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Rewinding a motor stator

Discussion in 'Electronic Repair' started by N Cook, Jun 14, 2007.

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  1. N Cook

    N Cook Guest

    Got a bit tired of electronics and as my old hand drill, i only use for
    counter-clockwise left-hand drilling, is playing up so I decided to give it
    a birthday present of a new coil. It was supposed to be for 240V but running
    off 110V via a variac was ok for my purposes, but now the part-bad coil was
    causing too much variation and excess current/contact arcing for the ammeter
    on the variac.
    I removed the relatively blackened coil , that putting a meter over that
    coil , in use, confirmed bad in comparison to the other. Cut through the
    hank and counted turns , weighed the copper to .2 gm and measured the wire
    diameter so I know how many turns and a good idea of the average diameter.
    Does anyone know a formula for a better guide for setting up a 2-part former
    ( for removal) with the right dimensions, to wind a replacement before
    squashing and placing in the channels with paper from an old high voltage
    capacitor and then swathing in lacquer. Would laying a length of rubber cord
    around the placement area inside the motor be a better idea for getting the
    winding former dimensions. any other tips ?
     
  2. N Cook

    N Cook Guest

    found a useful table in a 70 year old book.
    Wire qauges one way and columns of wires per sq in packing, weight per 100
    yards and ohms per 1000 yds. So the former dimensions are determined
     
  3. James Sweet

    James Sweet Guest

    That's pretty cool, I've toyed with the idea of rewinding a motor like that
    just for fun but never actually done it.
     
  4. N Cook

    N Cook Guest

    Making up a former was easier than I thought.
    The first thing to lay down is some loose loops of lacing cord, about 8
    loops diametrically , 45 apart, around the former before winding the turns,
    then cutting the cord into indivuidual loops and tying off after wire
    winding and before removing. So the exact shape of the bulking of the wires
    into a hank does not matter that much as the tying-off of the lacing cords
    while still on the mandrel would form the cross-secion of the hank into a
    circle. I will do the winding today. If it should be wrong in demensions ,
    then I've a large drum of 29 SWG wire to have plenty of other attempts. As
    always the winding on a coil winder takes no time at all, its the
    preparation thats time consuming
     
  5. N Cook

    N Cook Guest

    (via email response) For anyone else too embarrassed to ask on-thread why I
    use left hand drill bits. This week an amp, as received from a well
    respected UK maker, had a knob effectively seized on. The owner had never
    touched them. The grub-screws were brass and overtightened so one nib of the
    2 nibs, making a screwdriver blade slot, had broken off at assembly.

    Tip
    To free seized equipment knobs
    For the situation where the knobs are seized onto the shaft by rusted
    grub screws,especially where the screw penetrates the shaft;
    after you have butchered the grub screw slot try this.
    Make up some guide tubes,small enough to just slide into the hole
    in the knob containing the grub screw,these tubes drilled on a lathe with
    a clearance bore to take a drill bit. This drill bit usually needs to be
    extended by brazing onto a longish rod (so the chuck of the
    drill misses the face of the equipment).
    Use some cutting oil and drill into the grub screw.
    Ideally use left hand drill bits and left-handed power drill
    rotation, such drill bits are available from specialist suppliers ,
    other suppliers may kook at you as though you're trying to wind them up
    (anti-clockwise).
    To convert a right hand drill bit well enough for this use grind the
    cutting face back on the opposite rake angle, swarf clearance
    is not relevant here. Often the bite into the drill bit
    into the screw or the localised vibration or heating is enough to
    shift the screw.
    Now use a small "easi out"(maybe this is a UK trade name),but consist
    of a coarse left-handed cutting thread on a coarse taper.
    Wind into the hole in the grub screw and hopefully extract.
    If this fails repeat the first procedure with larger diameter drill bits
    until nothing remains of the grub screw,retap a larger hole and use
    a larger grub screw for knob reuse.
     
  6. N Cook

    N Cook Guest

    I thought that ovalling the axial parts to squash in the slots in the motor
    core would be a problem but all went fine, though 7mm diameter when squashed
    to a circle, rather than original about 6mm. The hank resistance of 7.1 ohm
    compared to 7 ohm was good. I could not decide if the original was 29 or 30
    swg but looks as though it was nearer 30 swg.
    A rifenement is to lay a dowel or rod axial and outside the core to tie the
    hank back to while pushing the axial sections into the core slots. The
    overall circumference was too long so the ends of the hank overhanged at the
    open ends too much. I will recalculate for 30 swg and have another go. There
    was space in the housing to try out my effort so did have a go assembling
    and running without lacquering in, and it worked fine.
     
  7. Out of curiosity, how much time have you spent reviving your $10US drill? :)

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

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  8. Ron(UK)

    Ron(UK) Guest

    Snipped account of rewinding stator.
    Ohhh - that`s not the point.. We Bwitish will spend forever trying to
    keep our old tat working. It`s a national pastime :)

    Ron(UK)
     
  9. N Cook

    N Cook Guest

    A change is as good as a rest. I wouldn't take on someone elses motor of any
    sort to repair.
    I like to have an excuse to dig out my old coil winding machine that I
    brought back to working order from a seized rusted mess combined with mice
    nest that was in a leaky shed for decades.
    I originally thought the hank lay up would have to be over a 2 part former
    like a pulley split in two, the awkward way, but with a semicircular laying
    up section. Then having to manually lay-up (as the auto traverse flip is
    only per item , not per layer) something like 3 turns,6,9,12,14,16,17,18 and
    down again to 3 for 190 turns. But I know now that a complicated former and
    intricate lay-up is totally unnecessary.
     
  10. m kinsler

    m kinsler Guest

    I like to have an excuse to dig out my old coil winding machine that I
    That explains a great deal right there. Otherwise, motor rewinding is
    a difficult and obscure art, at least for most of us. I've been
    building electromagnets for demonstrations at the science museum, and
    it doesn't take long for even the simplest coil to turn into a mighty
    mess if you're not careful.

    I have a vacuum pump that's essentially integral with its squirrel-
    cage induction motor, and the stator overheats. The fellow at the
    motor shop gave me some insane estimate of several hundred bucks to
    rewind the thing; I'm ready to try it myself.

    M Kinsler
     
  11. That will likely not be fun, winding machine or not!

    How badly/quickly does it overheat?

    I assume you're sure it's set for the correct line voltage, if that's
    changeable.

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

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  12. N Cook

    N Cook Guest

    If you can run it on reduced voltage with monitor lines added or probes to
    the stators then the bad one will be substantially lower volts than the
    other one. The hot coil may well be the ok one, being forced to take more
    current along with the armature, i didn't think to check that and too late
    now.

    My second hank was too small and the third attempt was Goldilocks.
    Waiting for the lacquer to harden and will reassemble tomorrow.
    I will write it up with data , dimensions, handy hints discovered along the
    way and a few pics and add it to
    http://www.divdev.fsnet.co.uk/repair4.htm
    probably tomorrow. It should give some idea of the dimensions for a similar
    sized motor.
     
  13. James Sweet

    James Sweet Guest


    It's not just you guys, I've done the same sort of thing on occasion. It's
    not so much because it makes practical or economic sense as it is just
    because it can be done.
     
  14. James Sweet

    James Sweet Guest

    You know, I borrowed a vacuum pump the first time I did some A/C work but I
    later found I could buy new surplus rotary compressors designed for window
    AC units for $5-$8 and they pull a stronger vacuum than the real vacuum pump
    I had! Pegs the mechanical guage all the way down to 30 in/hg which is
    plenty lots of things and the price is hard to beat.
     
  15. N Cook

    N Cook Guest

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