Battery to the boot ga sendan

[yno26galant]

hey guys is 2gauge big enough to run the battery to the boot.

[davetrees]

Not really.

Use welding cable, about 10mm diameter. The aluminium cored stuff is really good - light, carries heaps of current, and is nice & flexible.

[yno26galant]

dammmmm just spent 80 bucks on the stuff

[LukeAussie]

Excuse my ignorance, but what is the dia of gauge 2 cable? You can work out the resistance drop across a distance if you know this...

I would have thought anything larger than about 10mm is probably okay. The important thing to work out is the resistance across the distance, because of the large currents required to power the starter motor. If the resistance is too big, too much voltage will be dropped on the cable, and it'll get hot (probably not too much to worry about with cable that size), but more importantly, you won't have enough voltage at the terminals you're trying to power.

Also, I'm not 100% sure of the merits of aluminium as a conductor, but I can definitely tell you that aside from gold and silver, copper is pretty much the best conductor you can have :-)

Let us know the diameter and the length, and we can work out the resistance...

Luke.

[yno26galant]

off the top of my head i think its about 2.5metres long where im running my 2gauge, jaycar told me to buy gold plated terminals which ive done,


i just dont want to have to run the 2gauge and then have promblems

[yno26galant]

http://www.rbeelectronics.com/wtable.htm

[davetrees]

I would have thought anything larger than about 10mm is probably okay

For competition cars, 0 gauge is pretty common for the main cable - gives you plenty of "headroom".

It's not all about the cranking current, either ..... work out what your max continuous load will be, including lights on high beam, everything switched on, etc and how much voltage drop you can live with. Work out what minimum gauge you need, then go up at least 1 size from there.

(Remember that for halogen headlights, their rated output in watts is calculated at 13.8v, not 12v. Their output drops exponentially below that .... eg. at 12v at the globe, you are only getting about 80% or something of the rated output).

Something to keep in mind also is how you wire it up. Most people run the main cable from the battery to the starter motor, then take everything else from there. The downside of this arrangement is that a key join in the wiring system is then in a state of constant vibration, being attached to the motor. The way I did my rally car is :
- 0 gauge cable from battery to a fixed connection on the body (in my case at the kill switch, but if not running one of those you could use a bus-block of some sort)
- 0 gauge cable from kill switch to starter motor
- separate 2 gauge (I think) cable from kill switch to a bus-block under the bonnet. (I bought a brass one designed for 240v with multiple screw connections and a plastic cover for about $10 on eBay)
- separate wires from bus-block to alternator (2 gauge), main wiring loom/fusebox, and to a separate fusebox for accessories like driving lights/fan/fuel pump/etc.

This way, the only "floating" wires are the ones connected to the starter motor & alternator ... everything else is fixed to the body. Vibration in a rally car is the number one killer of electrical connections ! Less of an issue in a road car obviously, but avoiding vibration & stress on joints always improves reliability.

It's also worth considering running a separate earth cable from the battery to a good fixed earth point under the bonnet, and earthing everything to there rather than to the bodyshell ..... old shells aren't necessarily the greatest conductors, if you are relying solely on an earth from battery to body inside the boot !

Just my $0.02 worth ....

Dave

[A112H]

I have 0g positive running from my battery in the boot to the starter. I also use a 0g negative cable, 2 shodt cables, one from the battery to the rear bumper mounts and the other from the engine block the the chassis

[LukeAussie]

There's definitely some good points in there :-) I've done some research on the American wire gauge values and agree that you're best going for gauge 0, which is 8mm (I'm an electrical engineer, and we always use mm diameter for cabling specs). The point about running your wires to a separate point and then to the starter is a good one; I also have this arrangement in my road GC too. It's good practice from both an electrical and a mechanical point of view, as you also don't have any voltages sitting on top of a fat inductor (the starter) acting as a filter device across the rest of the car. In my car, since the battery is up front, I only have the fat cable running to the starter, and a second parallel line direct from the battery to everything else, though with a boot-mounted battery, a "hub" somewhere else upfront is a good idea.

I also agree with running a fat earth cable to the front of the car too, just so you have a good earth up there (where you need it!). By all means, connect parallel leads to the body in the boot, but a nice big earth cable to the front (it should be big to ensure low resistance) can alleviate future potential problems.

I'm also interested to hear the recommendations people are making about the kill switches... without being too revealing, I have my kill switches wired to the switching mechanism on the starter (and elsewhere), rather than the main power line. You'd want to be careful about the types of switches used inline to the starter because of the currents required, and unexpected properties of electro-mechanical devices (all switches are little bit like capacitors, though mostly we don't see it; at big currents it can become a problem). Further, it's a good idea to immobilise other parts of the car (like the coil!), since this will also stop the car from running full-stop, rather than just disabling the starter motor...

Just some ideas :-) Most of the suggestions are good ones though. And 2-gauge (6mm cable) is a tad too small to power the starter...

Good luck!

Luke.

[LukeAussie]

Oh, and I think gold-plating in a car is a bit wanky... great for high-precision electronics (okay, but still debatable in audio, due to the low frequencies, very good for digital), but I don't think you'll get much value from it in a car :-) Just my opinion though...
Luke.

[geezer101]

Gold plating is preeetttie. The coil disabler idea works brilliantly. I posted a thread ages ago in regards to this - http://www.sigma-galant.com/viewtopic.p ... ING#p64210 Now, back to the thread...

[davetrees]

I'm also interested to hear the recommendations people are making about the kill switches... without being too revealing, I have my kill switches wired to the switching mechanism on the starter (and elsewhere), rather than the main power line

Probably should have clarified ..... my kill switch has nothing to do with being an "anti-theft" device or similar. It's a designed-for-the-puropose motorsport type to shut down everything with the flick of the big red key in the event of an accident !