0

I have to buy a BLDC motor and I was expecting it to be a permanent magnet motor and also when I read on internet link

Where it was mentioned that BLDC motor are permanent magnet motor.

But when I contacted the seller if it is a permanent magnet motor or not they said it is BLDC motor not a permanent magnet motor.

I would like to know which between the two is correct.

Neil_UK
  • 158,152
  • 3
  • 173
  • 387
Tushar Dubey
  • 25
  • 4
  • I think they are, but I guess they could use DC field windings instead of permanent magnets but that might just re-introduce brushes unless there is a way not to. I've never seen one though but it could be the case on really big BLDC motors where large magnets are difficult and expensive to deal with. – DKNguyen Mar 16 '21 at 05:44
  • 1
    @DKNguyen I'm not knowledgeable enough to answer, but this was shown in one of my courses in a video. One set of windings is used to induce the drive current for another set, so neither requires physical connection. I had the impression it was new and used for rather large motors though. – K H Mar 16 '21 at 05:58
  • @KH That sounds like just the kind of trickery they would try to use to get around using both permanent magnets and brushes. Now that you mention it, I remember the guy at work saying that modern generator replaced brushes somewhere inside with transformer action. – DKNguyen Mar 16 '21 at 05:59
  • @OP could you clean up the links in your question? The correct format is to put square brackets around the text you want the link on and then follow that with the link in round brackets. – K H Mar 16 '21 at 05:59
  • https://electronics.stackexchange.com/questions/93710/how-do-dc-motors-work-with-respect-to-current-and-what-consequence-is-the-curre/93714#93714 –  Mar 16 '21 at 09:51

2 Answers2

2

People are inconsistent and lazy, which is why we've ended up with this confusing set of names for motors. What tends to happen is that popular motor types get named with just enough words to distinguish them from the previous popular motor type, and the name sticks.

(1) A 'BDLC' motor has a permanent magnet rotor, inside or outside a wound multi-phase stator. It may or may not have rotor position sensors. It is controlled by an electronic commutator, which in model engineering circles is often called an ESC (Electronic Speed Controller). It was named brushless, to distinguish it from its predecessor (2).

(2) A 'Brushed PM' motor has a permanent magnet stator, and a wound rotor supplied through a brushed commutator. The word 'brushed' gets dropped and this is known as a PM motor. Brushed did not distinguish it from its predecessor (3), whereas PM does.

(3) Before strong permanent magnets were available, DC motors had wound stators, and a brushed commutator.

There are other types of motors. For instance a 'universal' motor is essentially identical to (3), with the field and rotor connected in series. They are 'universal' as they will run on either AC or DC.

The three phase synchronous motor is essentially identical to (1), but it was intended to be run from 3-phase mains. Starting needs some auxiliary method of spinning it up to synchronous speed before connecting it.

Neil_UK
  • 158,152
  • 3
  • 173
  • 387
1

BLDC motors have permanent magnets, but they are usually not called permanent magnet motors to avoid confusion with permanent magnet motors that have brushes and commutators. You should ask the question of the seller in a different way. Ask the seller what kind of magnets it has.