Board Level Drivers FAQs

Can I drive a unipolar stepper motor with a bipolar driver?

A six-lead stepper motor, which is a unipolar stepper motor, can be used when a bipolar drive is being used to run the motor. Since bipolar motors only need four wires to run, there are options in connecting a six-lead wire to a bipolar drive. Typically, we refer to the six wires as A, /A, A Common, B, /B, B Common. Half-coil connection would be to use A, A Common, and B, B Common (or /A, A Common, and /B, B Common). To use full-coil, also known as series connection, you would use A, /A and B, /B. For full-coil the two common wires are ignored. The full-coil connection (or series) is ideal for lower speeds requiring more torque. The half-coil connection will give an overall amount of torque across a wider range of speeds.

How can an encoder be used to determine position and speed?

There are many different types of encoders. The basic function of an incremental encoder is to output signals that help the control electronics determine the speed and direction of travel of the motor. The control electronics then use calculations to determine the relative position of the motor. The basic function of an absolute encoder is to output signals that help the control electronics determine the exact position of the motor. The control electronics then use calculations to determine the relative speed and direction of travel of the motor.

What is continuous current? What is peak current?

Continuous current is the current that can be supplied from the driver indefinitely. The peak current refers to the maximum amount of current the driver outputs.

Non-microstepping drivers
Peak Current = Rated Current

When using a driver that only does full stepping, the rated current is the same as the peak current. (Rated current = Peak Current).

Microstepping Drivers
Peak Current = 1.4 x Rated Current

When using a driver that is capable of taking microsteps (at a rate of a half-step, fourth-step or any other fraction of a step), the definition of peak current becomes 1.4 times the rated current. Microstepping drivers are made differently in order to maximize their ability to drive the stepper motor. Therefore, step motors can handle up to their rated current multiplied by 1.4. (Peak Current = 1.4 x Rated Current). This will not damage the motor because the power output is more or less the same.

What is RMS Current?

RMS stands for "Root Mean Square." It is the effective average current. It is most commonly used when referring to AC current.

What is the difference between Unipolar and Bipolar?

Unipolar motors have two windings per coil, though they only employ one winding at a time. Each coil only ever has one polarity, always acting as either a north or south electromagnet, and must be switched on and off to create movement. This makes the drive electronics very simple. Unipolar motors are preferred for high-speed applications because they do not need the current to decay in one winding before the opposite polarity coil can be energized.

Bipolar motors, on the other hand, only have one winding per coil, and switch polarity to create movement. This means the current must fully decay in order to switch polarity and create movement. The drive electronics for bipolar motors are slightly more complicated than those for unipolar motors. Bipolar motors are preferred for lower-speed, high-torque applications.

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