Fish4Fun
So long, and Thanks for all the Fish!
What I have is a 120Vdc brushed, 16-field "surplus" motor in the ~1.5hp range @~18krpm with a date of mfg of 1978. What I am working on is a belt-drive spindle for a CNC router where the spindle speed needs to be variable from ~1krpm to ~6krpm, the belt reduction is 3:1. This is a one-off project so cost of components is trivial. I do not need reversing capabilities, so simple, low-side PWM is my plan....I do plan to have a Hall-Effect shaft sensor with 4 to 12 pulses per revolution for closed loop speed control. I plan to use an Arduino Mega 2560 as a dedicated controller. I would love a bit of input on a "starting" PWM frequency....and the pros and cons of increasing/decreasing the PWM frequency strictly from a motor performance point-of-view....it makes little difference if the switch(es) cost $1ea or $20ea if the expected motor performance is improved. I am also considering a fairly large capacitor bank both in the rectifier portion of the circuit and perhaps between the switch and the motor to reduce brush noise feeding back into the mains supply and to help provide a stable DC operating voltage. Again, thoughts/suggestions appreciated.
There are 8 armature slots and 16 poles, so the brushes should commutate @ 16 * 18,000 / 60 = 4.8khz @ 120Vdc no-load rated rpm....Intuitively I am thinking anything above 20kHz should be sufficient and was considering 25kHz to 30khz to keep the switching frequency out of the audible range....I thought I would **start** with IRF640s (I was thinking 4 in parallel)....I was thinking ~2000uF consisting of 6 * ECEC2DA331DL 330uF 200V capacitors + 2 * 4.5uF polypropylene 400V capacitors for both the post rectifier capacitors and the capacitors between the switch and the motor...mostly because I have all of these items on hand....but I am absolutely looking for suggestions in "general design", PWM frequency/duty cycle, and components. The above laundry list is just some items I have on hand that I think might be suitable as a starting place.
Any thoughts/advice/suggested reading on speed control algorithms would also be appreciated...
Thanks in Advance!
Fish
There are 8 armature slots and 16 poles, so the brushes should commutate @ 16 * 18,000 / 60 = 4.8khz @ 120Vdc no-load rated rpm....Intuitively I am thinking anything above 20kHz should be sufficient and was considering 25kHz to 30khz to keep the switching frequency out of the audible range....I thought I would **start** with IRF640s (I was thinking 4 in parallel)....I was thinking ~2000uF consisting of 6 * ECEC2DA331DL 330uF 200V capacitors + 2 * 4.5uF polypropylene 400V capacitors for both the post rectifier capacitors and the capacitors between the switch and the motor...mostly because I have all of these items on hand....but I am absolutely looking for suggestions in "general design", PWM frequency/duty cycle, and components. The above laundry list is just some items I have on hand that I think might be suitable as a starting place.
Any thoughts/advice/suggested reading on speed control algorithms would also be appreciated...
Thanks in Advance!
Fish