Volvo towbar wiring for ignition-on circuit

SimonWJ
SimonWJ Forum Participant Posts: 15
edited August 2018 in Towcars & Towing #1

i recently had a towbar fitted to my Volvo V50 (2005) using a Volvo cable harness and towing module. After getting the Volvo software update everything seems to be working except that the ignition controlled supply to pin 10 - the 'fridge' circuit - is live as soon as the ignition is switched on and doesn't wait for the engine to be running and the alternator charging. All the Volvo instructions I've been able to find on towbar wiring right up to the latest XC40 and V60 refer to pin 10 as 'Power supply - ignition on' and make no mention of the engine running so the behaviour of my car would seem to be consistent with Volvo practice. 

So my question is, do any owners of Volvos with Volvo towbar wiring find that this is how their wiring works and if so, does it cause any problems?  For example, the immediate live feed to pin 10 would connect the fridge to the car battery even before the car is started, and the habitation relay would connect the always live battery charging circuit on pin 9 leaving the possibility of starting the car drawing current from the caravan battery along wires intended only for charging. 

Can anyone throw any light on this?

Comments

  • Vulcan
    Vulcan Forum Participant Posts: 670
    edited August 2018 #2

    Before voltage sensitive relays became the norm that was how they were wired till about 10 years ago.If I remember correctly power is cut from the charging and fridge circuits whilst the engine is cranking.

  • NevChap
    NevChap Forum Participant Posts: 180
    100 Comments
    edited August 2018 #3

    Not a lot of help to you....But....I have an XC90 (2017) with factory fitted towball and electrics. I have never experienced any problem with fridge etc. I have parked up at service stations for about 45 mins and never had any problem on return. Never checked to see if fridge remains on when just plugged into car, though. I wouldn't worry about it.

  • meridienmick
    meridienmick Forum Participant Posts: 37
    First Comment
    edited August 2018 #4

    This seems to be how it is with most modern vehicles, and definitely with Volvos.  I had a Jag X-type new in 2004 and had just this issue, so I made the dealer fit a voltage sensor type relay so the fridge feed only came live when the charging voltage when over 13.5V.  My next car was a Volvo XC70 with dealer fitted towbar and I had the same thing that you are describing so I investigated a bit further and found thet the Caravan Club had updated their info regarding towing electrics to say that this is now the norm, so I left it and never had a problem.  I now have a 2017 XC60 and have the same set up, again with no problems.  So, I wouldn't worry about it.  Quote from the CAMC  guide on towbar wiring:

    "At one time, access to an appropriate connection on the vehicle alternator made it straightforward to ensure this point was only once the engine was actually running, and not just when the ignition was turned to on. Modern engine bay and alternator designs limit such access considerably, often making a direct connection to the alternator impractical. Some wiring kits just use a connection to an ‘ignition-on only’ power supply. These successfully prevent the fridge flattening the car battery while parked, but do not protect against the situation where the car battery is already flat and the engine attempts to start from the caravan one. However, the Club has no reports from members of such problems occurring in practice."

  • lornalou1
    lornalou1 Forum Participant Posts: 2,169
    1000 Comments
    edited August 2018 #5

    I would guess that the circuitry in the caravan has diode's fitted so the current only goes one way from car to caravan and stops it going from caravan to car.

  • SimonWJ
    SimonWJ Forum Participant Posts: 15
    edited August 2018 #6

    Thank you all for your comments and suggestions.

     

    @Vulcan

    I should have said that I checked to see if power was cut while cranking the engine, as it is for the radio for example, but it isn't: pin 10 remains live while starting the engine.

    @NevChap

    Pin 10 is only live when the ignition is on; it's pin 9 that is constantly live so a properly connected fridge, i.e. to pin 10, wouldn't get any power from the tow car while parked up with the ignition off.

    @meridienmick

    I have the Caravan Club document and had noticed the very point you make, i.e. this seems to be the norm but no one seems to have a problem with it.

    @lornalou

    Diodes in the circuitry would certainly prevent the starter motor drawing on the caravan battery via pin 9, but there is significant voltage drop when using diodes which could impact adversely on the charging rate although using Schottky diodes apparently largely overcomes this.

     

    It would seem that this setup is the norm and in ordinary day to day use is only going to cause a problem if the tow car battery is in poor condition.

     

    Thanks again.

     

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