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DC motor controls

  1. Apr 27, 2017 #1
    Okay, this is probably going to be way below your pay grade, but bear with me because I know nothing about electric motors except that you plug them in, turn the switch, and they work.

    I've seen some instances where people have taken DC motors from treadmills and used them to power lathes and other equipment via PWM. It just so happens I have a PMDC motor from a treadmill that I'd like to use on my lathe. The motor has 4 wires (two are blue and according to the wiring diagram they are for a thermal protection circuit) and the specs from the motor plate are as follows: 2.6HP 21.4 Amps, 1.5 HP continuous duty at 95VDC.

    I've been told this motor can't be used because the amperage is too high for a controller. Not sure what that means, but it doesn't make sense since it was used with a controller in the treadmill. I have the motor control board from the treadmill but no speed control. I attached everything and plugged it in but nothing happens, as I assumed it would.

    Can anyone please help and tell me exactly what I need to make this work? Please don't be too technical, just give it to me in layman's terms.
     
    Last edited by a moderator: Apr 27, 2017
  2. jcsd
  3. Apr 27, 2017 #2

    berkeman

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    Welcome to the PF.

    It sounds like you have not worked much with high voltages before, correct? What experience do you have working with AC-Mains powered circuitry?
     
  4. Apr 27, 2017 #3
    Hello BPress - welcome. I think this is very doable, but also very dangerous. The treadmills MC board will likely have a number of safety circuits, and if they are not all set properly it will not power up the motor.
     
  5. Apr 27, 2017 #4
    As I stated above, I know nothing about electric motors or high voltage, which is the reason I am here asking for advice. I'm not an electrician nor electronics expert. I'm just looking for advice on how this can be made to work, or if it is not possible or too difficult for someone who really knows nothing about it, what kind of DC motor and motor control do I need to convert my wood lathe from an AC motor with step pulleys to DC with variable speed? Is it possible to connect an AC motor to some kind of speed control device? Thanks
     
  6. Apr 27, 2017 #5
    As I stated above, I know nothing about electric motors, nor high voltages. My experience with AC mains powered circuitry is limited to household replacement of wiring, switches, outlets, circuit breakers, etc. I am not an electrician.
     
  7. Apr 27, 2017 #6

    berkeman

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    I asked because if you intend to make a lathe with an AC Mains powered motor, there are a number of safety regulations for how you handle the AC Mains connection from the wall to your lathe and motor. Things like how to size the fuse/breaker, where to put the switch, how to handle the grounding of everything, and how to make reliable connections. Also how to pick using a single-insulated or double-insulated transformer to transform the AC Mains input into the high DC voltage that the motor apparently needs.

    If you are not familiar with any of those things, you really should not be undertaking this project. It's just too easy to electrocute somebody or start a serious fire. Please consider finding a Mentor in your area who can help you with your project, and teach you some of those safety fundamentals. :smile:
     
  8. Apr 27, 2017 #7
    Ok, I'm confused because this motor came out of a treadmill which plugs directly into a 120 volt AC outlet, and I understand that the controller board rectifies the AC to DC to power the motor. Basically all I want to do is replace the tread with the lathe spindle. The motor plate says it is 95 VDC, which to me does not seem like high voltage. When I hear high voltage I think 600+ or more. The lathe is already running on an AC motor at 120 volts on a 20 amp breaker. I want to go to DC in order to utilize a speed control, because as it is I must stop the motor and remove several covers to change the belt position on the 4 step pulley.
     
  9. Apr 27, 2017 #8
    Hello Again, Almost any voltage can be hazardous, but generally above 50V is considered hazardous ( this is the OSHA regulation point for electrical hazards) - what it is called does not matter, High Voltage or not, what comes out of the wall is lethal. PF is pretty strict on advising on hazardous projects.

    There are certain best practices and procedures that qualified people utilize to stay safe on a project like this, I believe we pretty much all can understand what and why you want to do this. So the mentor / experienced partner recommendation is being given.
     
  10. Apr 27, 2017 #9

    jim hardy

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    My honest advice is try the hobbyist forums.


    I tried a search on phrase Treadmill Motor Lathe and got plenty of hits
    here's first three.
    http://www.cnccookbook.com/MTLatheDCMotor.htm

    http://bedair.org/Tmotor/Tmotor1.html

    There are so many people doing what you describe it doesn't make sense for you to start from scratch.

    I once tried running a treadmill motor with just a bridge rectifier and ordinary lamp dimmer to see if it'd work, and it did, but the parts i used were underrated for connecting it to any sort of load. You'd need a 2000 watt lamp dimmer that costs one or two hundred bucks, probably more than something already made for the hobby market specifically to do what you want.

    We could build one from scratch but you want a running lathe not an electronics research project.

    That's my honest advice, not a dismissal.

    old jim
     

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    Last edited: Apr 27, 2017
  11. Apr 27, 2017 #10

    jim hardy

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    Can you show a picture of that wiring diagram ?
     
  12. Apr 28, 2017 #11
    Thank you Jim, finally an actual answer. I will send that wiring diagram later.
     
  13. Apr 28, 2017 #12
    << Insult removed by Mentors >>
     
    Last edited by a moderator: Apr 28, 2017
  14. Apr 28, 2017 #13
    I am the son of a DuPont'r, and I was a safety coordinator / instructor for an electrical field service group... REF 1910.269 ( in this field High Voltage indicates > 70KV). I developed a philosophy that if you THINK you are safe you are not safe - you have to KNOW you are safe.

    There are many places on the interwebs where there is no or little regard for electrical safety.. but on PF I have always respected their willingness to lock a thread in the name of safety.
     
  15. Apr 28, 2017 #14
    Let me assure you that I have no desire to die nor start my shop on fire. I'm simply looking for an easy way to convert my lathe to a DC motor with an electronic speed control. That being said, and while I am not an electrician, I do understand the principles of electricity and realize that it can kill you. I am 62 years old and have been in the construction and wood working industry for most of my life and I still have both eyes and all of my limbs and digits, which should make you understand that I am safety conscious and careful in my work methods.
     
  16. Apr 28, 2017 #15

    berkeman

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    You simply do not have the skills yet to do this project safely.
    And with that good advice, this thread is done.
     
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