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OT Magslips, selsyns, synchros, resolvers.....and auto alternators.

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  • OT Magslips, selsyns, synchros, resolvers.....and auto alternators.

    I didnt want to derail Darryl's "OT- photo interrupter question" topic where these devices are mentioned (not the alternators).

    But it does appear to my eyes that a car alternator (some types at least) are very similar in design to magslips/selsyns/synchros et al.

    If the diode bridges are removed from a pair of alternators, the three stator terminals of one alternator connected to the stator terminals of the other and AC of a suitable voltage applied to the rotor coils will one alternator follow the positional movements of the other?

  • #2
    I have a feeling there may be too many poles in an alternator to get an absolute reading like with a resolver. Plus you would have to come up with your own reading method since you can't use any of the existing chipsets or resolver modules. The output on a standard resolver is 90 degrees out, the output on a alternator is 120.

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    • #3
      Originally posted by macona
      I have a feeling there may be too many poles in an alternator to get an absolute reading like with a resolver. Plus you would have to come up with your own reading method since you can't use any of the existing chipsets or resolver modules. The output on a standard resolver is 90 degrees out, the output on a alternator is 120.

      Yes, I thought about the multiple pole issues, one of my old alternators has 3 'fingers' on each end of the rotor that fold around and interlock to make three pairs of poles, I wondered what would happen if two were cut off from each end. I am thinking that would be two poles on the rotor but I am uncertain how they would interact with the pole pattern of the stator.

      I was not thinking of reading the output so much as having one machine track the movements of the other. With too many poles they might turn at the same rate but could become 120 degrees out of phase, maybe.

      BTW There used to be things in old GCA radar stations where the operator turned a little handle on what looks like a synchro the output of which went though big power amps and drove a much bigger positioning machine at the antenna site.

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      • #4
        Originally posted by The Artful Bodger
        BTW There used to be things in old GCA radar stations where the operator turned a little handle on what looks like a synchro the output of which went though big power amps and drove a much bigger positioning machine at the antenna site.
        LeBlond used exactly this method on their first CNC lathes, this was used to operate the axis in the Manual Mode, each hand wheel had a resolver under it.
        Also two stepper motors hooked directly up to each other, one can be used to track the other.
        Max.

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        • #5
          I am pretty sure I have read of some successful conversions of auto alternators to stepper motors. I think the pole arrangement would not be suitable for them to be used as synchros or resolvers.
          Don Young

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          • #6
            Originally posted by macona
            [ ... ] The output on a standard resolver is 90 degrees out, the output on a alternator is 120.
            If I recall correctly, 3-phase A.C. can be converted to 2- phase (and vice-versa) by using a "Scott-T" transformer.

            I just looked up the problem in my rather ancient copy of Dawes "Electrical Engineering, Vol 2" and the previous statement is true. However, explaining, or even understanding, it is 'way beyond me at this point in time. If you're interested a search on "Scott connected transformers" or "Scott T" may be helpful.

            I recall that they are/were used in servo control systems but beyond that memory fails me. Too many years have passed since Basic E. T. School.

            -bill

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            • #7
              Bill, if I understand correctly the typical resolver has two phases at 90 degrees and the power units, synchros etc, have three phases at 120 degree phase angles. I suppose there must be a place for the Scott-T transformers to interface the two.

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