A guide on identifying the lead wires of Unipolar Stepper Motors. Minimize screw ups and frustration especially for beginners and first-timers tinkering with stepper motors.
Stepper motor is an impressive piece of engineering. Instead of making full turns like a normal motor, stepper motor make steps, one small degree at a time. It is commonly used in photocopy machines, printers, CNC machines, robotics, etc where precision motion (steps) and controls are needed.
There are two major types of stepper motor, I’m going to focus on Unipolar Stepper Motor. They normally have 5 or 6 wires.
For the 6-wire variant, it consists of 4 Coil End wires and 2 Center Tap wires; and for the for 5-wire variant, there are 4 Coil End wires and 1 Center Tap wire.
How Stepper Motor Works
Although in reality there are several set of coils in a stepper motor forming what is known as a phase, for understanding purposes it is best to imagine the there are 4 coils in a stepper motor ( namely Coil 1, 2, 3 and 4). If any one of the coil is energized, the motor will make one step, then stays in that place (after 1 step is completed). The motor I have lying around as pictured above turns 1.8 degree per step.
In order for the motor to complete one full revolution, it needed to make multiple steps. The coils need to be energized in the proper sequence to achieve this. In all, 200 sequential steps (1.8 degree x 200 steps) are needed for the motor pictured above to make 360 degree turn (one full revolution). Read the specification of your motor carefully to find out the details.
The animation below on the other hand shows the steps and coil energizing sequence depicted in a simplified 90 degree per-step motor with 4 coils. Therefore it needed 4 steps to make one 360 degree turn. In principle, all stepper motor works in the same way.
If you are interested in reading on further, there are tons of resources to dig online. Google is your friend.
Step One – Identify The Center Tap Wires
This is the part where we map out the wires. You will need a multimeter, and set it to measure resistance. You will have to go through series of elimination process to map out which colored wire corresponds to which Coil End / Center Tap.
By referring to the diagram above:
1) The resistance between Coil End A and Coil End B is DOUBLE the resistance between Coil End A to the Center Tap 1.
2) The resistance between Coil End B and Coil End A is DOUBLE the resistance between Coil End B to the Center Tap 1.
3) The resistance between Coil End C and Coil End D is DOUBLE the resistance between Coil End C to the Center Tap 2.
4) The resistance between Coil End D and Coil End C is DOUBLE the resistance between Coil End D to the Center Tap 2.
NOTE: For a 5-wire unipolar stepper motor. Center Tap 1 and Center Tap 2 are internally connected together with just one wire out, but the rules above still apply. The resistance between Coil End B and Coil End A as well as the resistance between Coil End C and Coil End D are DOUBLE the resistance between any of the Coil Ends A, B, C and D to the single Center Tap.
NOTE: For a 6-wire unipolar stepper motor such as mine, There is no internal connection between (Coil End A - Coil End B - Center Tap 1) and (Coil End C - Coil End D - Center Tap 2). Therefore there is no current flow.