Alternator Voltage Regulator Burning Out?

[John Borland]

I see I posted same reply twice, deleted one of them.

[John Borland]

Well guys, got my alternator back from the electrical shop the other day; it turns out that the rectifier was wired incorrectly (will have to alert our local Advance Auto of the problem). The electrical shop also installed a new Delco voltage regulator. I re-installed the alternator and tested it with my new analog meter (that finally arrived yesterday). The output reads a little less than 15 volts, but it is impossible to read the meter in tenths. Might take the car to electrical shop and have them read it on a better digital meter than what I have just to have peace of mind – don’t want to burn my battery up on a long trip.

Now to my original problem of the coil heating up. Took the car out for a twenty minute 50 mph drive without the coil heating up. After the ride the coil was a bit warm, but I could very easily hold my hand on it. I’m hopeful that my electrical problems are over. The following are things (based much on your inputs) I did (and learned) in trying to correct the problem:

1) Cleaned all alternator bracket connections with wire brush.
2) Checked and cleaned both engine ground straps.
3) Checked points and found that they had somehow slipped to 0.016; reset them to 0.020.
4) Installed dedicated ground wire from alternator to frame.
5) Electrical shop found incorrectly wired rectifier and replaced voltage regulator with a Delco regulator. Cost was $40, but well worth it to me.
6) Ensured coil polarity was correct.
7) Checked and found no shorts in system. I did find a drop in voltage (~0.4v) on the distributor side of the coil when the key was on and the points were in the close position (I assume this is normal?). The voltage is the same when points are open.
8) Digital multi-meters (at least mine, which is a craftsman) don’t work with Model A’s when they are running.
9) A bit concerned that alternator may be putting out a little too high of voltage, but hopefully can check with a better digital meter. My alternator pulley O.D. is 2”.

Once again, thanks for all your great input. Fordbarn is a great asset for us all.

[100IH]

I guess that your not out of the woods yet but getting closer. A word to the wise; As soon as you were told about the ground, you could have just gotten a 6 foot piece of wire and put in the temporary ground and then watched for a change. I realize that there were issues with the alternators, its about the method of testing by supplying a bypass or temporary path. If that is the fix THEN build the permanent additional. All technicians have these jumper leads with some kind of medium size clips.

[MikeK]

Originally Posted by John Borland

. . . The output reads a little less than 15 volts, but it is impossible to read the meter in tenths. Might take the car to electrical shop and have them read it on a better digital meter than what I have just to have peace of mind – don’t want to burn my battery up on a long trip. . .

Just a heads up here- ALL the one-wire Delco 10/12SI regulators are made in china by Transpo and set at a whopping high 14.8V. with no temperature compensation or time setback like three wire regulators on more modern design alternators.

That 14.8V set-point is good for short runs only. Driving many hours @14.8V will cook your battery to an early death. That's why many prefer the three-wire regulators. They are available in several more reasonable voltage set point configs. Ask your alternator re-builder. Modern cars run at ~13.5V after 20 minutes or so.

Why are they set so high? Their market- classic and antique cars that sit un-run for a week or more then run only short distances. Also because the uninformed public likes the way brighter lights, which then burn out sooner! FWIW, the 6V versions are set at a whopping high 7.8V, they should be 7.1 or 7.2V MAX.

[Badpuppy]

The place to check is between battery posts while charging. This will eliminate any voltage drop in both supply and ground paths. Ideal float voltage is 14.4V for 12V battery (7.2 for 6V) and can vary a bit. You can use your DVM, it's electrically "quiet" there. Your battery shouldn't hydrate below 15V.

The regulators that are designed for one-wire applications are set higher because it is assumed there is some voltage drop across the circuit. But he 3-wire configuration provides much better control of what is delivered to the battery.

[GPierce]

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Originally Posted by MikeK

Just a heads up here- ALL the one-wire Delco 10/12SI regulators are made in china by Transpo and set at a whopping high 14.8V. with no temperature compensation or time setback like three wire regulators on more modern design alternators.

That 14.8V set-point is good for short runs only. Driving many hours @14.8V will cook your battery to an early death. That's why many prefer the three-wire regulators. They are available in several more reasonable voltage set point configs. Ask your alternator re-builder. Modern cars run at ~13.5V after 20 minutes or so.

Why are they set so high? Their market- classic and antique cars that sit un-run for a week or more then run only short distances. Also because the uninformed public likes the way brighter lights, which then burn out sooner! FWIW, the 6V versions are set at a whopping high 7.8V, they should be 7.1 or 7.2V MAX.

I rebuilt an alternator to make it 6 volt positive ground. I installed a Transpo regulator.
Just now checked at the battery; 7.25 volts with my Fluke digital. I’ll continue to keep a close eye on the water usage. For the past 500 miles it hasn’t used any.