zapp109

iTrader: (13)

Maybe a dumb question but I have a 160amp alternator im using and battery in the trunk about 12 foot away from alternator. Should i run 2 gauge or 1/0 gauge? I already have a 2 gauge wire that came with the car thats why im wondering. Next can you split off the alternator and run the wire to starter? Or do i need to run separate wire off the battery ?

rotor vs. piston

iTrader: (3)

1/0 gauge

zapp109

iTrader: (13)

Okay that answers the first part. What about running the starter wire? split off alternator or run separate wire from battery?

rotor vs. piston

iTrader: (3)

Sorry about that, the 2ga to the starter the 1/0 to the battery should work fine. Though I would go ahead and do 1/0 from the alt to the starter while you're at it. One less thing to wonder about down the road.

zapp109

iTrader: (13)

Cool I got a 20 ft section of 1/0 and ill run my existing 2ga wire to my starter. Thanks

BigEd_72455

iTrader: (7)

What the hell are you trying to start and run? a Cummins 15L engine?

almost every gm starter is only rated to 1700-1800 watts (160 amps)

I have run 4 gauge on every car I have raced regardless of distance to the starter or alternator and I have NEVER had a problem with starting.

I could see running the larger wire if you had a big booming stereo in the vehicle or something like that that takes a ton of juice to run. But most cars run on only 40-50 amps of power or something in that neighborhood, depending on if lights are on and such.

S10xGN

iTrader: (11)

Agreed. About the only time you'd have an issue is if the internal regulator went ****-up and the alternator actually started pumping out 160A, and even that would be "iffy". Those amp/wire-gauge charts are made for worst-case scenarios, if all your sub-systems are properly fused, you'll never get there...

rotor vs. piston

iTrader: (3)

Starter to the alternator isn't the question, it's alternator to the battery that's the question. He was asking if 2ga to the starter and FROM there 1/0 to the battery... which I'd agree is just fine. Would NOT run 4ga from the alt' to a remote mounted battery.

BigEd_72455

iTrader: (7)

I have 16 or 18 feet of 4GA cable about to go from battery, to cutoff, then from cutoff to starter. I am only going to need 8 gauge to keep battery charged from alternator back to battery.

If you go from alternator to starter with 4 or even 8 gauge wire, you will be just fine.
From there back it will be carried in the larger wire. I had 8 gauge going from alternator to starter, then 4 gauge going back to the battery from there. But what is above is what I am about to do since I am mounting a battery cutoff switch.

L92Firebird

Here is a link to a discussion of battery charging size. Specifically gives recommendations for trunk mounted battery. It is smaller than you would think.

Mad Electric- How to Size Battery Charging Wire

1981TA

iTrader: (7)

I saved a ton of weight in my car by going with a 15 pound braille battery mounted on the firewall. 4-gauge cable from battery to starter (2 foot long), 8-gauge from starter to "full time battery+ junction (2 feet), 8 guage from junction to alternator (4 feet), and 8-gauge from alternator to cooling fan relay (4 feet).

BigEd_72455

iTrader: (7)

Something to remember in all this discussion is that amp rating is the PEAK LOAD output from that alternator. you MIGHT hit that high of an output if you are jump starting a car with a totally dead battery. Heck, a service truck showed up down in Miami one day to jump start my Volvo big rig, C15 Caterpillar 15 Liter engine. And he only had 2 gauge wire on 30 feet of leads. BUT he did have a generator running 16.6 volts and rated at 500 AMPS on a 36HP diesel powered generator!!! he had my truck up and running in less than 1 minute!!

Conversation:

Tech: Turn on your key when I tell you to.
ME: OK
Tech: (hooks up positive) You ready?
Me: OK
Tech: (hooks up ground) Turn on your key
Me: It is on...
Tech: Start it up!!! NOW!!! (hostile voice on the now)
ME: (hits the key to crank) HOLY **** THAT STARTED FAST!!
Tech: (unhooks leads) Call dispatch and tell them you need a comcheck for $137!!
ME: HOW MUCH!!!!!!!????
Tech (laughing hysterically but totally serious) $137
ME: I hope they don't take it out of my paycheck!!
Tech: Companies usually do when it comes to dead batteries.
ME: Gee thanks for THAT INFO!!!

They did not take it out because I submitted the receipt.

Pop N Wood

iTrader: (1)

This table looks massively overdone. Google wire amp tables and most aren't as oversized as this. They must be shooting for an extremely low power drop over the length of the cable.

When the engine is running there is very little current running to or from the battery. I have my battery connected to the fuse box with a short piece of 10 gauge wire through a 40 amp fuse. The only time you move anything close to that is when the starter is cranking. If you run the alternator output to the starter then just have the normal starter cable from there back you can save a lot of wire. 4 gauge is almost more than you need, even for a trunk mounted battery.

rotor vs. piston

iTrader: (3)

Always thought this was already a standardized thing, not opinion based so I just grabbed the first chart that was well made.

Also figured since he had the wire already why not just run a 1/0 from the alt' to the starter. But then 1/0 isn't the easiest to work w/ and it is way over kill. So there's that.

Pop N Wood

iTrader: (1)

Yeah, I did too until I compared your chart with one I commonly reference.

That MADD link L92Firebird posted describes how they come up with tables like this. there is still a bit of a judgement call as to how much voltage drop across the line is acceptable.