A bench top motor dynamometer for drive testing
By G Craig, Techlyn
Electricity + Control, May 2015 (pages 20 – 22)
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Stepper motors are current driven, and even at standstill, testing has required only a test oscillator, power supply and appropriate motor. During a soak test, reliability and heatsink temperature could easily be assessed.
This follows standard practice by coupling the motor on test to another motor which acts as a generator to load the test motor. In this case (see Figure 3) a suitable sized dc brush motor and motor drive were to hand.
In operation the brushless motor was set to run at about 600 rpm. The brush motor was initially set to run at the same speed. Thereafter the brush motor was set to run slightly slower to run in the regeneration mode. The brushless motor was therefore continuously trying to speed up the brush motor. A clamp-on ammeter was used to measure the brushless motor phase current and the brush motor speed was set to a point where the brushless drive was fully loaded.
The energy recovered by the brake motor attempts to keep increasing the dc power supply voltage to store the recovered energy. Instead of a resistive power dump (and consequent power wastage) the drive supplies were paralleled and the dc power supply needed only to supply the system losses. This is standard practice in the drives industry.
- Traditional stepper motors can be easily tested.
- Testing a positioning drive cannot be undertaken in the traditional way.
- A bench top dynamometer has been developed to allow full testing of a positioning motor.