Designed to deliver peak torque in open-loop systems, such as applying labels to bottles on a high-speed conveyor system, stepper motors are a great choice for achieving optimal results at an affordable cost. But having done your research and chosen a stepper for your application, there’s still the other half of the motion system to consider.
To get the most out of your stepper motor, you need to pair it with the proper drive. There are three critical elements to keep in mind when making your selection: voltage, current and inductance. Each one plays an important part in a motor’s performance, and not accounting for these parameters can lead to poor performance or even cause the motor to overheat and fail—resulting in lost production time and increased maintenance costs.
Exceeding the motor's maximum rated voltage, or sometimes operating at higher supply voltages, can cause the motor to fail. That’s why when choosing a drive for a stepper motor, you need to know the motor's maximum rated voltage or typical rated voltages from catalog data or performance curves. Stepper motors are typically powered by drives operating on AC power, either 120 or 240 volts, or low-voltage DC power, such as 24, 36 or 48 volts. If you run a motor at a higher voltage than specified, such as running a motor designed for 24 volts DC at high voltage, it will quickly overheat. Conversely, running a motor at too low of a voltage, such as a high-voltage motor run at 24 volts DC, will produce less power, and if the load isn’t reduced this could cause the motor to stall.
When it comes to finding a motor’s rated voltage listed on the nameplate, it can sometimes be hit or miss. Never take a blind gamble on the drive. Instead, if the voltage information isn’t shown on the motor, you should consult the catalog or ask the manufacturer directly. Some manufacturers offer online design tools that allow you to create performance curves for stepper motors based upon the available voltage and current in your application. By using those same specifications, voltage and current, the tool will also output a temperature versus speed curve that will show you if you might overheat the motor.
When selecting a drive, you want one that can deliver the right amount of current to the motor. Current matching isn’t necessarily needed, but running at a lower current will produce lower torque. If the load isn’t reduced, this can cause the motor to stall. Setting the drive current higher than the current rating of the motor will cause the motor windings to overheat and fail. This will cause permanent damage to the motor. Whether it is a software setting or DIP switch setting, you’ll want to select the current rating that most closely matches the current rating for the motor.
Each motor has a winding inductance, and drives typically have an inductance range that needs to be considered when pairing the motor. Therefore, you’ll need to know the inductance of the motor and pick a drive that is compatible with the motor. Depending on the supply voltage, if a motor inductance is too high, the motor current cannot be delivered in the required time. If it is too low, then current is given too fast to the motor, causing the drive to potentially overheat and fail. And if the inductance is higher than an applicable motor inductance range for the drive, it might not turn at all.