Well yes. It does use pwm.

But, BLDC motors have three windings, connected star or delta internally.
Hence their controllers have three outputs.

If you can find a controller that can be configured to only drive two of it's outputs, maybe it would work?
I've never seen one.

 

And why is that?
I've seen a lot of arm waving saying it won't work, but no technical reason.

How does a brushless controller, such as the one I posted, control the motor speed?
Does it not use PWM?

 

BLDC motors have three windings, connected star or delta internally.
Hence their controllers have three outputs.

Okay thanks, now I understand.

 

And why is that?
I've seen a lot of arm waving saying it won't work, but no technical reason.

How does a brushless controller, such as the one I posted, control the motor speed? Understand that a BLDC motor runs like a synchronous motor, with the speed set by the phase rotation speed (the drive frequency)
Does it not use PWM?

The two types of motors: brushless, versus DC field with a commutator, are about as different as motor types can be. THAT is why a BLDC controller can not possibly control a wound-field brushes and commutator type of motor. THAT has already been explained very well.
Others have already provided very good information, from what I see.

 

There are also two methods of controlling the BLDC type motor, one with DC energising two of the three windings at any one time, (BLDC) , and using the identical motor with 3phase supply making it 3ph AC,
The BLDC is considered most efficient for a fixed model of motor.
The BLDC motor typically has 2 to 8 pole count which has to be kown for a given RPM rate.

 

Back in post #1 the motor was described and the label was shown. Armature current and field current were listed. That is about as different from a BLDC motor as can be.

 

True in a way but just wound field instead of PM which the original post describes

 

REGARDLESS of the description, the tag ON THE MOTOR describes a wound field BRUSHED motor.
The controls for a BLDC motor are not at all suitable, nor even adaptable, to that motor shown in post #1

A Brushless DC motor is a multiphase (At least 3 phases) AC motor. That type of motor requires a driver able to provide three outputs , although some BLDC motors require five or more phases.


I had this discussion with one of the salesmen at a company that I worked at many years ago. The issue was resolved when the sales guy received the price quiote for reworking the brushed motor to a three-phase AC motor. That price was a lot more than for a NEW motor.
NO amount of wanting it to be different can change that.
(Sorry for that bad news)

 

I have this motor. Should be a 72 volt, shunt DC motor as I understand it. However I have never heard of this type of motor until I received this one and did some googling on it. When googling for a shunt motor driver, I can't seem to find anything.

Before BLDC mptors these shunt wound field types were used extensively in industry, lathes. milling machine spindles etc, but one safety precaution was usually made which was to fit field loss protection.
The reason is that if a wound shunt field motor loses field when under operation, The motor can acelerate uncontrollably up to destruction.

 

A Brushless DC motor is a multiphase (At least 3 phases) AC motor. That type of motor requires a driver able to provide three outputs , although some BLDC motors require five or more phases.

Incidentally the reason for BLDC is that only 2 of the 3 windings are energised at any one time, If all three recieve energy, then it is ran as a 3ph version.

 

Incidentally the reason for BLDC is that only 2 of the 3 windings are energised at any one time, If all three recieve energy, then it is ran as a 3ph version.

Certainly MAX is correct. BUT 3-phase motors are specificly designed to be "3-phase motors". An actual BLDC motor is designed for that sort of operation, and I suspect that the rotors are quite different from three-phase induction motors. But since I have not investigated the internals of a BLDC motor I will not comment.

 

When used as AC motors, they do not rely on induction/slip, therefore run as synchrounous motors using the high magnetic, PM rotor field.

 

When used as AC motors, they do not rely on induction/slip, therefore run as synchrounous motors using the high magnetic, PM rotor field.

THAT mode is what I would expect!
AND, for those who asked about speed control for BLDC motors, that is indeed how it is done: The speed is set by the phase rotation frequency, just like a synchronous motor. Except that there may be some slip, like an induction motor. I THINK!
My GUESS is that within the broad catagory of BLDC motors there are both synchronous kinds and non-synchronous kinds. I HAVE NOT STUDIED THEM YET!!

 

Except with a BLDC motor, the three commutation device sensors indicates when conduction should occur.

 

Two points about shunt wound motors. 1/ The do not work on AC. I think the reason for this is the the field winding has a significant inductance so the the phase of the current will be out of phase ith the voltage. The armature has quite low inductance so that the armature current will be about in phase with the voltage. In the case of series motors the armature and field currents must be in phase as they are in series. 2/ Reducing the field current on a shunt motor increases it's speed and reduces the torque.
Les.

A separately powered field (shuntfield)brushed DC motor runs about the same as a PMDC motor, AND NOT at all like a brushless DC (BLDC) motor. the types are VERY DIFFERENT. IN a shunt motor the field strength depends on the applied field voltage, while in a series DC brushed motor the filel strength depends on the armature current. So the series DC motor can have a very strong starting torque! For the SHUNT DC motor that starting torque boost is not available, and so the torque is about the same from start to max speed.
Warning: If the field current fails in a series motor the armature counter-EMF drops off and the motor will draw a lot more armaure current and spin MUCH FASTER. That can be dangerous, like a clutch exploding on a dragster, only much worse.

 

A separately powered field (shuntfield)brushed DC motor runs about the same as a PMDC motor, AND NOT at all like a brushless DC (BLDC) motor. the types are VERY DIFFERENT. IN a shunt motor the field strength depends on the applied field voltage, while in a series DC brushed motor the filel strength depends on the armature current. So the series DC motor can have a very strong starting torque! For the SHUNT DC motor that starting torque boost is not available, and so the torque is about the same from start to max speed.
Warning: If the field current fails in a series motor the armature counter-EMF drops off and the motor will draw a lot more armaure current and spin MUCH FASTER. That can be dangerous, like a clutch exploding on a dragster, only much worse.

I think this thread came to a conclusion some time back.
Your last paragraph is completely wrong. It applies to shunt motors, not series motors.