Powering Fridge from Car

[Javert]

Our Swift Sprite 2025 has a Thetford full height fridge. When I was towing the car, I did as the dealer instructed and after connecting the car electrics up, I manually selected the battery picture on the fridge for 12V operation. After doing this, the fridge lights were all flashing. Normally this seems to indicate an issue i.e. no power?

Can anyone confirm that flashing means there is a problem and if so I’ll have to investigate further?

While I’m raising that point - here’s another daft question - is it ok to go into the caravan when it’s hitched up e.g. to make a cup of tea if you are parked up at the services or whatever?

 

[RogerL]

While I’m raising that point - here’s another daft question - is it ok to go into the caravan when it’s hitched up e.g. to make a cup of tea if you are parked up at the services or whatever?

Yes - we do it regularly - but understand how the car alarm and caravan alarm interact - with my outfit moving inside the caravan would set the car alarm off if it's locked - so we leave the car unlocked for short stops and disconnect the 13-pin plug for longer overnight stops.

 

[otherclive]

We left the car hitched up when stopping for lunch, or tea stop in the caravan. But did lower the rear legs as toilet was at the back.

 

[Javert]

Yes - we do it regularly - but understand how the car alarm and caravan alarm interact - with my outfit moving inside the caravan would set the car alarm off if it's locked - so we leave the car unlocked for short stops and disconnect the 13-pin plug for longer overnight stops.

Just to check, when I want the fridge to be powered from the car electrics, should the bottom which connects the mains power to the 12V power be on or off? There is a green button under the bench which has to be on if you want the mains to be charging the 12V circuit.

 

[otherclive]

Just to check, when I want the fridge to be powered from the car electrics, should the bottom which connects the mains power to the 12V power be on or off? There is a green button under the bench which has to be on if you want the mains to be charging the 12V circuit.

Don’t forget that the car electrics only power the fridge when the cars engine is running. When you are all connected to the car and parked up it’s the fridge’s insulation that keeps the temperature low.

 

[Andy Norfolk]

We have a Thetford fridge. We were advised to put it on auto and it will use the best power source. Your gas should be turned off whilst travelling so it should automatically use the battery via the car hook up. I find it does flash when you change anything but settles down.

Personally I never get in the caravan unless the legs are down. Others may disagree.

 

[ProfJohnL]

Quite a number of modern cars utilise what has become known as a "Smart Alternator" Prior designs (i.e. non" smart") were continually producing power when th e engine ran, but to save energy (and improve MPG) smart alternators obviously only work when the engine is running, but they may actually switch off automatically once the cars battery is adequately charged.

This means the towing electrics for caravan battery and refrigerator may also turn off once the alternator is satisfied. This has in some cases resulted in caravan batteries not being fully replenished and fridges not staying as cool as you would like whilst towing.

Some car models can detect when you have a trailer connected, and the smart function of the alternator is modified to allow for uninterrupted 12V power to the Aux pins in the towing electrics. Some cars need to have their software amended to enable continuous 12V power for trailers.

You would need to check with the supplier/fitter of your towing harness, or possibly your cars service agent for clarification.

 

[birdman101]

The fridge will only run on battery with engine running if PIN number 10 for fridge positive and pin 11 fridge earth are wired on car socket. Some towbar fitters do not wire these unless asked to as it is a separate harness. Lights flashing mean no power supply found.

 

[Javert]

The fridge will only run on battery with engine running if PIN number 10 for fridge positive and pin 11 fridge earth are wired on car socket. Some towbar fitters do not wire these unless asked to as it is a separate harness. Lights flashing mean no power supply found.

OK well the car ignition was on when I observed the flashing on the fridge, and the trailer lamp check had been successfully done.

Regarding the auto setting - the dealer told me to manually select battery - he seemed to think that the auto switch to car battery does not always work.

The car is a Volvo with the dealer fit official towbar and a software update has been done for the towbar. I would be surprised if the power pins for the fridge are not connected as it is obviously aware that it is towing - I get messages on the dashboard saying that certain safety features are disabled because I am towing. I also get a messages asking whether I want to perform a trailer lamp check.

Next time I hook the car up and I have a bit more time, I will spend a bit more time to wait to see whether it stops flashing after some short time.

The comments about the smart alternator might also be an issue - it’s a Volvo XC60 PHEV so I wouldn’t be at all surprised if it has some fancy alternator functionality, but Volvo seems to be pretty clued up on towing so I wouldn’t have thought they would cater for that and power the fridge anyway.

 

[RogerL]

OK well the car ignition was on when I observed the flashing on the fridge, and the trailer lamp check had been successfully done.

Regarding the auto setting - the dealer told me to manually select battery - he seemed to think that the auto switch to car battery does not always work.

The car is a Volvo with the dealer fit official towbar and a software update has been done for the towbar. I would be surprised if the power pins for the fridge are not connected as it is obviously aware that it is towing - I get messages on the dashboard saying that certain safety features are disabled because I am towing. I also get a messages asking whether I want to perform a trailer lamp check.

Next time I hook the car up and I have a bit more time, I will spend a bit more time to wait to see whether it stops flashing after some short time.

The comments about the smart alternator might also be an issue - it’s a Volvo XC60 PHEV so I wouldn’t be at all surprised if it has some fancy alternator functionality, but Volvo seems to be pretty clued up on towing so I wouldn’t have thought they would cater for that and power the fridge anyway.

Don't be surprised if the fridge circuit wasn't activated when the towbar was fitted - the standard on most factory-fit and after-market towbar fitting is not to include it unless specifically requested by the customer - trailers other than caravans don't generally have fridges so don't need those circuits. That omission probably applies even more to premium brands than mainstream

 

[ProfJohnL]

...

The car is a Volvo with the dealer fit official towbar and a software update has been done for the towbar. I would be surprised if the power pins for the fridge are not connected as it is obviously aware that it is towing - I get messages on the dashboard saying that certain safety features are disabled because I am towing. I also get a messages asking whether I want to perform a trailer lamp check.

Let me address the points in reverse order:-
The tow bar circuits must include the necessary wiring for the trailers "road lights" which are a legal requirement for all trailers. apart from the shared 0V returns, These circuits will be totally separate to any supplementary wiring for trailer batteries or fridges.

Whilst many novice caravanners might think that telling, a car dealer that you intend to tow when asking to have a tow bar fitted should imply your intention is to tow a caravan, its worth remembering that caravans represent a quite small proportion of of all trailers towed by cars, and are in fact a niche hobby. That is why standard towbar kits often do not include the supplementary
12V supplies for trailer batteries and fridges.

Its important to specifically request the supplementary supplies need to be fitted specifically for caravanning.

 

[Buckman]

I agree that the issue could be the Smart alternator in the car. A workaround is to switch on the main headlights.

 

[Javert]

Let me address the points in reverse order:-
The tow bar circuits must include the necessary wiring for the trailers "road lights" which are a legal requirement for all trailers. apart from the shared 0V returns, These circuits will be totally separate to any supplementary wiring for trailer batteries or fridges.

Whilst many novice caravanners might think that telling, a car dealer that you intend to tow when asking to have a tow bar fitted should imply your intention is to tow a caravan, its worth remembering that caravans represent a quite small proportion of of all trailers towed by cars, and are in fact a niche hobby. That is why standard towbar kits often do not include the supplementary
12V supplies for trailer batteries and fridges.

Its important to specifically request the supplementary supplies need to be fitted specifically for caravanning.

To be fair, I did tell the dealer that I was planning to tow a caravan so the dealer was aware of that. However I did not specifically tell them that I wanted to power the fridge in the caravan - I should have thought that this was obvious. I will ask them to confirm and if not I will get it installed next time.

Meantime - I asked the question on a Volvo XC60 group, and someone is telling me that if you have the dealer fit official Volvo tow bar, the fridge circuit is enabled but the fridge and battery on the caravan will only charge, if the car battery is full - car battery takes precedence

 

[JTQ]

We left the car hitched up when stopping for lunch, or tea stop in the caravan. But did lower the rear legs as toilet was at the back.

As we do, did, but with one added bit to my routine, left the steady winder on the driving seat.
No prizes for fathoming out why!

 

[otherclive]

As we do, did, but with one added bit to my routine, left the steady winder on the driving seat.
No prizes for fathoming out why!

Likewise

 

[borderbilly]

Think you will find powering the fridge when towing is a marmite subject, some will , some wont. Me personally, i wait till on site then power up with EHU. Yes you will need it when off grid , but me i dont bother.

 

[otherclive]

I would connect the fridge to domestic 240 v to reduce the temperature before leaving. The fridge contents would be pre chilled and loaded in to the fridge prior to leaving. Experience on 7 hour summer ferry crossings showed that the fridge kept its contents cool. We did not include frozen food in the ice box unless planning to use it on arrival in France. We would also include a couple of freezer blocks too.

 

[trevormonty]

Seen some people leave caravan hitched and legs up for overnite stop. Getting level maybe issue and van will move if you walk around. But it does allow for quick get away in morning.

 

[RogerL]

Seen some people leave caravan hitched and legs up for overnite stop. Getting level maybe issue and van will move if you walk around. But it does allow for quick get away in morning.

When I stop for an overnight I usually put the jockey wheel and rear legs down, to stop the car's air suspension constantly adjusting all night - but on one occasion in atrocious weather I didn't without noticing any movement of the caravan.

 

[otherclive]

Seen some people leave caravan hitched and legs up for overnite stop. Getting level maybe issue and van will move if you walk around. But it does allow for quick get away in morning.

I was never looking for a LE MANS start. Two minutes to wind up the rear legs was not an issue, and by only using the winder I would not disturb neighbours, but the 2.5 litre diesel would

 

[ProfJohnL]

....Meantime - I asked the question on a Volvo XC60 group, and someone is telling me that if you have the dealer fit official Volvo tow bar, the fridge circuit is enabled but the fridge and battery on the caravan will only charge, if the car battery is full - car battery takes precedence

Each car manufacturer may use different methods of determining when the alternator generates, but I do find the exact description you have related to be rather unlikely. I suspect either the description is wrong, or you have misunderstood the function.

 

[GaryB]

Having had 2 x Volvo tow bars and wiring fitted (2018 and 2022) I can confirm that the OEM wiring does include fridge/battery charging as standard. However, I also had issues with the trailer module in the boot so they aren't bullet-proof! On my 2024 Swift (and previous) I just leave the fridge set to auto to "do it's own thing" (as someone else has said) but as has been suggested previously, it only works with the engine running. We used to cool the fridge down on 230V at home first as the car will not cool a fridge down sufficiently over most journeys.

 

[birdman101]

When we had a Santa Fe I had to put headlights on to kick the Alternator in then switch fridge onto Battery. Once fridge running switched lights off. But every time after stopping for a break on journey had to put headlights on until fridge stopped flashing and then switched them off again. Do not have to do this with present Kuga as fridge switches directly engine starts

 

[RogerL]

When we had a Santa Fe I had to put headlights on to kick the Alternator in then switch fridge onto Battery. Once fridge running switched lights off. But every time after stopping for a break on journey had to put headlights on until fridge stopped flashing and then switched them off again. Do not have to do this with present Kuga as fridge switches directly engine starts

We had a 2011 Hyundai Santa Fe, the supplying dealer sent it out to a towbar specialist to fit the towbar and electrics - an appalling job was done this this "specialist" commoning all the earth circuits to give massive voltage drop and using a cheap voltage sensitive relay which just "chattered" in/out as the smart alternator cut in/out - once I realised all was not well I took it to a conventional auto-electrician who re-wired the car's towing electrics using a heavy duty (140A) latching voltage sensitive relay and 2x 80A cables from battery to the towing socket - never had an issue after that.

My VW Touareg's factory-fit towing electrics just work properly with no issues - although I did have to battle with the dealer to get the fan upgrade that should have been fitted at the factory.