1973 Huco voltage regulator

[denson]

My 1973 911 has a regulator which says, Huco 130428 15V. Does this mean I have a Marchal alternator as opposed to Bosch? If this is the case, what alternator would I use?

Thanks,

[gled49]

post a picture.

[304065]

It doesn't mean anything, Huco is an aftermarket regulator. To identify your alternator you need to look at the back of it,where the wires connect, under the fiberglass shroud.

[edmayo]

The Bosch alternator has a coarse thread pitch, 1.50 I think, and the Marchal is a fine pitch, maybe 1.00. Don't have them here to measure.

[denson]

Thanks everyone. I always thought that certain alternators (Marchall/Bosch) used certain voltage regulators. My thinking was there were "matched" sets. I see that is not the case.

[304065]

John,

Actually, that IS the case, it's just that the Huco is an aftermarket voltage regulator so it is impossible to infer which type alternator you have from it.

The need to use the same manufacturer comes from the fact that VRs have a "set-point" or a target voltage that they are designed to achieve. If you mismatch, you might end up with the wrong target voltage. I think it's more technical than that, because the VR uses pulse-width modulation of full strength field current to average into the set-point voltage-- think of this as duty cycle, the longer you have the field on, the higher the voltage goes. I can see different VRs using different voltages for the field (because the field windings and rotor design are different between brands) and therefore different assumptions about duty cycle.

Since all the setpoints are around 14V, practically speaking they interchange, or interchange with the Huco aftermarket, but nobody ever studies these things over 200,000 miles and analyzes then when they fail . . .

[denson]

304065,,, thanks very much. I always thought they were matched. The aftermarket VR throws this off as you said. I will take the fan blade off and check this out, so I know! Thanks again for the help.

[RSTarga]

The bearing just failed on the alternator on my 73, FYI it is an SEV Marchal and the regulator is also an SEV. Pretty good quality I'd say after 41 years of use.