Split charge relay, and towbar price. Help!

[Irishrebel]

We have a 99 Bailey Senator with twin sockets. Towed it for two years on single cable with our Audi. Now bought a 98 Merc E-class estate and need to get towbar and electrics fitted.

Since we are now going to tour around France, we may need the twin electrics to keep fridge going. On a post somewhere else, I read that WITHOUT a split charge relay on the car, the fridge can drain power from the car battery when sitting in a motorway stop, so not good. My brother believes the fridge powers off the van battery, which is then recharged by the car alternator when driving again, so not a problem.

Now, I have the best quote for a towbar, but the supplier believes that the split charge relay is only needed for cars from 2001 on. So I'm really confused - anyone enlighten me?

ALSO, all the quotes I got for a fitted towbar were between £190 and £250, with the twin electrics usually £25 to £60 more. The best quote is miles below these at £70+VAT. This supplier is a large, reputable car breaker, and my bro says he would trust them completely. The price is so low, I think it may be off a scrap car, but then again, if all towbars have lifetime guarantees, then why would I want to fit a new one to a 10-year old car? If the towbar on a scrap car is pristine, why not take the bargain offer?

Tim.

 

[rob_jax]

Tim,

There was a change to the way the caravans and the 12S supplementary socket on the car were wired in 1999 - basically after that date the fridge had it's own dedicated high power return and the battery charge function was moved from pin 2 to pin 4

And since your Bailey is a 1999 model - there is a possibility that it uses the old standard, but it's most likely wired to the new standard...

But in any case I'd suggest you have the car wired to the new (post-1999) standard - mainly because the fridge stands a much better chance of working. And adjust the caravan if necessary.

The fridge in a modern caravan draws around 10 or more amps - so that's like leaving the car head lamps on - and the split charge relay supplies power from the car alternator only when the engine is running. Then when the car is stationary or sitting with the engine off, the fridge is disconnected from the car battery.

And the caravan battery is never connected to the fridge - your brother has that part wrong. The caravan battery is recharged by the car alternator when towing - but it's two totally separate circuits.

Regarding the tow-bar - then if you can examine it and the donor car - and make sure it was not the victim of a rear end shunt - then it should be fine. If you cannot check the car, then check the tow-bar for distortion crash damage, check for corrosion and broken or bad welds.

You must use the correct grade of new bolts, washers and nuts to attach the tow-bar - it is safest to regard these as one-shot fittings - and in particular the lock-nuts cannot be reused.

I'm a little unsure who is going to do the installation - you or the breaker? - and I'd want some assurance that a car breaker knew what they were doing...

Robert

 

[Irishrebel]

So you're saying that the split charge relay is a standard part of the new setup for VANS from 99, yes? And the guy quoting me the cheap towbar believed it was only needed for CARS after 2001. Makes me think he doesn't know that much.

Though it would seem that fitting towbars and wiring is easy enough for DIY, since Halfords supply all the bits off their shelf. I wonder if I should be wiser to do it myself as I tend to be very careful over such things, but it's probably beyond the usual tinkering I've done with cars in the past.

I would be fairly certain my caravan was the modern wiring, as the previous owner was a mature caravanning veteran who had it made to order at the Bailey factory. I don't think he would have left wiring as it was if standards were changing.

 

[rob_jax]

Tim,

The "fridge relay" is mounted in the car - and switches the dedicated fridge supply to the tow-bar on and off depending on the charge delivered by the car alternator.

There are other relays already in place inside the caravan - and these have the purpose of detecting if the caravan is connected tot he car and under tow - and automatically disable / enable certain systems in the caravan. But you don't need to worry about that.

The task of fitting a tow-bar - the nuts and bolts side - is an easy if time consuming job.

The electrical side can be easy or it can be a more complex task.

I drive a W211 MB E-class and your W210 E-class also has the MB implementation of canBUS (MOST) - and that makes the user fitting of the tow-bar electrics a bit more complex.

In particular:

1. You can't twin the caravan lights with the car lights - running two bulbs off one bulb will cause problems because the canBUS system will detect a lighting error (too much current taken).

2. You can either use a dedicated wiring kit to plug into the special W210 trailer socket in the underfloor area of the boot, or use a relay wiring kit to use the car lights as "signals".

The dedicated wiring lom is

 

[Irishrebel]

Thank you VERY much, Robert. I've learnt a lot, but I've also been tearing my hair out.

To cut a long story short, the supplier of the cheap towbar was supply only, NOT fitting, and didn't include the wiring!! Knew it was just too cheap!

So I decided to source a complete bar+ twin electrics (found a Bosal swan-neck complete for