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remagnetising old magnets

Discussion in 'Electronic Repair' started by NumanR, Oct 8, 2004.

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  1. NumanR

    NumanR Guest

    I would like some help on increasing the magnetic strength of some
    magnets in some d.c motors. The motors are small 540 size,
    approximately two inches long and inch and a quarter in diameter with
    two half moon magnets inside approx 4mm thick. How can I increase
    their strength? As far as I know they are ferrite? magnets, I know
    they are definately not rare earth magnets.
     
  2. Bill

    Bill Guest

    I believe the usual method is to take a large DC electromagnet,
    build a pole structure on it to focus the field where you want
    it, and whack it with a big pulse of current.
     
  3. Aslaner

    Aslaner Guest

    I don't think that you can do much, it is all pre configured at the
    manufacture with the metal itself the density of the particles etc, sure
    you make it look like is holding a charge for a little period of time but it
    is about all, it will return to its original magnetism.
    There is saturation point after which you will be wasting your time.
    The smaller/stronger one are made that way not just charged that way. It
    took years of development to get to that point.


    I believe so anyway, I could be slightly wrong but not that far.
     
  4. << There is saturation point after which you will be wasting your time.
    The smaller/stronger one are made that way not just charged that way. >>

    Aslaner, Bill & NumanR-

    I believe you are correct that there is a saturation point, but the alloys are
    not naturally magnetized. They are "charged" in a machine that works about the
    way Bill described.

    The question is whether or not the magnets were magnetized to a point beyond
    their saturation point. If so, then the field would have eventually ended up
    at some maximum stable value. However, they may not have been magnetized to
    saturation, or there may have been some condition such as mechanical shock,
    that caused the field to be reduced. In either case, it may be possible to
    increase the magnet's strength using the magnetization process.

    One thing that might go wrong, is a field reversal caused by the magnetizing
    field (or current) being backwards. You have a 50-50 chance of getting it
    right!

    Fred
     
  5. NumanR

    NumanR Guest

    The motors are used for racing r/c cars, now please take this
    seriously as there is a tool on the market which costs £600 which
    appears to be just a high strength magnet.(This is used before each
    race by the top racers) What I want is a cheaper alternative, or an
    idea to help me build wht i need. The magnets are subjected to heat
    and I think this effects the magnets. I cannot stop the heat but if I
    could top up the magnets each time then this would help. Thanks for
    your ideas.
     
  6. PaPaPeng

    PaPaPeng Guest


    Is it possible to strap rare earth magnets on the motor casing to
    boost the strength of the motor's magnet?
     
  7. What I had already suggested via email is to try using the rare earth
    magnets from a high performance harddrive to see if this is possible.

    Experiment with a pair of magnets from a dead motor - one to test and
    the other as the "control".

    Of course, if you can affect the magnetizism at all, it would be possible
    to reverse the field or magnetize the megnet along any arbitrary direction
    so you'll have to figure out where the polse are on the motor magnets and
    disk drive magnets and orient them accordingly.
    I have a feeling this is against the rules.

    --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
    Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
    +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
    | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

    Note: These links are hopefully temporary until we can sort out the excessive
    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.
     
  8. Chuck Harris

    Chuck Harris Guest

    Boosting the strength of the field magnets doesn't necessarily do
    what you think it might. For instance, once a motor has started,
    and is up to speed, weakening the field magnets will cause the motor
    to speed up..drastically!

    Conversely, strong field magnets will give you high, lowspeed torque,
    but will limit the maximum speed of the motor.

    -Chuck Harris
     
  9. NSM

    NSM Guest

    | The motors are used for racing r/c cars, now please take this
    | seriously as there is a tool on the market which costs £600 which
    | appears to be just a high strength magnet (this is used before each
    | race by the top racers) What I want is a cheaper alternative, or an
    | idea to help me build what I need. The magnets are subjected to heat
    | and I think this effects the magnets. I cannot stop the heat but if I
    | could top up the magnets each time then this would help. Thanks for
    | your ideas.

    Does this tool connect to a source of power, AC or DC? I have the gravest
    doubts that this 'tool' works better than a chicken bone. Faith may not be
    able to move mountains, but it sure moves money, usually from someone else's
    wallet!

    N
     
  10. NumanR

    NumanR Guest

    Ok we are not allowed to use rare earth magnets in any form, there are
    two machines which i know about one is an electro magnet using 12v dc
    feed and presumably a capacitor, and the other is a box which is not
    powered which presumably has a high strength magnet inside. I have not
    been able to see inside these tools but vouch that they do work, on a
    recent test it made a second a lap difference (on a 18 second lap). It
    is not the speed of the motor but the power and torque I am after so
    strengthening the magnets is a major tuning aid. Every other way of
    making the motors powerful is already done and we are restricted on
    voltage allowed on board the cars. Thanks for your suggestions so far.
     
  11. NSM

    NSM Guest

    | Ok we are not allowed to use rare earth magnets in any form, there are
    | two machines which i know about one is an electro magnet using 12v dc
    | feed and presumably a capacitor, and the other is a box which is not
    | powered which presumably has a high strength magnet inside. I have not
    | been able to see inside these tools but vouch that they do work, on a
    | recent test it made a second a lap difference (on a 18 second lap). It
    | is not the speed of the motor but the power and torque I am after so
    | strengthening the magnets is a major tuning aid. Every other way of
    | making the motors powerful is already done and we are restricted on
    | voltage allowed on board the cars. Thanks for your suggestions so far.

    There have been a number of books published in the UK which might help. Look
    for books on measuring instruments or speakers, both of which use magnets.
    Those published in the '60's are probably most useful. I recall sections on
    'charging' magnets in these.

    Avoid 'magic' thinking, i.e. assuming there is some magic trick known to
    few. In most cases, whatever you try will help and if it doesn't, figure out
    HOW to figure out WHY. That's how most items are 'designed' anyway.

    N
     
  12. Asimov

    Asimov Guest

    "Fred McKenzie" bravely wrote to "All" (09 Oct 04 15:36:00)
    --- on the heady topic of "Re: remagnetising old magnets"

    FM> From: (Fred McKenzie)

    FM> << There is saturation point after which you will be wasting your
    FM> time. The smaller/stronger one are made that way not just charged that
    way. >>
    FM> Aslaner, Bill & NumanR-

    FM> I believe you are correct that there is a saturation point, but the
    FM> alloys are not naturally magnetized. They are "charged" in a machine
    FM> that works about the way Bill described.

    FM> The question is whether or not the magnets were magnetized to a point
    FM> beyond their saturation point. If so, then the field would have
    FM> eventually ended up at some maximum stable value. However, they may
    FM> not have been magnetized to saturation, or there may have been some
    FM> condition such as mechanical shock, that caused the field to be
    FM> reduced. In either case, it may be possible to increase the magnet's
    FM> strength using the magnetization process.
    FM> One thing that might go wrong, is a field reversal caused by the
    FM> magnetizing field (or current) being backwards. You have a 50-50
    FM> chance of getting it right!

    It is a little hard to identify magnetic polarity of a magnet. I'm not
    sure but the Earth's own North Pole is actually a magnet south and
    will attract a magnet negative. So using a "magnetic compass" actually
    finds the south on a magnet. Is this right?

    A*s*i*m*o*v

    .... Reactance: your imaginary friend.
     
  13. WEBPA

    WEBPA Guest

    One means of improving the performance of pm and universal motors has not yet
    been mentioned. That is: Altering the phase relationship between the brushes
    and the field magnets. This was (still is?) a common control method for
    traction motors in street cars/trolleys/buses. Was also used for elevators and
    motor-generator (dynamotors) sets (welding, arc lamps, etc.)

    Exactly how this might be applied to slot cars seems to offer lots of room for
    creative engineering.
    webpa
     
  14. << Ok we are not allowed to use rare earth magnets in any form, there are
    two machines which i know about one is an electro magnet using 12v dc
    feed and presumably a capacitor, and the other is a box which is not
    powered which presumably has a high strength magnet inside. >>

    NumanR-

    I can see where either method would top-off the magnets.

    It may not be worth mentioning, but I wonder if adding a coil of wire around
    the magnet, wired in series with the battery, would increase the motor's torque
    at slow speed? At slower speed I would expect current to be higher, which
    would aid the magnet if polarity was correct.

    Would such a modification be legal?

    Fred
     
  15. Jim Adney

    Jim Adney Guest

    Yes, that's right. The North pole on a magnet is the one that points
    north, so the pole that's near the Earth's north geographic pole is
    actually a South pole.

    -
     
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