Stepper motor wiring I'm looking for help

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AwilsonMZL

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Location
Berlin, Germany
Occasionally we may come across an old stepper motor salvaged from a printer or an ancient floppy drive. If we are lucky, there will be a part number on the motor and after some digging around, we will come up with a datasheet. Often though, we will have a motor with no markings whatsoever and four, or six colorful wires sticking out. First, we need to figure out how the wires are paired to form coils within the motor. (an example from http://www.powerjackmotion.com/product/2-phrase-110mm-stepper-motor/ )Trial and error may work, but there is a better way! All it takes is a multimeter.


How to identify 2 Phrase stepper motor coil pairs with a multimeter


Need to consider the following parameters:


1) Holding Torque Large motors require high torque.
2) Output Speed If the output speed is high, torque is lower and vice versa.
3) Pulses Per Second It refers to no-load starting frequency of stepping motor.
4) Phase 2 Phase motors are often used for normal applications. 3 Phase motors are used for high speed and high torque requirements.
5) Special Parameters, In addition, we may need to consider a few special parameters such as water proofing, output shaft length, and diameter among others.


I hope you people can help me about Stepper motor wiring for sure. Please give me a better solution. I will thankful to you forever.


Any better idea would be highly appreciated.

Thanks.
 
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gar

Senior Member
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Ann Arbor, Michigan
Occupation
EE
170830-1448 EDT

A 2 phase stepping motor has essentially two separate nearly identical coils. Each will have nearly the same internal inductance and resistance. Because there are two coils there will be 4 wires. However, internally the coils can be wired so only three wires are brought outside the motor.

Simple ohmmeter measurements will identify which wires belong to a coil. This will also provide you coil resistance.

Since each coil is an LR device it will have a time constant determined by its values for L and R.

Internal to normal stepping motors are permanent magnets (very strong ones). These are the field source and mounted on the rotor. Basically a stepping motor is a synchronous motor. Steady state stator current (your coil) produces a magnetic field that interacts with the magnetic field of the rotor (a fixed value). So holding torque is something less than the breakaway torque of the stator magnetic field from the rotor field. That means that breakaway torque is proportional to stator current because the rotor field is constant.

Running torque is a function peak torque and that is a function of how far up the LR curve you get per cycle. Thus, for a simple LR drive circuit torque drops off as speed is increased. There is an additional problem with speed and that relates to the mechanical resonant frequency of the system.

Simple drive circuits use an external resistance and higher source voltage to reduce the LR time constant. Thus, somewhat improve torque at speeds greater than zero. Better drivers will use a constant current source. There may be other innovative circuits to provide further improvement.

Power dissipation within the motor will determine maximum output power and torque.

There are lots of ways you can determine how to work with a given motor without a datasheet. However, max power or torque can not be determined without a knowledge of the temperature rating of the wire in the motor.

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