Trailer socket - correct wiring test

Just a quick question.

With modern 13 pin connectors there is a pin for providing power to a caravan fridge. Pin 10, ignition controlled.

As far as I can tell this is not supported by the standard wiring in German cars until ver recently.

Is there any obvious way (apart from tracing the wiring) to prove that this is a separate power supply and not just bodged from the existing pins?

Cheers

Dave R

Reply to
David
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Isn't the caravan supply relay controlled only live with the engine running?

Reply to
Dave Liquorice

Yes (Pin 10), but it occurs to me that you could pick up the battery charging, interior lights etc. circuit on Pin 9 (always on) and link that to Pin 10 with an ignition-driven relay. This would give you ignition controlled power on Pin 10 but I am assuming that there isn't enough capacity in Pin 9 to support battery charging, internal lights and the fridge (else why have a separate circuit?).

Which led me to wonder how to easily check if the correct installation (separate fused feed from the battery) had been wired in.

According to the Caravan Club Pin 9 and Pin 10 should both be of 21.5A capacity.

The main issue seems to be that modern large fridge/freezers require a lot of power to operate and so require their own dedicated supply (as large as possible).

Anyway, any non-destructive method of checking that Pin 9 and Pin 10 have independent 21.5A supplies?

Cheers

Dave R

Reply to
David

I'd say most cars probably wouldn't have an ignition switched supply readily available at the rear of the car. So unless provided by the car maker for this job would have to be added. And hopefully done correctly.

Reply to
Dave Plowman (News)

Maybe this pin should be considered and used as a battery charging supply for the dedicated battery in the caravan?

Reply to
Davey

David explained :

The big problem due to it being 12v, is voltage drop - as it is a long way from the front of the car to the rear.

One way to test it is adequate is to apply a load, measure the drop end to end, then from that - calculate the cable size.

Commonly, a single always live feed is used from the battery, to the boot area. Then a voltage activated split charge relay is installed in the boot. Problems occur when that single feed is not hadequetely sized and the relay clicks in and out constantly. Voltage rises, relay makes, load then causes volts drop so relay opens, voltage rises... and so on.

I always install 6mm or 2x 4mm for the common feed to the rear.

Reply to
Harry Bloomfield

It happens that Dave Plowman (News) formulated :

Most/many professional installers do not understand the need to rate the cable size for both current capacity and to avoid voltage drop.

Reply to
Harry Bloomfield

When we did this decades ago, we shoved a schottky diode in series with a fused wire direct from the battery and used this as the perm live to the caravan with a socket in the boot to charge my mum's disability scooter.

With 0.6V forward voltage drop, this worked fine - caravan's leisure battery seemed to charge OK when the car was moving, as did the scooter.

To protect the car from being flattened when the caravan was hooked up but being lived in (and the leisure battery running down), I made a voltage sensitive trip for the caravan that just cut all power when the voltage went below an adjustable amount.

Reply to
Tim Watts

Tim Watts formulated the question :

0.6V is a lot of voltage lost, when the charge voltage might only be 14v. I used a diode on one of my early caravans and gave it up as a really bad idea.
Reply to
Harry Bloomfield

And yet it worked for us... For years.

Our Fiat 131 would top at at 14.4 and we ran a 20A rated wire direct to the battery for this.

Reply to
Tim Watts

?

Pin 9 is for battery charging and always on.

Pin 10 is for the fridge and switched by the ignition.

Both circuits are needed, must be fully functional and separate. Pin 9 also powers the ATC Trailer Control as well as charging the battery and powering the internal lights.

If there is barely enough power to run the fridge/freezer it isn't going to be able to power all the other stuff as well.

Cheers

Dave R

Reply to
David

He used a Schottky diode, much lower Vf.

Reply to
Capitol

Check for lack of continuity between the pins.

Reply to
Capitol

In article , "Dave Plowman (News)" writes

Any car which offers an approved towbar will be equipped with a plug in socket for the wiring loom for a caravan conforming to EU standards (except it would seem from an earlier comment VW0

Reply to
bert

But I'm reasonably sure pin 10 shouldn't become live unless the engine is running, ie the alternator turning. So ignition on, ignition light not lit.

So if you have volts on pin 10 with ignition on, engine not running it's not being switched correctly and this may weel be just a link for pin 9.

Reply to
Dave Liquorice

I am not familiar with the 13 pin, but the above would seem to be wrong.

If pin 9 is always on, that means that with a flat battery on the tow vehicle, it will back feed from the trailer when any attempt is made to crank the engine.

One the 7S the battery charge pin is only connected when the primary battery is being charged, to avoid such problems.

Reply to
Harry Bloomfield

AFAIK there is ECU protection which cuts the current if the vehicle battery goes below a certain voltage.

Reply to
David

Good point!

That should pick up the first level of bodging.

Reply to
David

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