I guess the motor choice of Tesla over other EV's has something to do with "the last feet" of regen and halting.
Tesla uses AC induction rather than permanent magnet. Which means the Tesla motor uses some juice to keep both the stator and commutator alive when acting as a motor and also when acting as a generator. At some point during spin-down the electrical power costs of driving the motor outweighs the juice that can be harvested from regen. And "at rest" there are no forces holding the commutator still - it will spin by blowing on it.
Permanent magnet motors will slow down using no power and only generating power, and will stop with magnetic poles of stator and commutator aligning and magnetically holding. Costs no power to sit like that. Hence, it's free* to stop the car and hold it that way using just the motor magnets.
To accomplish the same slow-to-stop without using friction brake, Tesla would have to stop regen and reverse the circuit and actually apply power to allow the motor to continue slowing. I don't think we're talking gobs of power, but kinda defeats the idea of regen for those last few feet. So maybe when the magic cross-over point happens, Tesla just stops the regen process and the motor goes open circuit.
Or have I got that wrong?
*free - not free when you consider environmental impact and costs of mining scarce permanent magnet minerals. Did you know Tesla does not use a permanent magnet motor? (Hint: the company is named after the inventor of the kind of motor it uses!) Yes, I'm aware batteries all use Lithium these days... all EVs are guilty of that earth exploit. But Tesla is a little greener because no magnets.
Tesla uses AC induction rather than permanent magnet. Which means the Tesla motor uses some juice to keep both the stator and commutator alive when acting as a motor and also when acting as a generator. At some point during spin-down the electrical power costs of driving the motor outweighs the juice that can be harvested from regen. And "at rest" there are no forces holding the commutator still - it will spin by blowing on it.
Permanent magnet motors will slow down using no power and only generating power, and will stop with magnetic poles of stator and commutator aligning and magnetically holding. Costs no power to sit like that. Hence, it's free* to stop the car and hold it that way using just the motor magnets.
To accomplish the same slow-to-stop without using friction brake, Tesla would have to stop regen and reverse the circuit and actually apply power to allow the motor to continue slowing. I don't think we're talking gobs of power, but kinda defeats the idea of regen for those last few feet. So maybe when the magic cross-over point happens, Tesla just stops the regen process and the motor goes open circuit.
Or have I got that wrong?
*free - not free when you consider environmental impact and costs of mining scarce permanent magnet minerals. Did you know Tesla does not use a permanent magnet motor? (Hint: the company is named after the inventor of the kind of motor it uses!) Yes, I'm aware batteries all use Lithium these days... all EVs are guilty of that earth exploit. But Tesla is a little greener because no magnets.
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