Replace factory second battery to DC/DC

[RoadRunnerDU]

My T6.1 came with the leisure battery. I want to take it out and replace with my own dual battery setup with DC/DC charger 200ah lithium and so on.
I read multiple discussion here and had a look under my seat and there it LOTS of stuff. I get this is all connected to the brains of the car ECU and has smart alternator and other trickery built in.
Is there a way to remove/bypass most of this ?
Assume the little thing on negative is a BMS. 200/300A fuses seem a bit excessive for those cables. Also never figured out what actually is connected to that battery.

Anyway. What I'm after is just to disconnect most of this and connect a DC/DC charger that I can feed into my own battery. If someone knows a discussion in here and can point me in the right direction that would be great.

 

[RoadRunnerDU]

Followed a few cables and it looks like the 100A fuse goes to that green 40A fuse and the 60A yellow fuse goes to the fuse block with all the 30A fuses in it.
200A fuse comes from the relay from the main battery that a lot of people mention in here. From what I read I can just disconnect the 200A fuse and use that to feed the DC/DC charger ?
If so what is supplied with power from the 60/100A fuse and how do I power that stuff again after ?

 

[Richard T6.1]

I've been trying to get my head around the factory 2nd battery setup I have in my van too. Although still a little beyond my understanding of car electrics, I did find a lot more info in this huge document I found here, VWs Body Builders Guidelines for the Transporter. Section 2.5.4 Vehicle battery provides the most info > clickable from the Table of Contents.

It's a monitored system as VW calls it. The white/grey-ish thingy on the minus side of the battery appears to be a shunt. The starter battery under de bonnet has one too and they are used to monitor the batteries state of charge, working together with a CFCU (customer function control unit) under the dash and the isolation relay.
I tried to figure out what the charging system actually does with a Volt meter in the 12V socket on top of the dash. The charging voltage from the alternator varies depending on the SoC from the batteries when you start the engine (or that's how it looks). In my van it settles on a voltage - even as high as 14.6V - and stays there during that trip. On a next start-up it can sit at 12.5V and stay there as well appearing not to charge at all. I'm still a bit puzzled by the charging behaviour/pattern tbo.

To bypass or change this setup, or parts of it, requires a good understanding of how it works imo. I'm not there yet.

Hope this provides some pointers.

 

[RoadRunnerDU]

Thank you for linking the Body Builder Guide. Sure that will come in handy one day. Yeah they have a smart alternator so voltage keeps changing and everything is controlled with ECUs. All those shunts talking back and so on is a pain. Surely someone has a workaround or some electronic gimmick to deal with all this ? I have access to a VCDS as well if that helps. For testing I disconnected the first wire from the 100A fuse to see what stops working and so far everything works and no warnings. There must be some wiring diagram to wee what all those fuses are for.

 

[roadtripper]

This is a very common discussion - I'd recommend searching for @Dellmassive "How I dun it" threads around electrics.

With the "full" second battery you have 3 areas you need to think about

1. You want to replace the split charge relay with a DC-DC to get charging to 100% or use a different battery chemistry
2. You will need to find some way of replacing the battery mounted fuse box - this moves several important things in the van to the second battery like most of the 12v sockets, auxiliary heaters and one of the trailer feeds
3. You seem to have the absolute full setup with a shunt on the negative of the second battery - so that will need removing and the coding updating in the van so that your starter battery and start/stop continue to work correctly.

The first point is quite easy to do and will improve the fitted system, just use the signal wire to the relay as the DC-DC charger ignition enable.

The others take more work.

As an aside if you take out VIP Memberhsip the wiring diagrams for all this are available in the download section.

 

[RoadRunnerDU]

Excellent. I had a feeling my van has the lot also it's just an empty van. I have nothing in the back. No 12V sockets, heater or anything. I've seen the towbar module under the driver seat even though I have no towbar someone must have ticked the box.
I have
8AR Optional infotainment system
8GV Alternator 180A
1D7 Preparation for detachable trailer coupling
J0V Battery 420A (70Ah)
So maybe gets powered from the second battery.

1. Yes want to take the second battery out and have installed a Lithium battery in the back of the van
2. yeah these fuses. So many of them just seems strange given there is nothing in the back of the van and that would only be powered from that battery as well.
3. the fun bit. Car has start/stop but seems once you push the button that stays off. Since I bought the car it was never on. Removing those shunts and the programming will be fun and scary.

Just going away for a couple of weeks end of April and wanted to get my Lithium setup working as I have an inverter and fridge and so on. Hope I get this sorted before.
Will get the VIP membership as hopefully the diagrams show what those fuses are for. I had a look at @Dellmassive but it seems most in here don't have as much "stuff" around the battery as I have.

 

[roadtripper]

This post from @mmi should put you on the right track with VCDS to make the van forget about actively managing the energy in the second battery (point 3).

Post in thread '6.1 Immobiliser/Battery Short Carista Codes'

26 Oct 2023

134410 - activation of the second battery: Open circuit / short circuit to B+

I have a factory fitted leisure battery and installed a Redarc DC-DC

I guess it's because the energy management doesn't see "proper" behaviour of the second battery.

I would try changing status of second battery to "not installed" as below (in central electrics adaptations):

MAS01490-ENG142037-Energy management-Zweitbatterie

not installed

However, Carista probably can't do it. VCDS, OBDeleven or VW ODIS will do.

• mmi

• 

For point 2 I would seriously consider if you need such a large LiFePo battery. Currently you will have the standard AGM charged to around 80% (as it's split charge relay so will be in a bank with the starter - and start stop/smart alternator leaves headroom for regenerative braking) - so with the nominal 50% discharge rule you only have 30% (~30Ah) usable. Replace that with physically the same format LiFePo and a DC-DC charger and you will get 100% charge and can run them down to at least 20% - giving you 80Ah usable - so nearly tripling your usable capacity.

If you can still use the battery mounted fuse box it's a very compact and neat solution. Even if you have bolt type terminals on the new battery you should be able toi get post converters for this very reason.

 

[roadtripper]

Yep towbar prep means you have the module in and the van is configured for it so you can simply plug in a towbar later. I did a thread on the 6.1 towing socket (at least the UK version) here. I know some of the lower 7 pins behave differently for you with electric braking but I think the higher numbered power supply pins are universal. Pin 10 moves to the second battery if you have one under factory wiring - that's what your 60A fuse is doing feeding that strip of green 30A fuses.

Generally speaking the second battery often gets fitted when there is some other high electrical load option specified in the build so the starter is protected. For instance if the electric cool box was ordered, or one of the diesel cabin heaters that can run with ignition off. I would sort of expect to see the higher output alternator there (250 rather than 180)

If the start/stop remembers the state with the ignition off then someone has probably been tinkering. You may find if you look behind the switch a small plug in module that's not VW as that's quite a popular approach...

Don't remove the shunt on the starter unless you enjoy mysterious electrical issues - just remove the one on the second battery and tell the can to only worry about the starter.

 

[Jamesie]

I'm part way through doing exactly what you are looking to do. I've already got the Victron Orion XS 50 DC to DC charger in and working in place of the split charge relay. I've just replaced the mains charger I had which wasn't lithium compatible with a Victron IP67 one. My new Fogstar 100Ah lithium battery, smartshunt and various fuses and connectors are in a box ready to be installed as soon as I get a chance. I would say though, my T6.1 had the VW factory second battery but did not have that shunt device on the neg battery terminal, and didn't have anything on the 100A fuse on the battery fuse box. See pic of how I installed the DC to DC just before I cut out the SCR and transferred connections across. I'm planning to use in-line midi holders / fuses in place of what's on the battery mount fuse box. I'll post more photos of the install when I get the battery installed in the next few days.

 

[Captain Quick]

I tried to figure out what the charging system actually does with a Volt meter in the 12V socket on top of the dash. The charging voltage from the alternator varies depending on the SoC from the batteries when you start the engine (or that's how it looks). In my van it settles on a voltage - even as high as 14.6V - and stays there during that trip. On a next start-up it can sit at 12.5V and stay there as well appearing not to charge at all. I'm still a bit puzzled by the charging behaviour/pattern tbo.
.

@Richard T6.1 AFAIK the two cab sockets in a T6.1 are fed from the leisure battery and not the starter battery so bear that in mind when taking a voltage reading from either of them.

 

[roadtripper]

@Richard T6.1 AFAIK the two cab sockets in a T6.1 are fed from the leisure battery and not the starter battery so bear that in mind when taking a voltage reading from either of them.

It's certainly been confirmed by a couple of folks with Hillside conversions - and those had factory wiring.

Even on the "usual" T6 twin battery wiring it's the gear lever/selector socket that is the starter - the dashtop traditionally is second battery.

@Richard T6.1 the charging behaviour you note is what you'd expect with a smart alternator - they are higher voltage but will only run when needed until the starter battery is around 80% - they will then cycle on and off to maintain the charge in that region unless there is braking, in which case they will engage to do regenerative braking (i.e. they start charging hard to brake the engine and recover energy from the van motion into the battery)

For factory fitted the very basic system doesn't tend to have a shunt on the negative of the second battery and the system will just signal the charge relay to couple the second battery to the starter when sensible and the system will use the starter shunt to monitor.

The more advanced system fitted where there is more load expected and the batteries may end up a very different states of charge there is a shunt on every battery - and then the BCM will take this into account.

In the basic approach when the charge relay engages the second battery (which is likely to be lower state of charge) will draw current from the starter battery to try and equalise the voltage, the alternator will then step in if needed, so essentially the second battery acts as a load.

In the more advanced system the BCM will engage the alternator when any battery needs it, so it's a bit more reactive and puts a bit less wear on the batteries (as there is much less equalisation going on)

In the factory campers the advanced system is further extended in that via the camper control unit you can tell the van you're going to camp and it will then fully charge the batteries for that trip, rather than stopping at around 80% to leave space for regenerative braking.

 

[Captain Quick]

@Jamesie Snap. Like you I’m currently in the process of installing a Victron Orion XS DC-DC charger, Ablemail ABT12-2 maintainer annd a Smart Shunt into my camper. Also, like you I didn’t have any BMS device fitted on the -ve terminal of the auxiliary battery.

I’ve just got to figure out whether I need to take a wire from the small plug that was connected to the split charge relay to the Orion XS (presumably it’s an ignition-on or engine-run signal) or whether I just tape it up and don’t bother connect it.

 

[roadtripper]

I’ve just got to figure out whether I need to take a wire from the small plug that was connected to the split charge relay to the Orion XS (presumably it’s an ignition-on or engine-run signal) or whether I just tape it up and don’t bother connect it.

If you have it fitted you may as well use it - means the BCM will enable the Orion the same way as the old charge relay so you'll gain advantages like it will turn the charger off during heavy starts or during start/stop.

See the wiring notes in "3.10. Engine shutdown detection override wiring" in the install manual.

 

[Richard T6.1]

It's certainly been confirmed by a couple of folks with Hillside conversions - and those had factory wiring.

Even on the "usual" T6 twin battery wiring it's the gear lever/selector socket that is the starter - the dashtop traditionally is second battery.

@Richard T6.1 the charging behaviour you note is what you'd expect with a smart alternator - they are higher voltage but will only run when needed until the starter battery is around 80% - they will then cycle on and off to maintain the charge in that region unless there is braking, in which case they will engage to do regenerative braking (i.e. they start charging hard to brake the engine and recover energy from the van motion into the battery)

For factory fitted the very basic system doesn't tend to have a shunt on the negative of the second battery and the system will just signal the charge relay to couple the second battery to the starter when sensible and the system will use the starter shunt to monitor.

The more advanced system fitted where there is more load expected and the batteries may end up a very different states of charge there is a shunt on every battery - and then the BCM will take this into account.

In the basic approach when the charge relay engages the second battery (which is likely to be lower state of charge) will draw current from the starter battery to try and equalise the voltage, the alternator will then step in if needed, so essentially the second battery acts as a load.

In the more advanced system the BCM will engage the alternator when any battery needs it, so it's a bit more reactive and puts a bit less wear on the batteries (as there is much less equalisation going on)

In the factory campers the advanced system is further extended in that via the camper control unit you can tell the van you're going to camp and it will then fully charge the batteries for that trip, rather than stopping at around 80% to leave space for regenerative braking.

Thank you @roadtripper and @Captain Quick for your replies. Very helpful!

I'm surprised the 12V socket on the dash-top is connected to the second battery. So if I want to keep an eye on the starter battery using a voltmeter, I need to use the socket near the shift lever, correct? The reason I want to keep an eye on it is that we like to use the audio system (the large display unit in the dash) at night for some background music when we're in the van (it's a camper). This drains the starter battery but I'm not sure how much / how fast.

I assumed that the small white boxes on the minus site of the starter and second battery were some sort of shunts. It's VW part 7E0915181 and from what I can find it's referred to as 'Control Unit Battery Monitoring' or similar.

 

[Captain Quick]

Thank you @roadtripper and @Captain Quick for your replies. Very helpful!

I'm surprised the 12V socket on the dash-top is connected to the second battery. So if I want to keep an eye on the starter battery using a voltmeter, I need to use the socket near the shift lever, correct? The reason I want to keep an eye on it is that we like to use the audio system (the large display unit in the dash) at night for some background music when we're in the van (it's a camper). This drains the starter battery but I'm not sure how much / how fast.

I assumed that the small white boxes on the minus site of the starter and second battery were some sort of shunts. It's VW part 7E0915181 and from what I can find it's referred to as 'Control Unit Battery Monitoring' or similar.

View attachment 283416

View attachment 283417

Sadly not; the lower cab socket is also powered from the leisure battery. The rationale is to minimise the risk of draining the starter battery (which only ever gets charged to around 80% with a smart alternator) so you can’t start it. You’d be better off not using the head unit with the engine off and instead powering a portable audio system from the auxiliary battery.

 

[roadtripper]

Definitely fit a secondary audio system for camping, or use a Bluetooth speaker, using the "main" audio system is keeping a considerable amount of the van electronics awake and drawing power.

Keep in mind that the starter battery will also be powering any "normal" services such as the every day courtesy lights and any powered doors.

It's not unusual to camp and find the starter drained to the point it won't start the van as these loads mount up over a couple of days, hence many folks fit something like the Ablemail AMT-12 trickle charger.

A more popular way of keeping an eye on starter batteries is to fit one of the BM2 monitors, they are cheap and accurate enough and log voltage levels. You can query the data from an app on your phone over Bluetooth. It has the advantage of continually logging, which can be an advantage as you see trends.

A quick search of either model number will throw up a number of threads on these options.

And yes the white box that is part of the negative terminal is the shunt - never ever connect a load directly to the negative battery terminal, all loads must go through the shunt at all times.

 

[Captain Quick]

If you have it fitted you may as well use it - means the BCM will enable the Orion the same way as the old charge relay so you'll gain advantages like it will turn the charger off during heavy starts or during start/stop.

See the wiring notes in "3.10. Engine shutdown detection override wiring" in the install manual.

Thanks @roadtripper. That sounds like a useful approach. If I’ve got it right, I’ll need to connect the 12v engine run signal that I believe is on the black wire and connect this to the Remote H terminal with a link wire between the L and H terminal as shown in the LH diagram (Enable charging via an ignition switch i.c.w. remote Enable charging via an ignition switch i.c.w. external on/off option a). As there doesn’t seem to be a connection requirement for the ground wire (the brown wire) on the Orion XS presumably this brown wire can be tied off and left unconnected. Is that correct or is there another way to wire it?

 

[Jamesie]

@Jamesie Snap. Like you I’m currently in the process of installing a Victron Orion XS DC-DC charger, Ablemail ABT12-2 maintainer annd a Smart Shunt into my camper. Also, like you I didn’t have any BMS device fitted on the -ve terminal of the auxiliary battery.

I’ve just got to figure out whether I need to take a wire from the small plug that was connected to the split charge relay to the Orion XS (presumably it’s an ignition-on or engine-run signal) or whether I just tape it up and don’t bother connect it.View attachment 283376View attachment 283377View attachment 283378View attachment 283379

Yes I connected the engine live brown / black small gauge cables that went into the original SCR into the Orion XS. Definitely worth doing. I've now got my Fogstar lithium and Smartshunt in and everything working beautifully.

 

[Richard T6.1]

And yes the white box that is part of the negative terminal is the shunt - never ever connect a load directly to the negative battery terminal, all loads must go through the shunt at all times.

Would that include a BM2 monitor?

 

[RoadRunnerDU]

To get me running for the short term (2 week trip coming up) I left the second battery (factory AGM under seat)in place as my own second battery (lithium) is further back in the car. Connected a DC/DC to the second battery under the seat and connected the ignition wire (black) on the SCR to the DC/DC.
So DC/DC only gets engaged when car is running and the DC/DC just looks like any 35A load on the second battery. In my head that's not different to having a trailer or something connected that draws 35A which the system is designed for. When the ignition is off the DC/DC gets disconnected and the lithium battery is on it's own.
Obviously in the long run I don't want 3 batteries in the car so I have to look into disabling the second factory shunt on the battery under the seat via VCDS.