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  1. #1
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    Default Modified 110v 10,000rpm motor - modified how?

    Hi all,

    I recently acquired a small motor salvaged from some large unknown machine tool. The machine had a number of these motors in it - I got two of them. Label says 110v, 1/7hp, 10,000 rpm.

    But it came with a sticker over the plate saying it had been modified. Here is the motor (excuse the sidewards pics there - I rotated them on the PC but they still appear like this here. Weird):

    IMAG1910.jpgIMAG1909.jpgIMAG1908.jpgIMAG1907.jpgIMAG1906.jpgIMAG1905.jpg

    I tested it initially on a 12/24v car battery charger and it ran nice and smooth and, as you might expect, a lot slower than 10krpm. The speed would change as I changed the voltage.

    When I hooked it on to 240v (and I am not even sure I should have) it sure spins up, but it sounds more like a vacuum cleaner motor (20k+ rpm?) or my electric die grinder (27k rpm). And maybe a little like an F-18 Hornet or two taking off. But it didn't sound like it was about to explode.

    Excuse if my questions are stupid, I do not really have a head for electrickery.

    Any clues in what 'modified' might mean? Should it run on 240? and if it does ... would that mean circa 20k rpm and not 10k? Would is also mean circa double the stated 1/7hp?

    ... anything I can test too verify, erm, anything? I have a multimeter.

    Many thanks,

    Greg.

    EDIT: motor is intended to possibly power a small tool post grinder

  2. #2
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    Default

    DISCLAIMER

    No liability is accepted by MetalWork Forum's administrators
    or moderators for advice offered by members posting replies
    or asking questions regarding electrical work.
    We strongly advise contacting a Licensed Tradeperson for all electrical work.

    WARNING

    Information supplied within posts is not to be considered as detailed formal instructions to complete a task.
    Members following such information do so at their own risk


    Updated by Grahame - 29-9 -17 6.46 PM

  3. #3
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by StrayAlien View Post
    Excuse if my questions are stupid, I do not really have a head for electrickery.
    In that case my first piece of advice is I would not be playing around applying 240V to it.

    Modification could be anything, how it starts, speed, connections, or Voltage.
    It might well run on 240V for 2 minutes or even 5 before it overheats and catches fire or shorts out and kills someone.

    Before even connecting it to 240V the first thing would be to test the insulation can even support 240V. This is not done using 240V but using short pulses of 500 or 750V . This is done by an instrument commonly known as a Megger or an insulation tester.

    Even then, like I said above there's no guarantee it will run for any length of time on 240V as the current might be too high for the motor to cope with and eventually it will overheat. Instead of running it at 240V I would see if you can find a 240 to 110V transformer and test it at 110V first

    Another instrument you will need is an optical tachometer to work out the RPM - unless you know that you won't know if you can even use it for a tool post grinder. 10,000 rpm is too high for most grinding wheels and attaching most wheels and running it at these speeds could leave you with a piece of wheel protruding out of your face.

    If the motor owes you nothing you could see how long it runs for and if it gets warm or hot and if it overheats and dies "say la vie"

  4. #4
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    Thanks Grahame, I understand - though I've not yet felt the need to blame Australia Post for bad news letters so I think you're okay there.

    Thanks also Bill. The 240v thing was indeed an experiment. The motor was clamped, rotated in such a way as not to fling stuff in the direction of other stuff if it disintegrated, and then wired in with an extension cord that I could turn on from a distance.

    I guess my question about being modified was more from a 'when 110v motors are modified for 240v is there a standard set of stuff that is done' point of view. I am not from the industry so am not familiar with such things.

    re 10k rpm vs grinders, for 50hz my take is the speculated 10k rpm drops to circa 8300 or so and for a 3" wheel this gives about 6500 sfpm - I could be wrong but this supports it:

    Grinding Wheel Speed Calculator | Norton Abrasives

    But, at any rate, my intention was not to run wheels off the motor but to have it power a spindle. I am not wedded to the idea of using one of these motors for a TPG but if the mods were typical and 'well known' then I might get a element of confidence that it wont self destruct. I guess this post is about gaining some confidence, and if none eventuates, then the idea is binned. The motors were $10 so nothing lost. I like the idea of the 110v step down test. Those transformers are pretty cheap.

    Thanks. Greg.

  5. #5
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    This motor looks to be a universal series wound type, that can be fed with an AC or DC supply, consequently the speed of the motor is not fixed by the frequency of the supply voltage, series wound motors do reach high speeds and are commonly found in vacuum cleaners and mains powered tools such as angle grinders and drills.
    Without knowing for certain what 'modified' means it is probably best to stick to 110v - you certainly don't want to go to the trouble of setting it up only to have it fail after an hour or so of use. If you know anyone that has a variac then a safe way to test would be to slowly increase the voltage while monitoring the current draw, the name plate shows 1.9 amps at 110v so at 240v you would expect around 1 amp.

    I would not attempt to use this for a grinder however if you insist then gearing it down as you plan is a must, I've seen an abrasive wheel explode - pieces were sent through the maintenance shed roof.

  6. #6
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    If you need a small motor a good source is old sewing machine motors, readily available, 240 volt usually about 4000-5000 rpm, and if you get the foot control with it you can also easily control the speed.
    I have one set up on a wood thicknesser blade sharpening jig and it works a treat.
    Regards
    Bradford

  7. #7
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    Be careful of the bearings in a sewing machine motor. I used one to make a vibrating cartridge cleaner and the motor bearings wore out real fast.

    Dean

  8. #8
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    Bradford/Oldneweng, thanks - I have a small sewing machine motor as a backup plan to a backup plan. ) Doesn't feel very torque-y though.

    Familyguy, thanks, I'll see what I can find to test at 110v and if that is no joy (or too expensive) I may just ebay for a suitable small motor (with feeble-ish sewing machine motor in reserve). I have no intention of letting this thing spin at 20k - even if it does actually do it.

    Re wheel speed - looking at wheel specs, most 3" wheels are max rpm in 10k-12k range, so the circa 8.3k still seems ballpark for it - though my intention was for it to run a separate spindle to gear it up/down depending on wheel size.

    If I have any joy I'll post back here. If I start a hunt for an suitable small motor on ebay I'll start a new thread. That might be something interesting and search-worthy.

    Many thanks,

    Greg.

  9. #9
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    Picked up a 110v step down transformer this morning and hooked it up and the motor runs as sweet as a nut. Incredibly smooth.

    This guy:

    IMAG1915.jpg


    Also, regardless of which wire gets active the motor spins in the same direction. Is that expected?

    Greg.

  10. #10
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    Quote Originally Posted by StrayAlien View Post

    Also, regardless of which wire gets active the motor spins in the same direction. Is that expected?

    Greg.
    That's correct operation. If you require the opposite direction the internal wiring needs modifying.

    Insert standard disclaimer here regarding electrical safety.

    John

  11. #11
    BobL is offline Member: Blue and white apron brigade
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    To reverse the direction you need to reverse the connections to
    EITHER
    the run coil
    OR
    The start coil
    AND WHILE
    leaving the other coil connected in the same way

    When you reverse the wiring externally you are reversing the connection to both run and the start coil at the same time.

  12. #12
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    John, Bob. Thanks. No re-wiring being attempted here. )

  13. #13
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    Quote Originally Posted by BobL View Post
    To reverse the direction you need to reverse the connections to
    EITHER
    the run coil
    OR
    The start coil
    AND WHILE
    leaving the other coil connected in the same way

    When you reverse the wiring externally you are reversing the connection to both run and the start coil at the same time.
    The motor was rated in the 10K RPM at 110V 60Hz, so would be an universal motor rather than an induction motor. An induction motor operating from 60Hz has a theoretical max RPM of 3600RPM, but will run below that due to slip.

    BobL's info is correct for induction motors but universal motor do not have start and run windings, they have a field winding and armature windings interconnected by brushes and the commutator.

    To reverse these you need to reverse the current flow through the armature by swapping the connections to the brushes. However, some universal motors have their timing advanced by rotating the brushes relative to the field winding poles to produce more torque in one direction of rotation which may leave them somewhat wimpy if reversed, unless the timing can be adjusted to advance them for the opposite direction of rotation.
    I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.

  14. #14
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    Thanks malb,

    Good info. Though, at my level of knowledge ... I'll leave it as is.

    The reason for the reversing question was the design of TPG I was considering is compact and 'parts-reversable' so the grinding wheel could be at the left or right depending on requirements. My lathe is not very long.

    But, no issues, it is not too hard t think of a design where the motor stays mounted but just the spindle is swapped - or indeed, a double ended spindle.

    Thanks,

    Greg.

  15. #15
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    Old shower pump motors are a good source of 3K rpm, 1/3rd HP motors, and are usually double ended with 10 or 12 mm diameter shafts. They are often discarded because they start to leak and then are replaced. The pump is easily stripped off and the motor pressed into use for what ever purpose.
    Best Regards:
    Baron J.

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