Subaru Impreza GC8 & RS Forum & Community banner

1 - 12 of 12 Posts

·
Registered
Joined
·
1,994 Posts
Discussion Starter #1
The only wire I really need to worry about is the positive lead going to the starter right?

Is there a good place to run the negative to ground in/around the trunk?

What gauge wire works best?

Does the positive wire need to run through the inside of the car or can it be run under it and through a hole in the trunk?
 

·
Premium Member
Two Mini Coopers!
Joined
·
10,629 Posts
Last time I put a battery in the trunk of a car it was a second battery, so here is what I did:

1. Ran a 8 gauge wire to the trunk (if this is your primary, run 4 gauge, the same as what goes to your starter) through the firewall - using a rubber grommet - very important and then to the back of the car. If you fail to use a rubber grommet, the sheetmetal will cut through the cable sheathing and ground the wire, starting a fire.

2. Installed a battery box using sheet metal screws and fender washers to the floor

3. Ran a short (18" or shorter) 4 gauge negative wire to a bolt that was near the bumper, in the trunk. You could also drill a hole and put a large sheetmetal screw through the floor of the trunk, sanding away paint so the cable has a metal-to-metal contact patch.

If this is your ONLY battery, consider a fuse breaker on each end that can handle, oh I dunno, ~200 - ~300 amps? Enough to turn the starter over in cold weather, basically, without popping.

It does not matter how you run the cable, so long as it is not exposed to being cut by something.
 

·
Registered
Joined
·
1,994 Posts
Discussion Starter #3
Sounds good. This is the only bit I'm scratching my head about.

RS25.com said:
If this is your ONLY battery, consider a fuse breaker on each end that can handle, oh I dunno, ~200 - ~300 amps? Enough to turn the starter over in cold weather, basically, without popping./B]


So I should put a 200~300 amp fuse on the positive and negative cable? I dont exactly understand how they would help the starter in cold weather. My understanding of circuitry if fairly basic so could ya explain this a little further please?
 

·
Registered
Silver '99 Impreza 2.5 RS
Joined
·
118 Posts
The fuse is just a safety measure, to pop instead of frying your car if something bad happens (a short somewhere).

The reason it would need to be of big enough capacity to handle cold weather starting, is that's when your highest amperage loads will be. If the fuse is smaller than the amount of amps your car needs to start, the fuse will just blow, and your car won't start.

At least that's what I think he meant.

Happy Thanksgiving,

Sean
www.subrew.com
 

·
Registered
Joined
·
1,427 Posts
It wouldnt hurt to use 2 guage. Think about the size of the cable to the battery, you are more than doubling that length. I wish I could find the chart I have around here, it shows how much current a wire can handle at a specified length. On cars such as ours you shouldn't need 200-300A fuse, normally 150 does just fine. Also those are much easier to locate. If for some reason the 150 does blow on a cold start then upgrade to a 175A. A thermal breaker is a good idea too, thats just to be very safe. If the wire was to heat up from pulling for the starter yet not short out it would degrade the insulation on the wire and over time you could have bare wire.

Sorry for the long winded version, I work on vehicle electrical systems day in and out so I have seen very bad things happen. Just trying to make sure nothing happens to ya. :)

Buster

If this is your ONLY battery, consider a fuse breaker on each end that can handle, oh I dunno, ~200 - ~300 amps? Enough to turn the starter over in cold weather, basically, without popping.
Not sure why you would want a fuse on both ends. Normal spec is to fuse within 18 inches of the power source.
 

·
Registered
Joined
·
1,994 Posts
Discussion Starter #6
Awesome, thanks for all the replies. I think I have enough info to do this now.
 

·
Premium Member
overdeveloped beater
Joined
·
8,335 Posts
Just to add tidbits of info, remember that if you happen to blow a fuse, it'll be like resetting the ECU and the alarm will will go off when you re-power the system initially. A thermal breaker could catch you off guard and make for embarrassing situations.

The 2AWG would be better for a longer run like this and grommets are absolutely necessary for safety, as previously said.

Have fun...post pics!!!
 

·
Premium Member
Two Mini Coopers!
Joined
·
10,629 Posts
I was thinking of a fuse on the end from the alternator to the battery, and one between the battery and +/- 18". You would not want the end between the battery and the front of the car grounding and not being protected, nor would you want the end closest to the alternator grounding and destroying your alternator.

Make sense?

Alternator --18"-- Fuse --------------------------------------- Fuse --18" Battery

as opposed to:

Alternator -------------------------------------------------------Fuse --18"---batery

What happens if you short here ^^^? The power can still just fry stuff. Get it?
 

·
Registered
Joined
·
1,994 Posts
Discussion Starter #9
Ahh, I get it. Makes sense. Thanks.

So here's my shopping list:
connector for the cable to the starter
2 connectors for the cables to the battery
connector for the cable to ground
Big spool of 2 Gauge wire
2 150A fuses
Grommets (wire size)
drill bit (grommet size)
Battery box

Anything else?

Maybe I should pick up one of those fancy Optima batteries. Anyone know how much those usually go for?
 

·
Premium Member
Two Mini Coopers!
Joined
·
10,629 Posts
Again, I would recommend a circuit breaker, since you can reset it when (if) it blows. And then, you'll need two, and they are expensive.

Say, why are you moving your battery? Weight savings from the front end?
 

·
Registered
Joined
·
1,994 Posts
Discussion Starter #11
RS25.com said:
Again, I would recommend a circuit breaker, since you can reset it when (if) it blows. And then, you'll need two, and they are expensive.

Say, why are you moving your battery? Weight savings from the front end?
Circuit breakers instead of fuses?

Basically, it seems like a fairly easy and fun project. Plus the weight distribution. Plus it cleans up the engine bay.
 
1 - 12 of 12 Posts
Top