Thetford 3 way 185L fridge power consumption

Tailor · Veteran Member

Thetford 3 way 185L fridge power consumption

Ron-D · Guru

I have a Thedford fridge and it only draws 12 volt power from the dc to dc charger supplied by the alternator while driving,but it is only a top up measure from a fridge that's been bought up to operating temperature on 240 volt power before commencing the trip,and when freecamping gas does the work.

To bring the fridge up from scratch you will need a heavy duty 12 volt supply as a lot of people do ,but why bother what's wrong with gas if yours has it already plumbed ,Just my opinion unless you have a fridge that does not have a gas supply,then it makes sense....

Aus-Kiwi · Guru

On our fridge it says thermostat isn't connected on 12v it's mainly to keep temps as they are till gas or 240v mains power is available .. So if it's nice and cold before leaving home with all the contents cold ? You'll be fine ! They operate ok while vehicle is moving off alternator . But should have relay or some device to switch off when engine is turned off to prevent flat battery !!

Tailor · Veteran Member

Thanks for the replies.

Normally I only run 12V to the fridge when travelling, when the alternator charges the batteries.
I also run the unit at least 24 hours prior to leaving and pre freeze/cool food, drinks etc.

My query is to know the worst case scenario if I don't have 240V and run out of gas. Usually that will not happen, but if it does it's wise to have the knowledge.

Aus-Kiwi · Guru

Does 18amp seem right ? Remember it being higher than I thought ?

Tailor · Veteran Member

I have no idea if 18 amp is anywhere new correct, hence my query.
Looks as if I will have to try to do some real life testing next time we go away.

erad · Guru

We have a 90 L Dometic 3 way fridge - not Thetford. The power consumption is about 120 watts - on 12V or 240 V. From what I could see when I fitted the fridge, the thermostat does not operate on the 12 V circuit, so it would be pulling 10 amps all the time 12 V was available. I have fitted a fridge switch to safeguard the vehicle battery when we are not travelling. I imagine that the Thetford fridge would be a similar system and thus draw similar power.

Interesting thought - what about the Spirit of Tasmania? There would certainly be enough motion to switch the 12 V on and batten the flattery be the time we got to Tasmania.

PeterD · Guru

Tailor wrote:
I've been trying to find out some information on the Amps drawn by using this fridge on 12Volt.
I understand it depends upon a number of factors such as temp of fridge and freezer compartments, but I can't even get a starting point.
All I can find is an general average of about 13 A/H in the day, and about 5 A/H at night.

Where did you glean those figures from? I have just looked at the N604 handbook. I do not see any thermostat in the 12 V element circuit. This means that the fridge will be drawing up to 18 A continuously. If you don't have a manual you can download one from here. The 12 V consumption is on page 26.

My query is to know the worst case scenario if I don't have 240V and run out of gas. Usually that will not happen, but if it does it's wise to have the knowledge.

If you run out of gas run for a caravan park. If you attempt to run your fridge on a 120 Ah battery you will over discharge your battery in around 6 hours. I suggest you don't do it.

Aus-Kiwi · Guru

It can vary depending on airflow . Tmk the 12v is mainly used for safe traveling . Otherwise it's gas or 240 AC .. Runing an inverter only adds to the battery load . I have fitted a solar extractor fan on top roof cover and another fan blowing on heat exchanger tubes behind fridge. Plus filling the void on top of fridge so the draught ( draft) works better . Have found I can run thermostat much lower, gas bottle lasts 3 or 4+ weeks while in NT heat . Only 12v when traveling .

PeterD · Guru

erad wrote:
Interesting thought - what about the Spirit of Tasmania? There would certainly be enough motion to switch the 12 V on and batten the flattery be the time we got to Tasmania.

One of the reasons I don't like FridgeSwitches. The best way to power a fridge with its own cable and use an ignition switched relay for battery protection. If you have an AES fridge then use the "D" line to an ignition switched point in the tugs wiring.

If you have a FridgeSwitch then switch the fridge off 12 V before getting on the ferry.

erad · Guru

"If you have a FridgeSwitch then switch the fridge off 12 V before getting on the ferry."

I used to disconnect the van from the car when I parked it on the ferry. I will still do so, but the point of this issue is that I may forget to disconnect. Result - blat flattery, but I have seen the large battery packs the Spirit team have on board for just such an occasion.

Tailor · Veteran Member

Hi PeterD,

Tried to download the link but it just took me back to the forum page.

I googled the said manual, but it only had 16 pages, and no data on current draw. Incidentally, on the manual I found, there is a thermostat shown on the diagram, just prior to the fan.

The figures I got from another forum. I have no idea of their accuracy.

I only run on 12V when connected to the vehicle, and disconnect when stopped for more than a few minutes. All the same, as we are sometimes far away from any facilities for some weeks, it's good to know the limitations of our options even if we never have to use them.

We have 2 X 100 A/H AGM in both the ute and the van, and the ability to connect all four batteries as one bank. With 400W of solar, It would be good to know if we could get by.

Cheers

John

Aus-Kiwi · Guru

I have left fridge on a little too long at times . Same battery and solar capacity as you have . Reg is flashing amber .. Meaning around 12.5 V or less .. They draw heaps on DC .. My fans have thermo's too !i guess to save power for when required ? If it was easy to remove the 3way I would !! But it's 70mm larger than door . Have to remove window over lounge ! Rather have 60 litre Esky compressor fridge freezer for more important things like beer etc . Lol room constraint is hardly our problem Being a 8.5m motorhome .. Btw I often turn the compressor Esky OFF at night to save battery . Plugging it back in the morning doesn't take long to cool again . Temps hardly drop ..

Tailor · Veteran Member

Thanks Aus-Kiwi,

Likewise I have a couple of compressor fridges for important things. They are much more efficient on 12V. Problem is the van came with the 3 way, and it's too expensive to change it. Just needed to know it's limitations. thanks

Radar · Guru

Tailor wrote:
Hi,

I've been trying to find out some information on the Amps drawn by using this fridge on 12Volt.
I understand it depends upon a number of factors such as temp of fridge and freezer compartments, but I can't even get a starting point.
All I can find is an general average of about 13 A/H in the day, and about 5 A/H at night.
on those numbers it would require over 200 A/H per day to run just the fridge on 12V.
Can anyone throw any light on these numbers

Hi Tailor

I do realize this is Dometic spec, in most cases they are very similar with out getting to technical about it all.

May help to throw light on your thoughts.

It looks like 23 big amps per hour to run frig on 12 volt to me.

-- Edited by Radar on Sunday 6th of November 2016 12:54:35 PM

Tailor · Veteran Member

Hi Radar,

Thanks for that, I doubt there is much, if any, difference between Thetford and Dometic.

Looking at the whole scene, it depends upon the local weather, hot/cold etc. How many times the fridge or freezer is opened and for how long, and hopefully a drop in demand during the night.

All said, a 12V TV pulls about 5.8A, so at night this would probably offset any savings from the fridge.

As I said, I just want to know this. It will help decide what to carry eg. Honda Genny, fuel for it, more gas etc.. The less weight is often the better solution.

Tony Bev · Guru

I have a smaller 97 litre 3 way fridge, my manual says that without the engine running, it will flatten the battery within a few hours while on 12 volt

It draws 130 watts on 12 volt, which I have calculated but not measured, to be around 10 to 11 amp hours
The reason I have never measured this amperage, is that I have no intention of allowing the fridge to work on 12 volt, from the house batteries.

I have a 300 watt roof solar panel, and will eventually have 2 x 120 AH AGM house batteries.

In theory, without anything else being switched on, and the house batteries fully charged, I shall have the battery capacity to run the fridge on 12 volt for up to 11 hours, after the solar does not have enough sunlight to operate, without allowing the batteries to run down less than 50%

In practice, if I accidentally run out of gas, while parked up, it will be cheaper for me to throw away a fridge full of food, than to risk damaging the house batteries

As a sidenote, I always carry enough canned food to last a few days

I would never try to use the engine battery, to supplement the house batteries

In an emergency, if no one else was around to assist, I would use the house batteries to jump start a flat engine battery

Hope that this info is useful to you

Radar · Guru

Tailor wrote:
Hi Radar,

Thanks for that, I doubt there is much, if any, difference between Thetford and Dometic.

Looking at the whole scene, it depends upon the local weather, hot/cold etc. How many times the fridge or freezer is opened and for how long, and hopefully a drop in demand during the night.

All said, a 12V TV pulls about 5.8A, so at night this would probably offset any savings from the fridge.

As I said, I just want to know this. It will help decide what to carry eg. Honda Genny, fuel for it, more gas etc.. The less weight is often the better solution.

Hi Tailor

I run our frig on 12 volt while travelling, some seasoned travelling friends tell us they don't run there's on 12 volt while travelling. Switch to gas when they stop as I do, in 10 years they have never had a problem with the frig loosing it's temp.

We have 2 x 9 kg gas bottles, when one gets empty I know from experience that I have approximate 2 weeks to get it filled, I really am only new at this game now into our 3rd year caravaning and enjoying ourselfs. we try to keep everything simple as..

As for the weight Side of things, myself I left the genny at home, now have given it away to my sister to use in the event of a electrical black out as they relie on power for there water needs and live in a black out prone area.

Hope this also helps trying to find the right balance.

PeterD · Guru

Tailor wrote:
Tried to download the link but it just took me back to the forum page.
I googled the said manual, but it only had 16 pages, and no data on current draw. Incidentally, on the manual I found, there is a thermostat shown on the diagram, just prior to the fan.

Sorry I have not been on much lately and have missed this one. Try this link.

That manual has 28 pages. The electrical specifications are on page 26 under the heading "Connect the Electrical Components." The diagrams on pages 14 & 15 shows the thermostat you are talking about as "Fan T-Stat," I do not see one in the 12 V element line.