Recently I built a device to turn a stepping motor a pre-set number of revolutions and stop when the desired count was reached. The device can cycled repeatedly by pressing a start button. Run cycle time is less than 12 seconds. The average time between operation cycles is approximately 30 seconds but can go over one minute.
I used a 24v, SloSyn stepping motor (p/n SM-24-0065-RY) with 24 steps per revolution. (I chose that type of motor because I need high RPMs.) I’m using a 24vdc power supply. I made an adjustable stepping motor driver based on this kit http://www.kitsrus.com/pdf/k179.pdf.
There is an optical encoder on the end of the motor shaft that sends a signal to a settable countdown counter. When the countdown reaches zero, it’s output interrupts the step signal from the motor driver. The motor stops spinning and is held locked in position until the start button is pressed again.
The problem is heat. After only 5 or 6 cycles, the stepping motor is dangerously hot. So is the stepping motor control board. It gets so hot that the driver board stops working until the unit cools down. I have the MOSFETs mounted to a large heat sink. There are a bunch of ventilation holes drilled in the enclosure and a PC fan pulling air out.
Any ideas why it’s getting so hot? I don’t need high torque for this application. Would going with a smaller power supply, say 12vdc, decrease the amount of heat? Would using a motor with more steps per revolution generate less heat?
One thing I’ve been thinking about trying is to incorporate a power-off timer that will keep the motor coil energized for 3 seconds or so (after the step signal is interrupted), then cut power to the driver board. That should give the operator enough time to remove the product from the output shaft.
Thanks in advance.