Starter battery not charging on hookup

[briwy]

I have just realised that our starter battery is not charging when on hookup.
Its now reading 11.8 volts and doesn't go up when plugged in... Leisure batteries are charging fine.
I have taken the charging unit out of the back cupboard and checked that it outputting voltage which it is.
I suspect the split charge relay has packed up.. I have the 11.8v on one terminal and 13.86v on the other which comes from the leisure batteries.
What actually activates this relay. There is a small plug in terminal with a brown and a black wire. I guess this is the earth and the wire that activates the relay.
I'm going to take the relay off and see if it does activate.
Any other ideas please.

 

[WelshGas]

I have just realised that our starter battery is not charging when on hookup.
Its now reading 11.8 volts and doesn't go up when plugged in... Leisure batteries are charging fine.
I have taken the charging unit out of the back cupboard and checked that it outputting voltage which it is.
I suspect the split charge relay has packed up.. I have the 11.8v on one terminal and 13.86v on the other which comes from the leisure batteries.
What actually activates this relay. There is a small plug in terminal with a brown and a black wire. I guess this is the earth and the wire that activates the relay.
I'm going to take the relay off and see if it does activate.
Any other ideas please.

The Mains charging on the T5/5.1/6 was never designed to charge the starter battery. Confirmed by VW. But there was a current leakage through the system that gave a trickle charge to the engine battery BUT only when the Leisure Batteries were fully charged on Mains Hookup.
This was confirmed by many, but not all, by a rise in the Starter Battery voltage after 12-24 hrs on mains hookup.

 

[briwy]

Thanks for the reply Paul.
I'm nor convinced that is the case though. Ours has always charged the starter battery as well as the leisure batteries from new. A couple of years the charger unit failed and I replaced it with a secondhand one which only charged the leisure batteries. I then got hold of the correct charger and everything worked fine.
I have had the charger out and checked it over and it's fine and has two separate 13v outputs. The split charge relay is working fine so I'm at a loss as to what is causing it. No faults coming up on Carista or VagCom.
I have put it back on charge and will wait to see what happens before reinstalling everything.

Charger with a single output



Charger with two outputs. Part no has a B suffix

 

[sidepod]

I’m not sure why you think the split charge relay plays apart in this?
If you’re on hook up then it’s reasonable to assume the engine is switched off?

If the engine is off then the split charge relay is open or to put it another way, the starter battery and leisure batteries are disconnected from each other.

For your charger unit to charge the starter battery it is connected to the upstream side of the split charge relay and as such its operation is irrelevant.

 

[briwy]

Yes I realised this when I started to trace the wiring from the relay. It was just my initial thoughts that that seemed to be the only way for the charger to connect to the starter battery.

 

[sidepod]

This is why there are two separate outputs from the charger. One for each side of the relay.

 

[briwy]

Yes quite. Doesn't explain why it's stopped working though.

 

[sidepod]

Have you checked inside the box? Probs an internal fuse?

 

[briwy]

Yes checked the fuse on the charger. I'm looking at modifying that so that it could be changed without taking the charger out.