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?

http://lh5.google.com/MickeyTeoh/RohbTLa0l4I/AAAAAAAAAT8/5xBZfgSAyd8/s400/BMW_Battery.jpg

http://lh6.google.com/MickeyTeoh/RoPGtra0lzI/AAAAAAAAATM/AkeiqrPKSSE/s400/BMW%20E34%20Back%20Seat%20004.jpg

[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=com_gallery2&Itemid=18&g2_itemId=132
http://www.ow.no/index.php?option=com_gallery2&Itemid=18&g2_itemId=136
http://www.ow.no/index.php?option=com_gallery2&Itemid=18&g2_itemId=140
out of this link
http://www.ow.no/index.php?option=com_content&task=view&id=26&Itemid=13

[shogun]

http://memimage.cardomain.net/member_images/7/web/739000-739999/739005_79_full.jpg
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?

[ktteoh]

moots, there is already an existing heavy gauge wire - no (3) on my diagram - connecting the fuse A and fuse B - albeit it is not as thick vs the ones to the starter motor from the front battery terminal.


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

[ktteoh]

ferret, here's the existing front engine +ve connections and the front main fuse:

http://lh3.google.com/MickeyTeoh/RojDUra0l7I/AAAAAAAAAUU/sUo3LomhsZg/s800/BMW%20E34%20Front%20Fuse%20006.jpg

http://lh3.google.com/MickeyTeoh/RojDUra0l5I/AAAAAAAAAUE/GMh8fMnt2h8/s800/BMW%20E34%20Front%20Fuse%20004.jpg


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.

[Ferret]

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?

Hurr, it'd probably kick the engine over happily from a short burst. But, more than a few seconds cranking would cause that wire to heat up badly, and it runs under carpet. I'd hit a scrap yard and rip out the battery wire off something with an underseat battery rather than risk pushing that...

I had a look at my diesel one while I was just out doing the rear brakes, and it's around the 3/4" thick mark. (Though, diesels do take a hell of a lot of current to start and its got a massive battery.)

[Ross]

Yep, that little wire won't handle the starter load. 4 gauge is what you need.

[ktteoh]

what is a 4 gauge - would a battery cable that handles 60A do? or 100A?


Yep, that little wire won't handle the starter load. 4 gauge is what you need.

[BIGRED]

Seems like a lot of work at a fair cost to accomplish something that a month later will be forgotten (of course that is said without having an understanding of what you are experiencing).

Curious as to why this seems to be an important modification? I noted a mention of hot temperatures. Is it killing batteries that warranty won't cover or at such a rate that its a pain?

For myself, I would have preferred to have the battery located under the hood. Not all that keen on having something with acid sitting under my kids. I know of a couple of battery explosions, but trust that BMW knows whats best.

Regards
Don

[Ferret]

Seems like a lot of work at a fair cost to accomplish something that a month later will be forgotten (of course that is said without having an understanding of what you are experiencing).

Curious as to why this seems to be an important modification? I noted a mention of hot temperatures. Is it killing batteries that warranty won't cover or at such a rate that its a pain?

For myself, I would have preferred to have the battery located under the hood. Not all that keen on having something with acid sitting under my kids. I know of a couple of battery explosions, but trust that BMW knows whats best.

Regards
Don

Hmm, as well I've just remembered that the battery should have a heat shield up one side of it as standard fit on an M50 bay...?

Yours gone missing somewhere ktteoh?

[ktteoh]

ferret, the ones in malaysian market somehow doesn't come with the head shield (for the exhaust side) - i asked before. anyway can send me a picture of what the heat shield looks like?

for the wire (3), i notice that fuse B is rated at 80A - would that indicate that wire (3) is sufficient for 80A - if so would 80A be sufficient for all electrical load during starting.



Hmm, as well I've just remembered that the battery should have a heat shield up one side of it as standard fit on an M50 bay...?

Yours gone missing somewhere ktteoh?

[shogun]

item 14?
http://www.realoem.com/bmw/showparts.do?model=HB51&mospid=47370&btnr=61_0660&hg=61&fg=30&hl=92
here is all I found with the search for heat
http://www.realoem.com/bmw/partsearch.do?keywords=heat&model=HB51&mospid=47370

[ktteoh]

shogun, what are items 7, 12 & 14 - it is not in the description? i think i'm missing those items in my current setup.


item 14?
http://www.realoem.com/bmw/showparts.do?model=HB51&mospid=47370&btnr=61_0660&hg=61&fg=30&hl=92
here is all I found with the search for heat
http://www.realoem.com/bmw/partsearch.do?keywords=heat&model=HB51&mospid=47370

[shogun]

I do not know where they are in your car and if they should be there, justed wanted to show that heat shield.

[moots]

QUOTE: ferret, the ones in malaysian market somehow doesn't come with the head shield (for the exhaust side) :UNQUOTE

then you must be missing this on your ride as i still have the heatshield fitted as OEM,secured by 2 screws.this shields the battery from the exhaust manifold.and if you still intend to go ahead with this mod,you will have to route the same gauge cable that is used at the current setup.

[bones]

whats up grand master, iv'e got a 1989 525I and just completed the swap.its a breeze.you allready have the 4 guage starter wire and the 10 guage accessory wire under the rear seat.i simply cut the battery connector off the starter cable under the hood,crimp or solder a 4 guage copper lug with 1/4 inch mounting hole onto the big wire and do the same on the 10 guage wire.now using the existing shunt connector box mount the starter wire to the big wire side and the 10 guage wire to the other side of the bus.do the same thing under the rear seat,but you will only have one positive battery wire connection in this shunt connector box.make sure you are attaching the battery wire to the bus side.there is a spare screw mounting position in both of these shunt boxes but without the bus bar you wont have any contact.the existing 3/8 lug ground under the seat will work fine,mount youre negative battery terminal there and youre done.i even used the original battery holdown bracket from under the hood to secure the battery,youll have to flatten it out and drill a mounting hole further back to extend it to the battery.THE MOST IMPORTANT THING TO REMEMBER IS THAT YOU ARE CARRYING THE CURRENT FARTHER TO THE LOAD,DONT DO ANY MARATHON STARTER CYCLES,IF THE CAR WONT START WITHIN A 15 SECOND DUTY CYCLE STOP CRANKING AND ALLOW THE CIRCUIT AND STARTER TO COOL FOR AT LEAST 3 MINUTES BEFORE YOU TRY AGAIN.ALSO DONT HOLD THE KEY ON WITH A LOW BATTERY SLOW STARTER,THIS WILL ALSO BUILD ALOT OF HEAT REALLY FAST. Bones.

[bones]

whats up grand master, iv'e got a 1989 525I and just completed the swap.its a breeze.you allready have the 4 guage starter wire and the 10 guage accessory wire under the rear seat.i simply cut the battery connector off the starter cable under the hood,crimp or solder a 4 guage copper lug with 1/4 inch mounting hole onto the big wire and do the same on the 10 guage wire.now using the existing shunt connector box mount the starter wire to the big wire side and the 10 guage wire to the other side of the bus.do the same thing under the rear seat,but you will only have one positive battery wire connection in this shunt connector box.make sure you are attaching the battery wire to the bus side.there is a spare screw mounting position in both of these shunt boxes but without the bus bar you wont have any contact.the existing 3/8 lug ground under the seat will work fine,mount youre negative battery terminal there and youre done.i even used the original battery holdown bracket from under the hood to secure the battery,youll have to flatten it out and drill a mounting hole further back to extend it to the battery.THE MOST IMPORTANT THING TO REMEMBER IS THAT YOU ARE CARRYING THE CURRENT FARTHER TO THE LOAD,DONT DO ANY MARATHON STARTER CYCLES,IF THE CAR WONT START WITHIN A 15 SECOND DUTY CYCLE STOP CRANKING AND ALLOW THE CIRCUIT AND STARTER TO COOL FOR AT LEAST 3 MINUTES BEFORE YOU TRY AGAIN.ALSO DONT HOLD THE KEY ON WITH A LOW BATTERY SLOW STARTER,THIS WILL ALSO BUILD ALOT OF HEAT REALLY FAST. Bones.

[ktteoh]

bones, do you have some pictures of what you have done or modify for your case?

[ktteoh]

bones, some questions i have:

1. i have a black fuse box (call it fuse_B = your shunt connector) under the rear seat - refer picture 1. however it's just a single link - unlike the one in the engine bay which is dual link. there is black wire coming into fuse_B and a red wire coming out of it. using a multimeter i verified that the black wire is connected to the front shunt box (fuse_A).
- is the red wire 10 gauge and the black wire 4 gauge?

2. about your caveat "DONT DO ANY MARATHON STARTER..." - does this apply to cars where the battery is installed under the rear seat by factory default - are they having a thicker wire?

3. the 3rd. picture shows what i believe is the relationship between the 2 shunt boxes (rear seat and front engine) - is it about right? the dotted lines show where the 'moved' battery should be inserted.

http://lh6.google.com/MickeyTeoh/RoPGtra0lzI/AAAAAAAAATM/AkeiqrPKSSE/s400/BMW%20E34%20Back%20Seat%20004.jpg

http://lh3.google.com/MickeyTeoh/RojDUra0l5I/AAAAAAAAAUE/GMh8fMnt2h8/s400/BMW%20E34%20Front%20Fuse%20004.jpg

http://lh5.google.com/MickeyTeoh/RohbTLa0l4I/AAAAAAAAAT8/5xBZfgSAyd8/s400/BMW_Battery.jpg

[bones]

kitteoh,sorry for the delay on the response.under rear seat issue,the main thing to accomplish under the rear seat is to put the fuseable link in between the battery connection and the two outbound circuits,ie red and black wires.the black wire will carry your starter circuit current and the red wire will carry chassis power or accessory circuits.simply make sure that when you connect your battery under the rear seat that there are no other wires attached on the same side of the fusible link that your battery connection is on.your under hood connections look correctly terminated from a fused standpoint.in reguards to the starter duty cycle times,im simply limiting the potential for murphys law to occur.you know "anything that can happen might happen" ive changed the phrase a little to suit my needs since im faced with mechanical challenges in aviation on a daily basis.

[bones]

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?

http://lh5.google.com/MickeyTeoh/RohbTLa0l4I/AAAAAAAAAT8/5xBZfgSAyd8/s400/BMW_Battery.jpg

http://lh6.google.com/MickeyTeoh/RoPGtra0lzI/AAAAAAAAATM/AkeiqrPKSSE/s400/BMW%20E34%20Back%20Seat%20004.jpg
i keep looking at the photos of your wiring under the back seat and im not seeing the 4 guage black wire thats in my 89 525I.your black wire is a larger guage than the red correct?

[ktteoh]

yes the black wire is thicker than the red one - it's hidden under the mass of brown (earth) wires.

you can see the black wire coming out on the 2nd. picture (shunt connector in the engine bay) - it's the one having the fusible link across.


i keep looking at the photos of your wiring under the back seat and im not seeing the 4 guage black wire thats in my 89 525I.your black wire is a larger guage than the red correct?

[bones]

kitteoh,this might be misswired in the engine compartment.the fuseible link should protect chassis electrical from the starter circuit.the fuseible link cant be inline with the starter.it provides a fused conducter for all other circuits to draw from.i would connect the rear battery wire and the engine compartment starter wire using one screw on the bus bar.mount one side of the fuse next to it,then mount your smaller gauge wire on the other side of the fuse and that should be perfect.

[ericbendler]

I have been reviewing this strand to learn a little about setting up a dual battery system. Instead of relocating, I and going to put a PAC-200 (200 amp relay) on and charge 2 batteries. I have a pretty strong mobile electronics install.

When my audio/video system asks for a lot of current I really get a lot of dimming out of my headlights.

I am hoping the extra reserve will allow me to get the current I need of the 140 alt that I have in there. I think it's the Bosch. I'll check.

I hope someone wants to shoot holes through my plan. Again...one battery up front, one (low maintinance) under the rear passenger.

Here is a link to the PAC-200. (http://cgi.ebay.com/ebaymotors/PAC-200-PAC200-Amp-High-Current-Battery-Isolator-Relay_W0QQcmdZViewItemQQcategoryZ33574QQihZ007QQit emZ170128104998QQrdZ1QQsspagenameZWDVW) Planning on using 2-4 AWG for the whole install. Once I have it done I will put up some pics.