Odd alternator winding configuration. 12 pole rotor 11 pole stator.

[tcmtech]

I have been processing my scrap metals this week to sort the copper and aluminum out from the iron in all of my old transformers, light ballasts, electric motors, 6 and 12 volt DC generators, and old alternators. Copper is over $3 a pound locally if you are wondering.

While processing old alternators I have noticed over the years that the Motorcraft alternators from Ford vehicles tend to always have this odd setup of having a typical 12 pole rotor but an odd 11 pole stator winding configuration. Although I am knowledgeable of standard single and three phase motor and generator/alternator working theory this one has always had me pondering on why they did it that way.

On many of the aftermarket rebuilt Motorcraft alternators they are rewound with the expected 12 pole rotor and 12 pole stator configuration but on the factory units they have six of the 11 stator coils spaced normally matching the rotor pole spacing and the other five are spaced in uneven offset steps for the other half of the stator. This pattern is used in all three of the phase windings also.

So whats the deal with the odd factory 11 on 12 design?

 

[KeepItSimpleStupid]

Can I guess?

Suppose time = money. Further suppose it takes the same amount of time to wind the rotor and stator. Just so happens that the rotor gets one less turn in that time.

Or, in reality the rotor is a permanent magnet and thus the number of poles is irrelevant whereas in the stator, an evanly spaced pole arrangement makes sense so the ripple would be the same number of degrees apart.

 

[tcmtech]

They are not permanent magnet rotors just standard electromagnetic types.

I am trying to find someone who has a rational explanation for the design other than Ford was being cheap asses when they designed them.

I have considered that most of what Ford made was of reasonable quality but unfortunately I have never liked their alternators. They are always electrically noisy, have marginal to poor voltage regulation and to me seemed questionably rated for what the amperage numbers said on them. I just attributed that to the strange 11 pole stator winding configuration.

 

[crutschow]

It may have something to do with spreading the frequency of the alternator output ripple (sort of a spread spectrum) so that it is less noticeable in the radio or other susceptible electronic devices.

 

[KeepItSimpleStupid]

What I'm saying is that the rotor makes very little difference how many poles there are, I think.

I remember my first 1965 FORD and the acronyms Fixit Or Repair Daily or Found On the Road Dead. I was 15 Yo and in high school with no license yet, but I had a car that was wrecked. Cost me $25 for the car which wasn't road worthy. I put a lot of sweat into that thing, but things were wierd.

1. They switched the positive for the dome lamps.
2. A thermal breaker was integrated in to the headlight switch. It caused blinking when a headlight filament shorted. Very wierd experience.
3. The gas pedal was hinged from the top. A fully loaded 18 wheeler I took a spin around a parking lot had the brake hinged from the bottom so it looked like an accelerator petal. It confused me for a second or so.
4. The windshield wiper had a "park" winding. It's first sweep was from "park", but wasn't a full sweep. Subsequent sweeps were from a bit from park and a full sweep. When you turned the wiper off, it immediately parked and didn't make a full sweep. The strangest thing I ever saw.
5. Single master cylinder and I had a brake spring failure and totally lost brakes. A 1968 Chrysler that my parents' had did have a dual master cylinder.

When I got done with the vehicle I had a 6 CYL car getting 18 MPG in the early 70's. Biggest changes were the head was sent to a machine shop, an optical ignition system was retrofitted, the intake manifold was ported with a rotary file and the carb was rebuilt.