Split-Chargers & Bluemotion

[T6 Dave]

@Loz, without checking further, this could be solved by the inclusion of a one way diode on the input cable of the leisure battery, of sufficient spec, so that the current could pass into the leisure battery, but not flow back down the input cable. The output fused side would be OK.

But it has been a crap afternoon/evening for me so I might be wrong.... In any case.. Nice box..

 

[Loz]

@Loz, without checking further, this could be solved by the inclusion of a one way diode on the input cable of the leisure battery, of sufficient spec, so that the current could pass into the leisure battery, but not flow back down the input cable. The output fused side would be OK.

But it has been a crap afternoon/evening for me so I might be wrong.... In any case.. Nice box..

The only problem with a diode is the volt drop across it, I am tempted though to put the ctek in between the vsr and leisure side, that is if I don't sell the battery pack.

 

[MartyMoose]

To my mind the reverse current flow is just a symptom of how VW have deliberately set up the second battery installation. They want the main and secondary batteries to all charge at the same time and at the same rate. If it's a factory install then I would assume all the batteries are matched? Even in that instance you're bound to get a slight imbalance.

 

[T6 Dave]

@MartyMoose , the main battery can be 80% for the headroom of the sudden amp input from braking, but when you arrive on site etc, your leisure needs to be fully charged, to run your fridge etc.. As even starting the van, and ticking over will only otherwise charge the batteries to 80%, leaving headspace for the regen amps, which you won't generate unless you drive it.. I would have expected VW designers to realise this, maybe there is an update for the Cali leisure side, but I would inform VW and ask for their take on it, as might not realise they have a problem.

Forgive any blatant errors please, health is not great at the moment.

 

[MartyMoose]

Couldn't agree more. I'm just stating it as it is, and as I've said all along: there is no fancy charging system with the factory second battery installation or its relay. It's either on or off.

 

[T6 Dave]

Feeling slightly better, so......

I would have thought that it should work is that the VW bcm would control their leisure charging of the battery to 100%, and be like the smart charger, and not allow the excess amps or volts to the leisure battery as it would be 100% full and any more amps/volts will be a problem.. And yes the batteries should be matched type, as the bcm cannot be user programmed to take into account the different charging regime of a wet battery etc unlike the Ring dc30 or Sterling smart chargers etc, but need not be in amps in this instance, as not directly linked together as going through a seperate comp controller of their "VSR", namely the bcm. I would also have expected there to be some form of "one way valve" like a one way diode on the charge side of the cable input to the leisure battery to avoid the main sla battery becoming a parasitic drain as shown above, as if none of the above is true, then it's all waffle and lights on the Cali battery monitor.

So maybe VW need to informed so they can check the software in this instance? Or to sack a design team who are paid huge amounts for their technical expertise.....

Still not 100%, so might not be explaining myself well.... In which case my apologies

 

[mike]

As I had the passenger seat out to fit the swivel, thought it would be a good opportunity to take a look at the factory installed 2nd battery and investigate the charging operation.

The first surprise was revealed on removing the black rubbery cover from the 2nd battery:
This is the leisure battery

and this is under the bonnet


EFB main and AGM 2nd battery; I did expect to find two matched batteries but now don't know why.
The two batteries serve different purposes, why would they be the same?

Anyway, time to hook up some test gear:


Mutimeter to verify the voltage @ the 2nd battery, scope also displaying voltage @ the 2nd battery and the state of the 'charge relay' and the laptop using the VCDS graph function to display some interesting looking measurements from the Voltage Regulator.

Time to go for a drive....



Engine start:
VCDS
red - generator request voltage (?)
green - battery voltage
yellow - battery current

Scope is hard to see but shows the relay closes shortly after engine start and the voltage matches VCDS (confirmed by the multimeter).

The next image is a bit fuzzy for some reason.
(Yes officer, I was looking at the road)

Stop-start at the traffic lights in the next village.

Drove around for a bit to make sure everything was settled down before returning home and disconnecting most of it because VCDS provides all the information needed; the other kit just confirmed that the VCDS data was accurate and that I was looking at the right stuff.

One thing I can confirm - The 'charge relay' closes when the engine is running and opens again when it stops and that's it.... nothing clever there.
Don't even need to measure that, with the seat out of the way you can hear it.

I'll be driving around for the next day or so with VCDS hooked up and monitor the battery voltage/current.
I do have some initial data but something odd happened this afternoon that I want to investigate further before publishing.

 

[T6 Dave]

A. EFB batteries are an enhanced version of standard wet-flooded technology. The primary benefits of EFB technology are improved charge acceptance and greater cyclic durability when operating in a reduced state of charge (typical of Stop Start applications).

As the EFB is meant to run at 80% charge without damage, but you want the leisure at 100% for off grid, haven't seen under bonnet of mine, as still at converters.. But thanks for letting me know the sla is an EFB, that makes sense.

You still need to keep the 2nd to that type which is fitted, as I am assuming that the bcm has more to it than we realise, or is first apparent..

 

[mike]

humm....

 

[T6 Dave]

Might be useful to measure the amps as well as the voltage on both batteries? That way we can see if one is getting more amps into the battery than the other at the same moment?

 

[travelvolts]

I can't see how that would be possible Dave as it would mean some kind of voltage regulator inside the BCM (which there isn't) or a direct connection to the alternator for the cable supplying the split charge relay which doesn't exist either. I think (contrary to what a VW mastertech told me) that Martymoose is right, nothing clever going on here with the charging of the aux battery, just a bog standard relay. Probably the same in the Cali as they expect those vans to be on a hook up most of the time anyway and get charged that way.

 

[T6 Dave]

@travelvolts , know what your saying, but worth checking it out if your going to test it all anyway, if your hell bent on fitting a VSR to save about £150 towards your nice wheels, or your lowering kit.. Can never understand people who take shortcuts with kit just to splash it on bits that don't really matter in the long run.

 

[travelvolts]

@travelvolts , know what your saying, but worth checking it out if your going to test it all anyway, if your hell bent on fitting a VSR to save about £150 towards your nice wheels, or your lowering kit.. Can never understand people who take shortcuts with kit just to splash it on bits that don't really matter in the long run.

My sentiment entirely but I'm not sure there was any suggestion of a VSR being used by the OP.

 

[T6 Dave]

@travelvolts , know what you mean, but it would appear that the VW one is no more than a bcm controlled relay, therein is my likening to a VSR, not having a good day again, so probably not explaining myself as well as I could.. My apologies..

I would not be impressed if the Cali etc system is not as good as a smart charger system, and it will be interesting to see the results of the above.

 

[Loz]

I looked at the wiring diagram for the Cali split charge and its just basic relay that's all. I'll post it up tomorrow.

(Also had a very long chat with the Sterling power guys at the show yesterday)

 

[T6 Dave]

Looks like VW don't care for the leisure battery very well then.. That must be a right downer for those that have brought the camper variety then...

 

[mike]

OK, so after a couple of days with VCDS hooked up monitoring the following: Generator (spec) Voltage, Battery Voltage, Battery Current, Battery Level,
Battery Temperature and occasional verification of the 2nd Battery voltage with a multimeter, I'm pretty confident in saying that the Factory 2nd battery
charger circuit is just a relay, activated when the engine is running, and nothing more.
Does the presence of a 2nd battery have any effect on the charging algorithm? I occasionally removed the relay to see what effect that would have, most
of the time none at all but I think I need better weather to determine that.

Better weather? yes, there appears to be some temperature compensation in the charging algorithm. The other day when the temperature was below
about 5 degrees the minimum generator voltage remained above 14.8V for most of the day. I did about 100 miles, most of it dual carriage way, that day.
Later in the afternoon, when it warmed up a little, the voltage would dip to about 14.0V under hard acceleration but it returned to fixed 15V in the evening.

Today the temperature is warmer (9 degrees) and it returned to more normal behaviour, however I suspect that the minimum voltage may still be influenced
by temperature.

I have also noticed that minimum voltage is fixed at 13.5V if the lights are on - VW attempt to set the 'mimimum glow level' of the H4s ?

All very interesting; but not relevant to the main question.
What I need now is warmer weather to be sure that the temperature is not having any effect....

Edit: missed @Loz post before I wrote this.

 

[MartyMoose]

Your voltage readings are very similar to my own Mike, and bear out the simplistic approach VW have taken. I know my original post caused a bit of stir but I was only ever questioning the logic of the assumptions we were making. I think between us we have got to the bottom of things and now have a much better understanding of the whole VW charging set up. Hopefully that will help us all in choosing the right equipment for our beloved Vans!

 

[rod_vw]

@mike very interesting data you have published there, it was something that I wanted to do but haven't had time. Just for the record my Highline Kombi was supplied with just the normal engine battery and has an AGM fitted in the engine bay. I think it's the same part number as the one that you have under the passenger's seat, I can check if you wish.

One thought whilst you are monitoring the voltages etc. would it be an idea to disable the split charge relay in the BCM coding and see if that shows up any differences in the charge regime? Maybe the simple activation of 'Battery Isolation' has much more effect on how the charging is managed than we realise.

Please keep us posted on anything that you discover.

Rod

 

[Loz]

Here are the wiring diagrams for 2 and 3 battery setup Camper and transporter.
T6-Camper-battery.pdfT6-Second-battery_not_camper.pdf