Alternator help…

[454cid]

Confused..... says "charging cable". Why would a charging cable need to be that big? This chart is reccomending cables larger than my OEM starter cable.

 

[Schurkey]

I'd expect your battery-to-starter cable is 4-gauge.

Your "charging cable", i.e., alternator output cable would probably be 6- or 8-gauge.

Remember, the battery-to-starter cable is only seeing heavy load when the starter is cranking--typically a few seconds once per trip. The alternator cable is seeing less amperage, but longer duration. The time factor leads to conductor heating, which then increases resistance.

But, yeah, there's boneheads trying to push ordinary-length ground and alternator cables in 0-gauge, with SMALLER 2-gauge wire for the starter motor. Why? Because they can, and folks don't understand basic physics well enough to know they're being had.

 

[AuroraGirl]

Also, you should run battery to a junction point, and then from there to the alternator and the starter

 

[454cid]

I'd expect your battery-to-starter cable is 4-gauge.

Your "charging cable", i.e., alternator output cable would probably be 6- or 8-gauge.

That's exactly what I'm getting at..... the chart says "charging cable" and for a 125-150 amp alternator is specing a 2 gage charging cable, not the 8 guage that my truck has from the factory.

 

[AuroraGirl]

That's exactly what I'm getting at..... the chart says "charging cable" and for a 125-150 amp alternator is specing a 2 gage charging cable, not the 8 guage that my truck has from the factory.

Yes!

Because the 8 gauge is subpar and always has been

 

[PlayingWithTBI]

Also, you should run battery to a junction point, and then from there to the alternator and the starter

What junction point should you run the cable that goes from the battery to the starter? Every GM I've seen has a straight run to the starter.

 

[Kran]

Yes!

Because the 8 gauge is subpar and always has been

this is correct. same reason why the blower motor plug and wiring melts and can catch fire when the blower motor starts to go out. factory wiring is built to an absolute minimum spec. similar goes for the headlight switch. you get much brighter lights running your own headlight relay harness that has proper sized wiring.

look up "big 3" wiring upgrade. i'd do 0 gauge power and grounds on any vehicle even if it has a stock alt

 

[RichLo]

I this is why I like having a couple spools of welding cable sitting in my garage for anything that might need overkill.

Still really good info to have in this thread. Is there any way to 'sticky' this?

 

[454cid]

Yes!

Because the 8 gauge is subpar and always has been

I disagree. Batteries should never be in such a condition to pull a full amp rating from the alternator. I can understand needing a heavier charge wire on a semi with mulitple huge batteries, out behind fuel tanks, but not a single battery right next to the alternator in a pcikup.

 

[Schurkey]

Also, you should run battery to a junction point, and then from there to the alternator and the starter

Often, the starter solenoid IS the junction point. Some older GMs used the horn relay as a junction for most loads other than the starter motor.

That's exactly what I'm getting at..... the chart says "charging cable" and for a 125-150 amp alternator is specing a 2 gage charging cable, not the 8 guage that my truck has from the factory.

Consider "duty cycle". That "125 amp" alternator is putting out twenty amps most of the time; and almost never puts out 125. That's why it's the size of a softball. It's a 30-amp alternator with delusions of grandeur. It can throw 125 amps +/- 10%...for a few seconds.

OTOH, I used to install 100+ amp alternators onto City Buses, and the cabling was enormous, and the alternator was oil cooled and weighed 80 pounds. That alternator put out it's rated power for hours on end driving racks of lights, multiple heater/ac blowers, etc.

I have a suspicion that the chart was intended more for constant loads (City Bus) than for intermittent loads (automobile/light truck.)

the 8 gauge is subpar and always has been

this is correct. same reason why the blower motor plug and wiring melts and can catch fire when the blower motor starts to go out. factory wiring is built to an absolute minimum spec. similar goes for the headlight switch. you get much brighter lights running your own headlight relay harness that has proper sized wiring.

A lot of truth to that. Vehicle wiring often does not follow proper standards for voltage drop in a circuit. I was surprised when I took after my Luminas with a voltmeter looking for the three volt loss in the fuel pump circuit. I expected to find a 2+ volt loss somewhere. Instead, I found .1 and .2 losses...everywhere. The wiring was just too damn small for the amperage it was carrying and the length of it all.

look up "big 3" wiring upgrade. i'd do 0 gauge power and grounds on any vehicle even if it has a stock alt

The guy is nuts. He's pushing multiple ground cables and an alternator output cable that are bigger than the starter cable.

His 2-gauge starter cable is fairly reasonable. A little excessive, just like we like it. So a 2-gauge engine ground is similarly reasonable because the engine ground and the starter power cable carry approximately the same load--but he's using 0 gauge grounds. The body and frame don't see squat for amperage compared to the starter draw, he's using 0 gauge when 4-gauge (and maybe 6-gauge) would be overkill. And he's using 0-gauge for the alternator output, which is more cable than you could safely hang off the stud on the back of the alternator without additional support. The friggin' stud is threaded for a nut that takes a 10mm wrench! How can you need 0-gauge copper connected to a skinny-ass output stud?

Take the GM-spec cables, increase by "2" gauge numbers. What was 10-gauge becomes 8-gauge. What was 8-gauge becomes 6-gauge, what was 4-gauge becomes 2-gauge. That's all you need most of the time, unless you've got some enormous non-stock electrical load.