out their own way of doing things. On a previous thread one character of limited thinking ability argued against this idea, he thought he knew more than Dometic.

Whilst I advocate connecting your fridge hot wire to the starting battery so its connection is as close to the alternator I think it amount to very little gain for you to shift the connection now. You seem to know to use heavy cables and not the usual chain-store auto cable.

Dometic Fridge 12 V Wiring 2.PNG

The modern absorption fridges have 12 V elements around the same size as their 240 V elements. With the time taken to initiate the correct temperatures in absorption fridges it is pointless attempting to do it on 12 V, you would have to run your tugs motor too long for its own health. However the size of the 12 V element ensures that the fridge temperature will be maintained whilst travelling - provided your wiring is sufficient size.

Wanderlust · Veteran Member

I have been using one of these for 2 years without a problem...

FridgeSwitch

(There is also a 40A upgrade)

Quanger · Veteran Member

Why not just run an auxiliary battery & run the fridge off that? I've been doing that on a Jayco Swan for 20 years behind 2 different vehicles with NO issues, can't see the point in the bloody fridge switching off every time you stop the vehicle. Doing the tourist thing you can be away from your vehicle for hours at a time even on travelling days, we would have been chucking out food all the way to WA on our last trip if it was set up according to that diagram.

oldtrack123 · Guru

Quanger wrote:
Why not just run an auxiliary battery & run the fridge off that? I've been doing that on a Jayco Swan for 20 years behind 2 different vehicles with NO issues, can't see the point in the bloody fridge switching off every time you stop the vehicle. Doing the tourist thing you can be away from your vehicle for hours at a time even on travelling days, we would have been chucking out food all the way to WA on our last trip if it was set up according to that diagram.

Hi

WE do not Know what size fridge you had or what current it draws or what size Aux battery you had , but I would say you are b***# lucky if your your battery was not near dead flat in a few hrs & did not have a short life!

Most 3way fridges draw a minimum of 15A continuous & up to25A with the larger models

For batterries to have a long life, it is best they are not discharged much more than 50% before being FULLY recharged

A 100Ahr battery[ fully charged] with a fridge drawing 15A will be in that condition after around 3hrs

Easy to work out how long ANY battery will last smile

Also unless the supply cables to AUx the battery from the vehicle battery] are very HEAVY the battery may never get fully charged

Another point is that unless the FRIDGE is level when stationary, it can suffer pemanent damage [blockages]

The fridge makers are wise people, THEY know how & WHY it should be done, but it seems most van makers do not

PeterQ

-- Edited by oldtrack123 on Sunday 7th of December 2014 10:52:27 PM

PeterD · Guru

Quanger, a lot of travellers don't worry about switching their fridges to 12 V when travelling. They just run them on gas during lunch time if they are not already in their destination. The absorption fridges hold their temperature fairly well when not powered. Running them like that is no worse than when we only had ice boxes in our vans.

Most travellers don't empty their absorption fridges when they go across to Tasmania. Providing the fridge is not opened then they are OK. The frozen contents in the freezer act like the ice block in the old ice chests. After each of the four crossings we made on the Princess the freezer was still icy enough to refreeze the contents after getting across.

elliemike · Guru

PeterD wrote:
Quanger, a lot of travellers don't worry about switching their fridges to 12 V when travelling. They just run them on gas during lunch time if they are not already in their destination. The absorption fridges hold their temperature fairly well when not powered. Running them like that is no worse than when we only had ice boxes in our vans.

Most travellers don't empty their absorption fridges when they go across to Tasmania. Providing the fridge is not opened then they are OK. The frozen contents in the freezer act like the ice block in the old ice chests. After each of the four crossings we made on the Princess the freezer was still icy enough to refreeze the contents after getting across.

When we travel off the bitumen for long periods ( like 4 hours or all day) I have my fridge off and the Fridge air vents sealed, to limit dust getting into the van and the rear Fridge space.

We do not have problems with the fridge contents spoiling, the freezer still remains frozen (below Zero C)

Back on gas while camping/stopped it keeps up very well like this, for days of travel off road. Our system is similar to the wiring diagram.

If my fridge lost temperature so fast that I had to throw the food inside away after 4 or five hours, I would be looking at it's insulation and installation.

My van is pressurised while on the dirt roads.

Regards

Mike

Quanger · Veteran Member

The fridge we have is a 90 litre, we used to have a bit of drama with it being near useless when the van was new, the top of the sink drain board (directly above the fridge) used to get terribly hot & we then pulled the fridge out & had it tested, worked fine on all 3 modes, it was discovered that an air baffle above the fridge had dislodged or wasn't fitted correctly & the air wasn't circulating correctly & the hot air was being trapped between the top of the fridge & the sink drain instead of being expelled out the top air vent, once this baffle was refitted correctly we had a great little fridge & no trouble with the sink drain area heating up. 20 years on & I pulled it out again this year before Easter & had a new cooling unit fitted to it as it had basically died. 2 Darwin trips (from Victoria) & 1 over the west, we would simply travel all day with it on 12 volts including getting out to do walks etc (Kings Canyon 3 hours), on arriving at our destination for the day I would switch to lpg for the night & back to 12 volts to travel again in the morning, I've never had a drama doing this, had the last Landcruiser for 11 years & only replaced the auxillary battery once, this current 2008 Prado still has the same aux battery I fitted at new in it & still working well & it runs a 40 litre Engel in the back of the car as well. I'm no electrical wizzkid but if you've got an alternator that's capable of belting out 80+ amps all day & you are travelling 6-8 hours or more wouldn't that keep your battery charged?