Member Since: 14 Jun 2011
Location: Essex
Posts: 81
Towing electrics - Fridge power
My Thetford fridge (2008 Sterling Elite Searcher) shows an error 10 when towing. This means there is insufficient (or none) power to fridge whilst connected.
Reading other forums, it seems some towing electrics have a variable relay for the power to the fridge (so as not to drain the battery). I believe the electrics on my 2007 HSE are OEM.....can anyone tell me whether this would mean I have such a variable relay......and if so.....where is it-what does it look like and how do I turn it up? D3 HSE 06 with all the bells and whistles
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27th Aug 2013 10:29 pm
discoteca
Member Since: 08 Mar 2010
Location: Warwickshire
Posts: 1477
If I remember rightly the D3 OEM electrics come with an extra little fuse box accessible from the left hand boot cubby hole. One of those fuses would be for the fridge circuit in the 12S socket I would have thought (because of the high load on that circuit). Gotta be worth a quick check of those fuses first?
Assuming that you have 12n and 12s electrics rather than 13pin, pin 6 is the fridge live and pin 7 the fridge neutral in the white socket, put a meter across them and make sure you are getting a good voltage (with engine running). Socket pin out below:
27th Aug 2013 11:00 pm
Russell
Member Since: 23 Aug 2007
Location: Kent
Posts: 10564
On the 7 pin version of plugs there were issues with excessive heat on the earth pin due to fridges, this was overcome I believe by using one of the other pins as an additional earth point, pay be worth looking into this.MY17 D5 1st Edition Namib Orange
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28th Aug 2013 6:07 am
mcsimmo
Member Since: 08 Aug 2011
Location: North of the south
Posts: 1795
I have the same situation with my tin tent.
I queried the problem with other caravaners, and the general opinion was that it is very rare to come across electrics on cars that are set up to run the fridge from the car when towing. They thought it was to avoid the issue of car batteries being drained when the car engine wasn't running, or overloading the electrics on the car.
I had wondered if by installing a second battery on my D3 this problem could be overcome if the electrics could be set up so that when the ignition was turned off, then the caravan fridge would default to taking power from the additional battery only, and leave the main car battery in a charged state?
Perhaps some techie will come along and give us the definitive answer.Man with no D3 anymore, but cant leave the forum....how sad.
28th Aug 2013 6:21 am
Russell
Member Since: 23 Aug 2007
Location: Kent
Posts: 10564
My old D3 and both the D4's are set up for the fridge to operate on the tin tent. When the car is running the fridge electrics are live as soon as the car is turned off and locked the fridge electrics go dead, cannot remeber if they go dead with just the ignition off or if the car has toi be asleep/locked.MY17 D5 1st Edition Namib Orange
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28th Aug 2013 6:40 am
Biffysun
Member Since: 09 Jul 2011
Location: Central
Posts: 1790
My understanding (non-techie) is that if a fridge is connected directly to a car battery it will drain it in a very short time to avoid this, a relay is incorporated in that circuit and operated by the 'exciter' wire on the alternator, in this way the fridge can only draw current from the vehicle battery when the engine is actually running and the alternator is charging - ie if the ignition is switched on but engine not running the fridge will not operate thus safeguarding the vehicle battery from discharge
28th Aug 2013 7:20 am
DiscoDunc
Member Since: 08 May 2006
Location: Bristol
Posts: 16390
my D3 has OEM electrics and the fridge was fine - works fine on the D4 as well
I would start with checking the power from the tow socket first.
there should also be fuses in the caravan , usually tucked away right at the front inside the front cupboard on the floorDuncan
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28th Aug 2013 7:29 am
al cope
Member Since: 08 Nov 2005
Location: Oldbury, WM
Posts: 10361
In over 20odd years of towing, I've never had an issue with the fridge electrics, either on 12S or 13 pin plugs, but that doesn't mean there cant be problems, and on 12S the biggest issue is the earth return for the fridge.
Before that though, the 12v for the fridge should always be supplied by an ignition controlled feed. i.e, one that switches off when the ignition is turned off, so that the car battery doesnt get drained.
This is/can be done in a few different ways, a voltage sensing relay, or just a plain and simple relay that is switched on when the engine is running.
So - first, check that you've 12v on the 12S or 13pin plug, and that this goes off when you switch the ign off. Then check all the pins in you plug and socket are tight (dont wobble), and are clean, as the earth issue is caused by a high resistant joint/connection (on my mates Galaxy this high resistance caused so much heat it melted the center pin plastics on the 12S plug).
If all this is OK, then ign fed 12V should be reaching the 'van, so check fuses and habitation relay in the 'van is working OK.
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28th Aug 2013 8:06 am
northernmonkeyjones
Member Since: 11 Feb 2013
Location: Derby
Posts: 64
Another possibility if you have correct wiring is that the fridge relay, which is located in the caravan is faulty.
Power switching to the fridge is carried out by the caravan not the car.
The relay in the van detects voltage on the "ign on" pin from the car and then supplies power to the fridge via the constant 12v pin, so it will only come on when the car is running.
My thetford fridge shows error 10 when hooked up until the car is running then the blue light stops flashing and all is well.
28th Aug 2013 7:27 pm
Tufty
Member Since: 13 Jul 2010
Location: UK
Posts: 481
Re: Towing electrics - Fridge power
Eyeball wrote:
Reading other forums, it seems some towing electrics have a variable relay for the power to the fridge (so as not to drain the battery).
This is more for an aftermarket towing electrics kit as said above it's so the supply is only live while the engine is running (ie. the voltage is over 13v) the voltage that the relay switches on at is adjustable (variable).
28th Aug 2013 8:19 pm
DWH
Member Since: 24 Aug 2013
Location: Cornwall
Posts: 12
Hi new to the forum but i think i'm right in saying your fridge should only work when the engine is running and is connected on the charging curcuit so it can supply up to 40amps but as a previous post the earth pin often gets hot and starts to melt the 7 pin on the S socket. The extra earth pin may help. Not sure but there is a slight variation on some of the S pin wiring.
28th Aug 2013 9:35 pm
Ajpf5
Member Since: 13 Jul 2013
Location: Manchester
Posts: 84
Just had my twin sockets converted to single and they changed the fuse rating as mentioned above. I think 20 amps now.
Just a thought and I am sure somebody can confirm but, if your tin is 2008 with ats then I thought it uses the same power source?? Does that work?
28th Aug 2013 10:10 pm
mcsimmo
Member Since: 08 Aug 2011
Location: North of the south
Posts: 1795
northernmonkeyjones.
Now you mention that, I have realised that I have never checked the fridge operation with the car engine running when hooked up. Man with no D3 anymore, but cant leave the forum....how sad.
29th Aug 2013 6:37 am
northernmonkeyjones
Member Since: 11 Feb 2013
Location: Derby
Posts: 64
have a look next time you set off it should be working....
29th Aug 2013 4:15 pm
DWH
Member Since: 24 Aug 2013
Location: Cornwall
Posts: 12
Not sure but i have been told that the new 13 pin socket is now part of your mot
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to avoid this, a relay is incorporated in that circuit and operated by the 'exciter' wire on the alternator, in this way the fridge can only draw current from the vehicle battery when the engine is actually running and the alternator is charging - ie if the ignition is switched on but engine not running the fridge will not operate thus safeguarding the vehicle battery from discharge 
