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Figured I'd start a new thread for this, as it is neither M57 engine conversion related or really relevant to anything else I'm doing.

As some of you might know, I've had a split charge setup for a few years now after Marty FINALLY convinced me to get around to it. It is mainly for running my Waeco compressor fridge for longer periods of time without worrying about the starting battery. It has never been to combat any battery drain issues or anything janky like that - in fact it is isolated whenever the engine isn't running through a VSR.

It occurred to me though, now that I no longer need the LPG tank, I can remove said tank and refit a spare tyre. But then I got to thinking a bit more... I've never had a spare wheel, and have a few cans of goop and my TMax compressor should it come to it. So... why don't I make use of the space for something else?

The plan is to build a custom frame to live in the wheel well area that will hold not one but two 019 sized 110ah leisure / deep cycle batteries, plus a pure sine wave inverter. The split charge kit will also be relocated to this area too. Outlets for 12v will be mounted into the load space in a convenient spot, one for the fridge, and one for a 50amp take off - both using Anderson SB50 connectors, because I like them. A 230v outlet will also be present, and I have plans for another one elsewhere down the line.

First things first... the LPG tank needed to come out. Mine had been held in with two massive bolts through to a steel plate underneath, and then expanding foam was used to stick it down... made removing it a bit of a tit.

You can see the semi-temporary arrangement I had for securing the current battery. The straps are held to the body - they're not just wrapped around it :)

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Ideally I need to cut a section of the floor out and sort a new plate to deal with the mangled holes left from the LPG install, along with a drain of some kind.

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This was oddly satisfying to clean up.

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I figured rather than try and make a battery tray specifically fit the frame I make to bolt into the wheel well, I'd start with a tray alone and then build the framework and mountings to fit the floor of the wheel well second.

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Yes - I am aware the tie down bars don't allow for batteries of different heights. Conveniently... the two new batteries will be a matched pair and thus the same height :)

The rods screw into captive nuts on the tray, and I will likely weld the top nuts to the rods making them long bolts effectively - or something like that. I've yet to add a few bits of flat bar into the base to support the underside of the batteries a bit more - will do that before paint.

I'm happy with how its come out. Next is to look at the top bit of framework that will support the actual load space floor panel, and tie it in with the battery tray.

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Looks like an interesting project, I've been thinking of adding a split charge system to mine and utilising the cavernous area under the floor..

Like yours mine is full of tank, so that'll have to go!

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Do it how plod did it on mine, put the battery on the RHS of the boot. All you've got there is the satnav that is so many years out of date as to be about useless anyway.

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That looks great, and is a good use for the space as well!
I would suggest fitting Gel or AGM SVRLA type batteries (Sealed Valve Regulated Lead Acid) as there will
be hydrogen, oxygen, and sulfur dioxide evolved in the normal course of charging.
These can be annoying at the least, and explosive at worst......
If you do wind up with flooded type batteries, possibly you could work out a way to vent the compartment out the
large hole in the bottom?
Also, if you use flooded batteries, it would be a bad idea to place the inverter in with them. Electronics do not like
battery gasses, and the inverter is a source of ignition as well. I have seen both corroded to death electronics
as well as batteries which have blown their tops off due to an inverter or a solar charge controller being in
the same box as the flooded batteries. Sealed is not nearly as big an issue, but still not "Best Practice" to put the electronics too near.
Putting the inverter where your battery is now would be a good solution as it will be cool and dry there. Safer too!
Cheers!

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I've known a couple of cars with wet batteries in enclosed areas (one a Mazda Eunos) to have pipe connected to either end of the battery and then a tube (looked like windscreen washer tube in size and appearance) running down to vent under the car. Presumably for the reasons you mention above.

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Our works vehicles had auxiliary batteries in an airtight box with a tube run through a hole in the floor to vent any gases out. Something like this https://www.ebay.co.uk/itm/302537828590

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E46 Touring has the battery in the RH of the boot, with a vent.
useless fact #2134

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Yeah I forgot to say - both batteries will have their vents connected to tubes that will run out through the floor pan :)

Seems to be the usual way for cars with batteries within the vehicle interior, and caravans etc.

I hadn't really thought about the inverter being in there with potential gas buildup - but then it shouldn't really happen with them venting to outside so I think for now I will keep with that plan. The inverter itself is a fairly large unit despite its 700w output. It also makes an irritating whining noise while operating, so the more buried under the floor it can be the better.

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Well, the frame is bolted in and isn't going anywhere :)

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Need the batteries I want to order to come back into stock, but here it is with one sat in place and the inverter bolted in for now. Four of the top tabs are bolted into rivnuts into the body, and the bar along the bottom under the battery tray bolts through the floor. The weight of things alone would keep it in place obviously - but in the event of a rollover or something like that, I'd rather it stayed in place. If the rivnuts alone didn't hold it, the bar under the floor certainly will. This all stops it shifting about too.

Quite happy with finding this fusebox too - it will deal with most things under here with its selection of maxi fuses and two midi/strip fuses - one for the inverter, one for the split charge input.

Next up will be starting the wiring. To get the various cables I want to the right hand side of the loadspace, some IP rated flexible conduits will be used to go out through the side of the wheel well and back in behind the trim under the car - there is just too much I want to get it safely under the carpet.

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Very very neat, I'm impressed and if I wasn't running on LPG I'd be jealous!

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Thanks :)

This is definitely a perk of having gone diesel/not having LPG - there is a LOT of space under the floor that can be made use of.

Took a lot longer than I expected, but the split charge cable has been rerun from the passenger side to the drivers side and is now in the wheel well ready to connect up to the VSR. Just need to make a bracket to hold that this evening.

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Just waiting on batteries and some other supplies to turn up before I can really continue further - so thought I'd sort the loadspace floor panel.

Notched the areas where the frame tabs were rising it up, and it now sits nice and flat again, and is supported by the frame underneath in the middle where it used to sit on the wheel/tank etc.

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Nice to have the area on the left side freed up again.

The plan is to use the trims from a sat-nav optioned P38 on the right side, and mount various outlets and switchgear there. One SB50 fused at 50 amps for high current 12v devices like my tyre compressor, or a take off to use for whatever else. Another usual 12v outlet wired always-on from the batteries at 20 amps. A second SB50 that will be mounted underneath the trim hidden for the fridge, with a switch to suit. And finally somewhere in there, the usual 3 pin UK mains socket, along with an inverter on/off control and its status panel thing. Fire extinguisher will move to the left side in the same place as it is now.

I think that will take up minimal space and look as OEM as possible. I know the subwoofer looks out of place really, but the point of it is a) its farrrrr better than the stock offering, and its on a speakon connector with the amp mounted where a DSP amp would live - so it is removable to give me that space back very easily, which I often do.

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Hmm, mine has two rear facing seats, which never get used, so them out along with the old CD player bit, there's a fair bit more room.

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Looks really good!
This is basically exactly what I have in mind for mine (someday in the future). I was thinking of cutting out the whole spare wheel well and welding in a new box, which will allow me to make it more rectangular as opposed to the rounded current shape. Your frame idea is making me rethink my plan.

What are your plans with the space on the left of the batteries? I'd like to add in a reserve fuel tank as well as a water tank somewhere under the floor too, with the batteries. I suspect that in my mind there is more space down there than there actually is.

Nice work. Really cool fuse/relay box too!

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Following with interest ... great idea ot use the sat nav shelf for whatever else comes handy!

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Thanks :)

I've seen the wheel well cut out for LPG installations, but I wasn't that brave and it seemed like more effort than it was worth in my case - but its certainly an option. Having a level base would make it a lot easier to mount things for sure!

The space on the left is reserved for storage of stuff - I was thinking of putting a divide below the 'vertical' brace, although I have changed my plan slightly, and am going to make some guides that hold a storage box in place instead. I've gone that route because actually, there is a nice space under the inverter cradle that my big tow rope sides in nicely, and my tyre compressor tucks in another spot etc. I'll take a picture of what I mean later - my batteries etc turn up today so I'm hoping to get those in and clamped down, and maybe finish the wiring under here.

I've also had another plan with regards to the outlets above the floor in the load space - I may now forego the sat nav trim and build something else... but Fusion 360 let me down yesterday so I need to mock that up again now!

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New batteries are in and the cabling is almost finished up. Few more to run in, but it won't look much different from how it is now:

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Few bits and pieces now living under here too. Tow rope hides under the inverter, accessible by lifting the grey box out which has the jump leads, shackles and goop cans etc in it. Tyre compressor tucked next to that. Gets all those bits out from the load space and they're not hard to get at when needed.

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Next job is the switch/socket panel and custom inverter control. Might? get that somewhat done by the weekend.

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Just needs a full-on set of amateur radios and a big fridge!

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Looks very neat, I like it! Definitely making me rethink my plan for the wheel well.

What is the unit on the right with the blue and white label/sticker? I assume it is the split charge unit?

Any plans to add solar in future?

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Fridge you say? Check ;) Had a Waeco compressor fridge for years - recently got a second slightly different dimension one (right), which is the one that will end up living in the back:

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Yes - the thing to the right of the batteries is a 140amp rated voltage sensing relay essentially. As the alternators as standard fit to the P38 and (mostly) on my M57 engine are 'standard' - in that they always aim to wang out 14+ volts, I don't need a fancy DC-DC charger like you would with a modern smart charging thing. The M57 alternator is ECU controlled, but it isn't deactivated for fuel saving or anything like that.

The VSR I'm using is a simple automatic unit with no option for manual bypassing - the little white 2 pin connector currently looped around the frame is a disconnect I put in its ground connection, so I can disable it if I want to - eg if I have the starter battery connected to my Ctek smart charger, that stops the VSR kicking in and also charging the two rear batteries. That might seem beneficial to charge all three - but the VSR itself draws some current, enough that can confuse a smart charger.

I have considered other options, or even fitting a multi-position rotary selector often found in Marine installations that would let me isolate, join or connect via the existing VSR etc - might look at that one day. The front to back cable is fused at 100 amps either end, so it wouldn't let me start the engine with a dead starting battery, but I could manually link them and let it self-charge for a bit and then attempt a start if I really had to. Alternatively, currently I'd get my Anderson jump leads and the car would give itself a reach around effectively ;)

If I ever end up with roof bars and a rack, I'd consider a solar panel with an MPPT charger for sure.