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What will happen if permanent magnets of a PM DC motor are replaced by permanent magnets possessing double surface flux density?
Dec 29, 2018

Anyone's initial guess would be that the starting torque would be twice as great and the no load speed would be half as much. But that is not likely the real case. If the motor was economically designed, the magnetic circuit would have been designed with the weaker magnets in mind; meaning that the steel in the circuit would be just adequate to carry the lesser flux without going into saturation.

The stronger magnets would try to drive more flux through the circuit but the steel would become saturated and would not allow double the amount flux to pass.

In any case you would not get more load capacity out of the upgrade. There would be a mismatch between the load's speed-torque curve and the upgraded motor's S-T curve. Also, the windings will overheat if you try to draw out more power than what the motor was designed for.


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