DC Motor Commutator

Phoenix has a variety of endbell mounted and internal mounted three channel Hall Effect based commutator solutions for brushless DC motors. Phoenix can also design solutions using the magnetic fields generated by the motor magnets. Early involvement of the Phoenix design team will provide the most effective commutation solution.

Brushed motors typically have only two wires, one positive and one negative. They have carbon brushes which contact a rotating segmented drum that switches which coil is receiving current from the battery. Brushed motors are generally also 3 phase motors because they have three sets of windings. The motor’s commutator is a rotating drum made from copper segments which switch the coils in that motor that is receiving power at any time and hence maintain the revolving of the motor.

In brushless motors hall effect sensors replace the commutator. It is a method of switching which phase is being given current at any one time. Usually two phases will have power at any given time. Hall sensors allow a small current to flow through them. These hall sensors are switched on/off as a north then south pole passes it. This very small current flowing through them goes to a mosfet which in turn is switched on/off in sync with the hall sensors. The mosfets allow large currents to flow to the motor coils in a very precise pattern determined by their location near the magnets.

Hall effect devices are digital on/off sensors constructed of semiconductor material used to sense the presence of magnetic fields. In brushless servomotors, they are used as position feedback when six-step commutation is employed.

Some six-step drives incorporate this feedback for crude velocity sensing or coarse positioning. With sinusoidal current drives, they are sometimes used along with incremental encoder feedback to give a coarse power-up position indicator. In servo drives, they are commonly used as current sensors to close the current loop. In other industry applications, they are used for sensing the position of a crankshaft, cam, or another mechanical device.

In brushless servo motors, the halls are usually embedded within the motor windings and sense the position of the rotor magnets. There is one sensor for each motor phase, aligned with the stator winding.

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