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Thread: synchronous motors??

  1. #1
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    Default synchronous motors??

    I have an idea for a clock that I would like to build.
    I need a 60 rpm motor, and will gear from there.
    I don't know anything about motors really, but I'm thinking that I need a 120 vac 60 rpm synchronous motor.
    But what does that really mean?
    Synchronous to what?
    What if my line voltage varies?
    Do they have some sort of crystal that keeps RPM in line?

    Also, the motor needs to be relatively small. For instance:

    https://www.amazon.com/Synchronous-E.../dp/B012W0AMYE

    Please educate me.

    Thanks, Sid

  2. #2
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    Default

    It'll be synchronous to your line frequency not voltage.

    These motors were very common in the old analogue electric clocks.

    They never kept perfect time though as the supply company varies the frequency by tiny amounts to control demand, at least in the UK they do. Its only points of a Hz but it changes all the time.

  3. #3
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    OK, that makes sense.
    It would be optimal if I could get a more accurate motor.
    Where is Wes when I need him?

    By the way, I wonder how he is doing??

    Thanks, Sid

  4. #4
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    In the US, the powerco is required to keep a long term average within a small error. (there is a move afoot to remove that requirement)

    In practice, the frequency cannot vary much at all, as every generator must be in step with the grid, or it may either turn into a motor, or else be bogged down to grid frequency by being unable to drive the whole grid by itself. Keeping accurate time good enough for any normal propose is no issue at all for synchronous motor clocks unless they get so worn that the motor cannot drive the mechanism at full speed.

    More accuracy that that can be obtained b crystal-based oscillators, of varying complexity, etc. Clocks that self-correct by receiving a time from the NIST exist. You can buy such as clocks or watches, etc. They typically sych once a day, some may synch more often.
    Last edited by J Tiers; 07-12-2019 at 12:34 PM.
    1601

    Keep eye on ball.
    Hashim Khan

  5. #5
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    I don't think for my purposes I need a self correcting mechanism.
    I might just buy one of the motors from Amazon and see how well it works.

    Sid

  6. #6
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    Maybe just buy a timer, one of the old types with a synchronous motor and all the adjustable mechanical stops for on and off times. I see them all the time at flea markets and thrift stores. Chances are you will get what you need out of them. They are clocks after all.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  7. #7

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    Stepper motor controlled by a crystal oscillator would be a novel approach, there may be prior art however (-:

  8. #8
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    Sid, are you familiar with "gearotic motion" software? Its done by Art, the founder of Mach3 cnc software. On their forum are tons of clock mechanisms people have built, the software is exceptionally useful for that purpose. It also does many types of gears, I made the helical gears for my gatling gun with the software, came out great.

  9. #9
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    Many sources for synchronous timer motors, including the older washer & dryers, all used these 60hz synchronous timer motors.
    Max.

  10. #10
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    I've found several that ran at different speeds, but all had the same basic package. Some were 1 rpm, I've had 3 rpm, 4 rpm- the 1 rpm can easily be made to kick over a minute hand.

    In my experience, a clock with a synchronous motor can keep essentially perfect time. The synchronous motor is a counter really, counting the power line pulses coming in. Unless friction interferes with that, the motor will advance a gear train in perfect step with the incoming frequency. No matter if years go by, the 'count' will be exactly what the power company put through the lines over that time period. The big snag here of course is power outages, where you lose sync.

    These things will run for decades- surpassing the life times of electronics in many cases.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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