Emergency Plea for help- leisure battery

[andys]

Okay, so what you need to check is that the Relay with the mercedes logo on it operates when the engine is running..

Yes it does, one terminal stays at 12v regardless and the other one goes from 11.7v with the engine off up to 12.4v revving it. It would need to be well over 13v I would have thought if that's what's going to go to charge the battery

Edit: Actually that makes no sense at all does it, surely the voltage should be higher on both sides, those are the only 2 large terminals and it must be the the thinner contact that's switching the relay?

Edit again: Wait, there's 12v (ish) either side of that relay whether the engine is on or not, that can't be right?

 

[Loz]

Actually that makes no sense at all does it, surely the voltage should be higher on both sides, those are the only 2 large terminals and it must be the the thinner contact that's switching the relay?

correct, check the smaller wires are operating the relay.
Also the voltage might be low until the BCU tells the alternator to charge as the bluemotion tech switches out the alternator.

You could turn on the headlights and heated mirrors and screens if you want to add some load.

 

[andys]

Thanks, didn't realise that. Yes with the heated mirrors, ac and lights on the voltages are now 12.1v and 13.4v. This is the underside of the relay, if I remove the thin connection the voltages stay the same so is this the problem? The 12.1v is the same as the leisure battery so it looks as though the relay is permanently open and the voltages I'm measuring are from the alternator and from the leisure battery respectively. This is what the underside of the relay looks like.

The voltage across the blue/brown flicks rapidly from 0.07 to 0.11v so maybe a digital signal? Either it's not getting the signal to close the relay or the relay is faulty?

 

[Ed Webb]

I can't really work out what is reading what voltage, I got a tad confused.
Your possibly picking up voltages from your batteries and/or alternator giving you readings on the relay contacts even if the relay isn't operating as it should. @Loz seems to have a rough idea what to look for but I'd personally find it useful if you're able to photograph the little diagram that is possibly on the relay so that I can picture what voltage should be where.

 

[andys]

I can't really work out what is reading what voltage, I got a tad confused.
Your possibly picking up voltages from your batteries and/or alternator giving you readings on the relay contacts even if the relay isn't operating as it should. @Loz seems to have a rough idea what to look for but I'd personally find it useful if you're able to photograph the little diagram that is possibly on the relay so that I can picture what voltage should be where.

Thanks, yes that's what I meant, I'm getting the 13.4v from the alternator side and the 12.1v feeding back from the leisure battery. I'm assuming that its staying open or it would be 13.4v on both sides? Unfortunately it doesn't seem to have a diagram on it, the sides are blank apart from the number 147019, the back is as above and this is the front

 

[Loz]

Sounds like the relay or it's supply.
You could unplug the relay and introduce a 12v feed and see if it operates.

 

[Loz]

Okay I have found that relay, its a mercedes glow plug timer!

You probably need to change that for something more suitable, I would not use a relay but a dc-dc split charger to get the best charge with the regenerative system we have.

 

[andys]

Okay I have found that relay, its a mercedes glow plug timer!

You probably need to change that for something more suitable, I would not use a relay but a dc-dc split charger to get the best charge with the regenerative system we have.

That's horrific, it's a brand new Westfalia converted at the factory! I had also found that it was listed as a glowplug relay on google, but other sites list it as a Sprinter split charge relay. I was just reading about how smart alternators need a battery to battery charger but assumed that was in there too. It beggars belief that Westfalia could bodge something like that, supposedly they're the only outside converters that VW trust enough to give them semi-built vans specially for their conversions. Surely they would know about smart alternators and regenerative braking?! I'm starting to hate this van more every day. I think I'll do what you say and test the relay out of the van and hope that's the problem

 

[Loz]

Even my California has a split charge relay so not surprising...

I am sure it is a simple relay so might be the feed, if its a factory split charge I should be able to find where the feed comes from on the circuit diagram. But to be honest, not much of what is in your photos look like VW..

 

[andys]

Even my California has a split charge relay so not surprising...

I am sure it is a simple relay so might be the feed, if its a factory split charge I should be able to find where the feed comes from on the circuit diagram. But to be honest, not much of what is in your photos look like VW..

So even VW don't fit a proper charger? Yes I don't know why Westfalia don't just use the VW 2nd battery option instead of doing their own, the battery is even in the same place. This is how it's laid out before I pulled them out for easier photographing


And this is a closeup of the little box next to that relay, it translates to "charging adapter" so I wonder if this is responsible for sending the signal to the relay

 

[Loz]

Do you have a towbar?

 

[andys]

Do you have a towbar?

No

 

[Loz]

Then that is probably the culprit.. if it were a factory second battery setup you wouldn't have that as the vw split charge relay is controlled by the bcu.

 

[andys]

Then that is probably the culprit.. if it were a factory second battery setup you wouldn't have that as the vw split charge relay is controlled by the bcu.
View attachment 13452

Thanks, I'll check the connections on it tomorrow. Probably the hardest part to get hold of too, no trace of it in google so must be a bespoke part.

 

[Loz]

If you swapped the relay for a dc-dc unit you wouldn't need any of that, Martin @travelvolts does a nice one but you might be struggling for space now you have the safe under there.
Actually Martin might have some ideas.

 

[andys]

This is like detective work, I'm actually quite enjoying this now I'm not in howling gales and rain and can take my time. So, I've removed the relay and it tested fine, I then refitted it with the input and output bridged and the leisure battery immediately started charging, so that relay is fine. The control pins on the relay are blue and brown, I assumed the brown was earth and checked its continuity to earth, again fine. I followed the blue and it joined a thick taped loom that disappeared into the floor, but after unpicking the tape found that it looped back up again, where it went through a 5A fuse on a block, which tested ok too. From there it went to another relay, pictured below

This is beyond my understanding of relays, I get that supplying a low current to a terminal can switch two higher current pins but this totally confuses me and I've no idea how to test it. The blue connection is on 87, 15 is ground and there is no contact on the central 87a pin. Any ideas on what is switching what?

Should I bridge the blue and brown pins and see if charging kicks in?

 

[Loz]

That looks like a simple change over relay (like the big one but has a normally closed pin as well as a normally open one) and that relay has been added purely to handle the current the bigger relay needs so as not to draw too much current from the bcu.
What you need to find out is what is supplying that relay...

31 is the feed to operate the relay and 87z is the through feed.
is 87Z live?

 

[andys]

That looks like a simple change over relay (like the big one but has a normally closed pin as well as a normally open one) and that relay has been added purely to handle the current the bigger relay needs so as not to draw too much current from the bcu.
What you need to find out is what is supplying that relay...

31 is the feed to operate the relay and 87z is the through feed.
is 87Z live?

Pin 87Z is not live..
It leads back to pin 1 of the Westfalia badged control unit. Probing the terminals on that, the 12v battery side and 14.4v alternator side are present, along with ground and a thin green wire that does disappear under the floor. So that's the end of the road then, it's not recognising that it's receiving alternator voltage and switching the relays to charge? So I either get another control unit or spend even more on a DC-DC charger.

 

[Loz]

It looks like you are correct, that westy unit must also have the negative shunt connected to it and also feed a display unit of some kind??

 

[andys]

It looks like you are correct, that westy unit must also have the negative shunt connected to it and also feed a display unit of some kind??

It does have an LCD display showing charging status. Thanks very much for your help, I'll consider my options now