Ignition controlled power supply for caravans - pin 10
 

I recently fitted a Volvo trailer module and towbar cable harness to my 2005 V50 and find to my surprise that the ignition controlled power supply to pin 10 (often referred to as the 'fridge circuit') is live as soon as the ignition is switched on and not just once the engine is running. This seems very odd to me but the Volvo description of the connection, even on the latest XC40 and V60, is simply 'Battery voltage - ignition on' so it seems to be standard Volvo practice. It's actually referred to as 'Battery charging' in the instructions for fitting the wiring to the V50 which seems even odder!

The effect of this would be that the fridge (if present and connected to the tow vehicle) would be drawing current from the car battery as soon as the ignition is switched on and thus while the engine was being started, which doesn't seem like a good idea; and secondly the battery charging circuit - pin 9 - would be connected to the caravan battery by virtue of the habitation relay in the caravan being triggered by the fridge circuit, and thus starting the engine would draw current from the caravan battery on wires intended simply to charge it, which also doesn't seem like a good idea.

I had thought that perhaps the power to pin 10 might have been cut while starting the engine in the same way as it is to the radio, but seemingly not.

In reading through the threads I noted that on some cars, pin 10 isn't live until a fridge is connected to it (although how that would affect the operation of the habitation relay if a fridge isn't fitted isn't clear) but in my case pin 10 is live as soon as the ignition is switched on.

Can anyone throw any light on whether this is how it's intended to operate as it seems to me to be a flawed arrangement.

My dealer tells me that this behaviour, i.e. power at pin 10 as soon as the ignition is on, is standard Volvo practice.

Very odd.

Not odd at all.
Standard practice as defined in the ISO standard ISO-11466

Volvo adhered to the ISO standard.
Job done properly, well done Volvo.

References:
https://en.wikipedia.org/wiki/ISO_st...tor_(ISO_11446)
https://en.wikipedia.org/wiki/ISO_11446

The ISO standard doesn't preclude pin 10 only becoming live once the engine is running; it simply says that it's ignition controlled. My problem/concern is that with pin 10 being live as soon as the ignition is turned on then the fridge will be drawing current from the tow car battery at the same time as the tow car engine is being started - an unnecessary extra load on the car battery; and the habitation relay will activate the battery charging circuit on pin 9 which will mean that starting the tow car engine will also draw on the caravan battery across wires designed for charging, not starting.

Having pin 10 only going live once the engine is running avoids both of these situations.

I realise of course that a voltage sensing relay would solve this, but it seems odd that it's not done automatically.

With it all being done via the towing module would there not be a safeguard incorporated in the electronics of the module. The whole consept of these modules is control, and electronic control is far easier achieved than by physical relays.

Paul.

The trouble is, we don't know what the towing module actually does apart from make the physical connections to the 13 pin socket and handle reversing sensors, rear fog light and dash warning lights. My testing is very basic - a multi meter on pin 10 and earth. It may be that with a load on pin 10, from a fridge, for example, the trailer module cuts the power until the engine is started and the alternator is operating. But I simply want to use pin 10 to operate a relay to switch in the trailer battery to charge on pin 9, and as currently configured, the trailer batter would be connected to the car battery while operating the starter motor - not ideal.

So perhaps I'll have to fit a voltage sensitive relay to pin 10 to make sure the trailer battery doesn't connect to the car battery circuit until the engine is running.

A voltage-sensitive relay is the obvious solution to your problem

Remember that the car never knows what type of trailer is connected and thus never knows what pin 10 will exactly be used for in the trailer.

Be it for releasing the electric trailer brake, for powering a fridge, charging a auxiliary battery - all of these are possible.

While I could see that an ignition controlled power supply would be desirable for releasing electric brakes, are such brakes legal in Europe?

As for powering a fridge or battery charging, in both cases it would surely be undesirable to have these in action before the engine was running? It seems odd that these two pretty standard caravan features require a modification to the towbar electrics to make them work properly when they could easily be incorporated into the trailer module.
P.S. And when I think about it, you’d probably want the engine running before releasing electric brakes.

Unfortunately my hanes caravan book is too old for these issues and even a wiring diagram of a typical towing module is absent.
Having just baught a new van it's something I shall have to consider as well.
Seems a lot of Google searching is on the cards to find answers.
I fear dealers have as much clue as owners do at the moment.
I will certainly follow this tread with interest and post any information I find.

Does pin 10 offer power to the atc devise on newer vans?

Paul.

Pin 10 offers power to whatever is connected to it on the trailer/caravan. It is, I suspect, irrelevant to the car what is attached to either pin 9 or pin 10, provided the load isn't excessive. There's a 40 amp fuse for the trailer module which presumably covers both pins.

The issue to my mind is simply why does Volvo not delay providing power to pin 10 until the engine is running, something that would surely be simple to include in the trailer module software?