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  1. #1
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    Default Variable speed motors

    CMG makes a single phase 240V motor with a potentiometer speed control unit.

    The speed range is 600 - 1800 RPM.

    I would like to know how effective this is in comparison to the other speed control devices on the market. For instance, is the torque of the motor greatly affected?

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  3. #2
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    Default

    It is more than a potentiometer. It controls a whole heap of computer stuff in the motor.

    Fantastic unit.

    We have one fitted on a technatool 3000 and have done for quite a while.

    Neil Ellis runs one as well on his demo lathe.

    No loss of torque through the whole range which is more than I can say for some more expensive units.

  4. #3
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    Default

    My understanding is that GMC motor is a 3-phase motor and the control box is a very basic VSD/VFD which is why it has such a small full torque speed range. I thought about buying one of these GMC units to replace the 3 phase motor on my Hercus metal working lathe but the Metal working lads advise me against this because of the limited speed/torque range. It is cheaper top buy a fully speced VFD for about $150 - 250 and 3 phase motors can be obtained for next to nothing. The speed control range on a decent VFD is at least double that for the CMG unit since once can get least 6:1 with a decent VFD. If the motor is a well made 1440 rpm unit it can easily spin to 2800 rpm so a 10:1 range may even be possible.

    The implementation for my Hercus, enabled me to use the existing 3 phase motor, looks like this and is described here.


    Since then I have bought 4 more 3 phase motors (I have no more than $35 for any one of these) and two more VFDs and plan to change my Woodfast WW lathe and my DP to variable speed.

  5. #4
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    Default

    I don't know how effective this motor is , but provided that the motor does not loose torque at the lower RPM, or over heat, It should work well for Lathe application.

    What Hp is the motor and cost??

    Jeff

  6. #5
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    Thumbs up

    Thanks for that !

    Funny how I've been chasing information on the net and through other sources for months and I came across this motor "accidentally".I wonder why so many "experts"" could tell me nothing.

    Seems like a less expensive option than others I have been pursuing.

    Bob: I have been chasing motors to set up with a vfd. Problem is I only have access to 240V single phase power.

    vk4: there are several models. I need at least 1hp, and that motor runs from 600-1800 rpm. I would leave the pulley system on my lathe intact and could use that for extra gearing. There is also a !.5HP model running 900- 1800 RPM.
    This would definitely solve any torque problems but would force me to rethink the pulley set-up for lower speeds.

    Might have to get a pulley system speccially made.

  7. #6
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    Default

    Artme,

    The VFD takes single phase 240, changes it to direct currant, chops that into variable frequency 3 phase and sends that to the motor.

    You want a VFD with constant torque. I have a Teco VFD on a 1 hp motor that I turned down to barely moving and tried to stall it by grabbing the motor pulley. I could not stall it.

    See: Transformers, Phase Converters and VFD - Practical Machinist - Largest Manufacturing Technology Forum on the Web

    Variable-frequency drive - Wikipedia, the free encyclopedia

    One day I bought a nice slightly used 1 HP 3 phase, and a new in crate 3 HP 3 phase motor at my local junk yard for 50 cents a pound. With some steel my bill was under $40.

    I looked up the 3 HP in Granger catalog, it was $356.

    A motor shop might have used checked out 3 phase motors.

    The 1 HP Teco VFD was about $130 from an internet supplier.
    So much timber, so little time.

    Paul

  8. #7
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    Default

    Quote Originally Posted by View Post
    It is more than a potentiometer. It controls a whole heap of computer stuff in the motor.

    Fantastic unit.

    We have one fitted on a technatool 3000 and have done for quite a while.

    Neil Ellis runs one as well on his demo lathe.

    No loss of torque through the whole range which is more than I can say for some more expensive units.
    I noticed the Nova 3000 in recent photo's Grippy things after my own electrical problem and when I purchased the lathe going to a VS system was/is still in mind. How ever I have found that the flange fitting for the Nova is not off the shelf but needs to be a special order through a dealer to CMG to suit the Nova.

    How is yours mounted?? Is yours one of those Jim Carroll sells??

    Thanks for that PDF.

    If I go down this road I'll be fitting the 2.5Hp with 19mm shaft as mine is already 19mm and then no need for pulley change as well.


    Artme thanks for bring this up.

    As for people to talk to i spoke to CMG here in Sydney and they were of great value.

    Ray

  9. #8
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    Default

    Quote Originally Posted by artme View Post
    Bob: I have been chasing motors to set up with a vfd. Problem is I only have access to 240V single phase power.
    That is all you need. There are a range of VFDs out there but the most common ones being used change the 240 v single phase to 240 V 3-phase. Doing this doubles the current but most 3-phase motors are built like brick outhouses and can easily handle this also bearing in mind that there are not many situations where full power is required continuously for long periods.

  10. #9
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    May 1999
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    Grovedale, Victoria Australia
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    Default

    The CMG motor is a constant torque motor,
    When originally approached by CMG about the motor they indicated that through the electronics we could have variable torque or constant torque.
    We decided the constant torque is the way to go as most woodies want to get good torque down low as well as at high speeds.
    A lot of these motors have been retro fitted to mainly older Woodfast, Vicmarc and tough lathes and just recently to a symtec.

    The 1hp gives more than enough grunt for most applications and with using the correct pulley setup you can get quite good speed ranges.The 1hp is a 16mm-5/8" shaft which is pretty well standard for this size motor and has a B56 frame, we can also set up for flage mounting like some of the Nova 3000 lathes.
    Some of the early N3000 lathes are foot mounted.
    Here is some more info
    The motors now come with a reverse switch which is still mounted on the motor as a safety issue, some lathes are not suited for going in reverse and most guys do not have any way of locking their chucks etc for reverse work. You have to make a dedicated decision to run in reverse.
    Jim Carroll
    One Good Turn Deserves Another. CWS, Vicmarc, Robert Sorby, Woodcut, Tormek, Woodfast
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  11. #10
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    Thumbs up

    Thanks for that extra info Jim.

    I know I have brought this up before, but as things change I keep needing to get new info.

    My lathe is an old TL 1200. wth the same pully setup as the later Nova lathes. It has served the well over the years. The motor is footplate mounted.

  12. #11
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    Default eureka with a small "e' and no exclamation mark

    I may have found it.

    A mate made a variable speed controller for his metalwork lathe some years back using a Jaycar kit.

    Jaycar has a newer kit for $99.95 that will do the job. No need to change my motor either.

    For those interested: Jaycar catalogue number KC5478

  13. #12
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    Default

    I looked here:

    240V 10A Deluxe Motor Speed Controller Kit - Jaycar Electronics

    I would question carefully about getting full torque at low speeds.

    It sounds to me like a triac speed controller. It would be good to find a review, or talk to someone who put one on an AC motor.
    So much timber, so little time.

    Paul

  14. #13
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    Thumbs up

    TThanks for that Paul.

    I know it would be great to see a review or talk to someone who has installed such a kit. I'm working on it.

  15. #14
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    Default

    You are not able to put variable speed on any standard single phase motor as you can burn out the start windings and capacitors.

    One reason CMG have a low motor speed of 600rpm is that any lower and the fan is unable to cool the motor efficiently.
    If you are running the motor at low speed for an extended period then you should use a lower pulley setting so the motor is running at a higher speed to run cooler.

    Make the pulley speed work for you not the motor
    Jim Carroll
    One Good Turn Deserves Another. CWS, Vicmarc, Robert Sorby, Woodcut, Tormek, Woodfast
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  16. #15
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    Thumbs up

    Thanx Jim!

    There is more to this than meets the eye, of that I am aware. So I will keep posting and getting more info.

    Last thing I want is to stuphph up my good motor which, by the way, is a 1400 rpm unit.

    I have been in touch with CMG but no reply so far.

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