Author Topic: moving battery to boot  (Read 8332 times)

Offline hayesey

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moving battery to boot
« on: April 01, 2008, 11:54:32 am »
Has anyone done this?  Going to do it to my G40 soon and just wondered if anyone had any tips or the best way of wiring things up?  

So far I'm thinking that I should run a single thick cable from the battery +'ve to a connector block where the battery used to be.  Then crimp big rings onto where the original battery terminals were, the old +'ve goes to the connector block to the cable to the boot, the old earth goes to the stud on the shell where the original strap used to connect to.  Then run a strap from the battery -'ve in the boot to a decent point to the shell nearby it.  I'm also thinking that an in-line fuse in the long +'ve cable as close as possible to the battery terminal is essential.  

What size cable should I use?  Should it be thicker than the current starter cable due to it's length?  

What have people used to mount the battery?  I was thinking of buying either this:

http://cgi.ebay.co.uk/Battery-tray_W0QQitemZ270223945094QQcmdZViewItem?hash=item270223945094

or a gucci one like this:

http://cgi.ebay.co.uk/Alloy-Battery-Tray-Escort-Rally-Kit-Car-Mini-Subaru_W0QQitemZ280211727059QQcmdZViewItem?hash=item280211727059

Offline Andy

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Re: moving battery to boot
« Reply #1 on: April 01, 2008, 02:07:45 pm »
Sounds like the right way to do it. Have you got a Vehicle Wiring Products catalogue? They have all you need...

I'd use their PJ1 junction box for joining the positive battery cables in the stock battery location. Either that or join them through a battery isolator switch? The junction box seems preferable though, as you're protecting positive connectors that may otherwise be exposed.

Fusing at the battery terminal is a good idea in my eyes as you're running a lengthy cable through the cabin in a non-OEM location and can't be sure what might happen in a crash situation. At least VW crash-tested the car with the OEM setup. I'd go for a Littelfuse Mega fuseholder, and probably a 150A fuse - I know from experience that they blow sufficiently quickly from a dead-short, and I think should carry the cranking currents okay.

Make sure that wherever you pass cables through the bulkhead that they're suitably protected by a cable grommet or similar.

As for cable size, I'd go for 25mm² or larger - though 40mm² might be overkill!

Offline hayesey

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Re: Re: moving battery to boot
« Reply #2 on: April 01, 2008, 02:23:27 pm »
cheers dude, yeah I do have a VWP catalog and it's what I was looking at for getting the bits for this.  

I'll look for 25-30mm2 cable.

Not bothered about having a cut-off switch, don't want to look too much like some kind of "race-spec" spas.

Offline giorgio

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Re: Re: Re: moving battery to boot
« Reply #3 on: April 02, 2008, 10:59:43 am »
I just won 11m of battery cable from a BMW Mini to do this. If I end up using half then you can have the other half.

You shouldn't add weight behind the axel as this will increase the pendulum effect. The ideal place to have the CoG is dead centre with the wheels being the end of mass. I am putting my battery passenger side just infront of the rear axel.

As for wiring - Andy has pretty much got it spot on.

Try to find a BMW in a breakers yard as they have been running the battery in the rear for a while. The wire off that is plenty good enough.

As for battery trays - I read that you cant have a battery open inside a car as they give off a gas and they should really be vented to outside. And we actually need a battery box.


Will try and dig up a thread of Club GTi

Offline hayesey

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Re: Re: Re: Re: moving battery to boot
« Reply #4 on: April 02, 2008, 11:32:05 am »
it depends what type of battery you have, mine is a sealed one so I think I'm right in saying there should be no fumes coming out of it?  Definitely a good point though and I'll make sure before I buy a tray/box etc...

If you do have enough cable left over let me know and I'll send you some beer tokens for it.

Offline giorgio

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Re: Re: Re: Re: Re: moving battery to boot
« Reply #5 on: April 02, 2008, 01:16:41 pm »
hayesey - have you got a racing battery or just a normal one?
If I don't go racing then I am tempted to get a derv battery to help my car crank over.

Offline Andy

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Re: Re: Re: Re: Re: Re: moving battery to boot
« Reply #6 on: April 02, 2008, 02:37:45 pm »
[quote pid=633 author=giorgio date=1207130383]
As for wiring - Andy has pretty much got it spot on.[/quote]
My employer would be glad to know I'm pretty much not a complete retard...

Hayesey - even if it's a fully sealed battery I'd stick it in a proper battery box. Will make things a lot easier come MOT-time if the tester's a bit unsure. A lot of our prototypes run their LV battery in the boot with a plastic box - more for the electrical insulation rather than fumes.

Not too sure about regulations on fumes from batteries, obviously it'll depend on what battery you're using as to whether the fumes from it are harmful or not - for example the HV battery used in the Toyota Pious can apparently give off some stench according to the user manual, but they'd never get it homologated if it was in any way harmful. The Pious HV battery is vented in to the cabin, and not outside.

I don't know how BMW do their harnessing from the boot, but the vehicles I've worked on with LV batteries in the rear still tended to have the main fusebox under the bonnet - so had a single positive cable run to the fusebox in the front of the car. If that's the case with the BMW, then you can be confident that the cable can carry the current.

Giorgio - I think you'll find with a healthy Polo-sized battery it's the starter motor that's limiting your cranking torque & speed. A larger capacity battery won't gain you a single thing. Even with a 'charger creating extra drag and 9:1 CR 1341cc pistons you've not got an engine that's difficult to crank. The Mk3 Polo 1.4 diesel is much much higher CR, and they don't need massive batteries.
« Last Edit: April 02, 2008, 02:52:05 pm by Andy »

Offline DKnight

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Re: Re: Re: Re: Re: Re: Re: moving battery to boot
« Reply #7 on: April 02, 2008, 05:55:23 pm »
what a great idea, let me see how it goes, i may do it as i hate my battery where it is lol

Offline Andy

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Re: Re: Re: Re: Re: Re: Re: Re: moving battery to boot
« Reply #8 on: April 02, 2008, 05:58:19 pm »
I might have to do it because I cba fixing my battery clamp and minging battery tray.
« Last Edit: April 02, 2008, 05:58:33 pm by Andy »

Offline giorgio

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Re: Re: Re: Re: Re: Re: Re: Re: Re: moving battery to boot
« Reply #9 on: April 02, 2008, 07:20:38 pm »
Inspired by this morning conversation I got cracking.

I used the hole on the bulk head to the right of the heater matrix. It comes out just behind where the glovebox would be. From there it can run along the exhaust tunnel and into the back.

Also recommend pulling the starter cable +ive towards the passenger side to tidy things up abit.

Hayesey - I won 11ft not 11m so there wont be enough to go twice. Still got a few foot if you want it but I cant see it being much use

Offline hayesey

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Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: moving battery to boot
« Reply #10 on: April 02, 2008, 08:26:22 pm »
oh OK, no problem.  I assume when you say "won" you got it on fleabay and not some weird competition? :)

I'll have a butchers on there myself, to be honest the cable from VWP isn't exactly expensive anyway.

Offline giorgio

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Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: moving battery to boot
« Reply #11 on: April 02, 2008, 08:44:57 pm »
I won it in a tightrope walking contest. If you made it to the other side without plummeting to a messy death then you got to keep the rope. Turns out its made from battery cable. Crazy stuff

Off Topic - what are the smileys about. none of them make any sense. What is this -  >_<

Offline hayesey

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Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: moving battery to boot
« Reply #12 on: April 02, 2008, 08:48:02 pm »
[quote pid=610 author=Andy date=1207055265]
As for cable size, I'd go for 25mm² or larger - though 40mm² might be overkill![/quote]

Going to go for 25mm² cable, VWP says it's rated to 170amps so the fuse will blow before the cable reaches it's limits.  doesn't seem any point going up to 40mm².

Offline giorgio

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Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: moving battery to boot
« Reply #13 on: April 03, 2008, 02:07:16 pm »
managed to wire it all up and now my car doesn't want to crank over. Is it possible my immobiliser has got the hump?

Tried a spare starter motor but this didn't fix it. The alarm and remote c/l works fine so I am all out of ideas.

Offline hayesey

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getting any voltage at the starter when trying to crank?