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It would be theoretically possible to have a magnetic 'switch' which turned the permanent magnets off when not needed. Sounds impossible but it's possible[1].

[1]: https://www.goudsmitmagnets.com/en/solutions/magnetic-handli...



Yes, and.... the time constant of an LR circuit = L/R -- it takes finite time to 'turn off' the electromagnets. And, the collapsing magnetic field's energy has to go 'somewhere'; and it's of opposite polarity to the current that created it.

In other words, yes, possible, but more complicated than one might think. For example, we could build a circuit that "sucks out" the field by jamming very high currents in the opposite direction through the coils. To do this needs even higher voltages that the motor normally uses.

So, yes, it's possible. Not especially easy for optimal efficiency.




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