Connecting a BM2 to a T6.1 Starter Battery

[Captain Quick]

I'm just about to connect a BM2 battery monitor to the starter battery of my T6.1 and would welcome some input before doing so. My first query, is to decide whether to connect the -ve terminal of the BM2 directly to the battery post or to an earth point on the body. I know the BM2 has a very low current draw (1.5mA) but wondered if by-passing the factory-fitted Battery Monitoring Module that's attached to the -ve post would make any difference. Secondly, as I feel it's good practice to install an inline fuse (2A) and will need to cut one of the connectors off to do so, does the BM2 +ve cable have a Bluetooth antenna running through it or is it solely for power? Thanks.

 

[Dellmassive]

You can wire direct to the battery, but it's best to use a chassis neg. (Especially if the van is not used as a daily driver)

Adding a fuse is a good idea.... The wire has two cores inside, and is for power only.... The BT antenna is integral.

 

[Captain Quick]

You can wire direct to the battery, but it's best to use a chassis neg. (Especially if the van is not used as a daily driver)

Adding a fuse is a good idea.... The wire has two cores inside, and is for power only.... The BT antenna is integral.

That’s the approach I was planning to take. Many thanks for the reassurance and the helpful input on wiring in.

 

[roadtripper]

If you are a 6.1 then you have an easy way to connect it using the plate fuse on the top of the battery and earth it to the bolt on the wing.

Fuse plate:

Earth point (pointed at by multimeter probe):

I would still fuse it with a 2/5 amp fuse as @Dellmassive suggests, you do not want to rely on the 100A+ plate fuse it's just a very handy connection.

 

[Greenmachine]

I’ve been thinking of putting a monitor on too, so very useful info.
Could I also use a terminal on the top plate fuse to wire in a quick connector for my Noco Genius5?

 

[roadtripper]

I’ve been thinking of putting a monitor on too, so very useful info.
Could I also use a terminal on the top plate fuse to wire in a quick connector for my Noco Genius5?

Yep I was planning on doing that on the same two terminals for my CTEK before I did the 12v Trailer Socket EHU instead.

Again I'd advise using a suitable fuse (15A?) and not relying on the plate fuse. For a start it's unlikely to blow until the cable is on fire and if it does they're a custom VW part so likely very spendy.

 

[Greenmachine]

That’s brilliant, thank you. The Noco connection already has an inline fuse, but I’d put one on any monitor as well.
There isn’t a lot of room on the positive post, so this seems like a much better solution. Any reason why the charger and monitor couldn’t go on the same connection?

 

[roadtripper]

Any reason why the charger and monitor couldn’t go on the same connection?

None so long as the crimp connectors don't interfere with each other, being close together there isn't much room to offset them as normal. Unless you have a pressing need to use the other connections I'd just do 1:1 for simplicity.

 

[Captain Quick]

I finally fitted the BM2 battery monitor today. Before fitting it, I added an inline fuse (with 2A fuse) with a couple of butt crimps in the +ve lead to keep everything safe. If anyone else does this job, note that the leads from the BM2 have two small insulated wires running through the outer sheath. These are connected together in the crimp connector.

As you’ll see from the accompanying pictures, I secured the +ve lead to the spare +ve connection terminals (second from right) on top of the battery, and the -ve lead at the battery hold down point which was doubled up with the -ve lead from a CTEK plug. As there wasn’t quite enough room on top of the battery, I secured the BM2 unit to the loom with cable ties. Setting up the app was really easy and took about 2 minutes. The only disappointment was the Bluetooth range; about 9 metres maximum.

After installing, I measured the actual battery voltage with a Fluke meter - it showed 12.89V. The battery voltage displayed in the Battery Monitor app was 12.90V and the voltage reported on my tracker dashboard was 13.2V, so it looks like the BM2 is accurate enough.

Thanks to everyone for their help and advice.