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Old 07-01-2006, 05:17 PM
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How Much Alternator Do I Need?

I have a 56 Chevy truck with a 283. I added AC and now my 65 AMP alternator isn't holding the load according to my guage (when I kick the AC fan on high). How many amps is enough amps and how much is to much? I'm looking at a 100 amp now.

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Old 07-01-2006, 05:53 PM
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Doc here,

No such thing as "Too Much" except where a short is involved..the Alternator is regulated to provide system support and keep the battery topped off...It would probably never actually see 100 amps..That is only the max output rating..

First you just may be losing a lot of current if your fan system is not on a relay system with properly gauged wire..Is this what you have? If not I'd go that route first before upgrading the charging system..it's a bunch cheaper..

Next,. if you find you need to upgrade, you need to add up all the current draw of the total system as if it were on all at once (worst case scenario) and then upgrade your alternator and charging system to go "A little higher"..If your not sure , get a free load check with everything on..and go by those numbers..

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Old 07-01-2006, 06:41 PM
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Alternator AMPS

The AC is from Vintage Air and came with everything. The alternator is a one wire. And I understand this type kicks the alternator off when at idle. This is when I have the problem.
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Old 07-01-2006, 06:44 PM
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Doc here,

Install a smaller pulley..the alternator will turn faster..

Or upgrade to a 3 wire..

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Old 07-01-2006, 07:06 PM
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Doc ... our electrical forum Moderator has answered your question ... and he knows his stuff ...

Deuce
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Old 07-01-2006, 10:12 PM
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1 Wire Alternator to a 3 Wire

How much trouble is it to switch to a 3 wire? I found a site that sells a kit for under $30 and says its easy. Any advice is welcome.
http://www.madelectrical.com/electri...hreewire.shtml
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Old 07-01-2006, 10:57 PM
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Doc here,

The Kit is easy..

What alternator do you have now? Is it a CS series or an SI series..(I doubt the former most likely the latter) ....

If it's not a 3 wire configured as a one wire..you'll need to buy a new alternator..one with a BIG main output lug in the back , and two smaller plug in terminals on the top or side.

Make any mounting adjustments you may need for mounting (be sure the pulley's are dead in line...I use a carpenters Laser level beam for that..) To adapt to your engine / mounts, then wire as follows:



If your not having dead battery's now, and only see discharge at Idle, are you sure you want the expense of an upgrade? your choice..but I've found pulley changes to be the low buck curative..(at least a good first line of defense..) you can get a smaller pulley for about $9 bucks..a GOOD alternator can cost as much as $200...

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Old 07-02-2006, 08:00 AM
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Alternator AMPS At Idle

Thanks for the diagram. This really helps. Low amps is at idle only and thats when I have the AC on high. I usually turn the fan down to adjust for this. The alternator is an original one wire rated at 65 amps. What I read on this is a 1 wire shuts off at low idle and a 3 wire does not due to the exciter. Is this true? The pully is between 4 or 5 inches. How small can you go? $200 for a higher amp alt is an expense I would like to avoid. Also how does all this effect ignition performance? Once again thans for the advice!
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Old 07-02-2006, 07:39 PM
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Quote:
Originally Posted by youngc0@mchsi.com
The pully is between 4 or 5 inches. How small can you go? $200 for a higher amp alt is an expense I would like to avoid. Also how does all this effect ignition performance? Once again thans for the advice!
The real question is how fast you're going to spin the engine, you could drop
down to a 3" pulley, you'll need a shorter belt, and will speed up the alternator
about 30%...

Keith
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Old 07-02-2006, 08:14 PM
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Alternator AMPS At Idle

I finally got around to measuring the pully and it's 3 inches. I think I'll remove it and have it checked to make sure it's up to par. I looked at some 100 amp alts at JEGS for $100 and may end up going that rout after testing the old one. Thanks for all the help.
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Old 07-02-2006, 08:17 PM
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Doc here,

Keith is quite correct..

And you need only add about , what? about 300 RPM to keep the Alternator excited..over stock idle (assuming Automatic trans, 950 curb)..

A 1 inch reduction would put right in the ball park with about a 300 RPM increase on the alternator..

Ignition performance wise, If the system is starving for current, ( and I don't know what system you may have so my answer is "Generic" In nature) This would mean every time the Buss voltage drops below 12.5 volts, (Full load, no charge)

The Coil will starve for current..as well as any module associated with it, Or CD box..

It, basically, Should run like "crap in a can" when you first tromp on it after a long protracted idle , under full load, until the alternator "catches up"..

You might get away with it on a slow steady acceleration and never notice..But off the line...you'd need a handicap from muni busses..

Speeding the alternator drive is a good cheap solution for your problem via a smaller pulley..you can measure the diameter of your existing pulley, and apply a Little math based on your idle RPM's , as to how much smaller you need to bring it up to snuff..Those are available at even places like auto zombie under the "custom Crap" .. just measure the diameter of the one's they offer..

If that won't bring it into spec..I'd be seriously looking at a regulator diode pack..

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Old 07-02-2006, 08:37 PM
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Quote:
Originally Posted by youngc0@mchsi.com
I finally got around to measuring the pully and it's 3 inches.
As I said, you need more rpm for the alternator, so dropping
down to a 2.5" pulley may save you the cost of a new 100 amp
alternator.


Quote:
Originally Posted by youngc0@mchsi.com
I think I'll remove it and have it checked to make sure it's up to par. I looked at some 100 amp alts at JEGS for $100 and may end up going that rout after testing the old one. Thanks for all the help.
Just for the record, I'm a cheap Bastid, I'd rather buy a smaller
pulley than a new alternator...

Keith
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Old 07-02-2006, 08:42 PM
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Quote:
Originally Posted by bates_k
Just for the record, I'm a cheap Bastid, I'd rather buy a smaller
pulley than a new alternator...

Keith
Doc here,


Amen to that!!

9 bucks Vs $100 ...I'd just get the pulley AND a half a tank of gas....

Doc
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