Treadmill Motor for Mini Lathe

Discussion in 'General Electronics Chat' started by glyn254, Jun 14, 2018.

  1. glyn254

    Thread Starter New Member

    Apr 4, 2018
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    Hi everyone new here(mechanical guy)I am trying to retro fit a a DC treadmill motor to my mini lathe.It is off a Reebok Fusion (rev-1301).The motor control board is a Greenmaster GMC -TD20A-220v.I don’t want to use the operating control panel.Could I use a potentiometer?.The control board has a 5 pin connector on it not sure if it is a/c or d/c at that point.would be grateful for any advise
    Thanks
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Can you post a pic of the motor board.
    Max.
     
  3. glyn254

    Thread Starter New Member

    Apr 4, 2018
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    Trying to put picture on from my ipad
     
  4. glyn254

    Thread Starter New Member

    Apr 4, 2018
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    all about circuits.jpeg
     
  5. glyn254

    Thread Starter New Member

    Apr 4, 2018
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  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Do any of those cables shown go to the motor?
    Max.
     
  7. -live wire-

    Active Member

    Dec 22, 2017
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    I noticed some capacitors that looked like HV (up to 230V). Please be careful, as they may hold a fatal charge, even after disconnected! Please, inform yourself on electrical safety, before doing anything you might regret!

    Looking at it, I notice a fuse (you will want to keep that for safety), some capacitors, some diodes, some semiconductors, and other components. My best guess is there is a DC power supply for the microcontroller and main chips. It must control some transistors to control the speed of the motor. The motor may also need DC (some pictures and part numbers, etc, would be helpful). It may also run off of mains AC, or other types of AC (three phase AC). Either way, PWM or PAC (phase angle control/pulse width modulation) are far better for speed control. It looks like it implements that.

    You could maybe just modify the circuit to PWM/PAC based on some other input. The basic idea for both is you first get a switch you can turn on and off quickly. This would be a transistor, probably a mosfet. You then turn it on and off rapidly to control the average power and current. If it is on 50% of the time, it gets half the power. You chose the % it's on vs off. It is very efficient, and there are only minor losses. You generally do turn it on and off hundreds or thousands of times per second. Each on/off period (both the on and off) is one cycle, and hertz (Hz) is cycles per second. You can ignore the labels in the graphs. It is just voltage on the y, time on the x. When you do this with DC, it is called PWM.
    upload_2018-6-14_16-54-4.png
    With phase angle control, or phase angle firing, it is a similar idea. However, it is a little more complicated due to it being AC and the voltage constantly changing. Imagine you have a sine wave going to a load. It could be any other shape, but sine waves are used in mains and are the most common.
    upload_2018-6-14_16-49-48.png
    This is what mains looks like. You can't just turn it on and off 50% of the time randomly. It sometimes gets the higher voltage parts, sometimes the lower ones. It would be very unpredictable. So, what you do, is you turn it off for a certain amount of time after it hits 0 volts. This way it is more predictable. It may not be exactly linear, but it works well.
    upload_2018-6-14_16-52-29.png [​IMG]
    For BLDC motors, you change the speed by changing the frequency. These are the most complicated motors, as there are many things you need to properly control them. They do not even run off of normal (single phase) AC or DC. A commercial driver is definitely the most viable option, at least for someone without a very large amount of electronics experience.

    So why not use a large potentiometer? Well there are many reasons. First of all, only certain motors can be wired up with one. It is just impossible for certain types, or you would need many of them. But let's say it would work, and your motor is a simple DC or universal one. The unused power gets dissipated across your potentiometer. You may need to dissipate 100s of watts with a large motor, when reducing the speed. All the power that doesn't go to the motor gets wasted on the potentiometer. A potentiometer that size will be at least a few hundred dollars!
    https://www.mouser.com/Passive-Comp...0wn8mZ1y9815aZ1yz8imfZ1y98159Z1yyrcd4Z1yz8ij3
    Even if that was not an issue, do you want to pay for many times the power used on your electric bill? PWM/PAC can be incredibly efficient. Even a DIY solution may be just a few 10s of $ and over 80% efficient.
     
    Last edited: Jun 14, 2018
  8. glyn254

    Thread Starter New Member

    Apr 4, 2018
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    Yes Max the red and black cables in corner by I think the capacitor?
     
  9. glyn254

    Thread Starter New Member

    Apr 4, 2018
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  10. -live wire-

    Active Member

    Dec 22, 2017
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    Ok, so googling that part # it looks like it is a standard DC motor. That makes things pretty easy. It says it is 180VDC and I assume you want to operate it close to the maximum power. Rectified and smoothed mains is 170VDC but will drop under load. This means it is pretty likely it is running off rectified and smoothed mains.

    If you want to do away with what is there completely and make your own controller then do this. My understanding is that you want to do that. I am assuming it consumes the maximum of 20A from the 120V outlet. It may be less in reality. The total cost will be under $30, so it is more affordable. Get a bridge rectifier like this. That converts AC into DC.
    upload_2018-6-14_17-58-56.png
    Get a capacitor to smooth it out for cleaner DC. A higher capacitance means less ripple. But it can be dangerous (for multiple reasons) and it will be more expensive. More current means larger ripple, so for large loads you need a larger capacitor. But for a motor like that ripple will not be a huge deal. I recommend getting two of these and adding the capacitor they have in parallel. This should allow for a high enough total capacitance.
    upload_2018-6-14_18-0-23.png
    Then get a mosfet like this. That will allow you to PWM it and efficiently control the speed. You will also want an optocoupler for isolation.

    But even with that large capacitance, it still may drop the voltage significantly down. It will decrease over time. That means a PWM will have that issue where it is too random in turning on and off. And PWM can often require complex circuits to create those oscillations. A solution to both is this. Get a small mains transformer that turn 120VAC RMS into 2x 10-40V AC peak. It needs to be low voltage and two identical outputs. Google RMS vs peak if you don't understand. AAC itself has some good resources in education, too. Then make a peak detector/holder (rectifier + capacitor) to get pure DC. It must be stable, so use a large capacitor. Combat inrush with a simple resistor. Power a comparator with that. Then step it down with a potentiometer, to create a variable DC voltage from 0 to the peak. It will really be the peak minus the diode fV, but that is not too important. Then rectify the other identical output using the same number of diodes. This gets compared to the DC.

    That basically does this:
    [​IMG]
    Then have the comparator drive the optocoupler, controlling the mosfet.

    One last thing, get a diode and resistor to limit the inductive spiking when disconnected. Google "motor inductive kickback diode fixes"
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I think @glyn254 want to use the existing motor board, which would make sense.

    I don't recognize that board and it appears rather sparse, It would appear to be PWM rather than SCR bridge, but I don's see the expected Mosfets etc, where does the green VR conductor go?
    Also what is under the tin plated cover on the top pic?
    Max.
     
  12. tsan

    Member

    Sep 6, 2014
    84
    14
    I don't know about treadmill systems, but I googled for control board RT100POW and there is a good drawing of the system layout here,
    http://www.laufbandersatzteile.de/catalog/product/gallery/id/968/image/2410/
    (I don't know if saving the image here is ok or not)

    I assume you want to control the belt motor, althought the connector on one of your image is for incline/elevation motor. I combined snapshots from the system layout image and your image. Belt motor speed connector is marked with red square.
    treadmill speed control connector.PNG

    Somehow I found a board that is said to be a Greenmaster compatible board,
    http://www.partsfortreadmill.com/greenmaster-kxtl-230-fhtl-treadmill-controller-wired.html

    From there,
    "Control voltage 0-10 V calibrated on Greenmaster specifications."
    "Pilot signal: 0-10 VDC, initial calibration 8 VDC = 170 VDC voltage to the motor."

    It could be that it is enough to have a (something like 10 kilo ohm) potentiometer connected to pin 3, 4 and 5 on the connector.
     
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  13. Pedant Engineer

    Member

    May 27, 2018
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    18
    You've got a lot of very useful replies already but I can add that I have done this myself with a very similar system. 230Vac input, 180VDC motor at 1.25HP. I kept the original control board (it was an older treadmill than yours I think) and I hobbled together enough to mimic the speed control and on/off signals of the user interface board to control the motor. In my case it was an on/off signal and independent up and down signals which rachet the speed up and down. Other than a power indicator LED I only needed the switches and nothing else. Yours sounds similar in that respect.

    Keeping the motor driver board means not having to muck about with the high voltage and motor protection and in my case provided low voltage and isolated control signals that won't kill anybody if touched.

    Sounds like you might have the option of a simple pot to get a 0 to 10V control (or 0 to 8V in your case) which would be very kewl :)
     
  14. Pedant Engineer

    Member

    May 27, 2018
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    Sorry, but this is so oversimplified I strongly suggest you avoid doing this unless you are experienced and confident of mains powered circuits. Inrush current for a start is not considered and the isolation is not the trivial exercise portrayed.
     
  15. Pedant Engineer

    Member

    May 27, 2018
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    These drives have inrush limiting to avoid blowing fuse box breakers etc, bridge rectifier, large capacitor bank and PWM power stage. The PWM duty cycle is limited to provide no mo0re than the motors voltage rating (on average) even though the DC link is closer to 320VDC unless there is a PFC pre-regulator in which case it will be more like 400VDC. The PWM frequency will be in the kilohertz range and likely a minimum of 12kHz to limit audible noise but may well be over 25kHz for that and other reasons.
    Cycle by cycle current limiting will almost definitely be required to get the motor started without drawing truck loads of current and monitoring to avoid overdriving the motor voltage which could happen very easily given the voltages involved. The use of a 170V DC motor means the same motor can be used in 110V and 230V markets with the only down side that the 170V DC motor must operate properly from a 320VDC supply at a 50% duty cycle which is a combination of electrical insulation requirements in the motor plus a hefty fly wheel to provide the inertia to smooth the rotation.
     
  16. MaxHeadRoom

    Expert

    Jul 18, 2013
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    @glyn254 it seems that what @tsan has found that you may in fact be able to use a 10k linear pot.
    Most T.M. controls use a circuit to ensure the pot is zero at switch on or at least has to be taken to zero before it will run.
    Most remove the flywheel when set up for machining applications.
    Max.
     
  17. -live wire-

    Active Member

    Dec 22, 2017
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    I am trying to make it a little easier to understand. And I assume that the metal parts would be grounded here, making things safer.
    That does make more sense, I agree. But I was under the impression he wanted to do away with it. He said he wanted to completely do away with the existing board, right?
     
  18. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What I read is the control board , which is the T.M. operating panel, not the drive.;)
    Max.
     
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  19. Pedant Engineer

    Member

    May 27, 2018
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    @livewire: the design of the drive for this is a bit more complex than can be conveyed in a forum. No offense to the OP or any others watching with a similar purpose but if you need instruction at the level proffered by LiveWire you need to do some serious homework first please, I fear for your safety as there are things you must do to avoid this thing blowing up in your face or electrocuting you and it really is a huge thing to try to explain it all in a forum posting. If you have the original drive and it works, go with that is my advice. That's what I did and I have designed this type of thing before but why bother when it is already done. No shame in an artful repurposing :)
     
  20. Pedant Engineer

    Member

    May 27, 2018
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    I will take a wild guess and say the bridge is under the PCB and the mosfet and diode are on the vertical heatsink. Under the tin cover is the control board. The control board (under the tin cover) probable has a lot of small and maybe low pitch SMT parts and therefore needs a lighter Cu weight than the power board it is soldered into. Makes sense to me that way and a common enough arrangement but only a guess in this instance.
     
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