Electric Motor Burn Out?

Discussion in 'Electrical Engineering' started by TJ, Apr 13, 2005.

  1. TJ

    TJ Guest

    What happens to cause an electric motor to burn up or short out?

    I'm currently taking a physics class and this question was posed to
    the class by the professor. In the movie "The Grinch Who Stole
    Christmas" the Grinch has a large toy monkey that crashes two symbols
    repeatedly. He is letting the toy slam the symbols on his head to
    block out the noise of the Whos in Whoville singing. At some point he
    decides to stop the toy and just reaches up and grabs its arms and
    stops it from moving its arms. Sparks fly and the toy is burnt up or
    broken.

    What happened to the motor? Why did it burn up?

    My understanding of the electric motor (DC current) is that there is a
    metal loop that is between two magnets. When current is passed
    through the loop the magnet field causes the loop to torque. The
    amount of torque is dependant on the strength of the magnets and
    vertical length of the loop in respect to the magnets. When the loop
    is stopped and current is still flowing through the loop why does it
    burn up?

    Also is there more, less, or the same current on the negative leg when
    this occurs?

    Thanks in advance. If this is not the correct discussion group to
    pose these questions in then accept my apologies and could someone
    please suggest a more appropriate group.



    TJ


    ----------------------


    People like you and I, though mortal of course like everyone else, do
    not grow old no matter how long we live...We never cease to stand like
    curious children before the great mystery into which we were born.

    - Albert Einstein -
    TJ, Apr 13, 2005
    #1
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  2. TJ wrote:
    >
    > What happens to cause an electric motor to burn up or short out?
    >
    > I'm currently taking a physics class and this question was posed to
    > the class by the professor. In the movie "The Grinch Who Stole
    > Christmas" the Grinch has a large toy monkey that crashes two symbols
    > repeatedly. He is letting the toy slam the symbols on his head to
    > block out the noise of the Whos in Whoville singing. At some point he
    > decides to stop the toy and just reaches up and grabs its arms and
    > stops it from moving its arms. Sparks fly and the toy is burnt up or
    > broken.
    >
    > What happened to the motor? Why did it burn up?
    >
    > My understanding of the electric motor (DC current) is that there is a
    > metal loop that is between two magnets. When current is passed
    > through the loop the magnet field causes the loop to torque. The
    > amount of torque is dependant on the strength of the magnets and
    > vertical length of the loop in respect to the magnets. When the loop
    > is stopped and current is still flowing through the loop why does it
    > burn up?
    >
    > Also is there more, less, or the same current on the negative leg when
    > this occurs?
    >
    > Thanks in advance. If this is not the correct discussion group to
    > pose these questions in then accept my apologies and could someone
    > please suggest a more appropriate group.
    >


    alt.homework.answers

    --
    Paul Hovnanian mailto:p
    ------------------------------------------------------------------
    Just say 'No' to Windows.
    -- Department of Defenestration.
    Paul Hovnanian P.E., Apr 13, 2005
    #2
    1. Advertising

  3. TJ

    TJ Guest

    On Wed, 13 Apr 2005 14:52:34 -0700, "Paul Hovnanian P.E."
    <> wrote:


    >>
    >> Thanks in advance. If this is not the correct discussion group to
    >> pose these questions in then accept my apologies and could someone
    >> please suggest a more appropriate group.
    >>

    >
    >alt.homework.answers



    That group is not one listed by my newsgroup provider. I also did a
    search for that group on yahoo and google and I didn't turn up
    anything.




    TJ


    ----------------------


    People like you and I, though mortal of course like everyone else, do
    not grow old no matter how long we live...We never cease to stand like
    curious children before the great mystery into which we were born.

    - Albert Einstein -
    TJ, Apr 13, 2005
    #3
  4. TJ

    daestrom Guest

    "TJ" <insciens@_REMOVE_yahoo.com> wrote in message
    news:...
    > What happens to cause an electric motor to burn up or short out?
    >
    > I'm currently taking a physics class and this question was posed to
    > the class by the professor. In the movie "The Grinch Who Stole
    > Christmas" the Grinch has a large toy monkey that crashes two symbols
    > repeatedly. He is letting the toy slam the symbols on his head to
    > block out the noise of the Whos in Whoville singing. At some point he
    > decides to stop the toy and just reaches up and grabs its arms and
    > stops it from moving its arms. Sparks fly and the toy is burnt up or
    > broken.
    >
    > What happened to the motor? Why did it burn up?
    >
    > My understanding of the electric motor (DC current) is that there is a
    > metal loop that is between two magnets. When current is passed
    > through the loop the magnet field causes the loop to torque. The
    > amount of torque is dependant on the strength of the magnets and
    > vertical length of the loop in respect to the magnets. When the loop
    > is stopped and current is still flowing through the loop why does it
    > burn up?
    >
    > Also is there more, less, or the same current on the negative leg when
    > this occurs?
    >
    > Thanks in advance. If this is not the correct discussion group to
    > pose these questions in then accept my apologies and could someone
    > please suggest a more appropriate group.
    >
    >



    Two things are at work. The amount of heat generated in the rotating 'loop
    of wire' is a function of I^2*R (current squared times the resistance). The
    amount of heat removed is determined by materials, insulation, and the flow
    of air around the wire. When heat generated is much higher than heat
    removed, the temperature rises. If the temperature gets hot enough to melt
    insulation, then a short circuit develops.

    Anytime a motor is 'stalled', it runs the risk of burning out (except for
    very specially designed motors intended for constant stalling). When the
    motor stops turning, there isn't any air moving past the coils (or coils
    moving past the air, it's all relative). So there is less cooling to remove
    heat from the rotor. Secondly, with a stalled rotor, the current is very
    high so the I^2*R heat generated is very, very high. The combination of low
    cooling and high heat generation can quickly overheat the insulation and
    burn out the motor.

    Of course, in the movie, they undoubtedly added some pyrotechnics set off at
    the right time by someone off-camera. Usually real motors take a few
    minutes to overheat. The result is a lot of 'acrid odor' and smoke given
    off. Then simple flames and blown fuses.

    daestrom
    daestrom, Apr 13, 2005
    #4
  5. TJ

    Martin G. Guest

    Insulation can also wear out with the time even at normal ambient
    temperature and normal usage. Varnish is a polymer that is sensitive to
    thermal aging. With the time, oxygen will migrate into it and cause
    oxydation, chemical bonds will be broken and crack will appear. Then in
    these cracks, if voltage is sufficient you can have short-circuit, then then
    motor will burn.

    Martin G.


    "TJ" <insciens@_REMOVE_yahoo.com> a écrit dans le message de news:
    ...
    > What happens to cause an electric motor to burn up or short out?
    >
    > I'm currently taking a physics class and this question was posed to
    > the class by the professor. In the movie "The Grinch Who Stole
    > Christmas" the Grinch has a large toy monkey that crashes two symbols
    > repeatedly. He is letting the toy slam the symbols on his head to
    > block out the noise of the Whos in Whoville singing. At some point he
    > decides to stop the toy and just reaches up and grabs its arms and
    > stops it from moving its arms. Sparks fly and the toy is burnt up or
    > broken.
    >
    > What happened to the motor? Why did it burn up?
    >
    > My understanding of the electric motor (DC current) is that there is a
    > metal loop that is between two magnets. When current is passed
    > through the loop the magnet field causes the loop to torque. The
    > amount of torque is dependant on the strength of the magnets and
    > vertical length of the loop in respect to the magnets. When the loop
    > is stopped and current is still flowing through the loop why does it
    > burn up?
    >
    > Also is there more, less, or the same current on the negative leg when
    > this occurs?
    >
    > Thanks in advance. If this is not the correct discussion group to
    > pose these questions in then accept my apologies and could someone
    > please suggest a more appropriate group.
    >
    >
    >
    > TJ
    >
    >
    > ----------------------
    >
    >
    > People like you and I, though mortal of course like everyone else, do
    > not grow old no matter how long we live...We never cease to stand like
    > curious children before the great mystery into which we were born.
    >
    > - Albert Einstein -
    Martin G., Apr 14, 2005
    #5
  6. TJ

    Roy Q.T. Guest

    TJ: The motor burned out because:
    He is The Grinch after all.

    I guess the movie producers wanted curious viewers to see it this
    way};-)

    The dynamics of a motor are such, that when a voltage is applied and a
    current starts to flow in the coils.,considering a motor is optimally
    designed, meaning: It is made to make the best use of electricity to
    magnetically move the rotor on the stator, if the magnetic field
    produced by the stator isn't somehow dissipated or expended on the
    motors rotor function, it will heat up the Mechanism from the induced
    back emf on itself, Bust an imaginary Wire inside causing it to Spark
    Off the excess Electricity, brown out then burn up to a smoking halt.

    Of course that is just a Hollywood version made-up with special FX.

    Only a medium - high powered drive mechanism can possibly spark off and
    burn out (not necessarily in that order) and probably from excessive
    current on a Faulty Device or Part, A toy motor intrinsically would not
    explode from stalling or stopping in itself.

    Of Course: we could probably design one in here that could do as well
    };-)

    The real (Toy Scenario) thing would just run your batteries dead and
    probably ruin the motor in it's course., with only half of the described
    patterns above.


    ®oy
    Roy Q.T., Apr 14, 2005
    #6
  7. TJ

    Don Kelly Guest

    "TJ" <insciens@_REMOVE_yahoo.com> wrote in message
    news:...
    > What happens to cause an electric motor to burn up or short out?
    >
    > I'm currently taking a physics class and this question was posed to
    > the class by the professor. In the movie "The Grinch Who Stole
    > Christmas" the Grinch has a large toy monkey that crashes two symbols
    > repeatedly. He is letting the toy slam the symbols on his head to
    > block out the noise of the Whos in Whoville singing. At some point he
    > decides to stop the toy and just reaches up and grabs its arms and
    > stops it from moving its arms. Sparks fly and the toy is burnt up or
    > broken.
    >
    > What happened to the motor? Why did it burn up?
    >
    > My understanding of the electric motor (DC current) is that there is a
    > metal loop that is between two magnets. When current is passed
    > through the loop the magnet field causes the loop to torque. The
    > amount of torque is dependant on the strength of the magnets and
    > vertical length of the loop in respect to the magnets. When the loop
    > is stopped and current is still flowing through the loop why does it
    > burn up?
    >
    > Also is there more, less, or the same current on the negative leg when
    > this occurs?
    >
    > Thanks in advance. If this is not the correct discussion group to
    > pose these questions in then accept my apologies and could someone
    > please suggest a more appropriate group.
    >

    ---------------
    What else is involved in the motor? Why do you have a current? What happens
    when you turn a coil in a magnetic field (hint: Faraday). What effect does
    this have on the current? What makes you think that the current will be the
    same when the motor is not turning ?

    as for the current on the negative leg- at some time in class there must
    have been some mention of KCL (what goes in comes out).
    I'm sure that all the information you need has been given to you- hence
    Paul's reference to alt.homework.answers.
    All you have to do is think about it- that's why you were asked the
    question..

    --
    Don Kelly

    remove the urine to answer
    Don Kelly, Apr 14, 2005
    #7
  8. TJ

    TJ Guest

    On Wed, 13 Apr 2005 22:27:11 GMT, "daestrom"
    <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:

    >Two things are at work. The amount of heat generated in the rotating 'loop
    >of wire' is a function of I^2*R (current squared times the resistance). The
    >amount of heat removed is determined by materials, insulation, and the flow
    >of air around the wire. When heat generated is much higher than heat
    >removed, the temperature rises. If the temperature gets hot enough to melt
    >insulation, then a short circuit develops.
    >
    >Anytime a motor is 'stalled', it runs the risk of burning out (except for
    >very specially designed motors intended for constant stalling). When the
    >motor stops turning, there isn't any air moving past the coils (or coils
    >moving past the air, it's all relative). So there is less cooling to remove
    >heat from the rotor. Secondly, with a stalled rotor, the current is very
    >high so the I^2*R heat generated is very, very high. The combination of low
    >cooling and high heat generation can quickly overheat the insulation and
    >burn out the motor.
    >
    >Of course, in the movie, they undoubtedly added some pyrotechnics set off at
    >the right time by someone off-camera. Usually real motors take a few
    >minutes to overheat. The result is a lot of 'acrid odor' and smoke given
    >off. Then simple flames and blown fuses.
    >
    >daestrom
    >



    Thanks for your help. I appreciate you taking your time to respond.
    I think I have it now.




    TJ


    ----------------------


    People like you and I, though mortal of course like everyone else, do
    not grow old no matter how long we live...We never cease to stand like
    curious children before the great mystery into which we were born.

    - Albert Einstein -
    TJ, Apr 14, 2005
    #8
  9. TJ

    TJ Guest

    On Wed, 13 Apr 2005 19:13:30 -0400, "Martin G."
    <> wrote:

    >Insulation can also wear out with the time even at normal ambient
    >temperature and normal usage. Varnish is a polymer that is sensitive to
    >thermal aging. With the time, oxygen will migrate into it and cause
    >oxydation, chemical bonds will be broken and crack will appear. Then in
    >these cracks, if voltage is sufficient you can have short-circuit, then then
    >motor will burn.
    >
    >Martin G.
    >



    Thanks for the assist. Between you and daestrom I believe I
    understand.




    TJ


    ----------------------


    People like you and I, though mortal of course like everyone else, do
    not grow old no matter how long we live...We never cease to stand like
    curious children before the great mystery into which we were born.

    - Albert Einstein -
    TJ, Apr 14, 2005
    #9
  10. TJ

    TJ Guest

    On Thu, 14 Apr 2005 00:30:21 -0400, (Roy Q.T.) wrote:

    >TJ: The motor burned out because:
    >He is The Grinch after all.
    >
    >I guess the movie producers wanted curious viewers to see it this
    >way};-)
    >
    >The dynamics of a motor are such, that when a voltage is applied and a
    >current starts to flow in the coils.,considering a motor is optimally
    >designed, meaning: It is made to make the best use of electricity to
    >magnetically move the rotor on the stator, if the magnetic field
    >produced by the stator isn't somehow dissipated or expended on the
    >motors rotor function, it will heat up the Mechanism from the induced
    >back emf on itself, Bust an imaginary Wire inside causing it to Spark
    >Off the excess Electricity, brown out then burn up to a smoking halt.
    >
    >Of course that is just a Hollywood version made-up with special FX.
    >
    >Only a medium - high powered drive mechanism can possibly spark off and
    >burn out (not necessarily in that order) and probably from excessive
    >current on a Faulty Device or Part, A toy motor intrinsically would not
    >explode from stalling or stopping in itself.
    >
    >Of Course: we could probably design one in here that could do as well
    >};-)
    >
    >The real (Toy Scenario) thing would just run your batteries dead and
    >probably ruin the motor in it's course., with only half of the described
    >patterns above.
    >
    >
    >®oy



    Thanks for response. I appreciate you taking time to respond. With
    the other two individuals responses I think I understand. Thanks
    again.




    TJ


    ----------------------


    People like you and I, though mortal of course like everyone else, do
    not grow old no matter how long we live...We never cease to stand like
    curious children before the great mystery into which we were born.

    - Albert Einstein -
    TJ, Apr 14, 2005
    #10
  11. TJ

    Don Kelly Guest

    "Roy Q.T." <> wrote in message
    news:...
    TJ: The motor burned out because:
    He is The Grinch after all.

    I guess the movie producers wanted curious viewers to see it this
    way};-)

    The dynamics of a motor are such, that when a voltage is applied and a
    current starts to flow in the coils.,considering a motor is optimally
    designed, meaning: It is made to make the best use of electricity to
    magnetically move the rotor on the stator, if the magnetic field
    produced by the stator isn't somehow dissipated or expended on the
    motors rotor function, it will heat up the Mechanism from the induced
    back emf on itself,
    ----------------
    Where the hell did you learn this nonsense?
    --
    Don Kelly

    remove the urine to answer



    due
    Bust an imaginary Wire inside causing it to Spark
    Off the excess Electricity, brown out then burn up to a smoking halt.

    Of course that is just a Hollywood version made-up with special FX.

    Only a medium - high powered drive mechanism can possibly spark off and
    burn out (not necessarily in that order) and probably from excessive
    current on a Faulty Device or Part, A toy motor intrinsically would not
    explode from stalling or stopping in itself.

    Of Course: we could probably design one in here that could do as well
    };-)

    The real (Toy Scenario) thing would just run your batteries dead and
    probably ruin the motor in it's course., with only half of the described
    patterns above.


    ®oy
    Don Kelly, Apr 15, 2005
    #11
  12. TJ

    Roy Q.T. Guest

    I read a book on it by; D.Kelly

    Well maybe it isn't D.Kelly who wrote it, but some of it is in books,
    like " The Grinch that stole the Christmas "

    i see he's trying to steal the newsgroup too

    ®oy
    Roy Q.T., Apr 15, 2005
    #12
  13. TJ

    Don Kelly Guest

    "Roy Q.T." <> wrote in message
    news:...
    I read a book on it by; D.Kelly

    Well maybe it isn't D.Kelly who wrote it, but some of it is in books,
    like " The Grinch that stole the Christmas "

    i see he's trying to steal the newsgroup too

    ®oy
    ---------
    No, I am not trying to steal the newsgroup. It is simply that what you said
    was quite wrong. Should I applaud?

    Quote:

    "if the magnetic field
    produced by the stator isn't somehow dissipated or expended on the
    motors rotor function, it will heat up the Mechanism from the induced
    back emf on itself,"

    End quote:

    I simply wondered where you learned this as it is nonsense.

    Somehow, somewhere, someone led you badly astray.

    --
    Don Kelly

    remove the urine to answer
    Don Kelly, Apr 16, 2005
    #13
  14. TJ

    Roy Q.T. Guest

    Oh the Hell who you & your accusations Grinch Kelly .....you think just
    like horrne., everybody is wrong but you.... In time we'll see who is
    wrong and mislead....
    the stench that emanates from your post over a motor being a generator &
    a restricted motor not overheating is amazing. I don't have to see
    things your way... you dullard.

    You & horne are very adversarial and you can both go jump in a lake
    somewhere...

    State your case on the Topic and Leave me & my analysis alone... I know
    when to admit I'm wrong without someone trying to steal the sunshine
    from over me ..... Who Appointed you High Exhalted Mystic Ruler
    anyhow....

    ®oy
    Roy Q.T., Apr 16, 2005
    #14
  15. TJ

    Don Kelly Guest

    "Roy Q.T." <> wrote in message
    news:...
    Oh the Hell who you & your accusations Grinch Kelly .....you think just
    like horrne., everybody is wrong but you.... In time we'll see who is
    wrong and mislead....
    the stench that emanates from your post over a motor being a generator &
    a restricted motor not overheating is amazing. I don't have to see
    things your way... you dullard.

    You & horne are very adversarial and you can both go jump in a lake
    somewhere...

    State your case on the Topic and Leave me & my analysis alone... I know
    when to admit I'm wrong without someone trying to steal the sunshine
    from over me ..... Who Appointed you High Exhalted Mystic Ruler
    anyhow....

    ®oy
    --------
    I did NOT say that a restricted motor doesn't overheat. Of course it does
    but not for the reason that you gave.

    Read what I did say. What I did say was:

    a) DC and AC motors can be and are run as generators- no switching required.
    There are many examples of that. Others have mentioned some examples.
    The equations describing the behaviour of a generator are exactly the same
    as for a motor- all that happens is that the direction of the current
    changes (DC machine). Supply design (i.e. rectifiers) may prevent this
    from happening in some cases but the machine itself inherently doesn't care.

    b)Your statements regarding flux dissipation and heating due to back emf are
    simply wrong. No ifs and buts
    Note that when a DC motor is stalled, the back emf is 0 but the current and
    heating is a maximum. The stator (field in this case) flux is not affected
    unless there is a series winding present. With an AC machine, the mechanism
    will be different but the air gap flux is not greatly affected by load or
    the lack of it. No relationship between coil heating and flux exists.

    Sorry, but the theory and the facts back me up.
    Do you want an analysis of either DC or AC motors/generators? - I can give
    you that, from a simple to a complex approach but rather than take it from
    me, try a good book on motors and generators.

    I'm not trying to put you down and I am sure that there are areas where you
    know more than I do- this isn't one of them.
    --
    Don Kelly

    remove the urine to answer
    Don Kelly, Apr 17, 2005
    #15
  16. TJ

    Roy Q.T. Guest

    I am sorry but I am not in the mood to discuss this any further, the kid
    wanted to know How they Blew up the toy in the movie., they told him
    how, I just wanted to expand on a premise TV Land may employ to give
    some Hollywood Theory on how it happened....

    You took this post to serious, that's all, I am not offended, but
    surprise on the load of carp you can dish out on motors & generators
    yourself };-) I'lll be reviewing Both subjects to they're entirety soon
    enough... Thanx

    ®oy
    Roy Q.T., Apr 17, 2005
    #16
  17. TJ

    Roy Q.T. Guest

    (Don Kelly)wrote::/ No relationship between coil heating and flux
    exists.

    - this isn't one of them. ?????
    --

    You are too conventional to see it at work.
    surely there is nothing wrong with seeing things from the bottom up (or
    any parallel angle for that matter).....Look at it this way:) with out
    the down side of up, there just wouldn't be a whole. ®oy

    [like what happens to the electronitoes when the heat up, did you say
    rush the armature faster than usual ?] your right !
    Roy Q.T., Apr 17, 2005
    #17
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