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Stepper Motor Trick — Parallax Forums

Stepper Motor Trick

ercoerco Posts: 20,257
Dude runs a stepper motor without a driver, just using a transformer & electrolytic capacitor.

Comments

  • Pretty clever! I have some 110VAC 3-wire synchronous gear-motors that operate the same way. The cap provides a 90-degree phase shift.

    I'm not sure about using an electrolytic cap in a pure AC circuit, though, since it's polarized. I suspect that it would not last very long.

    -Phil
  • It's neat, but doesn't that defeat the purpose of a stepper motor?
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2017-02-11 03:35
    Martin_H wrote:
    It's neat, but doesn't that defeat the purpose of a stepper motor?
    If you've got a 200 ppr stepper and just need a 72 RPM motor, it seems like a pretty simple way to get it. Moreover, from a pedagogical standpoint, it makes a great applied lesson in capacitance and inductance.

    -Phil
  • Time to dig through the parts bin for some crossover caps?
  • ercoerco Posts: 20,257
    I'm not sure about using an electrolytic cap in a pure AC circuit, though, since it's polarized. I suspect that it would not last very long.

    Yeah, I wondered about that too. Caps blow pretty easily with reverse DC voltage applied.

    Moreover, from a pedagogical standpoint, it makes a great applied lesson in capacitance and inductance.

    Finest use of pedagogical in ages!

  • Two back to back electrolytics should be fine, no?
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2017-02-15 03:35
    Back-to-back in series maybe. The net capacitance would be half of the individual ratings, if they are equal.

    -Phil
  • Back-to-back in series maybe. The net capacitance would be half of the individual ratings, if they are equal.

    -Phil

    Exactly, and that should essentially make a non polarized cap. I use that trick in old radio restorations.

  • ercoerco Posts: 20,257
    Jonathan wrote: »
    Exactly, and that should essentially make a non polarized cap. I use that trick in old radio restorations.

    Nice trick! Much better than this trick filed under "fake Chinese capacitors". :)

    FakeChinesecaps.jpg
    603 x 400 - 48K
  • I use that trick too, but for the forces of good. This is a cap from a 1948 Zenith Transoceanic that is currently on the bench:

    20170202_202235_rsz.jpg
    800 x 450 - 70K
  • ercoerco Posts: 20,257
    Beautimous! A purist among us.
  • Jonathan wrote:
    I use that trick too, but for the forces of good. This is a cap from a 1948 Zenith Transoceanic that is currently on the bench:
    Please be careful breaking open old caps. The "oil" inside is likely PCBs.

    -Phil
  • erco wrote: »
    Beautimous! A purist among us.

    Yeah, I just couldn't stand to have new caps showing, at least on top. Although I may well re-stuff all the paper caps under the chassis too.
    Please be careful breaking open old caps. The "oil" inside is likely PCBs.

    -Phil

    These are just electolytics, no oil. One does have to be careful with the oil bath types. Luckily the oil bath types are often still good.

  • ercoerco Posts: 20,257
    Jonathan wrote:
    I use that trick too, but for the forces of good. This is a cap from a 1948 Zenith Transoceanic that is currently on the bench:
    Please be careful breaking open old caps. The "oil" inside is likely PCBs.

    -Phil

    Yikes! https://www3.epa.gov/region9/pcbs/faq.html
  • erco wrote: »
    Jonathan wrote:
    I use that trick too, but for the forces of good. This is a cap from a 1948 Zenith Transoceanic that is currently on the bench:
    Please be careful breaking open old caps. The "oil" inside is likely PCBs.

    -Phil

    Yikes! https://www3.epa.gov/region9/pcbs/faq.html



    I remember about twenty years ago, we had a bad storm. And one of those transformers that are on the side of a power pole came crashing down when the pole snapped. The transformer lost it's lid, and there was a big oil puddle in the road. Nobody called the EPA, the power company just cleaned up the debris. And replaced the pole and transformer. Wonder if that is the norm, could be an environmental disaster some day with our ground water.
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