# Understanding Stepper Motors

I am relatively new to using stepper motors and I plan on using two bipolar NEMA 17 2.1A stepper motors controlled using two TMC2226 motor drivers for a project. I am trying to understand how current and voltage affect the motors so that I can determine the power supply I will need to power these motors at the same time. Since these are 2-phase motors that can handle 2A/phase, would I need an 8A power supply? And in terms of voltage, the specifications for the motor doesn't list a rated voltage, but the torque curve that is given is for 24V. Would it be best to use a 24V power supply to get the most out of the motor? Any input on how current and voltage affect stepper motors would be much appreciated. Thanks!

• Doesnt directly answer the question, but I'd recommend getting a bench power supply so you can test out 12V vs 24V and so on and get an empirical measure of the current you need. i.e.: the drivers or motor might not be able to withstand 2A continuous and/or you dont need to drive them that hard. Nov 23, 2023 at 10:06

The rated motor voltage is determined from the winding resistance and the maximum permissible winding current by applying Ohm's law (R=U/I or U=R*I). Or to put it another way: If you just want to apply voltage to the winding (without current control, PWM or similar), it must only be as high as the motor's rated voltage, otherwise the permissible winding current can be exceeded.

Voltage alters the speed at which currents can raise/fall in your coils and currents produce the magnetic fields and heat.

To get a rotary movement, the stepper has to rapidly magnetize and demagnetize its coils in a certain pattern. The strength of the current determines the power of the fields, thus the torque.

To speed up the motor, you increase stepping speed.

As you may know, inductors work against rapid current changes. So you lose torque, the faster the currents alter. This will result in lost steps or motor stall if you raise stepping speeds too quick or beyond a certain threshold.

You can counter that by raising the Voltage, without exceeding max current. So for high speeds, you turn up the Voltage to speed up the current changes in the coils. The motor itself could (theoretically) handle up to 500VAC for one Minute. Depending on the load you may end up anywhere between minimum turning voltage, (which is <10V) and 48+V

However, you need to keep in mind heat and maximum dielectric strength. Raising the Voltage at maximum current gives you more power but also dissipates more heat. The total energy rise in your motor has to stay below 80°K!

Intelligent motor controllers heavily vary Voltage and currents to speed up quick (High amps, high voltage) but keep the motor cool when less power is needed (lower amps and voltage).