I was hoping someone with more knoledge then me on circuits and reolcating a battery can help me.

So ive already got the whole thing done. The battery is in the trunk I have 0 gauge wire going from the positive end to the fuse panel and then form the fuse panel to the starter cable I used the oem cable taht went from the fuse box to the battery.

Then for ground i have 2 gauge wire going from the battery to this ground plate that is in the left side of the trunk. There was alrady a bunch of grounds there so i figured it would be a good place to put it. I also ran a 0 gauge wire from the battery ground to the engine block i bolted it to one of the header bolts.

Now the wierdest thing happens. When i start the car usually it will hesitate alot, like the starter will wind a few times before it starts, where normally it starts without even winding once. Someitmes it doesnt start, but if i turn the key to start the car and let it wind maybe once or twice but then dont let it start, like stop turning the key before the engine starts, and then try to start it, it starts right away. ITs really wierd the battery is charging it always has a full charge before and after driving. I have no clue what the deal is. Like i said if you wind it once or twice and then try to start, it will start right away just like its supposed to.

Any thought or maybe a proper way of wiring it?

 

Post some pics of this.

Also I may not want to know, but why did you move the battery?

 

there are many reasons to move the battery to the trunk.

Free up room in the engine bay.
Take weight off the front wheels
make the weight distrubution more balanced

im doing it for all 3.

making room to run a cold air intake to the botom right of the bay

trying to lighten the front and balance the weight ratio

its a common modification. Most Bmw's are stock with the batteries in the trunk

 

I've done the exact opposite on my Cooper S as the battery cables weigh 2.2kg each , and there are 2 of them . I've also bought a Braille carbon battery at 6.2 kg . On removing the battery box and heat shield under it I shaved 7kg off the car too.
My wiring is being done tonight so I will watch this with interest .
Hope you get it sorted but it's not just a loose fitting on the starter is it ?

Oh and I'm mounting it behind the passenger seat to equal the meth/water kit out

 

Now that your battery is so much further away from the starter, maybe a slightly weak battery is being magnified.....I'd also check the voltage at the starter...and take a meter to all the grounds....it sounds like there is a bit too much resistance, or it may be possible that you created a ground loop.....running the ground wire from the battery to the engine block, as the engine block is already grounded to the frame, and the battery to the frame.

 

You'd have to do more than just check the voltage, you shold load test it. I would ground it directly to chassis (like weld a stud onto the frame of your car) and not to a ground bundle. Also, be absolutely sure that the battery is secured properly wherever you end up putting it. If it's in your trunk and you get rear ended, you may end up with an acid-filled projectile bouncing around your cabin.

 

Excuse my ignorance, but i thought all batteries on the Cooper S were in the trunck, mine is.

 

HE moved the battery in an R50.....hense the Non S forum...
Easy miss!!

 

Hahaha so many S people post in the Non S forum on accident

Ok so I will try grounding only to the chasis and eliminate the ground going to the block.

Excuse my ingnorance but How do you test the grounds?
And what is a load test?
I have a multimeter so im sure thats what ill be using for both

Oh and once i get it all wired properly and have it be reliable I will obviously get a battery tray and strap everything down tight. You dont want a lose battery in the trunk of course.

I didnt know the mini S had it in the trunk. Thats great. Doesnt that mean i can buy an oem Mini S trunk mount.
Hey neil could you take a pic of your battery in your trunk or at least tell me where exactly its located and how its held down? ( never mind. its under the trunk carpet there is a special well in the trunk right in the middle where the battery goes into. Base minis dont have it

 

yes i'm a noob! i just usually just click on the "new posts" tab, that's how i ended up in here-sorry guys.

 

The MINI OEM trunk mount is actually in a welded box that sits under the trunk...where your spare tire is. Then it has a strap over the top to keep it from bouncing.
I think Helix was also on the right track....I improve the grounding point in the trunk...you are likely overloading it. As for the ground loop, that is most likely to cause a problem in a humm in the radio's or gremlins in the computer. Still worth trying to fix IMO.
Just so you know, the battery in the trunk of the S has several safety features....it actually has 2 positive leads....one that is unfused (goes to the starter) if i remember right, that is connected to a pyrotechnic device that disconnects if the car is involved in an accident...such as airbag deployment. The other lead goes to the fuse box...and is fused normal. The danger is that if a fault happen in the wire between the battery and the fuses, is that it will spark, and weld itself to the area it touches...so I hope you have very careful routed the cable, and protected it from sharp edges, etc. Also the battery in the S is located Very LOW to maintain a good CG, and is out of the way, so if you are rear ended you don't get the battery or worse yet battery acid splatted around the car's cabin.
The mod you are do does have some advantages, but there are pitfalls, and I just want you to know them so you can safely compensate for them. Good Luck!!

 

Yes thank you i am aware of the dangers of having the mattery in the trunk. I plan to run a 30amp fuse right off the positive lead on the battery. So in case there is a fault in between the fuse box and battery that it will blow the first fuse.

Also can you possibly explain to me how to test a ground and what is a load test? im assuming the load test does test the ground haha but how is it done?

 

Update.

Yesterday I switched back to the front since I couldnt figure out what the problem was and the care wasnt realiable this way.

The last thing i tried was removing the ground going to the front becasue of what people said about a possible ground loop.

I also moved the rear grounding wire to a different bolt all on its own becasue of the overload possibilty

doing this seemed to make the situation worse. The car almost didnt start on me. The start clicked a few times, didnt even turn over like it used to so it was getting a worse signal then before.

Im going to do more research and expirements and let everyone know what I find.

 

If the starter winds at normal RPM it may be something else like inductance in the wiring to the ignition power. Another posibility could be the fuel pump being affected but if you leave the ignition power on for a second or two before cranking this should rule that out.

It sounds like you certainly have an adequate wire guage to avoid voltage drop to the starter. If it is a starter voltage issue it must be the lugs or other connections.

 

The chassis is more than capable of being a ground bus. You have a voltage drop in between your ground lead and the where you attached it. Also, why the 30amp fuse? The positive lead should to a junction point where it splits and goes to the starter and the front fuse box. The power steering pump alone that attaches to the front fuse box is capable of pulling just under 100 amps

 

sounds like that might be his problem. he has them wired in a chain when it should just split?

as in he has them like:

battery---fuse box---starter


when it should be:

_____________/fuse box
battery--------
~~~~~~~~~]\starter

(bad attempt, i know.)
??

30 amp fuse = bad idea.

 

Ive been trying to read up on the matter but havent gotten a chance to do much. but ive wired it the same way on a different car and didnt have any problems but anyhow im sure ill get it soon. If anyone out there has done it before on this car maybe you could tell what the best way to wire it is.

 

Helix is right you need to load test your battery.. If you have a harbor frieght next to you they sell them fairly cheap.
http://www.harborfreight.com/cpi/cta...emnumber=90636

I would load test batt then load test pos wire that is connected to starter that comes straight from the battery. Then hook up ground somewhere on the engine.

Now for battery relocation take a look at M7 Tunning.. They have a
M7 Rear Lower Diffuser that requires battery relocation. If you ask them they might sell you the battery relocation kit or send you some instructions on how to. Doesn't hurt to try.
http://www.m7tuning.com/parts/produc...roducts_id=147

Good luck