Ebikes are they AC, DC or?

[eMark]

Nope. BLDC motors are AC motors; the controller creates the AC. (Yes, I know, the letters "DC" are in the name, but that's because they are intended as a replacement for mechanically commutated DC motors.)

Is the alternating 3-phase sine wave of a BLDC and BLAC motor identical to the 3-phase sine wave of a traditional AC motor ???

Three-phase motors are motors designed to run on the three-phase alternating current (AC) power used in many industrial applications. AC electricity changes direction from negative to positive and back many times a second. The AC you get in your house, for example, goes from negative to positive and back again 60 times a second. AC changes power in a smooth continuous wave called a sine wave. Three-phase AC has three sources of AC power, all out of phase with each other. That means that no two AC waves are ever at the same point at the same time.

BLAC motors specifically use electromagnets and rely on an integrated power inverter, rectifier and sensor ... https://www.motioncontrolonline.org/products/ac-brushless-motors.cfm ... So, would it be correct to say that a BLAC motor uses its integrated power inverter, rectifier and sensor to create the same identical 3-phase sine wave as that of a BLDC motor?

Does a BLAC motor generate the same unique 3-phase sine wave identical to that of a 3-phase BLDC motor? Is it possible that the 3-phase sine wave of a traditional 220V AC motor (e.g. alternating from neg-to-pos 60 times a second) is not the same as the 3-phase sine wave of a BLAC motor or BLDC motor? If so, then both AussieRider and John in CR may be correct depending on how one defines BLDC alternating 3-phase current.

The controller sends pulsed DC to the phase 1 coils, Then switches to phase 2, then phase 3. The confusion rises because there are 3 sets of "phase" coils but it's not 3 phase AC.

Perhaps, in the sense that the sine wave of a 3-phase 220 AC motor is not the same as the sine wave of a 3-phase BLDC motor ???

With the current alternating direction through the motor phases, that is each phase sees current in each direction that alternates with the firing sequence, I'd call it a type of AC.

Here's a link for everything anyone ever wanted to know (and more) about Brushless DC Motor Fundamentals ...
https://www.monolithicpower.com/pub/media/document/Brushless_DC_Motor_Fundamentals.pdf ...

... The primary difference between AC and DC motors is the power type applied to the armature. From this vantage, a BLDC motor is actually an AC motor ... a brushed DC motor converts DC current in an armature coil to an AC current. ... (see pages 8-9)

So, BLDC is alternating current, but is it the same 3-phase sine wave of say, a traditional 220V AC motor?

 

[AussieRider]

Ok. So there's AC buzzing around inside the coils of all motors, be they 3 phase AC, induction, pm brushed DC, BLDC or. universal AC/DC. I can accept that.
3 phase AC has 1 phase feeding each coil all the time at a constant frequency, 50 or 60 hz. A BLDC controller feeds pulsed DC to 1 coil until the shaft rotates & the hall sensor causes the controller to switch to the next coil. If the shaft doesn't move, the controller doesn't switch to the next coil. Just pulsed DC to the same coil until magic smoke comes out from somewhere. I don't want to go in to sensor less coz it just confuses the issue.
I guess the final answer would be to connect a BLDC motor's phase wires to a 3 phase AC power source & see if you get torque or smoke!

AussieRider

 

[billvon]

Is the alternating 3-phase sine wave of a BLDC and BLAC motor identical to the 3-phase sine wave of a traditional AC motor ???

The waveform of the AC power to the motor looks similar. The big difference is that:

-For a brushless DC motor, the AC waveform is created such that it is always 90 degrees ahead of the magnetic field in the motor. It changes frequency to exactly match the desired rotational speed (or torque demand) of the magnetic core (or rotor magnets.)

-For a PM synchronous motor, the AC waveform is usually fixed, and the motor runs at exactly the same speed, all the time - based on the frequency of the AC input. The phase is between 0 and 90 degrees ahead of the rotating field (when used as a motor, that is.)

-For an AC induction motor, the AC waveform is usually fixed, and the motor runs at some speed lower than the frequency of the AC waveform. The difference between the frequency suggested by the AC waveform and the motor's actual speed is called slip; the slip is what creates the field in the rotor that the motor uses to generate traction.

Does a BLAC motor generate the same unique 3-phase sine wave identical to that of a 3-phase BLDC motor?

I don't know. BLAC sounds like a marketing term. From the description it sounds like a BLAC motor turns AC into DC*, then DC back into AC at a new frequency to drive the BLDC motor. If that's true, it's just a BLDC motor/controller with a rectifier in front to convert AC into DC.

(* - this DC is often called the link voltage.)

Is it possible that the 3-phase sine wave of a traditional 220V AC motor (e.g. alternating from neg-to-pos 60 times a second) is not the same as the 3-phase sine wave of a BLAC motor or BLDC motor?

At the most fundamental level they are all the same - AC current in three wires with a 120 degree phase relationship. But there are differences in frequency and amplitude. In general, AC synchronous and induction motors are driven by fixed frequency, fixed voltage drives. BLDC drives adjust both the magnitude and frequency of the current.

 

[amberwolf]

I guess the final answer would be to connect a BLDC motor's phase wires to a 3 phase AC power source & see if you get torque or smoke!

or...spin a motor mechanically, using it as a generator, and see what waveform you get out of it.

 

[AussieRider]

Not as much fun mate.

AussieRider

 

[eMark]

Hopefully, that link ... "everything anyone ever wanted to know (and more) about Brushless DC Motor Fundamentals ...
https://www.monolithicpower.com/pub/media/document/Brushless_DC_Motor_Fundamentals.pdf ..." with quoted posts and subsequent posts on this thread page (p. 3) has more than answered johndeere1's quest. Just one last comment (FWIW) from p. 9 of that link ...

The primary difference between AC and DC motors is the power type applied to the armature. From this vantage, a BLDC motor is actually an AC motor ... a brushed DC motor converts DC current in an armature coil to an AC current. ... (see p. 9)

should have been to a pulsed alternating current instead of "to an AC current" (JMO) ... hoping p. 3 of this Ebikes are they AC, DC or? thread has helped remove any alternating (AC) confusion :wink:

 

[billvon]

3 phase AC has 1 phase feeding each coil all the time at a constant frequency, 50 or 60 hz. A BLDC controller feeds pulsed DC to 1 coil until the shaft rotates & the hall sensor causes the controller to switch to the next coil.

Not exactly. Any AC induction motor, and any BLDC motor with a sine wave drive, feeds all three phases at the same time. There are points in time where the current goes to zero across any one winding - but that's true of all things AC.

BLDC motors WITHOUT sine wave drives have simpler waveforms, and so the zero cross times are often longer. But they are still feeding all three windings at once.

I guess the final answer would be to connect a BLDC motor's phase wires to a 3 phase AC power source & see if you get torque or smoke!

You could. In many cases you will get both.

If the AC waveform can't accelerate the rotor to synchronous speed fast enough you often won't get "capture" and the motor will either spin at an odd speed or will judder through a small angle as the fields alternate. Synchronous motors (and their drives) are designed so that that doesn't happen. BLDC motors are not designed that way, so they may not capture and work with a regular AC waveform.

In addition, the apparent AC impedance of each of the coils will vary depending on position and speed. So you may get a huge amount of current at first, sufficient to damage or smoke the motor. Again, synchronous AC motors are designed for this, and will handle the startup surge.