Battery Relocation - Wiring

[BradW]

3 no vehicle released from a factory ever had curcuit protection to the starter(includes all battery located in boot/under seats)

BMW actually had a recent model (last 5 years or so) that had a small charge installed in the battery terminal that is fired with the airbag in a collision and blows the lead out of the battery terminal. This cuts the main battery supply to the engine bay but still leaves power to all other circuits so you still have lights, hazards etc. Apart from that I have never seen another factory install with protection.

Its impossible to know if the cable your laying under the carpet is still going to be good in 10yrs time.

Think of the consequences Cruzida has outlined and combine that with the numerous plastics, carpets, and whatnots that would easily ignite given the temperature a short on this wire would create.

I would never run the battery cable through the cabin on a boot install of a battery. I only run them under the car, protected in conduit, grommeted where it passes through the body and securely mounted. There's generally a lot less carpet and plastic under there. I also wouldn't bother with a CB but I suppose the extra protection can't hurt.

There's only 2 reasons the factory doesen't use something and that's cost which is 90% of the time and the other is it doesen't need it. But in saying that they don't care if you car burns to the ground cause they can sell another one.

That's right, but if all their cars were burning, I don't think they would be selling too many would they .

[CrUZida]

For sure a small short wont trip a large breaker, which is why, as you mentioned, cable placement is probably the most important factor to consider when putting a battery in the boot.
That said, however, I'd rather have some form of protection than no protection at all.

The benefit of most circuit breakers is that with the push of a button they will trip, giving you instant disconnection. My CB doesn't have this feature, so I've installed an isolator switch on the negative terminal aswell.

[Talasas]

IIRC a starter motor will draw in excess of 120A and actually somewhere in the viscinity of 300-400A (im open to being corrected with proof) but these circuit breakers usually dont trip as they are designed to be a slow tripping breaker and can handle a few seconds of cranking. Keep in mind that a short on a cable of such size will be drawing every amp the battery can throw at it so that CB will trip instantly.

You are spot on, this is what you need to be mindful of when relocating the battery (and in general to understand why you don't constantly cranks the starter if the engine doesn't start). Automotive lead-acid batteries are capable of putting out roughly 600A (with some small amounts of charge left) and when you short circuit something it'll pump out everything it's got.

While I understand that it's best to have a good circuit from the battery to the starter to minimise heat/resistance during cranking, the thought of having and accident and being pinned in the car while it catches fire because the wire wasn't fused is not reassuring. Anything can happen and it's best to keep it as safe as possible.

[LeeRoy]

More support in favour of a started drawing 300-400A. Batteries are rated by CCA which is cold cracking amps. Most small cars run at least a 300cca battery and commodores etc run something like 550cca.

[Talasas]

Looking around today it's pretty damn hard to fine a decent sized circuit breaker, Jaycar's 120A bling model is pretty expensive I think ($44) considering the guy behind the counter tells me you can "fry" them easily.

I'm trying to keep an eye out for a decent CB for now, and just need to find a distribution post.

[CrUZida]

This is what I use.
http://www.alanco.com.au/view/pg?com...id=CBR-SDLM150

[TERRA Operative]

For what it's worth, my almost stock AE101 Levin with 4AGZE pulls a measured maximum of 222.6A when cranking on a cold start.

[CrUZida]

Any electric motor will pull 7 to 10 times more current upon starting than it will on running.

Most starter motors are around 700-1200 Watts.

So thats 60-100A upon running, and potentially up to 10 times that on starting (esp with a hydro-locked motor).

Most (if not all) circuit breakers are designed to 'ignore' this start current for a short period of time.

[Talasas]

There was a perfect 200A CB on eBay that would have worked perfectly and I forgot to bid on it! DOH! I hate it when that happens, went for half price too

[The Witzl]

Talasassasasasss - just use the 100A bastard at Jaycar. I promise you it wont trip.
Cat no. SF2266

[frag_dog]

Check out this website:

http://home.clear.net.nz/pages/phil....car_wiring.htm

Some pretty usefull information on re-wiring a car. I'm going to start on my RA28 in the next few weeks....