How long can a SmartMotor supply its peak torque?
The SmartMotor can supply peak torque until the heat generated from the maximum current in the stator winding raises the temperature of the electronics above 70 degrees C. This time will depend on the ambient temperature and way the application allows the motor to disperse heat. If a motor is fan cooled, in cold air, or bolted to a large metal surface (which aids cooling from heat conduction and radiation) the motor will sustain peak torque for longer periods. A general answer is that the motor could supply peak torque for 10 seconds every minute. If it runs longer, more heat is generated which raises the temperature of the microchip and electronics. Then the motor must run at a lower power output, or stop, until it has cooled.
How will the torque-speed curve change with a lower input voltage?
The downward slope of the curve will remain the same, just shifted to the left by the ratio of the input voltage and torque-speed curve voltage.
What do you mean by peak torque and continuous torque in your brochure?
Peak torque was measured using a dynamometer by attaching the SmartMotor face place to a 10" x 10" x _ " Al plate at room temperature. A pulley, attached to the shaft, connected to an adjustable brake and data was collected across a number of velocities. The continuous ratings were the highest torque/speed SOAC readings found for continuous operation. The published peak torque values will cause a SmartMotor starting from room temperature to shut down within 30 to 45 seconds. Normal de-rating techniques must be applied when considering any applications temperature and loading requirements. Note that the continuous operation specifications appear lower than those that would be calculated for a standard BLDC servomotor given our motors specifications and thermal capacitance. Thermal loading of system by the drive circuits account for these losses.
Is there a formula to relate torque speed characteristics when a SmartMotor is used with a power supply delivering less than 45V?
There is a complex relationship between the torque-speed curves and the applied voltage. You can predict the peak torque at a given speed by the formula:
Torque = Maximum current x Torque constant
Maximum current = the unit's current limit or max motor coil current, whichever is lower. For the SM17 and 23s, the unit current limit is 12.5A, while that for the SM34 is 40A. The RTC is 3A.
The max coil current is calculated as follows:
max coil current = (bus voltage - back EMF)
coil resistance
(where back EMF = motor voltage constant x RPM)
The continuous torque is a function of heat dissipation. Bus voltage has a negligible effect, as long as it is within the specified operating range.
Printer-friendly version