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is it harmful to stop a dc motor?

Discussion in 'Electronic Repair' started by W. Erickson, Nov 15, 2004.

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  1. W. Erickson

    W. Erickson Guest

    a motor like:
    http://www.jameco.com/webapp/wcs/st...toreId=10001&catalogId=10001&productId=130627

    I was trying to fix my friends playstation and I got into an argument with a
    friend. He tells me that stopping a motor of this type while it is in
    operation will damage it.

    My understanding of how this motor works is that it is just a rotor
    spinning on bearings. the driving force on it is magnetism. There are no
    belts or gears. I just don't understand how it can get damaged. does
    stopping the motor cause a runaway current or something?
     
  2. NSM

    NSM Guest

    | a motor like:
    |
    http://www.jameco.com/webapp/wcs/st...toreId=10001&catalogId=10001&productId=130627
    |
    | I was trying to fix my friends playstation and I got into an argument with
    a
    | friend. He tells me that stopping a motor of this type while it is in
    | operation will damage it.
    |
    | My understanding of how this motor works is that it is just a rotor
    | spinning on bearings. the driving force on it is magnetism. There are no
    | belts or gears. I just don't understand how it can get damaged. does
    | stopping the motor cause a runaway current or something?

    No

    How are you stopping it?

    N
     
  3. James Sweet

    James Sweet Guest

    You can overheat the windings on the armature by stalling it since only oen
    winding will have power 100% of the time rather than them cycling as the
    motor rotates. Current draw goes up with the load as well so it's possible
    to burn out the driver circuitry. In practice you probably won't kill a
    little motor like this by stalling it but larger motors can certainly be
    damaged.
     
  4. Depends on the motor type, but yes, there can be problems. A permanent
    magnet DC type will draw excess current through one coil. Eventually may be
    enough to burn out that coil, or possibly burn out a resistor in the power
    supply.
    A direct-drive type, like your friend was mentioning, will pull excess
    current through it's drive IC, sometimes enough to burn out the chip.
    Manufacturers warn against this, mainly for extended periods of time.
    Back-cueing a direct-drive turntable is OK because you're not doing it for
    long enough, plus the drive IC's are overspec'd for DJ models. In practice
    you're probably OK, but why risk it?

    Mark Z.
     
  5. Yes, it may if the power supply isn't current limited.

    When the current goes to excessive levels, the motor may self destruct
    from heat. The magnetic field also increases to excessively high
    level and if it's a permanent magnet motor, possibly to the point
    where it demagnetizes the permanent magnests.

    --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
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    traffic on Repairfaq.org.

    Important: Anything sent to the email address in the message header is ignored.
    To contact me, please use the feedback form on the S.E.R FAQ Web sites.
     
  6. If you stop it using your tongue it won't go over to good.
     
  7. Asimov

    Asimov Guest

    "Jamie" bravely wrote to "All" (15 Nov 04 12:16:03)
    --- on the heady topic of "Re: is it harmful to stop a dc motor?"

    My little nephew was given a Nikko remote controlled Hummer II for his
    birthday and he constantly switches it from forward to reverse all the
    time. The motor and drive electronics have been surviving this kind of
    treatment for over a month now. I'm a little surprised at its
    ruggedness. Knock on wood...


    Ja> From: Jamie <>

    Ja> depends on the motor type
    Ja> there are motors designed for
    Ja> tension operation in which you
    Ja> can stall them how ever, most of them
    Ja> have some kind of cooling and the
    Ja> windings are larger types and case
    Ja> venting.
    Ja> its best to use current limiting
    Ja> drives so that the motor windings
    Ja> do not heat up because you will
    Ja> produce more current stalling from a
    Ja> bind up then letting it spin since there
    Ja> are multiple poles and they won't be on
    Ja> constantly if spinning and air movement is
    Ja> also generated ..et
    Ja> oh yeah, there is always that problem of burning
    Ja> out the driver electronics since most them don't
    Ja> assume a lock up of any period of time.


    Ja> http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-
    Ja> 1&storeId=10001&catalogId=10001&productId=130627 >

    .... Power is obtained by current meeting resistance
     
  8. Jamie

    Jamie Guest

    depends on the motor type
    there are motors designed for
    tension operation in which you
    can stall them how ever, most of them
    have some kind of cooling and the
    windings are larger types and case
    venting.
    its best to use current limiting
    drives so that the motor windings
    do not heat up because you will
    produce more current stalling from a
    bind up then letting it spin since there
    are multiple poles and they won't be on
    constantly if spinning and air movement is
    also generated ..et
    oh yeah, there is always that problem of burning
    out the driver electronics since most them don't
    assume a lock up of any period of time.
     
  9. Rodney Kelp

    Rodney Kelp Guest

    Take your electric drill and put the chuck in a vice and tighten it. Plug
    the drill in, grab the handle real tight and pull the trigger. Hold it there
    for a few minutes. You will begin to hear sizzeling and notice some strange
    smells and possibly get some sparking and smoke. You decide if it's harmful
    or not.. Some motors have protection against locked rotor current. Some AC
    motors are impeadence protected.
    Some small dry cell driven DC motors will smoke very nicely. If you don't
    know don't do it. Then again, try it and if it don't smoke you're ok.
     
  10. da

    da Guest

    Some cheap dc motor designers get around UL/CSA/VDE requirements by
    designing motors that use their windings like fuses. The winding
    opens up and further concerns about locked rotor flammability ratings
    and performance of insulation systems becomes a non issue test wise.

    Ideally you'd have some sort of thermal protector that acts like a
    self resetting circuit breaker. (more $$$)

    Usually you're good for a reasonable amount of time.
     
  11. James Sweet

    James Sweet Guest

    Most of those things are actually fairly rugged, well and the motors aren't
    very powerful in the first place. The manufactures know how hard kids are on
    them, if they cut too many corners they'll all break the first day.
     
  12. W. Erickson

    W. Erickson Guest

    well my MP3 player sometimes locks up with the drive spinning. The only way
    to reset it is to remove the disk while it is spinning and pull out the
    batteries.

    Assuming the motor is just stopped for an instant, is this remarkably
    different than when initially starting from rest? or how about when the
    drive jams the motor into reverse bring the disk to a complete stop which
    it does every time you open the tray?
     
  13. James Sweet

    James Sweet Guest

    In this case it's a low powered motor and you're talking stopping it for
    just a moment, shouldn't hurt anything. Hold it stopped for 20 minutes and
    it might burn out. A larger high powered DC or universal motor such as in a
    weed eater, etc will burn out almost instantanously if you lock it up.
     
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