Car Audio Central - Ultimate Car Audio Forum and Community

that was why I mentioned an isolator and audio or dedicated batteries in the trunk (also helps weight distro if you have RWD, and want weight over the right rear tire for traction) but anyway, yes you don't need huge wire for the starter battery if you have dedicated audio system batteries on an isolator in the trunk.

I wouldn't move your primary battery back there unless it's back there to begin with. You would have to extend your alternator's wiring to the rear of the car and create a lot of work for yourself with a very minimal gain.

Best would be just to add a battery back there if anything.

you see i would never have known this stuff. luckly i'm not drawing anywhere near 200A but in the future that will help. BTW that moving the battery to by the amp is not a bad idea at all! that would save quite a bit on wirering cost.


thanks alot guys you really helped!

the wire size vs length charts are in the FAQ section, and always have been :)

an upgrade to the 'big 3' on a stock charging system is simply "over engineering" and is fine but isn't going to magically stop lights from dimming, or amps from clipping etc.. just be aware of that.

as for ground points, sanded bare metal works well but in today's world of spot and pinch welds and unibody subframes on cars, your typical car's resistance through the body is about equiv to 4AWG wire. If you're drawing over 200A of current through the wiring, sometimes you are better off to run the ground with 0AWG or larger back to the battery's negative terminal instead of keeping it short and at the amp. While it may require longer runs and thus larger wiring, the trick to this is to relocate the battery to the rear of the car so only the alternator-to-battery line needs to be run the length of the car. This is essentially the way my Charger is set up using 0AWG from engine and 300A alternator to the trunk, where the batteries are kept isolated, near the amps so I can keep a shorter overall wiring run, and carry more current through a unibody car.

woooaaahhh! i think i'm a certified professional in "the big 3" now thanks so much for the detailed responce... everything now makes perfect sense with reguards to the circuit and basically the entire "big 3".

[quote="geolemon"]Overkill won't hurt you, when it comes to power wire (other than in the wallet). Whether it'll help you, becomes the argument. It's likely past "the point of diminishing returns" compared to a 4 gauge wire.
[/quote]
I'd like to add:
Using a larger guage wire will also add less resistence than a smaller guage.

[quote="veggie-man"]alright... i'm looking to upgrade my big 3 in the next week but before i do that i have a few questions. i thought i was fine but after seeing a thread on Toyotanation.com i'm second guessing myself.[/quote] A few fundamental thoughts, after reading your thread:
Bear in mind, the current-carrying capacity of a wire is not just a function of "wire gauge" but also "wire length".
In other words, it's the total resistance of that "hunk of wire" that matters - and basically, a 20 foot length of 1/0 gauge fat cable, and a 1 foot length of 10 gauge thin cable might very well be exactly equal...
...meaning that for their lengths, each is appropriate to flow that amount of current.

There are charts available out there... I don't have any IASCA books handy right here, and I can't google it right now... :(

Anyway:

[quote]
1. i saw people using fuses... would this be a good idea to put a fuse in between the line going from the alternator to the positive terminal? if so how big (my alternator is 80 amps).[/quote] Well, fundamentally here - you ARE upgrading your "magic three" to ADD capacity to your system, correct? You want to make each of those wires (and contact points! ]One caveat:[/i] Make sure you route that wire excellently - at least as securely as the factory wire - maybe in fact exactly the same. If you don't, and for some reason it swings and melts against a hot manifold or something - you easily can cause a short, and in THAT case - to protect against [i]installer incompetence[/i], you might consider a fuse - but ruling that out, I wouldn't want to put extra joints, contact points, and failure points in this "critical link" between alternator and battery, if it were me. I just want a simple, fat wire to flow current with less resistance. ;)

[quote]
2. what gauge? i have 8 gauge wires going to my amp right now but i may upgrade them to 4 gauge in the near future (next month?). so would i go with 1/0 gauge or is that overkill?[/quote] 4 gauge will be fine. 1/0 would definitely be overkill. That being said, I'm a huge fan of overkill. Did I mention I have one run of 1/0 gauge running to a single Alpine MRV1507 in the headliner of my Pathfinder (it's a stereo amp)? :p

Overkill won't hurt you, when it comes to power wire (other than in the wallet). Whether it'll help you, becomes the argument. It's likely past "the point of diminishing returns" compared to a 4 gauge wire.

[quote]
3. for the grounding should i use the screws that go through metal or just try and find a place to put it? (one other thing my ground for my amp is under the bar that holes up my gas tank. that isnt a bad spot is it? One other thing about that is my ground on that is about 25 inches because it’s the only place I could use close enough)[/quote] Always, always, always ground to chassis metal.

Quick, pop your hood. Look at the battery. See that one wire you upgraded - the short wire from the battery - to the car's chassis metal? THAT wire completes the circuit... you know, battery to positive terminal on the amp, negative terminal on amp back to battery?
Ponder that circuit...

That's why the ground of the amp is so important, and so often discussed - because people don't understand it, and ground it to "some bolt" that's back there.
"Some bolt" might be absolutely ideal, btw - IF it is going to make a connection with your car's chassis metal.

And clean the paint off of ALL your power connection points - amp install, or magic-3... paint is an insulator, and no one wants noise in their system.

[quote]4. does the ground need to be under 18 inches? [/quote]No - but the shorter the better.
Again - reference my original point with regard to "wire gauge" and "wire length" - a shorter wire is always better. ;)
(and if you make your ground short, you can get away with a smaller gauge wire for that ground! ;) )
[quote]
5. does it matter if i dont use wire covers?
Other info: My system is about 400 rms.
My alternator is 80 amps[/quote]
What are wire covers?

If you've got a 400w amp, and an 80a alternator, chances are you don't even need to DO the "magic 3".
(but do it - it's all of benefit!)
If you take these fundamentals here into consideration, and understand the circuit you are wiring up, what's "Right" and "Wrong" becomes apparant.

BTW - back to those fundamentals...
...how IS the alternator in the circuit, anyway?
You've run your main power wire from the battery back to your amp - and you ground the amp to the chassis, where the battery is also grounded - so we've got a circuit to run the amp off the battery, right?

We've got a wire (that you are upgrading) going from the alternator to the battery. Make it nice and large too - the amp is drawing through that too, right? ;)

How is the alternator grounded though?
That's the third leg of the magic three...
It's chassis grounded to the engine - so you have to find the ground wire that goes from the engine block to the car chassis - THAT is, essentially, the alternator's "Ground wire" - and complete's IT'S circuit to the battery. :cool:

[quote="GlassWolf"]OE alternator. you're not really gaining anything with bigger wire for the big 3, unless the factory wiring was worn and frayed.[/quote]

haha so basiclly i should just leave everything alone?

thanks for informing my of everything here... once i upgrade my system i'll remember everything

1. i saw people using fuses... would this be a good idea to put a fuse in between the line going from the alternator to the positive terminal? if so how big (my alternator is 80 amps).

you fuse the alternator to battery line with a fuse rated for peak current capacity of the WIRE.
ex; 4AWG would be ~125-150A fuse.
this is to protect the wire, and the car from dead shorts nd engine compartment fires.

2. what gauge? i have 8 gauge wires going to my amp right now but i may upgrade them to 4 gauge in the near future (next month?). so would i go with 1/0 gauge or is that overkill?

4AWG is at most all you'll need for 80A, which is all you can pull from that alternator.

3. for the grounding should i use the screws that go through metal or just try and find a place to put it?

use factory points for the big 3.
I'd use sanded bare metal and a bolt for the amplifier ground point.
do not put it by the gas tank :rolleyes: one spark and you'll look like the human torch.

4. does the ground need to be under 18 inches?

5. does it matter if i dont use wire covers?

wire covers? you mean hoods over the connectors?
just leaves exposed metal carrying a charge.
drop a screwdriver on one and it makes pretty lights!

Other info: My system is about 400 rms.
My alternator is 80 amps

OE alternator. you're not really gaining anything with bigger wire for the big 3, unless the factory wiring was worn and frayed.

your putting a lot of thought into an 80 amp alternator and at 400 rms i wouldnt sweat anything other than proper install techniques