How back-drivable is the stepper motor 3D printer stepper motor?

How back-drivable is the stepper motor 3D printer stepper motor?

It help to understand what is a stepper motor. A stepper motor is a simple device in construction. It is has fixed, non moving, coils in the stationary part of the motor. These are called stator windings. The rotating part is called the rotor. The rotor has a series of magnetic poles. When you energize the stator coils, the magnets rotate to align with the coils. Then it stops. When the polarity of the current through the coils is changed, the rotor will again turn to align the magnetic poles of the rotor to the magnetic poles of the stator. This is called a step. When a controller performs this alternating of the current through the coils in a fast enough manner, the rotor appears to rotate continuously. The mass inertia of the rotor tends to smooth out each ‘step’ at higher speeds. AT slow enough speeds you can see and feel each step.

When a stepper is ‘back driven’ is means the rotor is spun by the connected load. The magnets rotating inside the coils create an alternating current generator. What happens to the voltage and current produced is totally dependent on the circuit that is connected to the motor. For an open circuit, the back EMF generated may be very high compared to the rated motor voltage. The motor’s back EMF specs will give guidance. If connected to a driver circuit, diodes in the output transistors may limit the voltage, or actual clamp diodes may be used. If clamp diodes exist then when back EMF generates enough voltage to induce current through the diodes, there will be a resultant resisting torque in the motor. A slowing, or holding the motor will occur.