Leisure battery planning - advice needed

[WillC]

Hi all, I have a 2022 T6.1 with this gubbins under the passenger seat base. From reading various posts on this forum I *think* what I have is:
Big fat red wire, medium red wire and skinny red wires, all connected together. Big fat red wire comes from main battery (positive). The medium and skinny red wires feed the fuse board. The medium red wire looks like it connects to a strip (but not all) of the fuse slots, one of which has a 20A fuse. The skinny red wire connects to a single fuse slot at the top with no obvious other connection.
My understanding of this setup is that it is in place to allow optional factory fitting of an under-seat leisure battery. The big fat red wire could be connected (via a DC-DC converter, Victron etc) to the leisure battery. The medium red wire would then feed off the leisure battery to the fuse board which currently has a single fused connection - which I’m pretty sure powers the 12v fag lighter sockets on the dash (because I blew it with my compressor fridge on holiday and have now broken the 12v socket itself, another story…).
So, I think I could buy a leisure battery and stick it under the seat, connect the big fat red wire to a Victron XS 30A DC-DC converter, connect the output to the leisure battery, then wire outputs via the fuse board for whatever I want to run off it (fridge, lights, USB etc). And all the earth stuff to the bolt under the carpet.
Q1: Is this all correct?!
Q2: Is the big red wire big enough for 30A charging vis the Victron? I am making assumptions here which I’d like to check before immolating myself. It looks pretty fat to me.
Q3: Reading other threads I don’t think I can get the Fogstar 230 under-seat battery to fit easily. So I’m thinking a 105 on its side will do fine. In the event I need more capacity I could always fit another battery in parallel under the drivers seat, but I think 105 should be plenty.
Q4: Finally, presume there’s no reason I cannot move the existing VW electrics (loom/relays? etc) to create space for the battery/Victron etc as long as they are tidy?
Thanks for reading this far, even more thanks if you can confirm/tear apart my thinking before I spend money

 

[WillC]

@Dellmassive sorry to bump this but I’d really appreciate your brief input on this

 

[EAN]

@WillC Your “thinking” is pretty spot on: Suitably fuse the larger positive wire before feeding it into the DC-DC. Suitably fuse the existing mid size wire at the leisure battery before feeding the existing fuse block. You’ll also need to get the right contacts for the fuse block if you want to make use of the unused fuse positions.
Hope that helps.

 

[WillC]

Very. Big thanks.

 

[ginkster]

Hi all, I have a 2022 T6.1 with this gubbins under the passenger seat base. From reading various posts on this forum I *think* what I have is:
Big fat red wire, medium red wire and skinny red wires, all connected together. Big fat red wire comes from main battery (positive). The medium and skinny red wires feed the fuse board. The medium red wire looks like it connects to a strip (but not all) of the fuse slots, one of which has a 20A fuse. The skinny red wire connects to a single fuse slot at the top with no obvious other connection.
My understanding of this setup is that it is in place to allow optional factory fitting of an under-seat leisure battery. The big fat red wire could be connected (via a DC-DC converter, Victron etc) to the leisure battery. The medium red wire would then feed off the leisure battery to the fuse board which currently has a single fused connection - which I’m pretty sure powers the 12v fag lighter sockets on the dash (because I blew it with my compressor fridge on holiday and have now broken the 12v socket itself, another story…).
So, I think I could buy a leisure battery and stick it under the seat, connect the big fat red wire to a Victron XS 30A DC-DC converter, connect the output to the leisure battery, then wire outputs via the fuse board for whatever I want to run off it (fridge, lights, USB etc). And all the earth stuff to the bolt under the carpet.
Q1: Is this all correct?!
Q2: Is the big red wire big enough for 30A charging vis the Victron? I am making assumptions here which I’d like to check before immolating myself. It looks pretty fat to me.
Q3: Reading other threads I don’t think I can get the Fogstar 230 under-seat battery to fit easily. So I’m thinking a 105 on its side will do fine. In the event I need more capacity I could always fit another battery in parallel under the drivers seat, but I think 105 should be plenty.
Q4: Finally, presume there’s no reason I cannot move the existing VW electrics (loom/relays? etc) to create space for the battery/Victron etc as long as they are tidy?
Thanks for reading this far, even more thanks if you can confirm/tear apart my thinking before I spend money

View attachment 304793View attachment 304794

Someone has been tinkering under there as that doesn’t look OEM. At least I hope VW don’t just twist and tape cables together!

In essence what you suggest is fine but I’d want to get a multimeter on there and see exactly what is what. I’d also use a separate fused busbar for my leisure electrics rather than the VW one.

The cable from the SB doesn’t look that thick. Does it have the size stamped on it anywhere? Anything less than 10mm2 could suffer voltage drop issues. 16mm2 is ideal. That cable also needs to be fused at the SB end as per the Victron instructions (they also recommend the cable size). The output from the DC-DC is then best to the fused busbar rather than direct to the LB.

A 105ah Drift fits on its side under the seat. The OEM cables can be tucked to one side. The battery needs to be fused at, or very close to the battery, then cable to the busbar. All your feeds can then be taken off the fused busbar.

Here is a pic of my setup with 105 Drift, 30A Orion, Ablemail AMT12-2 etc under the passenger seat.



You can see the OEM cables tucked away n the top right corner (covered in bubble wrap).

 

[EAN]

That is actually OEM; the 3 cables are ultrasonically welded together and covered with cloth tape.

 

[WillC]

Someone has been tinkering under there as that doesn’t look OEM. At least I hope VW don’t just twist and tape cables together!

In essence what you suggest is fine but I’d want to get a multimeter on there and see exactly what is what. I’d also use a separate fused busbar for my leisure electrics rather than the VW one.

The cable from the SB doesn’t look that thick. Does it have the size stamped on it anywhere? Anything less than 10mm2 could suffer voltage drop issues. 16mm2 is ideal. That cable also needs to be fused at the SB end as per the Victron instructions (they also recommend the cable size). The output from the DC-DC is then best to the fused busbar rather than direct to the LB.

A 105ah Drift fits on its side under the seat. The OEM cables can be tucked to one side. The battery needs to be fused at, or very close to the battery, then cable to the busbar. All your feeds can then be taken off the fused busbar.

Here is a pic of my setup with 105 Drift, 30A Orion, Ablemail AMT12-2 etc under the passenger seat.

View attachment 305013

You can see the OEM cables tucked away n the top right corner (covered in bubble wrap).

Hugely helpful, thank you. Did you fit ply to the seat base innards to use to attach all your gubbins to? Did you use existing holes or make your own? Your setup is exactly what I want.

 

[ginkster]

That is actually OEM; the 3 cables are ultrasonically welded together and covered with cloth tape.

Wow, fair enough. Looks really gash!! The cloth tape isn’t even tidy!

Hugely helpful, thank you. Did you fit ply to the seat base innards to use to attach all your gubbins to? Did you use existing holes or make your own? Your setup is exactly what I want.

Yep, some ply using existing holes to give something to mount to on the sides. That also hold the board that the DC-DC is mounted on. If I was to do it again I’d probably put a couple of extra holes in. There is a great thread on here somewhere showing loads of under seat setups. Worth a quick search.

 

[WillC]

Just checking where you fit the isolator switch (big red knob)? Is this immediately after the leisure battery output fuse, so as to turn off all leisure circuit devices, say for tinkering etc?

 

[ginkster]

Just checking where you fit the isolator switch (big red knob)? Is this immediately after the leisure battery output fuse, so as to turn off all leisure circuit devices, say for tinkering etc?

Yep, after the fuse. Doesn’t need to be close but does need to be before anything else. If you have solar (or fit it in the future) make sure you isolate the panel from the MPPT before isolating the battery. Then vice versa when switching back on.

 

[ben5560]

Did you do this in the end? I am looking to do the same, but also wondering if that cable is actually thick enough to feed a Victron XS 50A DCDC

 

[WillC]

Yes, all worked ok. I ended up putting the battery under the driver’s seat. There was less wiring/relay mess there. I unpicked the fat red wire from the loom between the seats and guided it under the driver’s side. Not sure about the current though. I’ve setup the Victron at 30A, which has been fine.

One word of caution: don’t turn the ignition on with the seat removed: and wire connection (air bag) unclipped - it’ll give you an air bag warning light that doesn’t go when the wire is reclipped. I had to get a Carista to fix that, an expensive irritation.

Very happy with my setup, and big thanks to @ginkster for the help.

 

[ben5560]

Awesome thank you! I have already moved the wires to the drivers side as well, though just now unsure about running the XS 50 at the max 50A, as the wire size is not the required 16mm2, but it seems ok for 30A?

Did you put another fuse on it?

 

[StratosFearXX]

I need to do this, also wondering why one could possibly need to charge at 50amps, surely 30amps is plenty?

 

[WillC]

I fused as per advice above. I used wires rated to way over 50A (70 maybe) in connections under the seat, but left the victron at 30A as (a) I wasn’t sure of the capacity of the main battery feed, (b) couldn’t be arsed changing it, and (c) figured 30A would be plenty. I also wondered if running the victron at max all the time might reduce lifespan, and possibly heat things up a bit. I’ve only a 105Ahr battery so only need 3hrs for a full charge. Maybe 50A makes more sense if you’re carrying something much bigger. I’m happy with my setup.
I used one of those metal brackets and some ply to keep things tidy, plus the foam that came with the battery to prevent it moving. And bundled up the relay to the side. Neat enough.

 

[ben5560]

Was it the same as this one? I might do the same and keep the charger at 30A

 

[WillC]

Looks identical. I removed the cloth on the end of the red wires and snipped off the smaller 2. One fed the 12v fag socket on the dash (don’t need or want this), the other looked to go to the local fuse strip but was unused. I had to carefully cut away the cloth wrap for quite a way up to get enough of the charging wire to reach the driver’s seat.

 

[WillC]

Got this diagram, I think from Wired Campers (useful store for bits). Busbar for common earth was handy. The scribbly ‘FS105’ is the leisure battery.

 

[ben5560]

Thanks mate that's really helpful, I'm going off a similar diagram, but I'll definitely save that!

I also wonder why they ran the wire for the cigarette lighter down there, I wonder if it's a second feed in case you want to run it from a leisure battery, but it's also fed from elsewhere as well?

Also need to try and work out what the little blue and red wire is!

 

[WillC]

Yeah I wondered that too. I guessed it was so you could run 12v stuff of the leisure when parked up, without depleting the main battery. But I’ve learned to hate those 12v fag sockets, they’re not reliable, and get very hot. I’ve used a couple of xt60s for my fridge and fan for hot nights - much better.