Alternator issues

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dartlove

dartlove

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so I have a strictly race 64 dart. 496ci engine with a 1 wire 90 amp alternator. Wire from alternator to battery. No disconnect in-between. Not sure what is going on but my alternator's keep going out. They quit charging after only an hour or 2 of total run time. On top of that my batteries are being drained. I am at a loss. Getting tired of buying alternator's. Any help or suggestions are welcomed.
 
You can calculate the rpm of the alt.

Engine rpm X crank pulley dia X alt pulley dia = alt RPM.

What voltage is the Alt charging the battery?

Over tightining the belt?
 
I also use a 1 wire 100 amp altenator. I ran my wire to a normally closed solenoid and shut it of before the burnout. I was throwing the belt a 8000 . Now I have no problems. If you spin them to fast you will burn them up.

The first picture is the wire running right to the positive terminal bulk head. The second has the solenoid installed.

You would not believe how much that alternator takes to spin with it turned on. Bench test it with a drill see what happens at 800 RPM's when it kicks in. LOL

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I haven't even spun this engine past 5500 rpm. I ordered a new disconnect switch with alt disconnect. We will see how that goes
 
5000 rpm, 6 inch crank pulley and 2 inch alt pulley = 15,000 rpm alt shaft.

Do the math, with your own sizes you might be surprised.

Some alternators list a max RPM in their specs
 
Over RPM is the only thing that makes sense here. I don't know what else it could be. You say you have wire direct to battery. How large is it?

Something you might try on the "next" one is to install it and before you do much else, monitor the output voltage from the alternator output stud (not at the battery) to the engine block. Rev it up some and see if the voltage wants to climb
 
You can just calculate the ratio of the diameters. 7/2 = 3.5. So at 5500 crank rpm the alternator is going 3.5 times faster, 19,250 rpm. Wow!
 
Wow that is a lot. This engine hasn't even been raced yet. That rpm was just to test rpm limiters. This was supposed to be a drag race alternator.
 
dartlove said:
Crank pulley is 7" alt pulley 2". Don't know the math. 8ga wire.
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It's simple. It's just a ratio. Divide one by the other. 7 divided by 2 is 3.5 so the small one is doing 3.5X the large one. Or you can do it the other way. 2 divided by 7 is .286, so the big side is doing .286X the small one

I "still remember" that the old 440-6 (70 RR) was nearly 4:1 so at 5K engine RPM the alternator was doing about 20K. I don't know if "at the time" that was the original pulley or not. I tore up several alternators on that thing physically and mechanically and that led to electrically LOLOL
 
So I went out and did some measuring. Crank pulley 5.75" alt 2.5". So if I did it right the alternator shaft is turning 15,400 rpm's, and will have to spin even faster when I take it to the track. At the strip I estimate turning anywhere from 6200 to maybe no more than 6800. I talked to the manufacturer. The gentleman I spoke with didn't really know much about their alternator's. All he could tell me that it was good up to 8000 rpm. But couldn't say if that was engine rpm oralt shaft rpm. Not sure how it can be a drag race alt and only be able to handle 8000 rpm at the alt shaft. Alternator's are a baffling part.
 
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A little more info might help.

1. You mentioned batteries, do you have more than one?
2. Have you changed out your battery?
3. Have you measured battery voltage at idle?
4. Have you measured battery voltage revved up?
5. What kind of alternator is it?

Seems unlikely that over revving is you problem if you don’t see any mechanical damage.
 
Most high RPM alternators I have seen have a large pulley like 4 inches

The math is: engine rpm times crank pulley dia and that result devided by alternator pulley dia
 
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I, like OMM have a shut off switch on my alternator. When I hit the box, switch goes off, when I hit the turn out, switch goes on. I'm crossing the stripe at about 6400 RPM.
 
Mike69cuda said:
A little more info might help.

1. You mentioned batteries, do you have more than one?
2. Have you changed out your battery?
3. Have you measured battery voltage at idle?
4. Have you measured battery voltage revved up?
5. What kind of alternator is it?

Seems unlikely that over revving is you problem if you don’t see any mechanical damage.
Click to expand...
I have only one battery. I do have a fully charged spare. When I found one dead, I changed swapped it out. That one drained as well. My father in-law checked it and just said no it isn't charging. I trust him because his years of racing experience and being a master mechanic. Alternator is a top street performance.
 
Demonracer said:
I, like OMM have a shut off switch on my alternator. When I hit the box, switch goes off, when I hit the turn out, switch goes on. I'm crossing the stripe at about 6400 RPM.
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Can you explain this OMM &the switch set up?
 
I don't know how you'd shut off a "one wire." Disconnecting it from the main charge wire is asking for trouble --alternator damage
 
OMM-Oldmanmopar. I have a switch that cuts out the charging of the battery when I make a pass. It may not work in your situation as you have a one wire alternator, I've never run that setup.
 
You have to use a solenoid to shut a one wire off. Otherwise you would need a very large wire and switch to andle what you are doing . Like a kill switch. I have a small toggle switch in the car and it controls the solenoid. This solenoid works the opposite of a starter solenoid I bought it a NAPA. It was on the car for 3 yrs street driven and raced with no problem.

I installed it as per Tony Hirschman. Kyle Busch spotters father who builds super modified Nascars. He plumbed and helped with my car. I know him since I was 13 yrs old. My son is now friends with his son Matt hirschman . Steve my son does machine work for them like squaring billet spindles and other items on the cars.

My motor would see RPM's of 9300 at times with me driving . I am old and slow on the shift when the light comes on. I ran a 69 lower pulley for the smaller diameter and depth to fit the fluid damper. I only drove the alternator off of the crank nothing else. I used the power steering bracket to mount the alternator. I had to change the bracket to metris to fit the alternator snug. That is what my 100 amp called for.

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Steve 106.JPG
 
so update : I talked to the alternator guy that is handling the warranty/ repair work for the company I purchased my alternator from. He said there was a problem with the regulators hanging open. He sent me a new regulator I put it in. Still no charging. Now I know all of you alternator pros think I am spinning this too much, but I was assured there would be more damage to the alternator than just not charging. Could there be some other underlying issue that is killing these alternators?
 
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