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Old 05-18-2012, 07:15 AM   #11
Mike Pearson
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Default Re: gauge of wire for Alternator to battery?

If you put an ammeter on the wire you could tell what the alternator is actually putting out to the battery. I would say its no where near 140 amps. Size the wire on the actual load. Thats probably why the small wire has been working for you. Just remember the lower the voltage the higher the amperage is. Thats why the starter has such a large cable going to it.
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Old 05-18-2012, 09:46 AM   #12
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Thumbs up Re: gauge of wire for Alternator to battery?

Quote:
Originally Posted by Mike Pearson View Post
If you put an ammeter on the wire you could tell what the alternator is actually putting out to the battery. I would say its no where near 140 amps. Size the wire on the actual load. Thats probably why the small wire has been working for you. Just remember the lower the voltage the higher the amperage is. Thats why the starter has such a large cable going to it.
Ahhhhhh......... I never thought of that Mike. Makes perfect sense. Thanks. Jim


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Old 05-18-2012, 12:12 PM   #13
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Default Re: gauge of wire for Alternator to battery?

I embarrassed to say this, but I've run 12 ga for years with no problems. I do intend to beef it up though. I run a fan, fuel pump, water pump, tail lights, Racepak, digital 6A and headlights.
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Old 05-18-2012, 12:46 PM   #14
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Default Re: gauge of wire for Alternator to battery?

The battery capacity has a lot to do with the load induced on the alternator. Think of it as the battery being a bucket, the bigger the bucket the more capacity it has, and does not ask the alternator for any more amperage than is being used to maintain the battery charge. The voltage from the alternator is also higher than the load from the battery. The higher the voltage the smaller the wire needed. Look at the overhead power lines coming from your local power plant they are extremely small diameter due to the voltage they are carrying.

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Old 05-18-2012, 12:48 PM   #15
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Default Re: gauge of wire for Alternator to battery?

I do harnessing for a construction equipment manufaturer. We run 6GA for all our alternator charge wires. And they are a much shorter run that to the back of a race car. And as some one already mentioned run an inline high amp fuse for protection.
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Old 05-18-2012, 02:14 PM   #16
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Default Re: gauge of wire for Alternator to battery?

If battery is fully charged(12.65 volts) then alt. will only put out amps to run all the race cars accy. requirements. Ign. system 10A, water pump 5A, fan 15A, lights 15A etc. These are approx. figures. An alt. is not intended to be a battery charger, just a device to maintain the elect. system during load. Therefore #10 Guage should be fine, most all autos from the 60's thru 80's had #10 off the alt stud. Just my thoughts on the subject,Tony.
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Old 05-18-2012, 03:09 PM   #17
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Default Re: gauge of wire for Alternator to battery?

You have to consider the lenght of the wire you are running when the battery (and kill switch) is in the trunk. Ask the guys at powermaster or East Coast.
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Old 05-18-2012, 06:08 PM   #18
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Default Re: gauge of wire for Alternator to battery?

Also keep in mind one wire alternators charge at full capacity (based on RPM) with no load sensing.
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Old 05-20-2012, 02:50 PM   #19
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Default Re: gauge of wire for Alternator to battery?

I'm confused. If a 100 amp one wire charges at full capacity based on rpm, does that mean it's putting 100 amps through the charging wire @ 7,000?
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Old 05-20-2012, 07:47 PM   #20
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Default Re: gauge of wire for Alternator to battery?

The 100 amp alternators in some stock Mopars about 30 years ago used 6 gauge wire and it wasn't real long--between 3' and 6' I guess. If you will only be using 30 amps, why have a 140 amp alternator? The point of using heavy enough wire is that the alternator can run up to its capacity when needed.
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