Fridge not working from car.

[Sam Vimes]

New car, new tow bar. First time today towing with caravan that needed to keep the fridge alive.

It worked with the old car but didn't work with the new one.

We're not far from the tow bar fitters so I'll call in and get them to check the wiring.

I like to be armed with some information so any other suggestions about the problem would be welcome

Thanks

 

[Jcloughie]

New car, new tow bar. First time today towing with caravan that needed to keep the fridge alive.

It worked with the old car but didn't work with the new one.

We're not far from the tow bar fitters so I'll call in and get them to check the wiring.

I like to be armed with some information so any other suggestions about the problem would be welcome

Thanks

Did you specify a fully wired socket. Many only wire lights unless asked. Beats me why they don't just ask the customer instead of making assumptions.

John

 

[Sam Vimes]

They did ask and I told them it was for a caravan. It's the same company that did my previous towbar and that worked ok.

 

[Dustydog]

13 pin? Sounds like pin 10 or it’s earth 11 may not be connected. Or the relay has failed .

 

[ProfJohnL]

If the caravan hasn't changed, and the condition of the contacts on the caravan's plug haven't deteriorated, then it very strongly points to a problem with the tow car,

Some modern cars do have smart alternators, which if it senses the car battery is fully charged, it shuts down. I don't know how it responds to the load a fridge creates. These modern cars sometimes need to have a software change to let them manage the tow bar electrics.

I'm sure the fitters will have the gear to check.

 

[Sam Vimes]

Thanks for the replies. I know they used a dedicated wiring harness or at least they were supposed to.

I'll let you know the outcome.

 

[Buckman]

New car, new tow bar. First time today towing with caravan that needed to keep the fridge alive.

It worked with the old car but didn't work with the new one.

We're not far from the tow bar fitters so I'll call in and get them to check the wiring.

I like to be armed with some information so any other suggestions about the problem would be welcome

Thanks

If the car has a Smart alternator then you will have an issue. It may need to have a relay fitted in the correct area.

 

[Sam Vimes]

Workshop tested the car and the fridge drive (or whatever it's called) was present on their test rig. Although it didn't come on immediately which they thought a bit odd...it took about 5 to 10 seconds.

There is a relay in the harness and they suggested I try the connection again and if it's still not working they'll change the relay...it takes about 20mins.

I'll try and test it later today.

 

[Buckman]

Workshop tested the car and the fridge drive (or whatever it's called) was present on their test rig. Although it didn't come on immediately which they thought a bit odd...it took about 5 to 10 seconds.

There is a relay in the harness and they suggested I try the connection again and if it's still not working they'll change the relay...it takes about 20mins.

I'll try and test it later today.

Apparently what happens with smart alternators is that they cut off the 12v as the car thinks the battery is fully charged. This is why it did not come on immediately.
A temporary workaround is to switch on the lights which then drains the battery and causes the smart alternator to top up the battery.
A more permanent fix is for the 12v to be taken directly from battery and not from other sources. I am not an electrical auto technician, but this is what we were told regarding the previous Jeep.
I didn't bother any further as the only time we would require the fridge working would be prior to embarking on a ferry. Now simply use the frozen food and ice blocks. Works just as well and will last at least 2 -3 days.

 

[Dustydog]

Apparently what happens with smart alternators is that they cut off the 12v as the car thinks the battery is fully charged. This is why it did not come on immediately.
A temporary workaround is to switch on the lights which then drains the battery and causes the smart alternator to top up the battery.
A more permanent fix is for the 12v to be taken directly from battery and not from other sources. I am not an electrical auto technician, but this is what we were told regarding the previous Jeep.
I didn't bother any further as the only time we would require the fridge working would be prior to embarking on a ferry. Now simply use the frozen food and ice blocks. Works just as well and will last at least 2 -3 days.

Sorry Buckman but imo that’s not good advice. Pin 9 is a constant 12 v live . If the fridge is not wired correctly ie via pins 10 and 11 it is almost inevitable when hitched , no engine on , the car battery will drain very quickly . Also it may cause problems with the cars electronics which are specifically designed for tow electrics.

 

[Buckman]

Sorry Buckman but imo that’s not good advice. Pin 9 is a constant 12 v live . If the fridge is not wired correctly ie via pins 10 and 11 it is almost inevitable when hitched , no engine on , the car battery will drain very quickly . Also it may cause problems with the cars electronics which are specifically designed for tow electrics.

As said I am going by what I was told, but general gist is that smart alternator is the culprit and will not supply a constant 12v to trailer. I have no idea which pin supplies the 12v.
Apparently some sort of relay needs to be fitted. However doing the light thing should work as a work around and to prove that the smart alternator is the culprit.

 

[Ferrodo]

I experienced this problem with my old tug. Tow bar wired correctly and the truck NOT using a smart alternator. Connect up, start the car and the fridge would just alarm. A meter across the tow bar socket confirmed everything was good. After much pulling of hair and deep thought I changed the cheaply VSR ( voltage sensing relay) that I had bought from a well known supplier, to a heavy duty Duritc unit. Problem solved. I can only assume that the old VSR wasn’t man enough to handle the draw that a modern caravan fridge demands. Maybe this will help.
Regards

 

[Paullus1959]

It might be a feature of the fridge to prevent it flattening the car battery when the engine isn't running. I know I get a warning on my Thetford fridge if I turn it on when hooked up to the car.
However, It also my understanding that when the caravan is hooked up to the car there is only enough power provided by the alternator to keep a pre-cooled fridge cold enough to store food. There certainly isn't enough power to get a fridge cold from scratch.
That is why most modern caravan type fridges albeit called three way, only work properly on mains electricity or gas. A fridge would flatten a leisure battery in no time at all.

 

[Sam Vimes]

I've been reading up about how smart alternators work and potential problems with leisure batteries and caravan fridges. So I'm now an expert 😁

I've decided to wait until I get home where I can do some more tests such as monitor the voltages on the towing connector and the alternator voltages.

This way I'll have some more info to discuss with the towbar fitters.

Mine can't have been the first car they've done with a smart alternator so I'm a bit surprised nothing was mention about potential issues.

A few points arose during my research.

It's been a problem for a long while as smart alternators have been around for years.

Not all car/caravan combo owners seem to have the problems.

Some experience leisure batteries discharging when towing.

Some relays can drop out due to the varying output from the alternator.

AGM and GEL batteries can be at risk also due to varying voltages which may peak to high.

I'll try the lights on, Aircon on, stop/start disabled methods on the way home.

 

[ProfJohnL]

However, It also my understanding that when the caravan is hooked up to the car there is only enough power provided by the alternator to keep a pre-cooled fridge cold enough to store food. There certainly isn't enough power to get a fridge cold from scratch.
That is why most modern caravan type fridges albeit called three way, only work properly on mains electricity or gas. A fridge would flatten a leisure battery in no time at all.

I'm sorry Paullus but that is just an old caravanner's tale. There are reasons why when running in 12V dc the cooling performance of the fridge can be compromised, but it's not from lack of power of the 12V element.

Whichever way you power the fridge, roughly the same amount of energy is consumed by the fridge (Watts per hour , and that means the potential cooling effect is also roughly the same.

The compromises arise, firstly becasue the 12V system only runs when the tow vehicle is providing power which is only when the engine is running, and producing enough excess charge. Depending on the vehicle and the journey that could mean the 12v is only intermittent, which reduce the overall cooling capacity of the fridge.

A second compromise, is the fridge is designed to normally operate when stationary, in virtually still air conditions. The motion of towing can cause unhelpful air movement around the fridge which can compromise the heaters operation.

So its not that 12V is incapable, its other factors indirectly associated with when 12V power is normally used.

Given time in still air 12V operation would be almost indistinguishable from mains or gas.

 

[Dustydog]

Prof
May I also add this is why caravans usually come with removable vent covers for travelling. They must be removed when pitched.

 

[Paullus1959]

I'm sorry Paullus but that is just an old caravanner's tale. There are reasons why when running in 12V dc the cooling performance of the fridge can be compromised, but it's not from lack of power of the 12V element.

Whichever way you power the fridge, roughly the same amount of energy is consumed by the fridge (Watts per hour , and that means the potential cooling effect is also roughly the same.

The compromises arise, firstly becasue the 12V system only runs when the tow vehicle is providing power which is only when the engine is running, and producing enough excess charge. Depending on the vehicle and the journey that could mean the 12v is only intermittent, which reduce the overall cooling capacity of the fridge.

A second compromise, is the fridge is designed to normally operate when stationary, in virtually still air conditions. The motion of towing can cause unhelpful air movement around the fridge which can compromise the heaters operation.

So its not that 12V is incapable, its other factors indirectly associated with when 12V power is normally used.

Given time in still air 12V operation would be almost indistinguishable from mains or gas.

I based my comment on the Thetford user manual that came with my fridge.

Thetford N3000 Series User Manual (Page 11 of 30) | ManualsLib

www.manualslib.com

Specifically Section 7 "Selecting Source" paragraphs 3 & 4

which in a nutshell says running the fridge on 12v is only effective when the vehicle engine is running and gas or mains should be used to pre-cool the fridge.

Maybe other makes of fridge work differently?

 

[Dustydog]

I based my comment on the Thetford user manual that came with my fridge.

Thetford N3000 Series User Manual (Page 11 of 30) | ManualsLib

www.manualslib.com

Specifically Section 7 "Selecting Source" paragraphs 3 & 4

which in a nutshell says running the fridge on 12v is only effective when the vehicle engine is running and gas or mains should be used to pre-cool the fridge.

Maybe other makes of fridge work differently?

Yes , but the point is even on 230 v or gas the fridge will take longer to cool than a journey of a few hours! Once chilled down over night the 12 v system is more than adequate to keep the temperature down subject to the Prof’s earlier points

 

[Buckman]

I based my comment on the Thetford user manual that came with my fridge.

Thetford N3000 Series User Manual (Page 11 of 30) | ManualsLib

www.manualslib.com

Specifically Section 7 "Selecting Source" paragraphs 3 & 4

which in a nutshell says running the fridge on 12v is only effective when the vehicle engine is running and gas or mains should be used to pre-cool the fridge.

Maybe other makes of fridge work differently?

I agree with the above as that is also stated in my Thetford owner's manual. The 12v will not cool down the fridge as it is only there to maintain the temperature. Sadly I can no longer find the mail where this was also stated by Thetford as this goes back to 2016 when the Jeep did not have a smart alternator but had the correct wiring.

 

[Hutch]

When I first recieved my SantaFe from the dealer, with the Towbar fitted by them, the fridge and ATC did not work. I checked out the wiring on the car and found the fridge return ( earth) pin 11, was connected to the live return earth pin 13 and also to the pin 3 Trailer lights return.
When I separated the pin 11 return and earthed it to the car Chassie, the fridge , and ATC, worked fine whilst towing.

 

[Dustydog]

When I first recieved my SantaFe from the dealer, with the Towbar fitted by them, the fridge and ATC did not work. I checked out the wiring on the car and found the fridge return ( earth) pin 11, was connected to the live return earth pin 13 and also to the pin 3 Trailer lights return.
When I separated the pin 11 return and earthed it to the car Chassie, the fridge , and ATC, worked fine whilst towing.

That’s a classic laziness grouping the earths that way! Hopefully it doesn’t happen anymore. Good job you are an Engineer😉👍

 

[Hutch]

I used to dream of being an Engineer, Now I is one. 🛠

 

[Hutch]

Yes , but the point is even on 230 v or gas the fridge will take longer to cool than a journey of a few hours! Once chilled down over night the 12 v system is more than adequate to keep the temperature down subject to the Prof’s earlier points

My Coachman 560 2013 fridge has worked fine whilst towing,after cooling down at home, always got to site ok, longest tow probably , 10 hours from home to site in France, including 4 hours ferry .

 

[Sam Vimes]

This is an interesting site for many things towing etc. There is some good stuff on the electrical issues we're discussing.

Caravan Chronicles

not just another caravan blog

caravanchronicles.com

 

[ProfJohnL]

I based my comment on the Thetford user manual that came with my fridge.

Thetford N3000 Series User Manual (Page 11 of 30) | ManualsLib

www.manualslib.com

Specifically Section 7 "Selecting Source" paragraphs 3 & 4

which in a nutshell says running the fridge on 12v is only effective when the vehicle engine is running and gas or mains should be used to pre-cool the fridge.

Maybe other makes of fridge work differently?

That is quite correct, but its not saying that 12V system can't cool the fridge, only that the intermittent nature of 12V availability in a caravan may not be enough to fully prepare a fridge to be used.

Similar fridges are fitted to canal boats and river cruisers on 12V operation, where the engine does tend to run for much longer periods , and they manage quite succesfully.