Everything You Need to Know to Drive a Stepper Motor （2）

Published:2011/7/26 3:48:00 Author:Amy From:SeekIC

By Horst Huber

2. Connections

Once you have determined what type of motor you have, it’s time to find out which leads belong to each of the windings. Measure the resistance between the connections using a multi-meter. Go through all possible combinations and make a note of the results. The resistance between the ends of a winding will be low. Between the centre tap and one of the ends of a winding you’ll have half the value measured for the full winding. Between separate windings you’ll find an infinite resistance, or at least several megohms. In this way you can determine which two or three connec­tions belong to each winding. When a unipolar motor has a common centre tap (5 leads), it is unfortunately not possible to find out which connec­tions belong to which windings. In that case, the centre tap will have an identical resistance to the remaining four leads. But as you will see later, we have come up with a solution for that as well.

3. Operating voltage

Unless it’s written on the motor, there is no way of telling what the operat­ing voltage of the motor is by looking at it. Often you do know what the supply voltage was to the circuit where the motor came from. A step­per motor from a floppy drive will work at either 5 or 12 V. If you have no idea what the voltage was, you can estimate it using the following method. For a bipolar motor connect one of the windings to a variable power supply. For a unipolar motor you connect two of the windings as shown in Figure 3. Set the output to a several volts and wait a few minutes. Feel if the motor becomes warm. If not, increase the voltage and check the temperature again after five min­utes. Repeat this until the motor becomes almost too hot to touch. This should give you the maximum operat­ing voltage for that particular motor.

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