Educate me on these motor waveforms....

[amdx]

 My son built a an electric skateboard and then ask me about how the
motors work.
I made and assumption that they were 3 phase motors (3 wires) and I
would see a
high frequency AC current waveform. I have not looked at the voltage, I
used an
inductive clip to look at the current waveform. The pictures show the
wave forms
at different throttle inputs. Right now it is software limited to 30% of
max,
so I can\'t show what 90% or 100% throttle looks like.
 To me, the wave forms looks like PWM, at least at the very start after
that,
I\'m asking for someone to explain what is going on.
> https://www.dropbox.com/s/cmsdyng4p5nx1lt/Motor%20Waveforms.jpg?dl=0

                            Mikek

 PS. probably doesn\'t matter, but my inductive clip is an old clip used to
monitor spark plug wires. It was a big signal out at 100kHz but at 100 Hz,
the signal is way down, dare I say 1/600! So, could the wave form be
missing
some low frequency information, confusing the issue?

PSS, even with a 30% software drive limit, it still goes 17 miles an
hour, drat,
I tried to change his mind to build a bicycle.


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[Lasse Langwadt Christensen]

onsdag den 4. maj 2022 kl. 16.59.06 UTC+2 skrev amdx:

My son built a an electric skateboard and then ask me about how the
motors work.
I made and assumption that they were 3 phase motors (3 wires) and I
would see a
high frequency AC current waveform. I have not looked at the voltage, I
used an
inductive clip to look at the current waveform. The pictures show the
wave forms
at different throttle inputs. Right now it is software limited to 30% of
max,
so I can\'t show what 90% or 100% throttle looks like.
To me, the wave forms looks like PWM, at least at the very start after
that,
I\'m asking for someone to explain what is going on.
https://www.dropbox.com/s/cmsdyng4p5nx1lt/Motor%20Waveforms.jpg?dl=0

Mikek

PS. probably doesn\'t matter, but my inductive clip is an old clip used to
monitor spark plug wires. It was a big signal out at 100kHz but at 100 Hz,
the signal is way down, dare I say 1/600! So, could the wave form be
missing
some low frequency information, confusing the issue?

PSS, even with a 30% software drive limit, it still goes 17 miles an
hour, drat,
I tried to change his mind to build a bicycle.

I suspect your timescale is way to short so you only see the pwm

https://www.physicsforums.com/attachments/bldcemf-png.47285/

 

[three_jeeps]

On Wednesday, May 4, 2022 at 10:59:06 AM UTC-4, amdx wrote:

My son built a an electric skateboard and then ask me about how the
motors work.
I made and assumption that they were 3 phase motors (3 wires) and I
would see a
high frequency AC current waveform. I have not looked at the voltage, I
used an
inductive clip to look at the current waveform. The pictures show the
wave forms
at different throttle inputs. Right now it is software limited to 30% of
max,
so I can\'t show what 90% or 100% throttle looks like.
To me, the wave forms looks like PWM, at least at the very start after
that,
I\'m asking for someone to explain what is going on.
https://www.dropbox.com/s/cmsdyng4p5nx1lt/Motor%20Waveforms.jpg?dl=0

Mikek

PS. probably doesn\'t matter, but my inductive clip is an old clip used to
monitor spark plug wires. It was a big signal out at 100kHz but at 100 Hz,
the signal is way down, dare I say 1/600! So, could the wave form be
missing
some low frequency information, confusing the issue?

PSS, even with a 30% software drive limit, it still goes 17 miles an
hour, drat,
I tried to change his mind to build a bicycle.


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typically these are brushless DC motors. The electronic speed controller controls the torque by PWM the current into motor. Typically the control voltage is 12v, but the current can be very high, 100A+

 

[Phil Allison]

amdx wrote:

==========

My son built a an electric skateboard and then ask me about how the
motors work.
-------
I have not looked at the voltage, I used an
inductive clip to look at the current waveform.

** That dumb idea will never work.

It\'s a BLDC motor and there are hundreds of pages on the net about them.
Shame most of them make no sense.


...... Phil