2nd battery not charging T6.1 Coast

[Private_Kelly]

A few days ago i was on EHU at Carsington Water CMC. On the 3rd day I had a warning in the CP telling me my 2nd Battery was low.
IMO both batterries should have been cooking (my term for full charge )
RCD was fine and power was getting through to the 230v socket. When i returned home i had a rummage around. The “kettle lead” type fitting was firmly attached to the charger on the 2nd battery ( one under the wardrobe at the back ) and everything looks fine.
So i bought a multitester and checked both batteries for charge. Battery under the seat at front was 13v so fully charged i think. 2nd battery was 11.9v so flat as a pancake. So the CP was reading correctly and not malfunctioning. I suspect the cube fuse may have blown on the 2nd battery but I’m not meddling with anything. It is going to the dealer tomorrow since my van is only 5 months old.
I thought i would just post this to see what you guys think. I’m really not that good with electrical type things.

 

[WelshGas]

A few days ago i was on EHU at Carsington Water CMC. On the 3rd day I had a warning in the CP telling me my 2nd Battery was low.
IMO both batterries should have been cooking (my term for full charge )
RCD was fine and power was getting through to the 230v socket. When i returned home i had a rummage around. The “kettle lead” type fitting was firmly attached to the charger on the 2nd battery ( one under the wardrobe at the back ) and everything looks fine.
So i bought a multitester and checked both batteries for charge. Battery under the seat at front was 13v so fully charged i think. 2nd battery was 11.9v so flat as a pancake. So the CP was reading correctly and not malfunctioning. I suspect the cube fuse may have blown on the 2nd battery but I’m not meddling with anything. It is going to the dealer tomorrow since my van is only 5 months old.
I thought i would just post this to see what you guys think. I’m really not that good with electrical type things.

Did you measure the voltage of the front battery directly or via the leads disconnected from the rear battery?

The reason I ask is that measuring via the leads would rule out a wiring problem and confirm the Cube fuse was responsible.

 

[Private_Kelly]

Hi Welsh Gas
I didn’t disconnect anything. I just measured the battery voltages in situ. I thought it best to try and figure out what was happening so I could give the “experts” at the dealership a heads up.
So would this confirm my blown cube fuse theory. Since all leads were connected. Thanks for your help. I’m a bit worried that the 2nd battery will be buggered now. I’ll certainly keep an eye on it when it has been mended because I doubt if they will replace the battery. I’m in two minds about insisting it should be replaced. It has been discharged for about a week now.

 

[WelshGas]

Hi Welsh Gas
I didn’t disconnect anything. I just measured the battery voltages in situ. I thought it best to try and figure out what was happening so I could give the “experts” at the dealership a heads up.
So would this confirm my blown cube fuse theory. Since all leads were connected. Thanks for your help. I’m a bit worried that the 2nd battery will be buggered now. I’ll certainly keep an eye on it when it has been mended because I doubt if they will replace the battery. I’m in two minds about insisting it should be replaced. It has been discharged for about a week now.

Yes, that would do.
If you had measured the voltage using the Top of the Red pole on the rear battery that would have been the front battery.

 

[Private_Kelly]

OK. That’s great. I think it’s best to try and point the grease monkeys in the right direction. I don’t want to mess with things incase I make it worse. May as well use my warranty.

 

[andyinluton]

It might be a silly question, but how does the rear battery end up being flat? once the fuse has blown its disconnected & cant be supplying power to anything.

 

[yossarian]

Ideally you don't want this fault rectified when the batteries are at very different states of charge. This is because a high current will flow from the high battery to the low battery.

You want to try limit current from each battery to about C/10 as far as possible which is about 7.5A for each battery.

Interesting that the control panel could detect the fault.

Simply replacing the fuse might just blow it again assuming battery internal resistance in the milli ohm range. Try to get VW dealer to charge the battery using a proper modern charger (6 to 12 hours) before fuse replacement.

 

[yossarian]

It might be a silly question, but how does the rear battery end up being flat? once the fuse has blown its disconnected & cant be supplying power to anything.

It may have blown with battery at that stage of charge?

 

[Loz]

11.9v won’t kill the battery it would need to be below 11v on an agm.
the t6.1 has battery monitoring on all batteries, so if the cube fuse is gone the second monitor will see no current flow and will just be counting down.

the cube fuse could have been blown since pdi and the battery in isolation, just slowly loosing voltage over 5 months.

 

[Private_Kelly]

Thanks Loz. I”m getting myself all worked up ‘cos I think my shiny new van is broken and the grease monkeys won’t know what they are doing. I don’t have much trust in garages I’m afraid. I will report back on this thread the outcome anyway. It goes in tomorrow 8th July.

 

[yossarian]

The t6.1 has battery monitoring on all batteries, so if the cube fuse is gone the second monitor will see no current flow and will just be counting down.

Any technical docs available? Might save me a bit of work...

 

[Loz]

Any technical docs available? Might save me a bit of work...

I have just posted a Technical resource of the wiring Diagram for the T6.1 Ocean.
Once it is approved you will be able to download it.

Technical Guide - Camping Electrical T6.1 Ocean (2 battery)

Wiring diagram for T6.1 Ocean

vwcaliforniaclub.com

 

[yossarian]

I have just posted a Technical resource of the wiring Diagram for the T6.1 Ocean.
Once it is approved you will be able to download it.

Technical Guide - Camping Electrical T6.1 Ocean (2 battery)

Wiring diagram for T6.1 Ocean

vwcaliforniaclub.com

That is just great! Thank you so much!

 

[briwy]

Check that it is the correct battery as well. Our leisure batteries never seemed to perform well from new and when I got around to replacing them the second battery in the cupboard was a lead acid one. Five years from new so no joy from the dealer, as usual.

 

[yossarian]

I sat down with some wine and the diagrams...

Diagram 75/3 ... I don't see any high side sense line before S339 (presumably the cube fuse)? Sensing seems to be limited to a low side LIN bus current sensor? Do we think the control panel alerted on uneven current draw from the two batteries?

 

[Loz]

I sat down with some wine and the diagrams...

Diagram 75/3 ... I don't see any high side sense line before S339 (presumably the cube fuse)? Sensing seems to be limited to a low side LIN bus current sensor? Do we think the control panel alerted on uneven current draw from the two batteries?

the cube fuse is directly on the battery post, so yes current sensor is on the negative, the sytem seems to use the old nasa BM2 voltage and current in out calculations to estimate battery capacity and these rely on regular charging to reset the “full” charge point at which they start calculating the capacity. So my guess is with cube fuse possibly open circuit, the unit sees no current in either direction so it just counts down the capacity estimate. They could have easily ran a + sence to the post, but I guess that would have meant a complete redesign of how they use shunt sensors.
Personally I add my own bm2 Bluetooth battery sensors directly across the batteries and ignore the control panel.

 

[yossarian]

Personally I add my own bm2 Bluetooth battery sensors directly across the batteries and ignore the control panel.

Yeah, or something similar that can be integrated into a cohesive system. The vw design is kinda at odds with good results. Any insight into the load management (ie fridge) control?

 

[yossarian]

the cube fuse is directly on the battery post, so yes current sensor is on the negative, the sytem seems to use the old nasa BM2 voltage and current in out calculations to estimate battery capacity and these rely on regular charging to reset the “full” charge point at which they start calculating the capacity. So my guess is with cube fuse possibly open circuit, the unit sees no current in either direction so it just counts down the capacity estimate. They could have easily ran a + sence to the post, but I guess that would have meant a complete redesign of how they use shunt sensors.
Personally I add my own bm2 Bluetooth battery sensors directly across the batteries and ignore the control panel.

It occurs to me that the sensor needs some sort of high side connection (for at least power) to participate on the LIN bus (B561). Will sleep on it.

 

[Private_Kelly]

Well, my van has been at the garage for two days now and it appears that the infernal new and “improved” Control Panel is the issue. Who”d have guessed it? I won’t know the outcome until early next week but suffice it to say that I am not at all impressed with the silly control panel.

 

[yossarian]

Battery under the seat at front was 13v so fully charged i think. 2nd battery was 11.9v

This is inconsistent with a control panel fault.

 

[Private_Kelly]

This is inconsistent with a control panel fault.

 

[yossarian]

If we assume

• your rear battery is not being charged
• your front battery is being charged correctly

the fault is almost certainly one of the items I've indicated on the diagram @Loz kindly provided. Of these, S339 is the most likely culprit. 4 of the items indicated are interconnects or wires, one of them could be loose.

Simply replacing S339 without charging your rear battery will quite likely blow the fuse again. I'll do this calculation to show why at the end. A VW commercial van technician unaware of this might go looking for additional faults instead of charging the battery. The problem is not particularly obvious.

Current calculation:

Assume a delta V between batteries of 1.8V (one full, one empty)
Assume negligible cable resistance.
Assume battery internal resistance of 3 milli Ohms.

Connecting batteries in parallel will give you a theoretical discharge and simultaneous charge current of around 300A (1.8/0.006). Not good for either battery, cables, eyes and the fuses.


Edit: wires interconnects or wires see #23; thanks Loz
front battery

 

[Loz]

Although it’s drawn as a wire, the fuse actually sits on the battery post. Personally I don’t like the design of the battery post fuse holder vw use, I have found a better one.

 

[Private_Kelly]

Getting tired of this now. My van has been gathering dust at the dealer for 10 days now and my issue with the 2nd battery not charging has still not been resolved. The dealer is waiting for VW to come up with a solution. I can’t believe I have paid so much for something and it doesn’t work because the stupid “new and improved“ control panel is a big pile of excrement. I bought a Coast thinking It would be reliable because there was no silly gadgets..oh well

 

[Ferryman]

Sorry to hear this @Coasterman. It look like I have likely the same issue on a coast that is 4 weeks old. I have been away for the last couple of weeks and pretty disappointed with the battery life (2 days or so down to 12.3v with the fridge set to 3 and not really using anything else). I did notice at full charge the voltage of the front battery measured 12.9 or so but the control panel itself was only showing 12.6/12.7 when fully charged so this may be a pointer to the issue.

This thread prompted me to get into the rear battery and I am seeing 12.78v above the cube fuse (front battery probably not quite fully charged) and 12.35v below. I managed to get the battery out and the fuse is blown - probably has been since I collected it I guess. Local VW centre cant look at it for a couple of weeks so I am going to just buy fuse from them and give it a shot as planning to go away again next week. Couple of questions if I may hijack your thread since all the infos here.

I was going to recharge the battery as you suggest @yossarian to reduce the differential a bit. Positive from front battery is removed and taped up. Should I charge via the other side of the shunt to include the battery monitor or directly on the battery itself? and do I need to disconnect the 2 pin connector to get it to recalibrate afterwards? Worried about upsetting the control panel..

Also I am not the best at gauging tightness so any advise on how tight to make the positive when I get the new cube fuse and reconnect front battery as understand they are easy to crush?