Hi Paul Thanks for the interesting posts. One of the common modifications on our track cars is relocating the batter from under the bonnet to in the car. The advantages are safety (the battery is far away from any impact zones) and weight distribution, in that the weight of the battery is no longer right at the front of the car. What most of us struggle with, is working out what cables are needed. If you could write up an article on sizing the cables, that would be great. I know you've done a generic cable sizing one, but I have no idea if that's relevant to this. Thanks Alex
Hi Alex, Sorry for the radio silence; I haven't been on here for a few days so missed your post. Thanks for the suggestion - battery relocation is a definitely a good one for an article. The main consideration here is the additional distance you'll be running the cable (causing voltage drop) and the fact that if you want to run only one cable it needs to be rated sufficiently to supply both the starter motor (the highest current consumption item on your car) and your running electrics. In standard setup the starter cable will only be a short length from the battery to the starter motor, with a separate lower capacity cable supplying power to everything else. You also need to consider how the battery is going to be mounted and vented (if it's a standard wet lead-acid type) and where to find a suitable, high quality earth point (ideally directly to a chassis member, not a body panel). Also remember your ground cable will need to be as large as your +ve cable. A basic scheme could be to have a large capacity power cable (say 50mm2 / 345A) running from the battery in the boot to a 3-way power jointing box in the engine bay. This would split 2 ways to feed the starter motor (using the same large capacity cable) and the main distribution fusebox (with a smaller capacity cable). I'll see what I can put together for the site in the next few weeks. Best regards, Paul
Mod is over rated, IMHO Have you felt the weight of 3.5M of 50mm sq? And cost, and danger if not properly bolted down? The volt drop? Smoke in cabin, during dead short (use LSF!!) Correct crimps, correctly crimped? How bad an accident do you have to have to damage the battery in the OE position? (I have experience...) Jon
All valid points, but if installed properly and is m&e sound, then fused down.... Live Starter and alternator are right behind an earthed front panel, as is battery but sure I've never heard of any problems there. 25mm is normally suffice (is on my mk2 20vt) tri-rated is a must. My fuse board feeds off the starter bolt, neat and tidy.
I used 35mm^2 but again is overkill. 25mm^2 seems to be the general size to use for relocation. Also I used welding multicore as it was way cheaper than audio grade stuff. My battery sits behind the passenger seat in a custom ally bracket that's bolted done with m8 bolts into rivnuts. Positive connection is run from the battery to a cutoff then through the bulkhead to the starter motor connection. Another length of cable goes from the starter motor connection to the old battery terminal point where all the positives are bolted together. Negative connection. I can't stress how important the grounds are. The battery grounds to the chassis via another rivnut and m8 bolt right next to the battery itself using the same sized cable as the positive. Being a very short run, the voltage drop is negligible. The engine grounding is critical for this to work. I run the same sized cable from the starter motor mounting bolt (mk3 onwards have an m8 stud sticking off the bolt head) directly to the nearest chassis ground. On a mk1 there is one under the old battery tray on the side of the chassis leg. Then I run another ground from there to the old battery terminal grounds again bolted together. Do not rely on just the original ground wire, it's way too thin. Gurds
Like I said, easy mod to make a right mess of. And for what gain? However, my pulsar battery relocation to behind the co-drivers seat is done to make way for the AFM and front mount pipes...( a must do..) Jon
I did it as the replacement battery is a tiny sealed unit and I wanted the space up front for other stuff. Also having 13kg hanging on the front corner can't be great for a track car. Sure it doesn't matter for a road car. Gurds
I did It to allow air filter relocation to begind headlight. Battery is in a battery box behind passenger seat which has m8 nuts welded to floor pan and stud and Uni strut over the top to secure it down. Washer bottle is in the back next to rear light cluster too. All for engine bay room really
