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Hi all,
i am pretty new to this topic and more the production-guy.

Could you tell me why its beneficial to have high speed/rpm motors in terms of efficiency?
What are the limits and why is the speed climbing just now? Are there limiting factors?

Thanks,

Patrick
 

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Hi all,
i am pretty new to this topic and more the production-guy.

Could you tell me why its beneficial to have high speed/rpm motors in terms of efficiency?
What are the limits and why is the speed climbing just now? Are there limiting factors?

Thanks,

Patrick
Hi Patrick,

As a designer, you have application requirements (performance) and constraints. You size the motor to power requirement and gear for the needed torque. Realize motor torque determines motor size.

If you had no constraints and designed for highest motor power per motor weight, RPM would be extreme. Strength and cost of materials would eventually be your limit.

Motor and system efficiency are constraints; actually design trade-offs. Weigh against cost, size, mass, etc.

Trend appears to be moderately high motor RPM. In most cases achievable without much of any hit on overall efficiency at reasonable cost, (high nonreoccurring cost like R&D, tooling, ect.).

Regards,

major
 

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In modern EVs the typical design is to use a single-ratio transmission, so the motor must work over a broad speed range. To achieve this, the motor is designed to reach high speed by using high voltage, with the same power available over most of the speed range. This also keeps the motor out of the high-load high-current low-speed regime most of the time, where efficiency appears to be low.

As major explained, the same speed range could be covered with lower motor speed by using less gear reduction, but it would need to put out more torque for the same low-speed acceleration, making the motor larger and requiring higher current from the controller.

My guess is that two factors which may have led to increasing voltage are that the high series cell count required might have been unworkable with earlier battery technologies, and that high-voltage power electronics are getting more reasonable in price. Of course before the switch to AC motors, the commutator and brushes of traditional brushed DC motors limited practical rotational speeds.
 
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