Ebikes are they AC, DC or?

John1deere

10 W
Joined
Jul 9, 2018
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Hello people,

I ways thought they were ac since they are 3 phase and 3 phase DC doesn't exist but someone came up to me with a lengthy explanation on how they are pwm driven and that was neither AC or DC

Anyone care to shime in? A good link with info? I can't find anything that clearly explain it myself.

Thanks.
 
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.

AussieRider
 
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.
 
Brushless DC (BLDC) motors are just permanent magnet synchronous motors (PMSM) with a trapezoidal back EMF. They are AC motors. They have (usually) 3 phases which alternate.

Whether the waveform is trapezoidal or sinusoidal, it is still alternating.

And if they are driven by a sinusoidal controller, then all 3 phases are being driven at once (not one at a time in sequence). A sinusoidal controller is producing genuine 3 phase AC electricity. The quality of the sinusoid depends on the quality of the controller.

BLDC are called "brushless DC" because they are driven by a controller which is powered by DC. The controller converts DC into multi-phase AC to power the motor.
https://en.m.wikipedia.org/wiki/Brushless_DC_electric_motor
 
Interesting. I had been thinking all these years it was just DC,, with each phase simply turning on and off in sequence to make the motor want to turn towards the next magnet. Or is that true, but just of square wave controller?

So still a Tesla type motor? Or is it that even Edison motor is ac? Ignorance makes me more confused all the time, with no EE degree here.
 
https://en.m.wikipedia.org/wiki/Alternating_current
Alternating current (AC) is an electric current which periodically reverses direction, in contrast to direct current (DC) which flows only in one direction.

Ebikes have DC motors that are electronically commutated through 3 successive phases.
 
serious_sam said:
Brushless DC (BLDC) motors are just permanent magnet synchronous motors (PMSM) with a trapezoidal back EMF. They are AC motors. They have (usually) 3 phases which alternate.

Whether the waveform is trapezoidal or sinusoidal, it is still alternating.

And if they are driven by a sinusoidal controller, then all 3 phases are being driven at once (not one at a time in sequence). A sinusoidal controller is producing genuine 3 phase AC electricity. The quality of the sinusoid depends on the quality of the controller.

BLDC are called "brushless DC" because they are driven by a controller which is powered by DC. The controller converts DC into multi-phase AC to power the motor.
https://en.m.wikipedia.org/wiki/Brushless_DC_electric_motor

How is a sine controller able to drive all three phases.. how is the back emf figured and wouldn’t driving all phases amount to all teeth involved in torque production and a 1/3 more efficient/powerful motor? Less likely to saturate?
 
My understanding was that for brushless motors it's DC in, 3 phase A/C out. Brushed motors are straight DC.

I won't even pretend that I know what I'm talking about though. I'm sure many here have forgotten more about this stuff than I'll ever know.
 
John1deere said:
I ways thought they were ac since they are 3 phase and 3 phase DC doesn't exist but someone came up to me with a lengthy explanation on how they are pwm driven and that was neither AC or DC
DC goes into the controller. AC comes out.
 
Motors need AC to spin. Even brushed motors take DC in, but they use their brushes and commutator to convert the DC into AC before it goes to the windings.

Switching DC turns it into AC. Just because it's not 60Hz doesn't mean it's not AC. BLDC motors take an AC input of varying frequency and amplitude. The frequency is locked to the rotation of the rotor in a synchronous motor as most ebike motors are. The amplitude is dependent on how much current the controller is trying to send to the windings aka how much torque is being requested.
 
seems like everyone has a different opinion. i keep looking but all i see is people saying 3 phase bldc motors are pwm driven. not a single mention of ac...

https://www.digikey.ca/en/articles/techzone/2017/jan/why-and-how-to-sinusoidally-control-three-phase-brushless-dc-motors

https://www.digikey.ca/en/articles/techzone/2013/mar/an-introduction-to-brushless-dc-motor-control

https://www.st.com/content/ccc/resource/technical/document/application_note/5d/04/eb/5e/87/77/48/cb/CD00041736.pdf/files/CD00041736.pdf/jcr:content/translations/en.CD00041736.pdf
 
Let's say the firing sequence is A-B-C-A-B-C etc on the BLDC motor. The pulses of DC at the PWM frequency first go down phase A returning to the controller through phase B, and then down phase B returning back up phase C, then down phase C back up phase A and so on. That means the motor phases see current that alternates direction and whose alternating frequency is determined by the hall sensor pulses (rpm).
 
John1deere said:
seems like everyone has a different opinion.

Funny about that. Perhaps youll find it easier to understand why i have so little interest in opinions.

I keep looking but all i see is people saying 3 phase bldc motors are pwm driven. not a single mention of ac...


Yeah, was sorely tempted to give you my simplified misunderstanding of that BLDC becoming AC, decided to let someone else take the wrap for faking expertise. Thanks B.
 
Most articles describing the differences refer to the difference in the stator windings. Hard to find illustrations comparing the stator windings of a BLDC (trapezoidal) motor vs. BLAC (sinusoidal), but found this one:

ucJpw.jpg
 
John1deere said:
seems like everyone has a different opinion. i keep looking but all i see is people saying 3 phase bldc motors are pwm driven. not a single mention of ac...
Look at figure 4 in your first reference. You will see a sine wave alternating between + and - current. That's AC.
 
John1deere said:
seems like everyone has a different opinion. i keep looking but all i see is people saying 3 phase bldc motors are pwm driven. not a single mention of ac...
Does this help ...
The everyday e-bike hub motor or mid drive motor is a BLDC motor. The motor can’t run on DC directly, it needs a controller. The controller takes the DC and converts it into a variable frequency 3 phase AC. So electric bicycles already have AC motors. But you may be thinking of Tesla’s induction AC motor, which is also 3 phase AC but has a rotor that is electrically induced to have a magnetic field, with the 3 phase coils fixed around the motor body. The BLDC motor has the opposite construction, with the interior of the motor fixed with the 3 phase coils, and the rotating part made of high strength rare earth magnets. Not much difference. At low speeds the BLDC motor is probably more efficient, as no energy is required to create the magnetic field.

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eAutoPowr can provide up to 100kW of electrical power, with either 700V direct current (DC) or 480V variable frequency three-phase alternating current (AC) available.

[youtube]kEj6_m5WtbQ[/youtube]
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Nothing Runs Like A Deere
 
As a big Deere fan beginning with our 4010 couldn't resist posting Deere's recent electrically powered innovative transmission ...
eAutoPowr can provide up to 100kW of electrical power, with either 700V direct current (DC) or 480V variable frequency three-phase alternating current (AC) available.

[youtube]kEj6_m5WtbQ[/youtube]
english begins again at 0:56 ... it's about time ... long overdue ... no diesel smell ... clean power :thumb:

Nothing Runs Like A Deere
[/quote]

progress is nice but being a farmer and knowing some about batteries i just can't see it happening anytime soon. when we are in a rush working 24/24 we just can't wait hours for a tractor to be charged... unless the price is so appealing that you can get let's say 3 instead of 2 conventional tractor (not just the cost of tractor but also operation.) same for custom worker they will need a way to charge in the field.
 
Glad to see JD with first [real] farm etractor ... was only a matter of time with electrification proven for locomotives and heavy construction equipment ... Going Clean and Green!
https://www.tesla.com/en_CA/semi

don't mean to derail ... just another green/yellow JD farming fan

Are you planning to build your own sporty two-wheel EUV fat tire as a winter project?
 
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