GEC Gemini motor controller is working

I got a Boxford TCL 125 CNC lathe a few years ago that I have been working on getting up and running. I gutted all the electronics except for the spindle motor controller, and replaced the stepper drivers and built a PC right into the lathe enclosure. I’ll post more on those upgrades later. All the new stuff I added is working fine, it is the old GEC Gemini motor controller that was giving me a hard time. But, after reading this post I got it working, it looks like I was just missing the kill switch connection.

So here are the connections to the big orange header:

  1. NC
  2. 0-8 VDC – This sets the motor speed
  3. 10VDC – Supply voltage for the controller
  4. NC
  5. NC
  6. NC
  7. GND
  8. GND
  9. Kill switch input – This needs to be connected to pin 3 for the motor to run
  10. GND
  11. NC
  12. NC

It looks like there are traces on the PCB that go to the pins that I have labeled as NC, but I’m not sure what they are for and the motor is working without them. If you know what they are used for leave some feedback.

2 thoughts on “GEC Gemini motor controller is working”

  1. Hi,

    I have just bought myself one of these lathes, The intent is to gut most of the electronics like you. It was nice to find some info on the motor controller. The 0-8v input is probably going to need a micro-controller somewhere in the mix. I have a number of mini ATX boards more than capable of running say EMC2 so the idea of building a PC into the enclosure appeals greatly to me. I am keen to see how your project progresses and will keep an eye out for your net bog post.



    1. Eric,

      I’m not quite sure yet how I will do the interface between the computer and the Gemini controller. The PC puts out a PWM signal for speed, which I was thinking of putting through a low pass filter and then a DC gain using an opamp to get the level up. I had also like you thought of using a micro with a capture compare to look at the in coming PWM signal and output a signal on a DAC. I guess you would still need an opamp to get the needed 8V full scale. You could also use the micro to take care of controlling the relay for changing spindle direction.
      I’m interested to hear how your conversion goes for you.

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