Caravan Fridge

[birdman101]

The 12 v display control panel must be working or the gas or mains voltage would not of worked. But unless they applied a voltage to the fridge via the caravan 13 pin plug of 13 +volts,the fridge element cannot work on 12 volt setting, as the fridge relay for the 12 v element will not operate.

 

[Martin_E]

They usually use a test box I mentioned this in post #8 some have amp meters on so you can see what is being drawn. I think workshops use a test box that is mains powered a lot of mobile workshops often have a battery power test box.

Like https://www.ebay.co.uk/itm/15649602...586&gbraid=0AAAAAC5ena0_A9H46w61TppfP3n4LUWZz

 

[ProfJohnL]

Thank you, no tow car is the same, it’s just the service people said when the van was serviced that the 12v fridge wasn’t working. I’ve not yet tried it when connected to the car. All the other electrics work fine through the tow bar.

I find it hard to justify the dealer quoting you £70 to investigate.

With the right standard workshop gear and a well informed technician it would take about 2mins to establish if the fridge does not work in the 12V aux wiring. And 5 mins to follow the wiring to the vicinity of the fridge checking for problem connections.

In my opinion based on the comparative simplicity of the fridges 12V circuitry the charge a charge of £20 would be more realistic, and it should be refundable if the fridge or the caravan wiring is found to be at faulty caused by manufacturing.

Assuming the wiring is correct and the fridge does not work, the fault lies with the installation of the fridge or the fridge itself, both of which are manufacturing errors and should be dealt with under either manufacturers warranty or the your statutory rights established by the Consumer Rights Act 2015 by the retailer.

You will probably find the caravan manufacturer defers a warranty claim on the fridge to the Fridge manufacturer.

 

[birdman101]

The test boxes only test road lighting as I have watched dealer check. Does not check fridge on 12 volt for towing

 

[ProfJohnL]

The test boxes only test road lighting as I have watched dealer check. Does not check fridge on 12 volt for towing

That will depend on the design of the test box. I'm surprised if they don't have a battery charge and fridge tester, they certainly should if its a caravan workshop!

 

[birdman101]

Tests wiring but does not put enough voltage on to operate the fridge as the tow car does

 

[Martin_E]

The test boxes only test road lighting as I have watched dealer check. Does not check fridge on 12 volt for towing

You are wrong there, I have seen one being used, it showed the amp draw when the fridge circuit was being used via the towing electrics

 

[Martin_E]

That will depend on the design of the test box. I'm surprised if they don't have a battery charge and fridge tester, they certainly should if its a caravan workshop!

The two I have seen do have both.

 

[Martin_E]

Tests wiring but does not put enough voltage on to operate the fridge as the tow car does

They definitely can (the ones I have seen, anyway)
as an example https://tow-tester.com/product/powered-remote-control-caravan-electrical-tester/

 

[IanB1485]

Most caravans use wire with a conductor size of 1.5mm CSA this has a resistance of 0.012 Ohms per metre With a current of 10A that means it will cause a voltage drop of approx 120mV per meter length.

Err the fridge heater wires in a caravan aren't 1.5mm2 , they are 2.5mm2 which has a resistance of 0.00798 Ohms per metre, so the voltage drop will only be 66% of the value you calculated. It's still a factor though , the other one being the 12V heater wattage compared with 240V heater wattage is lower. On a tall RML8230 fridge/freezer its 170W compared with 190W for the 240V heater. On smaller under bench fridges like the RMS8551 its closer 12V= 120W, and 240V = 125W ,small differences, but they all add up.

I wonder how they went about checking the 12v supply from the car battery to the fridge? Not quite the same, but the fridge requires 12v to the control panel for the fridge to work on 240 or gas. however that 12v comes from the caravan battery? Confusing isn't it.

I have a free standing battery and control unit I can plug in to the 13 pin socket and run the fridge for about a minute on 12V , just to check the element and control system is OK. To run it for longer I have recently purchased a 280A.hr Li PO4 battery. Also I have an extension 12 core lead so I can plug it into my car if pushed, Motorhomes are so much easier -just start the engine!

 

[Buckman]

I have a free standing battery and control unit I can plug in to the 13 pin socket and run the fridge for about a minute on 12V , just to check the element and control system is OK. To run it for longer I have recently purchased a 280A.hr Li PO4 battery. Also I have an extension 12 core lead so I can plug it into my car if pushed, Motorhomes are so much easier -just start the engine!

Excuse my ignorance. How would that work as surely it would be the same as if using the caravan 12v battery especially if the car has a Smart alternator? Would you connect the 12v battery up at source i.e. the plug connector for the car? Surely if you are doing that you would need to run the fridge for at least an hour or more to test it the load the fridge would be drawing as the fridge will be "warm" and be drawing a lot more amp before the thermostat kicks in. As said a numpty regarding caravan electrics etc.

 

[ProfJohnL]

Err the fridge heater wires in a caravan aren't 1.5mm2 , they are 2.5mm2 which has a resistance of 0.00798 Ohms per metre, so the voltage drop will only be 66% of the value you calculated. It's still a factor though , the other one being the 12V heater wattage compared with 240V heater wattage is lower. On a tall RML8230 fridge/freezer its 170W compared with 190W for the 240V heater. On smaller under bench fridges like the RMS8551 its closer 12V= 120W, and 240V = 125W ,small differences, but they all add up.

Standrads have changed since I last had to deal with car/caravan connector, some 25 years ago, when cables seemed to 1.5 csa as defined by the NCC 's electical compliance notes. A 1.5mm csa is acrually rated to 20 A but its resistance might cause enough volts drop at 10.8 to produce a problem.

Even though standards may have changed there are still reports which could be volt drop related.

 

[birdman101]

How does 12 volt actuate the fridge voltage sensitive relay to power the element when the small Orange wire on Thetford fridges, is only getting 12 volt feed. The relay wire needs a higher voltage as it gets when the Engine running and Alternator putting out up to 14.2 volts.

 

[Hutch]

How does 12 volt actuate the fridge voltage sensitive relay to power the element when the small Orange wire on Thetford fridges, is only getting 12 volt feed. The relay wire needs a higher voltage as it gets when the Engine running and Alternator putting out up to 14.2 volts.

By Magic. I will look up wiring diagrams.

 

[birdman101]

By Magic. I will look up wiring diagrams.

Ian said he had a free standing 12 v. test box. I ask how it engages fridge 12v heating element with only 12 volt on the engine running wire. As this is what signals the engine is running and Alternator putting out higher volts . I think you have the answer It’s MAGIC. I have repaired many caravan fridges over the years and the Engine running wire has to recieve higher volts than that produced just from the 12 volt Battery.

 

[IanB1485]

The fridge control system ( powered by the 12V leisure battery) is a microprocessor controlled system, part of it senses the voltage on the 12V fridge heater circuit electronically (not by some voltage sensitive relay) it compares the voltage with two values in its fixed memory (one =turn on , the other set lower=turn off), if the voltage is above the turn on value then it will turn on the 12V heater, after a short time ( usually 10 seconds to one minute -known as polling) it measures it again, if it has dropped below the lower threshold it will turn off the fridge heater and signal an error by flashing the battery symbol and will sound an alarm.It will keep checking the voltage as long as 12V is selected, same for the 240V heater , the threshold on a Thetford is 208V r.m.s.
Re the time for testing the heater element, The 240V and 12V heater elements are both cartridge types , they each sit in their own tube , welded to the gas flue pipe and fridge pipe, surrounded by a layer of insulation and an outer metal jacket.It would be extremely unlikely if the 12V tube came adrift from the fridge pipe and even so it would still be surrounded by the insulation and outer jacket, so the heat it produced would still transfer to the fridge pipe. The only other way it would fail to boil the ammonia/water in the fridge pipe would be if it wasn't inserted into its sleeve , which I check for when looking at the gas flame and the general condition of the wiring at the rear. When I have had to replace a heater element the opposite is normally true - a lot of tugging and swearing is required to extract it!.As prof says there have been lots of reports of voltage loss when measuring the voltage at the car plug end and at the fridge heater end, this could be due to aging of the connectors(there are several intermediate ones in a caravan wiring harness), and fuses over time.I've seen a few motorhomes with melted 20A fuses and wiring feeding the 12V fridge circuit as they have the larger 170W elements , taking about 14A at 12V and 16A and 14.2V

 

[RogerL]

The fridge control system ( powered by the 12V leisure battery) is a microprocessor controlled system, part of it senses the voltage on the 12V fridge heater circuit electronically (not by some voltage sensitive relay) it compares the voltage with two values in its fixed memory (one =turn on , the other set lower=turn off), if the voltage is above the turn on value then it will turn on the 12V heater, after a short time ( usually 10 seconds to one minute -known as polling) it measures it again, if it has dropped below the lower threshold it will turn off the fridge heater and signal an error by flashing the battery symbol and will sound an alarm.It will keep checking the voltage as long as 12V is selected, same for the 240V heater , the threshold on a Thetford is 208V r.m.s.
Re the time for testing the heater element, The 240V and 12V heater elements are both cartridge types , they each sit in their own tube , welded to the gas flue pipe and fridge pipe, surrounded by a layer of insulation and an outer metal jacket.It would be extremely unlikely if the 12V tube came adrift from the fridge pipe and even so it would still be surrounded by the insulation and outer jacket, so the heat it produced would still transfer to the fridge pipe. The only other way it would fail to boil the ammonia/water in the fridge pipe would be if it wasn't inserted into its sleeve , which I check for when looking at the gas flame and the general condition of the wiring at the rear. When I have had to replace a heater element the opposite is normally true - a lot of tugging and swearing is required to extract it!.As prof says there have been lots of reports of voltage loss when measuring the voltage at the car plug end and at the fridge heater end, this could be due to aging of the connectors(there are several intermediate ones in a caravan wiring harness), and fuses over time.I've seen a few motorhomes with melted 20A fuses and wiring feeding the 12V fridge circuit as they have the larger 170W elements , taking about 14A at 12V and 16A and 14.2V

While that applies to modern caravan fridges, older ones simply ran a nominal 12v from the car/caravan plug to the 12v heater coil via a on/off switch on the fridge fascia - certainly our 2000 Bailey fridge worked like that. It did mean that the heater element was using 10-14 volts dependent on the wiring quality and voltage drop, or lack of it.

 

[birdman101]

1973 our caravan had an Electrolux fridge on gas only I fitted a heater in that for towing straight off ignition via relay when car was running. Kept things simple I them days and did not leave ignition on when engine not running

 

[birdman101]

Ian all I am asking if your portable test box, with Battery power of 12.6 volts if fully charged and Caravan 13 pin plug in it,pin 10 will have 12.6 volts. Which the sensor wire will have same as the positive supply. How do you get an increase in volts as Alternator gives when kicked in for the wire to sensor. As you know many people have engine running but fridge will not operate unless they switch headlights on to kick the Alternator in. All am am looking for is a simple answer.

 

[Martin_E]

On older fridges say Dometic series 7 when using a test box the relay would chatter/tick, on newer fridges they don’t seem to do that, Thetford fridges from what I have been told the relay will power on, then power off, giving the amperage of draw, so like the smart alternator cutting in and out. But will give the value of amps

 

[birdman101]

I always found that Thetford fridges needed a kick from the Alternator of 13 volts or higher for sensor wire. Once it had received this fridge would merrily stay on and Alternator then continued to charge, due to the load of the fridge element taking.