E34: Battery transfer (front to rear seat)

[ktteoh]

folks/shogun/ferret, i did some multimeter tracing and have some ideas. wanted to run it past these forum for feedback and advice.

the 1st. diagram shows what the wiring is right now and the dotted lines are where i'm going to tap into after the transfer.
2nd. diagram show where the 2nd. fuse holder (item in center of the picture).

questions:
1. will the main fuse (FUSE a) in the engine bay take the current load when starting the engine bay (now that the current is coming from the back)?

2. will the wiring harness (3) (the one connecting front to back) take the load?

3. where is the best grounding point in the rear seat - can i use of the rear seat belt bolts?

[Atl530i]

If you do move the battery to the back, make sure it is vented.

[ktteoh]

where is the vent tube/hole normally located? would this apply if i use maintenance-free battery?

[shogun]

Yes, ALLl batteries should be connected to a vent hose, does not matter if maintenance-free or not. Think about toxic gases.
The hose is directly next to the battery usually and goes thru the floor.
Vent hose pic
http://www.bimmerboard.com/forums/posts/182396

and the ground connection is on the E32 usually the seat frame, see here
http://www.ow.no/index.php?option=co...&g2_itemId=132
http://www.ow.no/index.php?option=co...&g2_itemId=136
http://www.ow.no/index.php?option=co...&g2_itemId=140
out of this link
http://www.ow.no/index.php?option=co...d=26&Itemid=13

[shogun]

Even sealed batteries still produce off gasses.
Note: the gray tube is the venting tube in the e34/e32...if it is missing, you can buy plastic tubing from a hardware store or pet store to run from battery thru the floor to vent gases to the exterior

[ktteoh]

shogun, thanks for the links. i'm at work now and will go back and see if i have a hole for the vent tube.

still two questions linger in my head:
1. without me routing another cable, would the existing cable #3 be sufficient to cope with the current draw especially during starting?

2. the way the existing front battery is clamped differs from the picture shown for the rear seat battery - you folks seems to have a metal thingy holding the battery down. the front clamp has a base plate onto which a small plate clamps the base of the battery - could i re-use that in the rear (it may add to the height of the battery - which from what i'm seeing is already pretty tight in the rear seat) - thoughts?

[Ferret]

shogun, thanks for the links. i'm at work now and will go back and see if i have a hole for the vent tube.

still two questions linger in my head:
1. without me routing another cable, would the existing cable #3 be sufficient to cope with the current draw especially during starting?

2. the way the existing front battery is clamped differs from the picture shown for the rear seat battery - you folks seems to have a metal thingy holding the battery down. the front clamp has a base plate onto which a small plate clamps the base of the battery - could i re-use that in the rear (it may add to the height of the battery - which from what i'm seeing is already pretty tight in the rear seat) - thoughts?

From what I remember... the battery on the 525i didnt have an up-and-over type clamp, it just had a foot clamp which should transfer quite happily to under the rear seat.

Also from what I remember, the battery positive clamp should just unbolt from the fuse holder under the bonnet/hood and quite happily bolt into the fuse holder under the rear seats.

I think my current one as a diesel is radically different though, will snap a shot later.

[moots]

ktteoh,

the basic components that run off the +ve terminal are :
1. the ecu and other elect components - via smaller sized wire
2. the starter motor - via thick hi gauge wire for hi current

so to answer yr Q 1 - no.what you currently have,connected to yr battery,needs to be duplicated when u relocate the batt.

Q2 - we don;t have the metal case which houses the battery.but if you notice,on the floor of the batt compartment under the seat,there is a lip to hold the battery,similar to the one on your battery tray.i have thought about yr project but i think there must be a reason why the engineers put the battery in the front on our model.or maybe on hindsight they decided that under seat location is better....go figure...

yes perhaps the batt will last longer located away from the engine heat but i really am not keen to route a thick gauge wire from the rear seat....tell us how it goes shud u decide to proceed.....me Malaysian too....he he

[Ferret]

Kttroh, snap us a photo of the +ve batt terminal and the leads coming out of it plus where they anchor... I was sure my 525i only had small leads coming off the batt to the fuse point.

I may have a warped memory though as there seems to be some question over this now...

[ktteoh]

ferret, ok. i will snap that when i get home. meanwhile i would still like to know if the wire no (3) - connecting fuse A to fuse B - can cope with the current load demand of the starter motor.

it looks like a heavy gauge wire but the one (at the front battery) to the starter motor is "thicker".

thoughts?