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  1. #706
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    Useful score.

    Michael

  2. #707
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    Default YEEEHA ! That Worked !!!!! . Learned how to speed control a Universal Motor

    So after that dramatic title ..... many thanks to BobL and BaronJ for the comments about dimmer switch speed control. You can believe anything these guys say ...... !!

    I bought one of these for $20ish, might be useful for other electrical novices.

    https://www.ebay.com.au/itm/220V-4000W-AC-Variable-Voltage-Controller-for-Light-Fan-Speed-Motor-Dimmer-VIC/352502099195?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649



    Thats $8 more than the one BobL recommended, but for the extra $8 I got
    - Earthed device with metal enclosure
    - Corded with Aussie plug to plug into wall
    - Universal socket output - will accept US/UK/European/Aussie plugs

    So being as I am an electrical knownothing, I thought for an extra $8, thats a lot of stuff I dont have to do.

    ....and it worked .... tested it on a little old black singer sewing machine motor first

    0 to 80 volts nothing
    80 volts approx 3000rpm but low power so easily stalled
    90 volts approx 6000rpm bit more guts
    220volts approx 12000 rpm seems quite powerful

    Sherline motor had very similar behaviour.

    Don't think I need those high speeds am more interested in the 1000 to 2500 rpm range but the pulleys will do that for me and the motor will deliver higher power at higher rpm.

    This now allows me to setup the Mill/Drill version of the machine and maybe even a toolpost grinder on the Hercus .... see photo 4. Although .... I think it would be a very flimsy mill.

    Maybe there is a tiny and flimsy horizontal mill alignment possible as well

    So please ..... BobL and BaronJ, any suggested further reading for me - Jim Cox Electric Motors Book is now making a lot more sense to me, but keen to see other relevant books/websites that you think are good. ie Keen to learn how to insert a toggle switch to reverse direction, how to set up motor inside a bridge rectifier would be logical next targets. Have got various old motors I can experiment with and maybe build something useful.

    PS a bit of trivia - These lathes originally cut tapers by deliberately swinging the headstock around a bit and running the cutter along the inclined workpiece - so this little tiny lathe can theoretically cut full size Morse tapers - which is more than the 9" Hercus can do.

    That was a bit of a rant - .....

    Bill
    Attached Images Attached Images

  3. #708
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    Hi Bill, Guys,

    Be a little bit careful there Bill, some motors can be damaged by feeding them rough DC (chopped AC) !

    The clue is if the motor has carbon brushes it is a universal motor and can run on both AC and DC. It basically doesn't care which.

    An induction motor does not have any brushes and can be severely damaged by trying to use a Thyristor or Triac speed controller with it. This type of motor requires a special kind of controller that is able to provide an alternating voltage of variable frequency in order to vary its speed. A very common device called a VFD is used to alter the speed of three phase induction motors. You can get single phase VFD controllers but they are as expensive as a three phase one.

    Referring to my circuit drawing putting the motor inside a bridge rectifier is exactly as the drawing indicates. The proviso is only that the bridge rectifier must be capable of handling the amount of current expected, normally three or four times the load current, taking into account the starting current surge.

    I'll do a reversing switch diagram later if you want one.
    Best Regards:
    Baron J.

  4. #709
    BobL is offline Member: Blue and white apron brigade
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    Like BJ , before commenting I would like to know if the motor was a Universal or Induction motor.

  5. #710
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    BaronJ and BobL,

    Thanks for your comments.

    My current understanding is that if an AC motor has brushes then it is a Universal Motor and not an Induction Motor.

    So that is why I thought the Sherline motor mentioned in my previous post was a Universal Motor. There are two diametrically opposed screws on the outside of the motor casing that allow me to access, remove and inspect the brushes.

    The speed controller seemed to work quite well and I was quite happy about that, no that's not correct, lets say absolutely delighted instead. Thanks for your previous advice.

    Have got a few books ordered at the local library and hope to improve my understanding of electrical things I might bump into in the future. Have started with the 2 workshop practice books by Jim Cox and hope to end up doing as Bob suggested above and installing VFDs on three phase motors. Am aware of our own electrical forum and will start lurking.

    Bill

  6. #711
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    Hi Bill, Guys,

    I'm glad that you understand the difference between the two motor types, If you have any questions, I'm happy to help.

    Incidentally the two speed controllers that I picked up are Triac ones and apparently were originally used in a vacuum cleaner. At least that is what I've been told ! I must confess I don't recall that I've ever seen one with a motor speed control.
    Last edited by BaronJ; 26th Mar 2019 at 04:01 AM. Reason: spelling
    Best Regards:
    Baron J.

  7. #712
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by BaronJ View Post
    Indecently the two speed controllers that I picked up are Triac ones and apparently were originally used in a vacuum cleaner. At least that is what I've been told ! I must confess I don't recall that I've ever seen one with a motor speed control.
    They are very common. Our 40 year old "National Panasonic" vacuum cleaner had both a manual and auto speed controller on it. When the flow rate decrease the vacuum would increase and dial in more speed. The Chinese vacuum I picked up on the side of the road that powers my gas forge has the same thing.

  8. #713
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    Jan 2016
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    I picked up a drill press with a cooked motor for free a while back and recently fitted a treadmill motor to it that I picked up for $5, wish I spotted this thread earlier.

    I plan on controlling the motor from a 10,000W Chinese SCR unit from eBay, a 50A bridge rectifier, and I purchased a lower value potentiometer on the advice of a youtube tutorial video.

    I ran the drill from a little 12V supply and it looks promising.

    I hope it all works out, I'll link the electronics below for you to look at and a pic of the drill, I'll give it a good cleanup when I know it all works properly.


    DSC_1132.jpg

    https://www.ebay.com.au/itm/Electron...0f99%7Ciid%3A1

    https://www.ebay.com.au/itm/KBPC5010...0f99%7Ciid%3A1

    https://www.ebay.com.au/itm/2-Pcs-B2...torefresh=true


    Cheers,

    Ben

  9. #714
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by NedsHead View Post
    I picked up a drill press with a cooked motor for free a while back and recently fitted a treadmill motor to it that I picked up for $5, wish I spotted this thread earlier.

    I plan on controlling the motor from a 10,000W Chinese SCR unit from eBay, a 50A bridge rectifier, and I purchased a lower value potentiometer on the advice of a youtube tutorial video.
    Before you do that maybe have a read of this.
    DC motor performance
    The Youtube videos don't mention any of this and shows what can happen following something blindly.

  10. #715
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    Quote Originally Posted by BobL View Post
    Before you do that maybe have a read of this.
    DC motor performance
    The Youtube videos don't mention any of this and shows what can happen following something blindly.
    Hmm.. probably should have done a bit more research first, I'll see it through and report how it turns out

    Edit; BobL, could you go into a little bit more detail regarding the use of a fuse to protect the elec system, amperage and placement in the circuit are what I'm wanting to know, should the fuse be placed between the motor and bridge rectifier? and would an inline, automotive type fuse and holder be ok in this circuit?

    Thanks.

    Ben

  11. #716
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by NedsHead View Post
    Hmm.. probably should have done a bit more research first, I'll see it through and report how it turns out

    Edit; BobL, could you go into a little bit more detail regarding the use of a fuse to protect the elec system, amperage and placement in the circuit are what I'm wanting to know, should the fuse be placed between the motor and bridge rectifier? and would an inline, automotive type fuse and holder be ok in this circuit?

    Thanks.

    Ben
    Ben I should state I am not a sparky so you should take anything I say with appropriate care and check it with a sparky.

    Any fuse should take into account the motor HP. eg if it is a 1.5HP than would make it about 4.5A at full power.
    I would then probably consider using something like a 5 or 6A slow blow fuse on the mains side of the SCR.
    I would not use an automotive type fuse and holder on the output side of the BR as automotive stuff is often only rated for 30V DC whereas the output of the BR will be much higher than this.

    If the motor is not rated to 240V (a lot of them are just 180V) just make sure you don't exceed the V rating so it does not "Run Away". Maybe something like a large knob with a physical stop on the SCR pot so that it does not go over 180V.

    I just don't like the rather miserable power curve characteristics of those motors used in this way. Admittedly it matters very little in the case of a small drill press where it is very unlikely you will need to use large bits at slow speed.

  12. #717
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    Hi Guys,

    First of all treadmill motors are a universal type motor rated to run on a fixed or variable DC supply. In addition to the fact that they are usually fitted with field magnets rather than a field coil, and that feeding them with AC tends to reduce the magnets strength, usually permanently.

    Most of these speed control power supplies do not output pure DC, In the sense that the voltage that they do provide is one that varies depending upon where about in the AC mains cycle the Thyristor or Triac is switched on. Putting the motor inside a rectifier bridge doesn't alter this, it only guarantees that the motor will be provided with a unidirectional voltage. It allows for more power because it takes care of both half's of the AC cycle.

    Putting a suitable electrolytic capacitor, making sure that it is connected the right way round, across the motor will provide for a more constant DC supply. There are issues with doing this apart from the danger of having capacitors charged with a high voltage around. Large value electrolytic capacitors are expensive !

    Now "Fuses" A normal ceramic fuse will withstand anything from three to five times its rated current for a short time. I would use a fuse that is rated at about twice the maximum expected current, taking into account that the startup surge could be much higher. One way of reducing this is to start the motor at a low speed. Any fuse should be in the supplying feed to the system, ie before anything else. An additional fuse between the controller and the bridge would probably be a waste, since in the event of a fault the electronics in the controller would die much quicker than the fuse could save them.

    Chassis or panel mounted fuse holders should be used since these are usually rated for 500 volts or more. Chassis mounted fuse holders usually come with a plastic protective cover designed to prevent debris from being scattered should the fuse explode, and of course accidental contact.

    I hope I've covered all the points here, if not shout out.
    Best Regards:
    Baron J.

  13. #718
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by BaronJ View Post
    Now "Fuses" A normal ceramic fuse will withstand anything from three to five times its rated current for a short time. I would use a fuse that is rated at about twice the maximum expected current, taking into account that the startup surge could be much higher. One way of reducing this is to start the motor at a low speed. Any fuse should be in the supplying feed to the system, ie before anything else. An additional fuse between the controller and the bridge would probably be a waste, since in the event of a fault the electronics in the controller would die much quicker than the fuse could save them.
    The other type of fuses that are often used on motors are thermal cut out fuses. Using a melt type fuse that allows for a continuous draws about twice the maximum current can still be a problem as a motor can still overheat quite quickly quickly if running continuously on say 1.5X max current. A thermal cut out fuse will pick this up and cut power to the motor.

    These button pushing resettable fuses are readily available from electronics stores and their cut offs are defined by temperature eg 65, 70, 75º etc. They can be mounted directly to the outside of a motor but need to be mounted away from motor fans or covered over in some way. My 3HP Table saw has one of these fuses and a few years back I attached an ammeter and a thermocouple and tested its temperature and how long it took to cut out. The cut off temp was pretty accurate (with 5º) . Starting from room temp with the TS drawing 15A it took about 45s to cut out. Drawing 17A it took about 25s to cut out.

    This is less relevant for intermittent, low load, use operations like a drill press but would be a good idea on something like a table saw or buzzer.
    .

  14. #719
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    Hey Bob and BaronJ,

    What sort of jobs give people the experience to know this electrotrickery stuff ?

    I imagine that in industrial applications its cheaper to just buy new units rather than mess around installing new capacitors resistors potentiometers etc.

    But somebody somewhere has to be paid to design the circuits and controls for the motors churned out by factories.

    Have been reading a few books about motors but its heavy going.

    Bill

  15. #720
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    Hi Bill,
    That would be the Electrical Engineers work. They're the ones that also design the circcuits and controls for machinery, your white goods, anything that has electronics in it.
    I've found that reading on ANY new subject is hard going, sometimes I have to read it several times before it sinks in!!!!!
    Kryn
    To grow old is mandatory, growing up is optional.

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