Low RPM ( 100 rpm) motor without gear box

Discussion in 'General Electronics Chat' started by t00t, Nov 25, 2015.

  1. t00t

    Thread Starter Member

    Jan 22, 2015
    55
    1
    Hi All,
    Have been searching online but can't seem to find any 3 phase AC motors (without gear box) that has low RPM .

    I need roughly about 100 to 125 RPM motors .

    Any experienced guys please advice :)

    Thank You .
     
  2. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    2,803
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    While I cannot claim to entirely fit that 'demographic' -- I'll give it a go anyway;););)

    Sounds like a job for a VFD (i.e. variable frequency drive) controller -- even so - derivation of significant torque at low AV from an induction motor could prove challenging...

    Best regards
    HP
     
    Last edited: Nov 25, 2015
  3. t00t

    Thread Starter Member

    Jan 22, 2015
    55
    1
    Is there any VFD that can drop an AC frequency to 3 hertz ?
     
  4. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    In theory, of course! - As a practical matter I rather doubt it (IOW I see your point:oops:) --- Why, if I might ask, is gear reduction undesirable in your application?

    Best regards
    HP
     
  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,018
    1,536
    Don't think a motor can/is made to go that slow. The number of poles in the motor vs the AC cycle sets the speed of the shaft. A 'c' face motor and an inline gear box would be the only way to get that slow of a RPM. For something with a 'small' foot print, a parallel shaft motor would be what I mean. Like this - http://www.grainger.com/product/BOS.../rp/s/is/image/Grainger/49T795_AS02?$smthumb$

    A VFD won't go that slow.
     
  6. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
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    we have exhaust fans that turn that slow to exhaust chemical tanks, then speed up to different speeds depending whether the tank coverf is open or not. they were previously squar d brand and now allen bradley vfd's . since the smallest one is 20 hp, might be a bit big for you.
     
  7. MrSoftware

    Active Member

    Oct 29, 2013
    504
    124
    How big do you need? The motors used on electric RC planes and drones are 3-phase AC variable speed. The motor controller varies the speed. I don't know how to figure out the minimum speed, but it might have something to do with the inertia of the load, so that it has enough flywheel effect to keep it rotating between poles at very low speeds. They come in various sizes, here is a random example:

    http://www.hobbyking.com/hobbyking/store/__523__517__Electric_Motors-Specialised_Motors.html
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,566
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    With the right style, encoder feedback for e.g. VFD's have been known to control down to 0rpm, as in elevator usage.
    In this case it may be advisable to go with the highest pole count motor you can find.
    Any reason you do not want to use a gear box?
    Max.
     
  9. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    What motor power do you need?
     
  10. PeterCoxSmith

    Member

    Feb 23, 2015
    148
    38
    A permanent magnet AC motor should be able to do what you want, for example:
    http://www.electricmotorwholesale.com/BALDOR-CSPM3546T/
    They also do variable frequency controllers to give the speed you want.
     
  11. t00t

    Thread Starter Member

    Jan 22, 2015
    55
    1
    Thank for the replies so far ,

    Reasons for not wanting to use a gear box is cost and maintenance .

    I will probably be buying an 8pole motor .

    Thanks
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You do not mention the motor size you need, there are AC stepper motors that run synchronous on AC at 72rpm on 60hz or 60rpm on 50hz, instant stop/start.
    Max.
     
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  13. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    Inasmuch as the above implies three pole construction (given that AV @ 3Hz = 120RPM) --- I have to wonder if the motor in question is some manner of selsyn?
    In any event more info as regards your application would be helpful (BTW you will be pleased to know many {most?} folks on these fora are far wiser in the ways of electro-mechanics than I:oops::))

    Best regards
    HP
     
  14. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,041
    1,673
    If you need any amount of torque at that speed I would not recomend trying to do it with a standard 3 phase induction motor and VFD unit.

    I would go with a properly sized multi phase servo motor and driver unit. You will be money and time ahead.
     
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  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    There are some makes of VFD which are particularly designed to operate down to zero rpm such as ABB ACS800 series.
    There are some others also I do not have the number for now.
    Max.
     
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