DC motor design information- 3 pole versus 5 pole

Don M

I am looking for information about small PMDC brush motor design. What I specifically want to know is why some motors have 3 poles inside while others have 5 poles. Is there an advantage of one over the other? I spent the afternoon looking through the internet but it seems I must not be posing my question correctly to find specific topics on this.

If someone here has some websites for further reading or can just point me in the right direction·that would be wonderful.

Thanks for your help.

Don

ErNa

It is a common misunderstanding, that the commutator commutates coils of the rotor. In a DC-motor all windings form a single coil, which has a odd number of tabs. As the brushes slides over the commutator elements, they contact one on one side and two on the other side. So for a short moment on segment of the rotor is shortened. The more taps exist, the smaller is this segment and therefor the decrease of torque, for the shorted segment generates no useful magnetic field component and the current in this segment will reverse after the rotor segments leave the shorted position. From this is clear: the more taps exist, the less is the influence during commutation. To repeat: the current has to change direction twice during one rotation. But this current reversal takes place only in small single segments while the current continues to flow in all other segments. The more segment fit into a motor design, the smaller the torque ripple is.

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