battery

jeremy · #1 18th September 2009, 04:19

I am mounting the battery in the back of the car, and like the idea of a red top, as it has an alloy carrier available, which can be bolted in for safety.Would a red top or equivilent be able to power lights, radio etc.?

MartinClan · #2 18th September 2009, 09:50

In fact the battery doesn'y really power anything under normal engine running - all of the enerrgy is supplied by the alternator. It's when the engine isn't running, or if it is only at idle that the battery supplies any juice. So as long as

1. The red top can supply sufficient cranking power (amps when starting)
2. You don't have too much turned on for too long when you are idling

I would say that the Red Top would be fine.

Make sure that you use a HUGE cable to go from front to back and that is is very well protected. I would consider using a fusible link at the battery end. But it would have to be a big-un. (Less than the battery short circuit current but more than the cranking current)

Robin

Chris Cussen · #3 18th September 2009, 10:58

That's going to be a f**king big fuse! The starter motor initally draws in excess of 200amps, though it drops rapidly as the motor spins up. It would be difficult to choose a fuse that could discrimate between a short circuit and the ordinary current drawn.

MartinClan · #4 18th September 2009, 12:33

Some of the larger fuseable links are rated at 250 amps. I would have thought this would be OK. As the starter motor consumption drops rapidly I don't think it would blow. But it would blow if the battery had a dead short to ground for any period.

Maybe I am over cautious but the thought of running the power from the battery all that way without a link would cause me some concern.

Robin

jeremy · #5 18th September 2009, 16:20

can anyone remember how the original bmw does this with the battery in the boot?

MartinClan · #6 21st September 2009, 07:44

Quote:

Originally Posted by jeremy

can anyone remember how the original bmw does this with the battery in the boot?

Yep.....

They run two cables up to the front. A naffing great big one for the starter and a smaller one for the other electrics and engine management system. The reason for a seperate one for the engine management is to stop any voltage fluctuations while the engine is cranking from affecting the ECU.

I still have some of the cable left that I stripped from the donor if you would like me to check on its size....

Robin

jeremy · #7 21st September 2009, 23:36

thanks for the advice..red top it is,as i set the standard 069 in the back area,and it is just to big and heavy.Next question..red top 25 or 30?It is to run a 2.5i e36 engine.

GreatOldOne · #8 22nd September 2009, 07:21

Just as a matter of interest Jeremy, why are you putting the battery in the boot? Why not use the battery tray in the front?

I got a standard sized Bosch battery in there along with the swirl pot and brake fluid res with space to spare.

If Red Tops are smaller, you'd have plenty of room, and could bolt the carrier into the shelf the battery sits on. You'd then not have to have a massive run of battery cable to the boot.

jeremy · #9 22nd September 2009, 10:19

mainly due to lack of space at the front.I have the e36 lump in there, and it takes up more space -length and width,and have mounted my expansion/header in the battery space,with the swirl pot.The area in front of the passenger bulkhead is taken up with the fuel pump and filter, my wiring loom entry into the car, and the modified air entry inlet for the beast.

GreatOldOne · #10 22nd September 2009, 10:33

Ahhhh - I see.

As they're small, could you mount it on top of the scuttle? The brackets that Red-Top do say that they're ok on their side, so you could lay the battery down.

You just need to see if you have enough clearance between the scuttle and the bonnet.

http://www.varleyredtop.com/products_25.htm

The 25 is only 77mm wide, (or high if you lay it flat)

MartinClan · #11 22nd September 2009, 12:45

Quote:

Originally Posted by GreatOldOne

Ahhhh - I see.

As they're small, could you mount it on top of the scuttle? The brackets that Red-Top do say that they're ok on their side, so you could lay the battery down.

You just need to see if you have enough clearance between the scuttle and the bonnet.

http://www.varleyredtop.com/products_25.htm

The 25 is only 77mm wide, (or high if you lay it flat)

Another possibility is the passenger footwell. A lot better than at the rear and having to run a long cable. There was somebody else doing this - can't remember who.

Robin