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Trouble With The Towing Electrics


Guest Hobbybod

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Guest Hobbybod

Ok folks, I usually consider myself fairly adept at sorting out electrical problems bit I'm rather 'puzzled' by this one.

 

The electrics were working fine (through a 2x7pin to 13-pin adapter cable) until a few months ago, when I became suspicious that the frig power was not working.

 

I've checked it, belatedly, this afternoon, and this is what I found.

 

No 12V power on pin 6 (goes to pin-10 on the 13-pin socket) {frig feed}, but there is 12V power on pin-2 (old battery charging feed); both when the engine is running. There is always power on pin-4 as it should be. (This is how I've always had my cars wired).

 

Looking behind the side panel in the boot of the car I came across what I presume is a modern 'split charge' relay gizmo, which is powered from the boot accessory cigar lighter socket, but there is NO feed to the relays from the ign. switched alternator power.

 

I have no idea how such a system works, but it looks as though this split charge relay gizmo has gone t!t5 up. The garage from where I obtained the car, and who did the wiring, has also gone t!t5 up, so it's case of DIY or spend money on someone trying to sort out someone else's wiring!! Always a fraught task!

 

Any advice, folks?

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Hi Hobbybod. Sorry to hear that your chips are down (and your t1t5 are up)

 

I was about to ask how the 2x7 to 1x13 cable should be connected, as my fridge is powered from the driveway, and then again from the site EHU, but doesn't seem to be powered in-between!

 

Does your car have a standard wiring loom or it it one of these computer controlled ones? Since getting the Touran wired, my driver's door mirror controls both mirrors, while I can also work the left one independantly!

 

The joys of computers!

 

I hope someone gets you fixed.

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Tony

 

Might be worth trying Tony Maris this is Tony Maris's company you might remember him from UK. Rec Caravanning newsgroup? He also suggests doubling up on a couple of wires on the S socket to prevent pin burn out. Got mine wired like that and it works so much better than the old van. Mind you wired this way will blow fuses in conventianal S socket testers!!

 

David

David - Milton Keynes

Bailey Alliance 66-2 Motorhome for holidays and a Kia Venga for home.

 

Caravan Travels

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Hi Hobbybod. Sorry to hear that your chips are down (and your t1t5 are up)

 

I was about to ask how the 2x7 to 1x13 cable should be connected, as my fridge is powered from the driveway, and then again from the site EHU, but doesn't seem to be powered in-between!

 

Does your car have a standard wiring loom or it it one of these computer controlled ones?  Since getting the Touran wired, my driver's door mirror controls both mirrors, while I can also work the left one independantly!

 

The joys of computers!

 

I hope someone gets you fixed.

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Candlefish,

 

I presume that you have 2x7 pin sockets on the car and 13 pin plug on the van.

 

You may find is that the adaptor cable grey plug is wired to pre 1998 standard.

 

Both door mirrors are controlled together when adjusting the drivers mirror. This is standard on most VAG vehicles after a certain year and is also common on other manufacturers models. Check your drivers handbook.

 

Frank

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Guest Hobbybod

Right folks, thanks for all the help and I'll reproduce here, roughly what I posted on the other forum.

 

The split charge (combination) relays are in the boot and seemingly this 'intelligent' relay unit senses the voltage change from no engine/alternator running (~12. 6V) to engine running (14. 1V) and switches the relays to feed power to pins 2 & 6 accordingly.

 

Doing it this way means that the car's accessory/cigar lighter 12V feed can be used as the power lead to the 12S socket, and no connection to ign. ON/alternator is needed. Easier to wire in, but less satisfactory electrics-wise IMHO.

 

After more checks it became apparent that one of the P. C. relays (the one for the frig. pin-6) was not working.

 

So I came back from GT Towing £13 lighter with a replacement 'intelligent' split relay gizmo. A slightly later version of this clip_image002_000.gif

 

On looking at the old one, on the connection side of the P. C. board, you could see that it had overheated and gone all black on one of the relay terminals.

 

Now this isn't surprising given that the relays are rather small (15mm cube) and the connecting copper strip on the P. C. board isn't very wide for a possible 10A or so.

 

In the past I've used larger (25mm cube) relays near the battery, but requiring a signal feed from the alternator/ign. ON connection and also cable needed routing from the battery to the rear of the car. These have never given a problem.

 

I'm now using both 12V feeds to pins 2 & 6 to connect to pin-10 of the 13-pin socket in the adapter cable so that frig. current is shared between pins 2 & 6 and the associated cables and relays. Hopefully this will prevent it happening again.

 

Progress eeeh; don't you just love it.

 

P. S. For Candlefish.

 

Hi C-F, the frig. feed for your Hobby is pin-10 on the 13-pin socket. If you do not have 12V-14V on this pin when the engine is running, but it is on pin-6 of the 7S socket then the adapter cable is naff.

 

Now this isn't unknown! My adapter cable was incorrectly wired when I got it and I had to re-wire it properly!!! You must have a wire going from 7S pin-6 to pin-10 on the 13-pin socket. If you also have 12V on 7S pin-2, then feed that to pin-10 as well as I mentoned above.

 

If you haven't got any 12V on 7S pin-6 then it's back to the towbar electrics place, . . . . . unless you are willing to phaff around like me!!

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I'm afraid I can't add anything to what has already been said, but a word of warning - in my case the towbar fitter picked up the 12v feed from the cigarette lighter in the boot - apparently this is common. However, the voltage drop in the caravan (with 12s connected) was substantial - at times it was down to 8. 5v and was causing relays to trip in and out and, on occasions, not to operate at all. The caravan was fully checked by the supplier (and by me) with no obvious fault found. When I told the towbar suppliers about it they suggested that they would change the 12v feed to either the battery or the fuse box, and a thicker gauge of cable should be used. This was done a few weeks ago, with great improvement. So, it may be the case that tapping off the cig lighter in the boot isn't always the best way of doing it, even if it's quicker and easier for the fitter.

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There is certainly nothing wrong with the Smartcom voltage sensing relays. However using the accessory socket provided in many car boots as primary feed to towing 12S electrics is an unusual and I would have thought an inadequate supply. I would doubt the size of cable installed to this accessory socket is up to the job. I am surprised that a professional outfit would adopt this method.

 

One heavy cable from the battery,fused at the battery and led to a Smartcom box at some convenient place in the boot is a far more acceptable solution.

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Guest Hobbybod
There is certainly nothing wrong with the Smartcom voltage sensing relays. However using the accessory socket provided in many car boots as primary feed to towing 12S electrics is an unusual and I would have thought an inadequate supply. I would doubt the size of cable installed to this accessory socket is up to the job. I am surprised that a professional outfit would adopt this method.

 

One heavy cable from the battery,fused at the battery and led to a Smartcom box at some convenient place in the boot is a far more acceptable solution.

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Frank, I basically agree with your criticism of using the accessory/cigar lighter feed in the boot as the 12V feed for the 12S electrics, but I can see why it is done. You don't need to feed an extra cable from engine bay to boot, which can be a bloomin' fiddle; . . I've done it on three different cars! And it it is not that unusual seemingly; it's the very reason why they sell the Smartcom voltage sensing relays, so NO ign. ON/alternator signal wire is required, and it can be positioned in the boot.

 

I beg to differ on this point. The metal P. C. B. strip carrying the current (~10A or more) from the P. C. B relay, does not appear sufficient, and the small relays get d@mn warm, and although rated at 20A, it is this that went t!t5 up with a black mark on the P. C. B connection. see herepost-735-1128888689.jpg

 

If you are going to feed a fused cable from the battery into the boot then you might as well use a a larger relay in the engine bay switched from an ign. ON/alternator connection. This is how I, and towbar specialists, have wired my previous cars and I never had any relay failure.

 

Interesting to see that the newer model Smartcom relays I've got, now have provision for two 12V feed cables going into the device rather than one, but the circuit board is still the same.

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Hobby,

 

I don't think they sell Smartcom units to enable the use of boot mounted accessory sockets as not all cars are thus equipped. It is also unlikely that the manufacturers of Smartcom and similar products would advocate the use of unsuitable power supplys. It is more likely to facilitate 12S installations on the latest multiplexed systems where picking up the required feeds for a more conventional approach can have repercussions on the vehicles electrical system.

 

A main battery feed and a Smartcom is an acceptable halfway house, and without doubt better than utilising the accessory socket in the boot.

 

I am still surprised at 'professionals' using an inadequate supply source no matter how convenient it might be!

 

Personally I have always used heavy duty relays, fused battery feed and alternater excitation with no problems,then again my cars have never been that modern. The Passat is the first vehicle I have owned that could not be repaired with a rock and a pointed stick. :lol:

 

Frank

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Hobby,

 

 

I am still surprised at 'professionals' using an inadequate supply source no matter how convenient it might be!

 

Frank

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Frank,

 

There are two types of "professionals"- trained ones and "so-called" ones.

 

The former are those that have been on the NTTA course where they learn how to measure voltage drops and even use Ohms law so that they can work out what size of wires, connectors and fuses to use. They are trained to get the supply from the battery or busbar with a fused supply if the car's own supply is inadequate.

 

The latter are just cowboys who will use every short cut possible to get more jobs done in a day but are paid for their so called work! They will even take the power supply from the boot light - 5 amp!!

 

The problem is that the wiring standards on cars are not the same as caravans. On a car the power feed wire has to be 2. 5 sq mm cross sectional area whereas the caravan's fridge needs a minimum of 6 sq mm and on long vans 10 sq mm!

 

Tony Maris's advice about doubling up on the power feed is very valid and solves many problems. Elecrolux tell me that if the voltage drops below 11. 5V then the fridge efficiency graph's line is like jumping off a cliff - it just plummets. So many fridges just do not work when the van is being towed. You are really using it as a cold box.

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:D Just a quick "thank you" to Frank for the advice to RTM, which I have done now, and Hobbybod for the pointers to what to look for inside the convertor cable.

 

I am waiting for winter to arrive, and will work on it before the spring, as the school holidays are over for a while, and the in-laws are due a visit at Christmas so we won't be going away in the van.

 

Cheers

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  • 1 month later...

I'm pleased that Hobbybod (alias d. o. c) got his problem sorted but as he and David (Klyne) will know, 12S wiring is a subject on which I have been known to get on my soap-box about from time to time!

 

I thought I'd take the opportunity to make a few comments though.

 

With regard to the relay's mentioned, the TF1170 has been markedly improved by the manufacturer following results presented to them and produced by students on the NTTA Training Courses, which I tutored.

 

As Hobbybod inferred, there are now two inputs but I can also confirm that the track on the circuit board is *significantly* wider and with a 20 amp load applied, our tests showed that the voltage drop THROUGH THE RELAY has been reduced from around 0. 4 volts to around 0. 1 volt. This is in line with that experienced in a good normally open 4 pin mechanical relay.

 

A SMARTCOM relay is a brand produced by another company which I have also supplied results to (though I can see how confusion could easily arise). This company is also reacting to the voltage drop issue.

 

Under NO circumstances would I use a cigarete lighter type socket supplied at the rear of a vehicle to supply a 12S feed. These are usually limited to a 10 amp supply and have inadequate wire size. Most of the V. A. G. group of vehicles have a really heavy BUS bar under the dash (not far from the fusebox) which is ideal for the purpose.

 

I've read some good stuff in this thread and was about to give Frank a pat on the back :) until I read the comment about scotchlocks and soldering :o (I also have a VW Passat 130ps)! My information is that VW no longer approve of soldering directly to their wiring looms. I have to say that I opted to fit a plug in type wiring kit to mine (with my own modified 12S system) working through a 13 pin socket.

 

A 'Scotchlok' is a brand name for a group of connectors which strictly speaking are Insulation Displacement Terminals and these are used by many OE manufacturers in their wiring kits. (The BMW X3 is one). I have used them for many years on lighting circuits without problems, So much so, I can offer a lifetime warranty on electrics that I fit. However, I would not recommend them for heavy duty use like the 12S system.

 

I would like to thank David for his obvious support in my absence and also Tall Limey (haven't worked out who you are yet!) who, from the way he talks, could well have been on one of my courses!! Bravo!

 

Regards to all,

 

Tony.

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In the Connections section,pages 12 to 16 of the Ryder Towing Training Manual who work to NTTA recommendations,Scotchlocks,Crimped and Soldered joints are all advocated in their place.

 

As they state Scotchlocks should never be used where there is any chance of damp,which to my mind rules out their use on a road vehicle.

 

http://www. rydertowing. co. uk/pages/trainning_standards. htm

 

Our Passat is the first vehicle where I have not fitted the towing kit. It was done professionally as the Passat was new and I wanted some comeback in the event of a warranty issue. The connections are a combination of crimped and soldered joints.

 

The Passat is a 2003 so maybe I got in there just in time. :)

 

Frank

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in my case the towbar fitter picked up the 12v feed from the cigarette lighter in the boot - apparently this is common.

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I've just finished fitting a Witter bar to my new C5. What an easy job compared with some of the towbars I fitted to my previous towcars. No careful measuring required, no drilling of holes, and then fitting of bushes. The whole experience went together like an Airfix kit.

But to the point - I fitted seven way relay for road lights, and a smartcom relay for fridge and battery. The instructions from Ryder Towing specified 17amp cable from the battery to the relays. There's no way that a pickup from the 12v socket in the boot would suffice.

Citroen C5-X7 Tourer+Avondale Rialto 480/2
https://jondogoescaravanning.com

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Tony, thanks for your comments and Tall Limey is in fact . . . . . B. B. !! :D

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Thanks for that Doc, fancy it not clicking with me!! i should have known. ........

 

Kind regards

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I've just finished fitting a Witter bar to my new C5.   What an easy job compared with some of the towbars I fitted to my previous towcars.   No careful measuring required, no drilling of holes, and then fitting of bushes.   The whole experience went together like an Airfix kit.  

But to the point - I fitted seven way relay for road lights, and a smartcom relay for fridge and battery.   The instructions from Ryder Towing specified 17amp cable from the battery to the relays.   There's no way that a pickup from the 12v socket in the boot would suffice.

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Hi John,

 

Are you sure he only quotes 17 amp? Explorer Group are fitting some Dometic fridges with a 225 watt element. Thats a whopping 18. 75 amps at 12 volts and the feed for the relay needs to handle the battery charge current too.

 

I wire through on 84/0. 30 cable which is rated at 45 amps by the manufacturers. This is simply to reduce voltage drop. In my opinion, the way cable manufacturers rate their cable is somewhat misleading as they deem it acceptable to have 1/2 a volt drop over a distance of one metre when running at its rated current. This is clearly unacceptable with fridges which need a minimum of 11. 5 volts to stand a chance of working.

 

Bearing in mind that the vehicle battery is normally at the front of the towing vehicle and the fridge could easily be 20 ft back from the 12S socket, there is enormous potential for voltage drop. Even the best alternator/battery combinations can only manage 14. 2 volts in ideal conditions, so it doesn't leave a lot to play with!

 

With a 20 amp current draw, I can manage less than 0. 6 volt drop through the vehicle, but there is still the plug/socket interface, the 12S cable on the caravan and the fixed wiring to the fridge. Its vital to save every bit of drop we can. ......

 

Regards

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Guest Dave Elcome

Do we know if the caravan is wired up with the correct rated wiring from the 12s plug to the fridge? In my instance the caravan is a Bailey.

 

If the answer to my question is no, then it seems logical that a lot of re wiring is required in order that the fridge actually works whilst on 12v?

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Do we know if the caravan is wired up with the correct rated wiring from the 12s plug to the fridge? In my instance the caravan is a Bailey.

 

If the answer to my question is no, then it seems logical that a lot of re wiring is required in order that the fridge actually works whilst on 12v?

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Hi Dave,

 

When I did a technicians course at Dometic on their appliances, they recommended 6mm cable for most of their fridges and 10mm for some.

 

The regulation covering 'extra low voltage' (that means 12 volt :) ) installations in 'Leisure Accomodation Vehicles' (a caravan :o ) is EN1648-1 dated Oct 1997.

 

In there it specifies a 2. 5 mm feed from pin 6 to supply the fridge and a 2. 5 mm feed to pin 7 for the fridge return. With the fixed wiring, no cable sizes are given though it does require that appliances running on the 12 volt system do not suffer more than 0. 8 volts voltage drop through the fixed wiring.

 

Given the 0. 8 volts drop the caravan manufacturer is allowed, the 0. 6 volts drop that we get through our fixed wiring in the car, the 12S cable fitted to the towbar, the 12S plug/socket interface and the 12S cable in the caravan, it surprises me somewhat that ANY fridge works on 12 volts!

 

I measured the voltage at the 'Fridge' on my test board the other day (using 3 metres of 12S cable as representative of the caravans wiring) on a new Land Rover Disco 3 equipped with the factory wiring kit. The reading was a paltry 7. 5 volts. ........

 

Regards

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Hi John,

 

Are you sure he only quotes 17 amp?

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Whoops! My mistake. The supplied cable was in fact 35strand/030 which I believe is 21amp, not 17 as I thought.

Citroen C5-X7 Tourer+Avondale Rialto 480/2
https://jondogoescaravanning.com

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This thread has got me worried now! I have a 2005 Passat TDI 130 that was fitted up with towbar & electics by the VW supplier. I know the 12v is wired from one of the two sockets in the boot (it has already blown the other one!) No wonder the fridge doesn't seem brilliant from the car - perhaps I better go back with a warrenty claim????

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This thread has got me worried now!  I have a 2005 Passat TDI 130 that was fitted up with towbar & electics by the VW supplier.   I know the 12v is wired from one of the two sockets in the boot (it has already blown the other one!) No wonder the fridge doesn't seem brilliant from the car - perhaps I better go back with a warrenty claim????

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I doubt that VW would approve of wiring a 12S system into the boot feed. I've wired my own Passat to the busbar in the drivers footwell. This is also convenient for the fusebox so any fuses fitted are easily accessible.

 

I wonder how many caravanners know where their 12S fuse is? Most fitters don't tell you!

 

Regards

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