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IndustryArena Forum > MetalWorking Machines > Benchtop Machines > PM25-MV Electronic Spindle Speed Control from GRBL
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  1. #1
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    PM25-MV Electronic Spindle Speed Control from GRBL

    Here is my first information on PM25-MV spindle drive control:

    The machine comes with 750W brushless hall-based spindle motor which is controlled by the electronic controller. I am posting the pictures below. As a first finding, the controller has a 2200pF capacitor from power lines to ground (EMC filter). When I connected this to GFCI protected power outlet, the current through the capacitor will occasionally trip the GFCI protection, which is inconvenient. Do not connect the machine to GFCI outlets.

    A quick disassembly shows the modular BLDC controller which is molded in epoxy in place after assembly, so it is not repairable. The molding protects from moisture which is good. The hall sensors and the direction/speed controls are powered from on-board low voltage regulator which is NOT galvanically isolated from the power lines. This makes it dangerous to wire speed control to PC or microcontroller! Direct connection may lead for complete failure of electronics and it cannot be repaired.

    The speed is controlled by the DC voltage which may be from 0V (stop) to 5V (full speed). The controller has a label which apparently specified the maximum speed of this version of the controller (see Motor_Controller_2). Mine is 0-2500rpm, but there are options to set it to 0-3500rpm. However, since it is molded, apparently the maximum speed cannot be changed.

    Since there is a need of isolation to control it externally, one needs to install an optocoupler as shown on schematics. Two options are available: using a transistor optocoupler (PC817, H11Ax, H11Bx, 4N23, etc) (opto_1) and using a logic optocoupler (H11Lx, NTE309x, 6N137) (opto_3). The second option will be more accurate. Transistor option will provide zero (or close to zero) voltage when the LED is off; and 5V when the LED is on. The logic version will output zero when LED is on and ~+5V when the LED is off.
    The connection of the LED to controller may vary - it may be connected between power and PWM output of the controller, or between PWM output and ground. Depending on the way it is connected, the PWM will be effectively inverted.

    Once the optocoupler is built, it makes sense to check what is the idle state of the controller and set the inversion appropriately.

    In some cases, it makes sense to retain the manual control of the spindle speed - that can be easily done with two diodes as shown in the third ("enhanced") schematics (opto_3).

    One disadvantage of the logic optocoupler is the fact that it sets the full speed when the CNC controller is powered down. It is possible to fix this by adding one logic inverter gate between the output of the optocoupler and the RC filter.

    Disclaimer: use the information herein at your own risk, no warranties of any kind, and you need to understand what are you doing. When testing, make sure that you do not touch energized parts on the motor controller and the high side of the optocoupler to avoid electric shock!
    Attached Thumbnails Attached Thumbnails Motor_Controller_1.jpg   Motor_Controller_2.jpg   Motor_Controller_3.jpg   Opto_1.jpg  

    Opto_3.jpg  
    Last edited by dmderev; 01-12-2020 at 12:25 AM.

  2. #2
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    Additional pictures of the BLDC controller... I could not find schematics or any other information so far. Apparently it is microcontroller driven and there is a programming (?) connector in the middle. The control input impedance is apparently 100kOhm.

    Disclaimer: Use information herein at your own risk, no warranties of any kind.
    Attached Thumbnails Attached Thumbnails Opto_2.jpg   Motor_Controller_4.jpg  

  3. #3
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    Re: PM25-MV Electronic Spindle Speed Control from GRBL

    I am researching doing exactly this, and this is great information. Have you looked into reading the tach output from the spindle as well?

  4. #4
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    Re: PM25-MV Electronic Spindle Speed Control from GRBL

    For some reason I can't seem to be able to access the pictures. It just says :
    "Attached Thumbnails".

    I am very much in need of this diagram. Can you upload it again ?

  5. #5
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    Exclamation Re: PM25-MV Electronic Spindle Speed Control from GRBL

    I lost original files with pictures. However, I bought "Weiss WBL290BV" Lathe recently, it was painted into a surprisingly similar blue as PM25. And, surprise, it had the same motor controller. This time it is 1500W and has a brake switch with external brake resistor. So I took the pictures of this - maybe they come out with better resolution.

    This controller has an improvement: there is external IGBT switch (G20N65 connected with optocoupler) to connect external 300W brake resistor. I guess that this controller has slightly different firmware from that of PM25.

    Since it has a brake, I am building external controller which allows to specify the number of rotations of spindle between start and automatic stop. The controller is connected to "Switch" pins using HL817 photocouplers (remember, these pins are not isolated from mains power). The CW and CCW are pulled up to 5V and the optocouplers (in parallel with the manual switch) short one of the CW/CCW pins to 0V. Don't pull both to ground!

    P.S. - it looks that this site scales down images - they are still small!
    Attached Thumbnails Attached Thumbnails Pinout_BLDC_Driver.jpg   BLDC_Driver_Brakes.jpg   BLDC_Driver_Top.jpg   BLDC_Driver_Brake_Switch.jpg  

    Control_Compartment_1.jpg  

  6. #6
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    Re: PM25-MV Electronic Spindle Speed Control from GRBL

    Picture of pinout one more time.
    Attached Thumbnails Attached Thumbnails Pinout_BLDC_Driver.jpg  

  7. #7
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    Re: PM25-MV Electronic Spindle Speed Control from GRBL

    I found the seller on Aliexpress: https://www.aliexpress.com/item/2255799890270658.html
    Attached Thumbnails Attached Thumbnails H03f51ec00f7741debe49a222abfbcc09h.jpg   Hf3381478467b4b1885bdb81d94f1e66cP.jpg   s-l400.jpg   Lathe-Control-Board-For-DC-Brushless-Motor-850w-750w-dc-brushless-motor-control-board-control-bo.jpg  


  8. #8
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    Re: PM25-MV Electronic Spindle Speed Control from GRBL

    Quote Originally Posted by dmderev View Post
    P.S. - it looks that this site scales down images - they are still small!
    So small they are invisible! Are you using a mobile phone to post pictures? Other sites using 'older hosting software' have problems with images from phones!

  9. #9
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    Re: PM25-MV Electronic Spindle Speed Control from GRBL

    About the picture size: original pictures are in ~2x2K resolution. They are ~2MB in size. This site scales then down and changes resolution to ~300x200 when uploading, the "uploaded size" is reported as ~25kB. The same happens if I try to fool it and upload as *.zip file: the max size of *.zip allowed is <100kB. They are still somewhat readable to me (and can be downloaded). It also shows "attached thumbnails".
    I posted better pictures here:
    https://sites.google.com/view/dmelec...and-automation

  10. #10
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    Quote Originally Posted by dmderev View Post
    About the picture size: original pictures are in ~2x2K resolution. They are ~2MB in size. This site scales then down and changes resolution to ~300x200 when uploading, the "uploaded size" is reported as ~25kB. The same happens if I try to fool it and upload as *.zip file: the max size of *.zip allowed is <100kB. They are still somewhat readable to me (and can be downloaded). It also shows "attached thumbnails".
    I posted better pictures here:
    https://sites.google.com/view/dmelec...and-automation

    Interestingly. I came across this with a schematic from Franco using the original PM speed drive and a KB spindle board driven from an Acorn CNC control system:
    I've never tested this circuit myself.
    Adapting the diagram from the Acorn to the grbl shouldn't be too hard.

    https://www.cnczone.com/forums/attac...0&d=1640999031

    https://www.cnczone.com/forums/bench...ml#post2488096

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