Alternator Voltage Regulator Burning Out?

J

John Borland

Junior Member
Hello All,
I have a 1931 Model A Coupe that I converter to 12 volts twelve years ago. Until recently I have had no problems with the electrical. However the car has started to burn through coils. An epoxy filled Pertronix 3 ohm coil will now only last about 500 miles. The coil gets hot to the touch after just a few miles of running (oil filled coils are even worst). I have been unable to find any electrical shorts with my multi-meter, but did find (with a multi-meter) that the alternator output jumps around so much that it is impossible to read on the meter (this made me think that the internal voltage regulator was bad). I was hopeful that the erratic alternator voltage to the coil was my problem.

I took the alternator to Advanced Auto for testing, and they confirmed that it was shot. I purchased a rebuilt 7127 SE, 12v, single wire, negative ground alternator. I installed the alternator and immediately tested its output. For a few seconds it showed an output of 15 to 17 volts, but then it went to bouncing around so much that a reading could not be had. I took the alternator back to Advanced Auto; it tested bad, and they gave me another one. They tested this alternator before I left the store and it tested good. Took home, installed, and experience exactly the same erratic readings.

Not sure what to do at this point. Please respond if you have any experience or suggestions that may help in troubleshooting the coil, and now alternator problem. I have pretty well exhausted my limited knowledge. As a point of fact, this problem may of been going on for some time without my knowledge, since I have only recently been taking the car out on long tours where it is run for extended times. Thanks in advance for any help you may be able to provide.

-John
 
First things first, you know that the alternator is not right take it back and get your money back and try a different brand /style and or supplier
Get that voltage stabilized then go from there, that might even fix it
Electrical problems suck I feel your pain , good luck
Phil
 
If an alternator does not have an excellent ground path to the battery it is going to fry the internal regulator. Bracket tight to engine, engine/trans has dedicated ground lead to frame. Henry's original collection of ground paths are subject to intermittent variances.
 
Bad ground is most suspect. Most alternators have a threaded hole on the back plate, maybe a ground post. Run a #12 wire from there to a hood latch nut, or all the way back to the battery if you want, to be sure the alt. is well-grounded.

Check battery level while you're at it.
 
I also agree with the bad grounds. However, if you are just buying rebuilt Alternators, then you are getting less than great units. The rebuilt ones are nowhere as good as a NEW one.
I use a small Denso 3 wire unit rated at 55 amps. Cute & works great
 
Thanks guys, I have the engine grounded from the battery ground position on the frame to the ******, and also from the flywheel casing to frame. Will check to see if I can ground the alternator separately as suggested.

I really don't think I'm been getting bad alternators from Advanced Auto since three alternators all exhibited the same symptoms. Don't want to take it back until I have some insight on what is going on. I’m sure Advanced Auto doesn’t want to keep giving me replacement alternators until I can get to the root of the problem. Of course if the current alternator is fried, I will have to get another to see if improved grounding is the culprit.

The car runs great, would this be the case with a ground so bad that it fries the voltage regulator in a manner of seconds? Will keep all informed; please keep any suggestions coming in.
 
Good afternoon...If the car ran fine for years, then you most likely have a loose ground or dirty ground or a loose wire or battery cable terminal that has come somewhat loose. Start with your battery and check each and every wire and connection in your system. Clean, clamp, and re-tighten at each point. A second 00 gauge ground cable from one of the major suppliers or NAPA from your transmission to the frame can be very helpful...Ernie in Arizona
 
Bob C said:
Are you using an analog meter, digitals don't like the Model A ignition system.


Bob
Click to expand...




I too have a cheap Digital Multi Meter that was bought from a home improvement store be unusable, as long as the engine is running
Thing goes haywire. Borrowed a Fluke meter from work and it was OK, not saying all Fluke Meters are OK.


Also have an inexpensive IR Temp Gun, same issue. Have to turn motor off. Not a big issue, just take readings quickly after motor shut off.


That's the difference between consumer cheap tools, and professional grade electronics, things like susceptibility to electrical noise - arcing (points, plugs, rotor gap, generators, etc.), anything with a DC motor, radio waves, lightning generated electrical noise, etc .


I used to perform electrical noise testing at a place I worked at, and having design changes made to improve product.
 
Thanks to all of you who commented “bad ground”. You just outlined my project for today; run a ground wire from the lug on the back of the alternator to the battery ground. I’ve been relying on the alternator’s mechanical attachment to the engine for a ground and so far have gotten by with it. No more.
I have a ground from the transmission to the frame ground lug the battery post is connected too.
 
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Got’er done. Alternator ground lug wired to the radiator shroud attachment bolt and the battery ground post both.
 
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John Borland said:
Thanks guys, I have the engine grounded from the battery ground position on the frame to the ******, and also from the flywheel casing to frame. Will check to see if I can ground the alternator separately as suggested.

I really don't think I'm been getting bad alternators from Advanced Auto since three alternators all exhibited the same symptoms. Don't want to take it back until I have some insight on what is going on. I’m sure Advanced Auto doesn’t want to keep giving me replacement alternators until I can get to the root of the problem. Of course if the current alternator is fried, I will have to get another to see if improved grounding is the culprit.

The car runs geat, would this be the case with a ground so bad that it fries the volv tage regulator in a manner of seconds? Will keep all informed; y keep any suggestions coming in.[/QUO TE]






You say above that alternator fries in seconds ... Maybe original was positive ground alternator? If your battery is positive ground and you are installing neg ground ones from parts store that could be why they are burning up!

Many parts Stores do not know the difference.

Most parts stores sell NEG ground alternators ... POS ground ones are special order!
Click to expand...
 
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Still haven't heard what the battery voltage is with the engine not running.


Benson brings up a very important point.
I've even seen + ground alternators that still had the NEG ground marking on the case.
 
John, just a thought here.

Maybe go back to original 6V with a generator, with Tom's EVR and a diode cutout. Or a good original cutout either way.

We have that on the Roadster and the '36 Ford and I couldn't be happier. It works great.

Please I don't mean to open up the genny vs. alternator thing that has been hashed out here about as badly as whitewalls, BUT Tom's EVR is what Henry would have probably run had Tom been around back then:)
 
Just a status update on my alternator problems (and coil overheating problem). I took the alternator to a highly recommended electrical shop to have them have a look at it. Hopefully I will hear from them shortly. In the meantime I have installed a ground wire from my battery ground location and extended it to the alternator location. Think I will invest in an analog meter for future testing. Will get back with everyone once I get the alternator back. Thanks for all your comments.
-John
 
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