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Discussion Starter #1
Hey guys, I am having a really interesting issue with the car. For the last 4 years so, the car was mostly sitting in the garage, but when I would drive it, it would burn out alternator, where it would stop charging after about 200 – 300 miles. I’ve used various brands, from AutoZone, to MotorCraft, to something else I forget, but can’t seem to get any luck with this. Can someone please help me with understanding the issue? A couple things to keep in mind

1. This doesn’t seem to be related to the battery size: This coincidentally started around the time I’ve decided to try the Odyssey PC680 battery, but I’ve recently went back to a normal sized Optima, and the issue is still present

2. This doesn’t seem to be rpm related: Someone I know suggested that I’m possibly overspinning the alternator, but 6500 rpm doesn’t seem like that much to me, considering that I’ve use to track the car for years, shifting at 5500 rpm, and had 0 issues. I even had a two year period with the build motor when I would shift at 6500 rpm and still had no charging issues.

I am honestly stomped. This has a feeling of an electrical issue to me…
 

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what electrical tests have you done?

when you say you are burning them up, what specifically is the failure?

reg?
diodes?
windings?
 

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Discussion Starter #3
All I know is that the alternator would stop charging. I haven't performed any tests yet, I've been just changing them out, and hoping that the problem would go away, but it's beyond that now. What kind of tests can you suggest that I perform?
 

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why do you think its not battery related?

why do you think its not rpm related?
 

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Discussion Starter #5
I don't think it's battery related because I'm on a regular sized battery at the moment, which is well within factory requirement spec. I don't think it's rpm related because I've ran at the 6500 rpm for almost 2 years, with multiple track days, before this started to happen every 200 miles or so. Had it been an rpm issue or battery issue, there would have been a correlating behavior when the components were changed, but this hasn't happened. At some point within 200 miles, the alternator stops charging.
 

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Did you test the alternators before changing them out?
You might be swapping good alternators for no reason. It could be as simple as a short in the alternator plug, and you disconnecting/connecting it makes significant contact for a little while, ...
 

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I don't think it's battery related because I'm on a regular sized battery at the moment, which is well within factory requirement spec. I don't think it's rpm related because I've ran at the 6500 rpm for almost 2 years, with multiple track days, before this started to happen every 200 miles or so. Had it been an rpm issue or battery issue, there would have been a correlating behavior when the components were changed, but this hasn't happened. At some point within 200 miles, the alternator stops charging.
when it stops charging does the amp or batt light come on?
 

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Does the car have any aftermarket items that use power? I had 93 GT convertible that I installed an amp and sub in and it started eating alternators. On hooded amp no more trouble. If you have not upgraded to a 3G now is the time.
 

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Discussion Starter #9
when it stops charging does the amp or batt light come on?
I remeber one of the occasions that the light went on, but this time the light is off. The only way I'm able to tell that the car isn't charging is by watching the battery gauge slowly show less and less charge.

Did you test the alternators before changing them out?
You might be swapping good alternators for no reason. It could be as simple as a short in the alternator plug, and you disconnecting/connecting it makes significant contact for a little while, ...
I've had an issue with that plug before, but it has been repaired since then. Also, if I remember correctly, a loose plug would also trigger a battery lights, and at the moment the battery light isn't on.

Does the car have any aftermarket items that use power? I had 93 GT convertible that I installed an amp and sub in and it started eating alternators. On hooded amp no more trouble. If you have not upgraded to a 3G now is the time.
I have added a small amp and a small sub about a month ago, but these issues have started long before that, so I don't think a larger stereo is the culprit here.
 

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THE light is part of the charging circuit

If you want to diagnose, that is where we start

Does the bulb come on with key in run?

Does go out when running?

Next will be a meter
You have one, do you know how to use it?
 

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An alternator needs 1800-2000 RPM at idle to make power and will make maximum output at 6000 rpm but will FAIL at 16,000 alternator pulley RPM
Measure Alternator pulley size (for example 2.5")
Measure Crankshaft Pulley Size (for example 5")
The Ratio is 2:1 (5 divided by 2.5 = 2)
To find MAX RPM: take your Max engine Speed (for example 5800 RPM) and multiply it by the calculated ratio (5800 x 2) = 11,600 shaft RPM
To find IDLE RPM: Multiply Idle RPM x Ratio (for example 1000 x 2) = 2000 shaft RPM @ Idle

Other things to look at:
1. Powder coated alternator bracket or alternator? Is mounting hardware clean and free of rust?
2. Visual inspection: Look for loose alternator connections and damaged/cut cable/wiring. Also check your battery for a loose connection.
3. Electrical test: Check your battery for over & under charging while under load and no load conditions.
4. Fusible link
5. Is your alternator sized correctly?

Good luck
Michael Plummer
 

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Discussion Starter #12
THE light is part of the charging circuit

If you want to diagnose, that is where we start

Does the bulb come on with key in run?

Does go out when running?

Next will be a meter
You have one, do you know how to use it?
I don't remember for sure if the light comes on when the key is in the ON position prior to ignition, but it's not on while the engine is running. Today I tried to check and see if the wire was loose, and I've noticed that if I pull the (stator?) plug completely out, the battery warning light doesn't come on, like it used to previously.



An alternator needs 1800-2000 RPM at idle to make power and will make maximum output at 6000 rpm but will FAIL at 16,000 alternator pulley RPM
Measure Alternator pulley size (for example 2.5")
Measure Crankshaft Pulley Size (for example 5")
The Ratio is 2:1 (5 divided by 2.5 = 2)
To find MAX RPM: take your Max engine Speed (for example 5800 RPM) and multiply it by the calculated ratio (5800 x 2) = 11,600 shaft RPM
To find IDLE RPM: Multiply Idle RPM x Ratio (for example 1000 x 2) = 2000 shaft RPM @ Idle

Other things to look at:
1. Powder coated alternator bracket or alternator? Is mounting hardware clean and free of rust?
2. Visual inspection: Look for loose alternator connections and damaged/cut cable/wiring. Also check your battery for a loose connection.
3. Electrical test: Check your battery for over & under charging while under load and no load conditions.
4. Fusible link
5. Is your alternator sized correctly?

Good luck
Michael Plummer
Based on the measurements of Crank Pulley (6.5 inches (165 mm) diameter = 20.41 inch circumference) and Alternator Pulley (2.2 inches (56 mm) diameter = 6.91 inch circumference), you end up with 2.95 ratio. This means that at 6500 rpm at the crank, I'm seeing about 19200 rpm on the alternator. That is quite a bit higher than previously mentioned 16000 rpm limit. One thing that still didn't make sense to me is why did the alternator work the whole time prior to this, and I had to go back and really dig deep into my memory. I remember that this all started, when I changed from conventional battery to a sealed cell small battery (Odyssey). When I went to a full size battery to try and fix this issue, the battery type was still sealed cell (Optima), not regular battery like the kinds you'd get at the parts store. My theory is, that maybe a regular non sealed cell battery allowed for something to happen that would put the excess stress on the battery itself, because I do specifically remember that battery would always have corroded posts, melted corroded cable terminals and at some point there was corrosion forming at the bottom of the battery tray, because the acid would spill from the battery itself. I wasn't sure if that was due to overcharging or dealing with lateral g-forces, but something was causing battery to get seriously affected.

1. Mounting hardware and brackets are all clean and rust free
2. No visible damage on either the alternator or the wires running to and from the alternator
3. Have not performed the test, will do so soon
4. Not sure what fusible link is
5. The alternator was ordered for the specific application of 94-95 Mustang GT, so I can only make an assumption that it's the correct spec.
 

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I'm not sure how your making out with your electrical tests and inspections but I wanted to cover the following briefly.

Q. I'm seeing about 19200 rpm on the alternator. That is quite a bit higher than previously mentioned 16000 rpm limit. One thing that still didn't make sense to me is why did the alternator work the whole time prior to this?
A. I'm not exactly sure when the failure is suppose to happen but I went through my share of alternators before I figured out I was over spinning them. I had to order a custom alternator pulley to keep my alternator pulley rpm under the 16k rpm limit.

Q. I remember that this all started, when I changed from conventional battery to a sealed cell small battery (Odyssey). When I went to a full size battery to try and fix this issue, the battery type was still sealed cell (Optima), not regular battery like the kinds you'd get at the parts store. My theory is, that maybe a regular non sealed cell battery allowed for something to happen that would put the excess stress on the battery itself,
A. I have no idea why the battery type would cause your alternator to fail.

Q. because I do specifically remember that battery would always have corroded posts, melted corroded cable terminals and at some point there was corrosion forming at the bottom of the battery tray, because the acid would spill from the battery itself. I wasn't sure if that was due to overcharging or dealing with lateral g-forces, but something was causing battery to get seriously affected.
A. Over-charging is when the corrosion is on the battery's positive terminal and Under-charging is when the corrosion is on the battery's negative terminal. Dying/Failing alternator has me thinking faulty connection, or wire shorting.

Q. No visible damage on either the alternator or the wires running to and from the alternator, and not sure what fusible link is
A. Fusible link: Several wire gauges smaller then the circuit it protects. Looks like somebody heat-shrinked the wire together and you may see bare wires ends coming from the ends where the insulation is. Trace that cable from the alternator all the way back removing wire loom and harness wrap.

Good luck
Michael Plummer
 

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no electrical meter nor a test light at the least has been used

the mark 1 eyeball can only go so far
 

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should you change the bulb or check if it is supposed to be lit with a test light?

ie pretend to be the bulb
 

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A blown fusible link won't "look broken" like a regular fuse. It would be like a stretched out rubber band. You must physically check them.
 

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Discussion Starter #19
should you change the bulb or check if it is supposed to be lit with a test light?

ie pretend to be the bulb
yes

A blown fusible link won't "look broken" like a regular fuse. It would be like a stretched out rubber band. You must physically check them.
I'll take a look at the harness. I haven't dealt with much harness work before, so all this is fairly new to me. The car is also in storage, which means that I can't really pop into it and check things right away, but definitely something I will take a look. I've done some reading on the side about fusible links, definitely need to buy a multimeter as well.
 

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Discussion Starter #20
I'm not sure how your making out with your electrical tests and inspections but I wanted to cover the following briefly.

Q. I'm seeing about 19200 rpm on the alternator. That is quite a bit higher than previously mentioned 16000 rpm limit. One thing that still didn't make sense to me is why did the alternator work the whole time prior to this?
A. I'm not exactly sure when the failure is suppose to happen but I went through my share of alternators before I figured out I was over spinning them. I had to order a custom alternator pulley to keep my alternator pulley rpm under the 16k rpm limit.

Q. I remember that this all started, when I changed from conventional battery to a sealed cell small battery (Odyssey). When I went to a full size battery to try and fix this issue, the battery type was still sealed cell (Optima), not regular battery like the kinds you'd get at the parts store. My theory is, that maybe a regular non sealed cell battery allowed for something to happen that would put the excess stress on the battery itself,
A. I have no idea why the battery type would cause your alternator to fail.

Q. because I do specifically remember that battery would always have corroded posts, melted corroded cable terminals and at some point there was corrosion forming at the bottom of the battery tray, because the acid would spill from the battery itself. I wasn't sure if that was due to overcharging or dealing with lateral g-forces, but something was causing battery to get seriously affected.
A. Over-charging is when the corrosion is on the battery's positive terminal and Under-charging is when the corrosion is on the battery's negative terminal. Dying/Failing alternator has me thinking faulty connection, or wire shorting.

Q. No visible damage on either the alternator or the wires running to and from the alternator, and not sure what fusible link is
A. Fusible link: Several wire gauges smaller then the circuit it protects. Looks like somebody heat-shrinked the wire together and you may see bare wires ends coming from the ends where the insulation is. Trace that cable from the alternator all the way back removing wire loom and harness wrap.

Good luck
Michael Plummer
Michael,

I've just called BBK, and they say that their alternator pulley is 3.25 inch diameter, which means that I don't even have to combine it with the other pulleys to get the desired ratio ((6.5/3.25)x6500) = 13000 rpm). 13000 rpm may be pushing it a bit, but it's still way under 16000 rpm limit, which I was getting close to even when I was tracking the car with stock engine and shifting at 5500 rpm. You have mentioned that you've bought a custom pulley, may I inquire where? I'd prefer to change just one pulley, and I have no interest in underdriving the rest of the accessories, especially the power steering pump, since I'm running a full hydroboost conversion, and would like to keep the assists in line with factory settings.

Regarding the cable corrosion, I would like to say that it was positive side, but it's been such a long time, that I honestly, can't recall anymore. I'll have a shop go through the harness regarding the fusible link as well, and just the harness all together, to make sure that there isn't exposed wiring anywhere. The car is 25 years old, has 246k miles on it, anything is possible at this point.

BTW, the diameters of BBK pulley are following, per BBK customer support:
Crank: 5.25
Water Pump: 6.0
Alternator: 3.25
 
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