I was looking for a way to use the Mach3 PWM spindle motor speed control feature for my Mill that is a build in progress. So With the Help of Bill Grumble from the TC robotics Group, I built this PWM Motor controller that I thought i would share with you.
***First and foremost**** This design is connected to the AC power line and has a large capacitor that can store a deadly charge for hours after it is unplugged. THIS IS NOT FOR THE INEXPERIENCED OR FIRST TIMER! You can and will be hurt if you are not careful! build at your own risk!
with that said....
I plan on using a modified Dremel 395 as my spindle motor. I have removed the Dremels internal Triac based speed control as the internal motor is a universal motor that will run on AC or DC. I added a IR LED and a Phototransistor to the dremel motor to send a speed pulse back to Mach3. I removed the AC power cord and added a 5pin CB radio type connector on the rear for the 2 wires for the motor and 3 for the speed sensor system(details on that later...thats next).
next I needed a way to take the PWM signal from the printer port and control a motor with it. I was talking with Bill Grumble at a TC Robotics group meeting and he pencil sketched this basic design. I took it a bit further and worked out the details to make it run.
The PWM signal from the PC's printer port is Optically isolated from the Motor controller through a H11L2 Optocoupler. the output from the Opto then feeds the PWM signal to a IR2109 Mosfet driver. I am only using the low side of the driver. and I choose to use a IRG4BC30S IGBT instead of a mosfet for higher current handling should the Dremel lock up. this is the basics of it. For the power supplies, I basically took apart an old switching power supply and robbed all the AC line components. the AC line enters through a fuse to an In rush limiter, then to a MOV or Zener surge suppressor. to a cap and to the bridge rectifier. the bridge converts the AC to DC and a large filter cap cleans up the ripple a bit.
I choose a 100uf 200V cap as it is what i had on hand. this is a very small amount of capacitance and a larger cap would be better...however. there is some debate on if any benefit would be had as it seems to run perfectly fine as is.
there is also a 12V Zener regulated supply that feeds 12V to the IC's. The mosfet really needs 15V but I choose 12V to start with. mosfets tend to die if the voltage exceeds 18-20V or so. so i choose caution to start with. you can experiment with 15V if you like. less loss through the mosfet if the mosfet is turned on all the way.
You will not a large inductor on my PCB...this was in the original supply so i added it but its a bit overkill and really doesn't do much as it was originally part of a Pi filter. it has since been removed.
This design works well! and could be revamped to handle as large of a motor as you like! a bigger heatsink is needed if you plan on running a motor larger then 1 amp. I found with the dremel tool that the heatsink isn't even needed! the Mosfet/Igbt never even gets warm running without a load. but its a good idea to have some form of heatsinking.
The IR2109 has a saftey lockout should the IC's voltage drop below 10V. this threw me at first. Also the rectified and filtered AC line is about 170vdc, the dremel needs to be speed limited to about 70% pwm so as not to over run the motor. you could use a 80-90vac transformer to provide 120vdc instead. would be a degree safer too.
Enjoy
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