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told alternator not turning fast enough

1490 Views 35 Replies 16 Participants Last post by  scote79, 
scote79
i have an 84 mustang with a built 302. the alternator is not giving me enough volts when heat ect are on. was told my alternator isn't turning fast enough and i need a bigger crank shaft pully. any suggestions on what to do?
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Racer-X-
Three choices:
  1. Bigger crankshaft pulley (will increase speed of all accessories on that belt)
  2. Smaller alternator pulley (will only increase speed of alternator shaft
  3. More efficient alternator that will operate at lower alternator shaft RPMs.
Not enough details about your accessory drive belt(s) and pulleys and alternator to make a recommendation among those three choices.
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scote79
it has a serpentine belt, has 4 grooves. has a gmc single wire alternator
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scote79
should i go to a regular ford alternator with the original wire hookup?
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scote79
Racer-X- said:
Three choices:
  1. Bigger crankshaft pulley (will increase speed of all accessories on that belt)
  2. Smaller alternator pulley (will only increase speed of alternator shaft
  3. More efficient alternator that will operate at lower alternator shaft RPMs.
Not enough details about your accessory drive belt(s) and pulleys and alternator to make a recommendation among those three choices.
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it has a single wire gm alternator with a serpentine belt with 4 grooves. would i be better off going to the ford alternator with the original wire hookup?
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E
scote79 said:
it has a single wire gm alternator with a serpentine belt with 4 grooves. would i be better off going to the ford alternator with the original wire hookup?
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Definetly.
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joe_padavano
scote79 said:
has a gmc single wire alternator
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And THERE'S your problem. Why are people so enamored with the one wire alternator? Keep in mind that GM scrimps to save every penny on the manufacturing costs of their cars, yet they NEVER installed a one-wire alternator in a production car - they spent the money to use all three wires. The one-wire alternators were designed for agricultural and construction equipment that tends to run at a fixed RPM. Most do not activate until the RPMs exceed 1500 or more. Get a real three wire alternator, wire it correctly, and don't look back.
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scote79
joe_padavano said:
And THERE'S your problem. Why are people so enamored with the one wire alternator? Keep in mind that GM scrimps to save every penny on the manufacturing costs of their cars, yet they NEVER installed a one-wire alternator in a production car - they spent the money to use all three wires. The one-wire alternators were designed for agricultural and construction equipment that tends to run at a fixed RPM. Most do not activate until the RPMs exceed 1500 or more. Get a real three wire alternator, wire it correctly, and don't look back.
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thank you
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Racer-X-
Are you having other issues? What electrical items have been added or upgraded on the car?

If the electrical system is basically "stock," then the "stock" ford alternator might be the best bet. If you've added electric fans, electronic fuel injection and electric fuel pumps, or other high draw electrical accessories, you might need more alternator capacity than the original stock alternator. This usually means going to a more modern alternator design that produces more current at idle than the original.

And I agree with @joe_padavano. GM wouldn't spend $0.02 on a part that wasn't needed, but they always bought connectors, wires, terminals and everything to fully wire all of their alternators (3 wires or more usually). They work great if they're wired up properly. But the "one wire" hacks tend to be nothing but trouble.
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joe_padavano said:
And THERE'S your problem. Why are people so enamored with the one wire alternator? Keep in mind that GM scrimps to save every penny on the manufacturing costs of their cars, yet they NEVER installed a one-wire alternator in a production car - they spent the money to use all three wires. The one-wire alternators were designed for agricultural and construction equipment that tends to run at a fixed RPM. Most do not activate until the RPMs exceed 1500 or more. Get a real three wire alternator, wire it correctly, and don't look back.
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And yet my rebuilt GM 1- wire 100a small case alternator has performed flawlessly for 50k miles over the last 20 years . Hmmm ?
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Crosley
Like most stuff, there seems to be high quality 1 wire alternators and low quality alt.

I ran a 1 wire GM for years on my 1961 Morris Minor.
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johnsongrass1
Make a 3 wire a one wire in about 5 minutes and a 3" piece of wire.
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B
scote79 said:
should i go to a regular ford alternator with the original wire hookup?
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Yes!

One wire alternators require more RPM for self excitation the three wire uses battery power to excite itself so is not as dependent on rotor speed.

Bogie
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'49 Ford Coupe
Well the first thing I think would be logical for anybody is to test the alternator yourself. Get yourself a clamp type volt/ ammeter that measures DC amps many clamp type and meters do not read DC amps so be careful when you order it. They are about $45 on Amazon. Get one that also has the probes. Measure both the voltage and the amperage at various RPM. Yes the one wires generally need to be excited by giving it a shot of gas when you start up but after that it should continually output. Target voltage is around 14 plus volts and amperage should go up in a direct relationship with RPM if you have a low battery and it is calling for full output. . The amperage will not necessarily vary with RPM but the voltage will. If you run the battery down a little bit by cranking it but still can get it to start your initial readings will show you higher amperage. The amperage will only vary with the load that it sees. Also with everything else OFF INCLUDING THE IGNITION, read your amperage at the battery to see what your parasitic drain is it shouldn't be over I think around 0.8 amps as I recall.
If after you do the above have your battery load tested at an auto parts store. You could have a bad battery. report back..

I guess this will work... Here is my thread from a few months ago where I went through exactly the same issue... Be sure to go through the entire 38 responses..

www.hotrodders.com

I should be able to figure out my Alternator issue.. but...

This has been an issue since I built the car... off and on... and other minor issues... Picture attached but I didn't show the other connections to the fuse box, etc. except on the first drawing. When I first built the car I had a 60 amp alternator and it wouldn't keep up with the two fans...
www.hotrodders.com www.hotrodders.com
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C
After testing the GM alternator, I don't see any reason to not use it if it's good. You just need to run the other wires. It's not like GM alternators suck and Fords rock. They're chunks of aluminum and copper that make juice. I think you just need to wire up the other wires, which you would have to do if you bought a Ford alternator anyway.

Google it and you'll find a bazilion videos, photos, tutorials, etc on how to add the wires. The short version is that the alternator won't charge until you tell it it needs to. Since it doesn't know, (one of the missing wires) it won't charge until you rev it up and get the alternator over a certain RPM.
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Gorf
While there are lots of folks out there with streetrods and hotrods with 1-wire setups that work great, from an electrical engineering perspective the 3-wire regulator is more reliable and more consistent. As pointed out above, you don't really see 1-wire alternators in use in production street cars/trucks. In fact, now a days the alternators are controlled carefully through ECU feed back. OK, anyway before you pull that SI off and redo the serpentine and pulleys, you can convert your existing 1-wire to a 3-wire pretty easily. The difference is the internal regulator. You can buy the part on line and then just open the alternator and replace it. Viola, 3-wire. Usually you can find them for less than 20$.
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ogre
And those who say it can't be done, should get out of the way of those of us that have done this for years without a problem.

Having run 1 wire GM alternators for the past 30 years on multiple vehicles, I honestly can't see the problem. We used to jumper right on the alternator. I currently run a 130 amp, 1 wire on my 58 TRUK. I do keep a heavy duty rectifier and regulator in stock, it will fit and convert any heavy duty SI to 1 wire. Haven't needed it in 10 years.
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Steve69SS396
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I call BS. For years I ran a huge Moroso alternator pulley on my car to keep from throwing the alternator belt. The only time it was noticeable was at idle with the A/C, lights, etc. running. Above idle it was fine. This was back when I ran a V-belt to the alternator and water pump. At 8,000rpm the belt would turn inside out, it wouldn't actually throw it. For the last 10 years I've run 1 wire 100-150 amp alternators with a dedicated V belt or a multi ribbed belt and they provided plenty of power at idle and above.

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Racer-X-
I think we've run off the OP here.

But there's some serious misinformation on this thread. GM SI series alternators (the most common "1 wire" setup) produce very little current at idle speed. They aren't a good choice for a vehicle where the primary cooling fan(s) is/are (an) electric fan(s).

A 100A CS130 alternator will produce much more current at idle than even a "high performance" 150A "1 wire 10SI."

More modern designs (AD230/AD244) produce even more current at idle, and are more appropriate for modern fuel injection systems and electronic systems combined with electric primary cooling fan(s).
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U_Boat
If it is working as it should, the first time you rev over 2000 or so it will turn on and charge even down to idle after that. if this is not the case... 1. bad alternator. 2. the wire between the alternator and the battery / load is too small (it is making what is the right voltage AT ITS TERMINAL) and you are dropping voltage over the tiny connection wire . 3. you have a monster load and the alternator is too small.
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