We bought a 2019 Octavia with a factory fit towbar and full wiring.  We always believed that it worked just fine (a couple of trips before lockdown) but having just collected the 'van from storage where it had sat for an extended time, which was the death knell for the leisure battery, we found that switching on the fridge kills the switched power to the 'van.  We suspected the dead battery was causing the problem.

 

We've replaced the battery but still have the issue, sort of.

 

We've found that the car can be connected to the van and the engine started with the fridge switched off the power to the van is ok, ie leisure battery charging.  The fridge can then be switched on and works.  This was good for a 60ml journey including auto stop/start serveral times.

 

However, more often than not the car refuses to supply power to the 'van and it is necessary to swich off, dissconnect, reconnect and restart before the car is happy to provide power.

 

I have tested the car independently and using pretend loads and it all appears to be working.  A halogen headlight bulb with both filaments in parallel draws 10A which is a similar current to the fridge (as does all 3 cores of a 60m extention cable wired in series (that is 180m of 2.5mm cable).  I've also added in a brake light bulb to simulate battery charging current.  Road lights are no problem.

 

My feeling is that whatever the car is sensing is too sensitive and it cuts out but will not resart untill the van is disconnected and the engine restarted.

 

Can anyone shed some light on how the wiring is organised, where the relays are, how and under what circumstances the power can be cut to the towbar wiring?  Any help really.

 

I ought to say that as we don't have enough space at home to have both car and 'van together investigation is a protracted affair.

 

Thanks

 

Russell

It should only power the fridge when the car engine is running the car battery fully charged and the engine revs high enough to maintain the charge in the vehicle against the current drain of lights, screen heaters etc and charge the caravan battery, power the fridge etc.

 

The voltage threshold is say 13.3 volts, thats an educated guess based on battery voltage vs charge level.

 

I would buy a little plug in voltmeter for the cigarrette lighter socket to compare readings with what you are measuring at the caravan or towing socket.

 

Could your vehicle perhaps be one with Stop/start and the battery management bull***t system for charging on the over-run & while braking etc? They keep the battery undercharged which could play havoc with a caravan towing set up especially if the battery is a little tired.

Edited 4 July, 20214 yr by J.R.

A caravan fridge shouldn't charge without the engine running, the cut out 'relay' for that is in the car, if a factory fit it must be a dedicated module?

But the biggest problem with towbar wiring is usually the earthing, old 7N/S (S for fridge) being much worse than on a modern 13pin system, try cleaning the earths first. 2nd biggest problem is the resistance between pins and sockets in the 7S (13 pin far better) so you should try cleaning the pins with emery paper and you could try spreading the heads of the pin VERY slightly, they should have a cross shaped slit that'll pry slightly.

If voltage was an issue then I would expect the circiut to reestablish itself when the alternator is proving enough.  This doesn't happen - when it's gone it's gone and doesn't come back until the connection is disconnected and the engine restarted.

 

Agree it's worth checking the earths (it's a 13 pin system) but again doesn't explain why the fridge power is cut and does not return.

 

The caravan does not have any major issues as it has worked as the 60ml trip proves and I have checked the fridge with a battery and it draws the 10A that I expect it to do.  The battery charger in the van is a Schaudt booster, effectively a dc-dc converter with an enable connection that is connected to the fridge power pin, this works.