What gauge wire should I be using?

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JJRJR

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Hey guys, still wrestling with a charging problem. This is the alternator that's in the Runner. http://www.summitracing.com/parts/tff-7 ... e/plymouth

The car has 560 miles on it and this is the 2nd alternator. 1st one tested bad, so Summit sent another one. This "new" one is putting out 45 amps, not 100 as advertised. We have the car in a really good auto electrical shop, so he's trying to chase down the problem. Tested the "normal" places for voltage drop and he said we seem fine, but just not enough current coming from the alternator.

First, any opinion on these Tuff Stuff units? I want 100 amp unit, any recommendations?

Second, what gauge wire should we be using from the alternator to the battery. I think we have 10, but I'm told it should be 6 gauge?

When does the fun start?? LOL

Thanks guys.

John
 
Do you need a 100 amp alternator? Newer cars have high amperage alternators because of things like rear window defrosters and A/C. Some guys need them for their high wattage stereo amplifiers.

Unless you really have a use for it, it's a waste of money... and a waste of horsepower too. It takes more power to make more power. As long as the alternator keeps up with battery discharge, you are all set. :soap:

If you really want to run a 100 amp alternator, run a #6 wire from the battery terminal on the alternator to the battery terminal on the starter relay.
 
Big John said:
Do you need a 100 amp alternator? Newer cars have high amperage alternators because of things like rear window defrosters and A/C. Some guys need them for their high wattage stereo amplifiers.

Unless you really have a use for it, it's a waste of money... and a waste of horsepower too. It takes more power to make more power. As long as the alternator keeps up with battery discharge, you are all set. :soap:

If you really want to run a 100 amp alternator, run a #6 wire from the battery terminal on the alternator to the battery terminal on the starter relay.
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Thanks Big John. Gonna go with a #6 wire and an alternator that puts out what it advertises and see what happens.

Thanks,

John
 
So, turns out the 100 amp unit was pushing good voltage but only 70 Amps. The guy at the electrical shop said he did a test on my car and it draws 90 amps with everything on (A/C, lights, stereo, electric fuel pump, etc.) Is that possible?? That seems super high to me.

Anyway, Summit took back the Tuff Stuff 100 AMP and we changed up to a nice Power Master 140 AMP unit. Guy at the electric shop said no charge since he couldn't fix it. Nice. I've asked to see that calculation of 90 AMPS, but wanted to get your guys thoughts? Seems crazy high to me. Also going to run 6 gauge wire instead of the 10 that's on there.

Thanks,
John
 
BIG JOHN IS RIGHT.....QUESTION.....DO YOU HAVE THE ORIGINAL AMP GAUGE IN YOUR DASH........MINE TOASTED ITSELF AND I BY-PASSED IT AND WENT WITH A AFTERMARKET VOLT METER.....THAT WAS A BIG DRAW ON THE CHARGING SYSTEM
 
george68hemirr said:
BIG JOHN IS RIGHT.....QUESTION.....DO YOU HAVE THE ORIGINAL AMP GAUGE IN YOUR DASH........MINE TOASTED ITSELF AND I BY-PASSED IT AND WENT WITH A AFTERMARKET VOLT METER.....THAT WAS A BIG DRAW ON THE CHARGING SYSTEM
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George,

yes, i had the ampmeter redone and I think they did something so it's not a fire hazard, but not sure if we actually hooked it up, I'll have to ask Gary. I've heard that too. I have a nice aftermarket under the dash that works great.
I'll find out.

Thanks,
John
 
10 guage stranded wire is barely large enough for 30 amps. In reality #6 wire is good for around 50 amps, granted how often would the alternator be charging at full capacity? Inadaquate wire size will limit the amount of current passing through it (and heat up), so this is most likely the problem. Just my thoughts.
 
jerrysdustydog said:
10 guage stranded wire is barely large enough for 30 amps. In reality #6 wire is good for around 50 amps, granted how often would the alternator be charging at full capacity? Inadaquate wire size will limit the amount of current passing through it (and heat up), so this is most likely the problem. Just my thoughts.
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You're right on the money. I found a chart that shows what wire should be used depending on length and AMP output. For length between 5 and 10 feet: 0-60 AMPS 4 AWG, 60 to 100 AMPS 4 AWG, 100 to 150 AMPS 2 AWG.

John
 
Are you running a big Amp on your sound system? I had a completely stock harness with a 37 amp alternator , when I came to a stop with my lights on holding the brake at idle my dash lights would dim and the turn signals would almost stop. I took the alternator because I didn't want to loose the #s correct piece and put the guts from a 54 Amp unit all freshened up into it and NAPA tested it on their machine at 58 Amps. Problem solved .
 
69hemibeep said:
Are you running a big Amp on your sound system? I have a completely stock harness with a 37 amp alternator and a hemi pulley which is a different diameter so as not to rob HP, in other words not charge as well. When I came to a stop with my lights on holding the brake at idle my dash lights would dim and the turn signals would almost stop. I took the alternator because I didn't want to loose the #s correct piece and put the guts from a 54 Amp unit all freshened up into it and NAPA tested it on their machine at 58 Amps. Problem solved still using the hemi pulley
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.
No I don't have anything special for stereo. My constant draw would be: (in the daytime) Mallory 4110 Pump = 5 amps, MSD Ignition is 1 amp per 1,000 RPM, so call it 1 amp at ilde, Stereo is maybe 5 or 6 amps, but I do have two big electric fans that I run 100% of the time, not certain but they gotta be 20 to 30 amps? Total is about 36 to 40 amps. But, throw the headlights, brake lights, turn signals, etc. into the mix and it adds up fast. I'm sure the Power Master 140 will do the trick along with a 2 AWG wire.
 
jerrysdustydog said:
10 guage stranded wire is barely large enough for 30 amps. In reality #6 wire is good for around 50 amps, granted how often would the alternator be charging at full capacity? Inadaquate wire size will limit the amount of current passing through it (and heat up), so this is most likely the problem. Just my thoughts.
Click to expand...

I should made myself just a little clearer. That #6 wire is in addition to the stock wiring.

That said.... 12 volts DC, 100 amps with 3% loss over about 5 feet of wire calculates out to #6 wire.
 
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