Cooling fridge question?

[Buckman]

If your car is fitted with a SMART alternator, the fridge will not cool down as the 12v kicks in and out. Besides buying an expensive Sterling battery to battery charger at £227, is there another way around this issue? I am asking on behalf of someone else.
We have a 2012 Jeep GC with a SMART alternator and have never bothered with checking to see if the fridge will work on 12v however one day we may require it. It did not worked on our previous 2005 Jeep GC which did not have a SMART alternator.

 

[RogerL]

Yes - don't use "smart" relays in conjunction with Smart alternators - go back to the old-fashioned" wiring - direct from battery via an ignition-triggered relay and a fuse - this will supply constant current and the Smart alternator will sense when the battery needs topping up.

 

[Buckman]

Roger being a bit of a numpty with modern car electrics, not too sure about your post regarding the comment "direct from battery via an ignition-triggered relay and a fuse". Can you perhaps elaborate a bit? I am guessing that the battery that needs topping up is the car battery?
Is it any different on a car with stop start technology. Thanks.

 

[RogerL]

Roger being a bit of a numpty with modern car electrics, not too sure about your post regarding the comment "direct from battery via an ignition-triggered relay and a fuse". Can you perhaps elaborate a bit? I am guessing that the battery that needs topping up is the car battery?
Is it any different on a car with stop start technology. Thanks.

A substantial cable needs to run from the car battery +ve via a fuse to a relay under the bonnet which is controlled by an ignition-on connection - the substantial cable then connects to the 13-pin socket at pin #10 - this circuit will give a constant supply to the caravan fridge - the car's Smart alternator will monitor the car battery condition and charge it when necessary.

Most cars disable stop-start when towing but if it doesn't then the above will work the same, with the engine forced to restart if the car battery voltage drops below a predetermined level.

I don't hold specialist towbar fitters with any great regard, a historical thing having seen some of their work - they certainly haven't kept up with advances in car technology like Smart alternators - if you need a professional, use a proper Auto electrician.

 

[Raywood]

The first point is that the car will not cool the fridge but only keep it cool if it is cooled down before you set off. If cooled the stop start mechanism would normally only be a problem if you are stuck in a long traffic jam as the continuous use on most runs should keep the fridge cool if it started that way. A bit of stop start driving in a town or road with lots junctions should not be a problem.
If it is not doing this I would check that it is wired for the fridge. Standard wiring will not include this as it is not needed for other uses. If you do not know the correct wiring check

https://www.caravanclub.co.uk/globalassets/pdfs/content/advice-and-training/towbar-wiring.pdf

 

[otherclive]

The first point is that the car will not cool the fridge but only keep it cool if it is cooled down before you set off. If cooled the stop start mechanism would normally only be a problem if you are stuck in a long traffic jam as the continuous use on most runs should keep the fridge cool if it started that way. A bit of stop start driving in a town or road with lots junctions should not be a problem.
If it is not doing this I would check that it is wired for the fridge. Standard wiring will not include this as it is not needed for other uses. If you do not know the correct wiring check

https://www.caravanclub.co.uk/globalassets/pdfs/content/advice-and-training/towbar-wiring.pdf

I thought that stop-start turns off when the caravan is connected. Although any car I’ve had or driven hs given the driver the ability to turn off the stop-start. I always switched it off on a diesel Superb DSG as it seemed to have too much time lag for my liking although the current Kia petrol manual is up and ready as soon as the clutch is touched.

 

[JTQ]

The first point is that the car will not cool the fridge but only keep it cool if it is cooled down before you set off.

The Wattage of the mains and the DC heater elements are in our case very similar, so the only difference inhibiting the DC being as effective as mains, is if the wiring for the DC is so inadequate the wattage never gets there.

That indeed is very probable seeing the puny wiring involve at both the car and van ends, but makes a nonsense of the DC provision by the fridge maker.

We do use your routine getting the fridge well cooled on mains 24 hours before leaving, and whilst the fridge indicates it is working when towing I doubt that it is very effective.
The experience of it not being "on" in any sense for 5 hours on a ferry with everything in the freezer compartment rock solid, does beg the question does it really matter if it does not work on the road for the time spans typically involved?
I note German cars and some of their caravans have no provision for on route fridge operation, that on the continent where long journey times and higher ambient are common, so are we just chasing a pointless requirement. I suspect so knowing how poor the wiring involved, really is, we only fool ourselves that powering the fridge has some value.

 

[Buckman]

On our previous Jeep when we tried it, the temperature had actually risen in the 80 mile trip. Not tried it yet in the newer Jeep with Smart alternator but suspect it may be the same. Now we simply cool down the fridge as much as possible, lock the door closed and hope it works. Kept fridge cool from leaving Portsmouth site to arrival at site in Zaragoza in Spain.

 

[Raywood]

The stop start will turn the supply to the fridge off when stopped, but normally this is for only a very short time and should not seriously affect things. If you are stopped in a traffic jam with long delays, the stoppages may start to build up and affect the cooling.
Assuming the fridge connection is there, then the wiring might also be affecting performance. It can be a long way from the engine bay to the fridge and if the wiring is too thin that will affect performance. The resistance in thin wiring will be higher than a thicker one reducing the performance.
A couple of ice blocks in the fridge does help.
My problem is forgetting to switch the fridge over and that is not good.

 

[otherclive]

The stop start will turn the supply to the fridge off when stopped, but normally this is for only a very short time and should not seriously affect things. If you are stopped in a traffic jam with long delays, the stoppages may start to build up and affect the cooling.
Assuming the fridge connection is there, then the wiring might also be affecting performance. It can be a long way from the engine bay to the fridge and if the wiring is too thin that will affect performance. The resistance in thin wiring will be higher than a thicker one reducing the performance.
A couple of ice blocks in the fridge does help.
My problem is forgetting to switch the fridge over and that is not good.

Wouldn't the stop-start restart the engine if it senses battery capacity lowering? My wife's car will restart if you have AC on or full lights and screen heaters.

 

[RogerL]

The stop start will turn the supply to the fridge off when stopped, but normally this is for only a very short time and should not seriously affect things. If you are stopped in a traffic jam with long delays, the stoppages may start to build up and affect the cooling.
Assuming the fridge connection is there, then the wiring might also be affecting performance. It can be a long way from the engine bay to the fridge and if the wiring is too thin that will affect performance. The resistance in thin wiring will be higher than a thicker one reducing the performance.
A couple of ice blocks in the fridge does help.
My problem is forgetting to switch the fridge over and that is not good.

That depends how the towing electrics are wired - if a "smart" relay has been used then the fridge will get switched off when the stop-start operates, or the smart alternator reduces voltage - that's why "smart" towing relays shouldn't be used on cars with Stop-start or smart alternators, ie any modern car.

Your point about voltage drop over the long distance (and back through the earth circuits) is well made and often the cause of caravanners' complaints about poor fridge performance under tow.

 

[bertieboy1]

The stop start will turn the supply to the fridge off when stopped, but normally this is for only a very short time and should not seriously affect things. If you are stopped in a traffic jam with long delays, the stoppages may start to build up and affect the cooling.
Assuming the fridge connection is there, then the wiring might also be affecting performance. It can be a long way from the engine bay to the fridge and if the wiring is too thin that will affect performance. The resistance in thin wiring will be higher than a thicker one reducing the performance.
A couple of ice blocks in the fridge does help.
My problem is forgetting to switch the fridge over and that is not good.

Hi Raywood,
Our car has stop/start function,but we switch it off at the start of every journey.(diesels don't like frequent start/stop)
When we are towing the fridge is off all the time,we switch fridge on the night before to cool it down,keep the door shut and everything stays cool all day.

 

[ProfJohnL]

The first point is that the car will not cool the fridge but only keep it cool if it is cooled down before you set off. ...

Technically this is not true. In most multifuel fridges, the wattage of the 12V system is usually roughly similar the mains and the gas options, so given enough time and all other factors being equal the fridge will cool on 12V just as effectively as on any other fuel.

However all other things are not equal. Others have pointed out that some of the 12V effectiveness may be lost due to the resistance of the wiring used, and there can be problems with smart alternators and stop start systems. There is also the fact that many journeys only last few hours, where as it can take 12H or more to fully chill a fridge, so there is simply not enough time for the 12v to chill down.

But there is also another quite significant factor and that is as you tow there is quite a rush of wind past the fridges external vents, and some of that will find its way in through the vents, and that increases the air flow around the fridge, which will affect the fridges ability to maintain the internal cooling.

There is no doubt in my mind that if you have 12V available whilst towing its makes sense to use it to help keep the fridge chilled.

 

[RogerL]

Regardless of power source, it can take 24 hours to cool a fridge down from ambient - towing trips are almost always much less than that.

 

[littlebasher]

I've never actually thought to check whether my fridge actually does anything when connected to the car, i just assume it auto switches to 12V.

On the other hand, i always chuck a couple of freezer packs in there before we leave to help keeps things cold.

 

[Guzzilazz]

My Kuga without the van on start/stops at the drop of a hat. With the van on, it takes potentially 2-3 hours before the start stop kicks in again, I guess, because the caravan current draw (charging the van battery ?)...

 

[ProfJohnL]

Each manufacturer may have a different detail approach as to how Stop Start systems operate. In addition these systems are still being continually developed, so how one may work in a car bought today may not be the same as one bought tomorrow.

If you are unsure check with your supplier or specialist.

 

[Johnb]

I've never actually thought to check whether my fridge actually does anything when connected to the car, i just assume it auto switches to 12V.

On the other hand, i always chuck a couple of freezer packs in there before we leave to help keeps things cold.

I'm not sure why people are so worried about caravan fridge operation whilst towing.

Surely whoever fitted the towing electrics will know perfectly well what is required and fit accordingly. It amazes me to think that some feel a professional tow-bar fitter doesn't know his/her job! I would expect a few disgruntled customers making their views known if the fridge did not perform adequately.

I would also imagine that everyone turns their fridge on (if possible of course) at least 12 hours prior to beginning a journey. If they don't then I respectfully suggest they should.
We've never had a problem with any fridge and that includes overnight ferry travel as well as towing in the upper 30ies in Europe.

I imagine that older fridges/caravans will not all have the sophisticated electronics of the newer ones. In our case I always turn off the gas when towing and set the fridge to automatic. Whilst the fridge will prefer electricity over gas if available turning the gas supply off is good practice anyway for obvious reasons whilst towing. As soon as the electrical supply is turned off the fridge beeps and as soon as the car engine is started it stops beeping and works on 12v. The fridge is invariably cold upon arrival at a site!

Am I the only person who has never questioned the operation of my fridge whilst towing?

As for stop/start technology then as previously mentioned whilst towing this should be turned off if the car does not automatically turn it off. The reason, I believe, is to allow the turbo and cooling fans and any other cooling oil circulation to continue when stopped since towing will have placed a greater stress on the engine and probably increased temperatures.

 

[RogerL]

Surely whoever fitted the towing electrics will know perfectly well what is required and fit accordingly. It amazes me to think that some feel a professional tow-bar fitter doesn't know his/her job! I would expect a few disgruntled customers making their views known if the fridge did not perform adequately.

The evidence seems to be that these professionals haven't kept up with modern automotive developments - Ford have been fitting smart alternators since 1996, other manufacturers sin the '00s - and yet the towing electrics fitted to many cars don't suit smart alternators.

 

[ProfJohnL]

It's easy to forget that caravanning is just one type of trailer, and most other trailers will not need supplementary 12V power circuits. Thus the standard trailer circuits will be road lighting only.

Consequently its necessary to make clear to the towbar fitters that you need the supplementary services to be included.

 

[Raywood]

I appreciate the Prof's view that the fridge will cool if you tow with it but this is contrary to the manufacturers advice. Possibly they say that to avoid complaints in the cases where cooling is not taking place but it cannot be guaranteed and I would not rely on it. I agree that if you can run the fridge from the car you should but do not rely on it cooling it.
I do agree that you have to specify the fridge wiring when ordering a tow bar but most independent fitters are well aware of the point and will check this before quoting. If you order from a garage you will normally get a salesperson who may simply not have the knowledge to check the point so it is vital to make this a condition of the order.

 

[ProfJohnL]

I appreciate the Prof's view that the fridge will cool if you tow with it but this is contrary to the manufacturers advice. ....

I have looked at several on line copies of instructions for Dometic and Electrolux fridges designed for caravans (RM models), and I have not found the part that says it doesn't cool down on 12V. If it didn't work why would they fit 12V elements?

 

[JTQ]

I have looked at several on line copies of instructions for Dometic and Electrolux fridges designed for caravans (RM models), and I have not found the part that says it doesn't cool down on 12V. If it didn't work why would they fit 12V elements?

Plus as the 12 volt and mains element Wattages can be identical or quite similar, so why would one perform differently to the other?
IMO, the voltage loss on the DC side is simply is so high, that the rated Wattage is never realised. Under sized wiring for the current involved, in both the car and caravan, would be my contender why the rated power at the element is never there.

 

[RogerL]

I've long thought that voltage drop due to total circuit length and use of minimum-sized cables is the reason so many caravanners complain about lack of cooling under tow - on several tow cars, I've used 80 amp cable to wire the fridge circuit in order to minimise voltage drop, with good results - although I've never been anorak enough to rewire the fridge circuits on the caravan with equally oversize cables.

 

[Damian]

I appreciate the Prof's view that the fridge will cool if you tow with it but this is contrary to the manufacturers advice

I have to take exception to the part which says it is contrary to manufacturers advice that the fridge will not cool on 12v when being towed.
I have no idea where this nugget of misinformation has come from but I can assure you that it is certainly NOT Dometic, and never has been, neither has it ever been said by Thetford.

The main reasons why it appears that the 12v does not cool the fridge are either not suitable wiring allowing enough power to be drawn, and not a long enough period of time with the engine running to allow the fridge to cool.

All three power sources are quite capable of operating the fridge at its optimum .