Any difference - BLDC vs PM?

[electricpete]

What is the difference between a BLDC motor and a permanent magnet motor? Same thing?

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[CJCPE]

BLDC motors have permanent magnets, but comutator/brush type DC motors with permanent magnets are also manufactured.

 

[Skogsgurra]

You may be asking about PM rotor and BLDC difference? The difference there is that a BLDC has all electronics and switching built into the motor. A PM (servo) motor usually has all these things external to the motor. It (usually/always) has a much more sophisticated control system (vector control and PWM)and a much faster torque and speed response.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[cswilson]

Skogs -- No! The vast majority of motors sold as BLDC motors do not have any electronics built into the motor. A few companies now sell them with electronics built in, but this remains a niche product type, mainly because you are putting two big heat sources (power electronics and armature winding) together. Overwhelmingly, these motors are controlled by a separate drive.

To expand on CJCPE's response, the permanent magnets can either be on the stator or the rotor. If they are on the stator, the armature is on the rotor, so brushes and a commutator bar are necessary to get the current into the spinning rotor. This is a PM brush DC motor.

If the permanent magnets are on the rotor, the armature phases are on the stator, so no brushes are required to connect the phases. This is a PM "brushless DC" motor -- a horrible term, but one we are stuck with. (BLDC is a marketing term -- these motors with accompanying drives were originally sold as drop-in replacements for brush DC motors with their drives. These are technically AC motors -- you must feed the motors AC waveforms to get continuous movement in one direction.)

Curt Wilson
Delta Tau Data Systems

 

[IRstuff]

Fans and motors in PCs are typically BLDC, with the electronics built-in.

I've taken apart a fair number of them. Even the little 5VDC fans are BLDC, with a small PWB of parts.

Their typical construct is a rotor of PMs and stator coils on the outside driven by the electronics on the board.

TTFN

 

[aolalde]

Hi Electricpete.

BLDC is in reality a synchronous motor with permanent magnet rotor, normally the stator has 3 phases and the DC power supply is converted to AC feeding the stator winding. The idea is to eliminate the mechanical commutator and brushes.

The PM DC motor is a traditional commutator motor with a fix field provided by permanent magnets.