What passes as Pulse Width Modulation in DC Motor Control?

"Rich Grise"


I _know_ from personal experience that this is true -
Click to expand...


** The only personal experience YOU have is public masturbation.

FUCK OFF.



....... Phil
 
"Rich Grise"
Sjouke Burry wrote:
John Fields wrote:

You have just demonstrated that you know
nothing of electricity and motors.
Please study some, before you try to
correct people.
Or they will see you as a troll.

No, actually, John is right.
Click to expand...

** John knows what he posted is wrong and is now just playing games with
words.

He has never admitted error in his whole life and it not about to break the
habit.

Being the psychotic asshole that he is.



...... Phil
 
On Thu, 29 Jan 2009 08:21:17 -0600, "Jon
Slaughter" <Jon_Slaughter@Hotmail.com> wrote:

"Bob Masta" <N0Spam@daqarta.com> wrote in message
news:4981a930.807047@news.sysmatrix.net...
On Wed, 28 Jan 2009 10:24:06 -0600, "Jon
Slaughter" <Jon_Slaughter@Hotmail.com> wrote:

The easiest way to do PWM with arbitrary function without being to
ambiguous
is to use periodic functions that are 0 after a portion of the period.

Actually, there is a much easier way, which is
what my previously-mentioned industrial DC motor
controller does: Monitor the output current (or
power, RPM, etc), compare to the setpoint, and
let feedback take care of the details. This
allows you to use any arbitrary waveform, even one
that is non-periodic.



But that isn't PWM and it isn't as efficient as rectangular PWM.

As my post proved that any function is equivalent to PWM. i.e., whatever
waveform is being generated by your feedback can be done using rectangular
PWM and since most likely(I didn't look at your circuit) your dissipating
power continuously in the component that is controlling the current your
wasting that power. It would only be efficient if the component has
extremely low power dissipation but chances are mosfets would be even more
efficient.
Click to expand...
Perhaps I wasn't clear.. The controller I spoke
of (didn't give a circuit link) is a commerical
unit ("mine" only because I bought it!) that uses
a rectangular PWM drive signal applied to SCRs
that chop the incoming mains supply. That PWM
drive is controlled by a feedback circuit that
compares the actual motor current (and maybe back
EMF or something) to a setpoint. So the duty
cycle of the PWM is modulated as needed to
maintain the desired setpoint.

Now, it's true that this circuit is applying the
PWM to the sinusoidal mains, but it should be
clear that due to the feedback the exact nature of
the mains waveform is not very important... it
could just as well be random noise or an opera
aria. Assuming the waveform has a reasonable RMS
voltage and there are minimal SCR switching
losses, the waveform should have little (if any)
effect on efficiency.

Best regards,


Bob Masta

DAQARTA v4.51
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!
 
On Fri, 30 Jan 2009 12:39:13 +1100, "Phil Allison"
<philallison@tpg.com.au> wrote:

"Rich Grise"
Sjouke Burry wrote:
John Fields wrote:

You have just demonstrated that you know
nothing of electricity and motors.
Please study some, before you try to
correct people.
Or they will see you as a troll.

No, actually, John is right.


** John knows what he posted is wrong and is now just playing games with
words.

He has never admitted error in his whole life and it not about to break the
habit.
Click to expand...
---
You must have me confused with another John, since I make mistakes every
once in a while and gladly own up to them when they're pointed out to
me. I even own up to them myself if I catch them before someone else
does after I've posted.
---

Being the psychotic asshole that he is.
Click to expand...
---
If standing my ground makes me a psychotic asshole, then open the doors
to the asylum, honey, I'm ready to go!

BTW, instead of all that fuming and fussing, why don't you simply post
what _your_ interpretation of PMW is and prove me wrong intellectually?

JF
 
"John Fields"


** John knows what he posted is wrong and is now just playing games with
words.

He has never admitted error in his whole life and it not about to break the
habit.

Being the psychotic, lying asshole that he is.



....... Phil
 
On Sat, 31 Jan 2009 01:42:12 +1100, "Phil Allison"
<philallison@tpg.com.au> wrote:

"John Fields"


** John knows what he posted is wrong and is now just playing games with
words.

He has never admitted error in his whole life and it not about to break the
habit.

Being the psychotic, lying asshole that he is.
Click to expand...
---
???

You already said that.

JF
 
"John Fields"
** John knows what he posted is wrong and is now just playing games with
words.

He has never admitted error in his whole life and it not about to break
the
habit.

Being the psychotic, lying asshole that he is.


You already said that.
Click to expand...
** It's worth repeating:


John knows what he posted is wrong and is now just playing games with
words.

He has never admitted error in his whole life and it not about to break the
habit.

Being the psychotic, lying asshole that he is.



....... Phil
 
On Sat, 31 Jan 2009 10:57:21 +1100, "Phil Allison"
<philallison@tpg.com.au> wrote:

"John Fields"


** John knows what he posted is wrong and is now just playing games with
words.

He has never admitted error in his whole life and it not about to break
the
habit.

Being the psychotic, lying asshole that he is.


You already said that.

** It's worth repeating:
Click to expand...
---
Your rational technical stuff is generally a good read and might be
worth repeating, but your grotesque attempts at dog-paddling by using
insults in order to keep from going under, when you're clearly sinking,
aren't.

I've already, graciously, given you the opportunity to prove me wrong by
soliciting your technical rebuff of my position but, from the lack of
anything technical coming this way, you seem to not to want to go there.

Moreover, since I generally respond to constructive criticism in a
positive way, I can only conclude that your refusal to delve into the
details means that you're afraid you'll lose even more face in the arena
when the lions descend upon you.

Why worry about it?

You're pretty much down to bone now, as it is, and you weren't all that
good-looking when you started.
----

John knows what he posted is wrong and is now just playing games with
words.
Click to expand...
---
Ah, words...

"A Rose, by any other name", even called a turd, "would smell as
sweet".. .

Thanks, Bill, for the original :)
---

OK, you get another chance: Using your best words, _Why_ is my
description of PWM wrong?
---

He has never admitted error in his whole life and it not about to break the
habit.
Click to expand...
---
"it not?"

Well, I thought I was wrong once, but then I found out that I'd made a
mistake in thinking that.
---

Being the psychotic, lying asshole that he is.
Click to expand...
---
That's two.

Which reminds me of a joke.

Wanna hear it?

JF
 
"John Fields"


** You are playing silly games with words.

You have ALREADY been proved wrong.

So FUCK OFF !!!

Asshole.



..... Phil
 
On Sat, 31 Jan 2009 12:25:24 +1100, "Phil Allison"
<philallison@tpg.com.au> wrote:

"John Fields"


** You are playing silly games with words.

You have ALREADY been proved wrong.
Click to expand...
---
By whom, and how?
---

So FUCK OFF !!!

Asshole.
Click to expand...
---
Tough, ain't it, when your silly little games don't work?

JF
 
"John Fields" <jfields@austininstruments.com> wrote in message
news:n84un4pdjlplqlk0uoapb4ppdpue7803b5@4ax.com...
On Tue, 27 Jan 2009 13:38:51 -0000, "Rich" <notty@emailo.com> wrote:

Can PWM control consist of dc pulses that rise and fall in voltage in a
sinusoidal fashion?

---
No.
---
Click to expand...

But it would be PWM control if the "width" of a dc pulse was a function of a
sinusoid waveform.
 
"Rich" <notty@emailo.com> wrote in message
news:6uj19oFf9pqsU1@mid.individual.net...
"John Fields" <jfields@austininstruments.com> wrote in message
news:n84un4pdjlplqlk0uoapb4ppdpue7803b5@4ax.com...
On Tue, 27 Jan 2009 13:38:51 -0000, "Rich" <notty@emailo.com> wrote:

Can PWM control consist of dc pulses that rise and fall in voltage in a
sinusoidal fashion?

---
No.
---


But it would be PWM control if the "width" of a dc pulse was a function of
a sinusoid waveform.
Click to expand...
Of course, if the frequency of the sinsoidal wave was really low, the
motor's speed would change at the frequency of the sinusoidal wave.
 
On Jan 27, 1:38 pm, "Rich" <no...@emailo.com> wrote:
Can anyone please tell me what passes as PWM in Motor Control?

Is it limited to supplying the motor with a square wave, where a set and
constant level of voltage is switched on or off to the motor?
Click to expand...
this is a long thread, here's just my opinion, i'll try to keep it
simple:

the speed of the motor is directly proportional to the supply power.
turning the supply source on and off very fast is a way of varying the
supply power.
In practice, the supply voltage is usually constant, the best way to
switch on and off the supply is to put a FET or some kind of high
speed switch on the supply rail, to connect or disconnect it.
when you switch on and off that switch really fast, square wave will
from, constant supply voltage for ON and 0v for OFF.
in the switching control circuit, there's a clock. in the PWM the
clock frequency is usually fixed. and the Duty Cycle which is the % of
ON time over 1 period (period(T)=1/switching frequency(Fsw) ) controls
the average power being supplied to the motor.

and example of duty cycle control is, if you using a clock of 300kHz,
then the period is 1/300k=3.33uS. if you ask for 10% duty cycle, the
switch will be turned on with the rising clock edge, and turned off
after 0.1*3.33uS=0.33uS. and stay off in the rest of the period until
being turned on again with the next clock rising edge.
the turn on timing is control by the clock, but the control of when to
turn off the switch is not by timing. normally is by measure the
voltage or current and feed into a comparator. they are called Voltage
Mode and Current Mode control.

in many cases we don't define things and implement them, but rather
find a way to implement then put it into context. in this case we
don't define it has to be a square wave, but rather the square wave is
the easiest we can make and control.

now,
if supply voltage is 1V, the impudence of the motor is 1ohm, then DC
supply will allow 1A flow, give the motor 1W of power. but if you
turning the rail on and off with 10% duty cycle, the average current
is now 0.1A and the average power becomes 0.1W. the motor will slow
down.




Or can other waveforms consitutute PWM control of a dc motor? Such as where
voltage does not drop to zero, but has periodic peaks having square,
triangular, sawtooth or some other waveform?
Click to expand...
sure you can do that, it's a waveform on top of a DC signal. what
matters is the average power goes into the motor. by integration, it's
the area below the waveform that matters.

Can PWM control consist of dc pulses that rise and fall in voltage in a
sinusoidal fashion?
Click to expand...
you can, BUT sinusoidal same as the sawtooth, are signals with fixed
50% duty cycle (think about it). and the idea of PWM is to be able to
control the duty cycle to change the power.
so those signals won't fit here.
and if you asking if it has to be square wave, the answer is no. as i
said above, it's just happen to be the easiest we can get. and with
some capacitance on the rail, if you look closely, there's always
round edges and corners in the wave form. and with certain
capacitance, 50% duty cycle square wave will looks like sinusoidal
same as the sawtooth waves!

hope it helps.
 
Rich wrote:
But it would be PWM control if the "width" of a dc pulse was a function of a
sinusoid waveform.
Click to expand...

If you use a sine wave, you lose efficiency, and raise the losses as
waste heat.


--
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There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.
 
"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:S7CdnW5j1KxRPRnUnZ2dnUVZ_sHinZ2d@earthlink.com...
Rich wrote:

But it would be PWM control if the "width" of a dc pulse was a function
of a
sinusoid waveform.


If you use a sine wave, you lose efficiency, and raise the losses as
waste heat.
Click to expand...
There is no lss if you chop a waveform into pulses with a switch. Running
the motor steady, with dc motors, all pulses are at some set voltage and a
set constant duration. Speed up the motor by extending the pulse width, not
the dc voltage.

If you chop the sinewave to a universal motor with a switch (however which
way) still no loss as waste heat when speed controlling the motor. Slightly
less *motor efficiency* probably because pulses do not retain the most
efficient voltage level. I mean, for a 12v dc motor I imagine that for*motor
efficiency* the most efficient level for a pulse is dc 12v. Or perhaps we
can afford to have a greater pulse level, like say dc 20v.

Yea, if I have a 12v dc motor, is it better to have say 20v pulses? Why
stick to 12v pulses with PWM.
 
On Sat, 31 Jan 2009 14:04:43 -0500, "Michael A.
Terrell" <mike.terrell@earthlink.net> wrote:

Rich wrote:

But it would be PWM control if the "width" of a dc pulse was a function of a
sinusoid waveform.


If you use a sine wave, you lose efficiency, and raise the losses as
waste heat.
Click to expand...
Industrial DC motors are often controlled via PWM
acting on the AC mains (in a rectifying
configuration). Switching losses are not a
problem.

Best regards,


Bob Masta

DAQARTA v4.51
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!
 
Bob Masta wrote:
On Sat, 31 Jan 2009 14:04:43 -0500, "Michael A.
Terrell" <mike.terrell@earthlink.net> wrote:


Rich wrote:

But it would be PWM control if the "width" of a dc pulse was a function of a
sinusoid waveform.


If you use a sine wave, you lose efficiency, and raise the losses as
waste heat.


Industrial DC motors are often controlled via PWM
acting on the AC mains (in a rectifying
configuration). Switching losses are not a
problem.
Click to expand...

What I've seen rectifies the AC with a full wave bridge, does minimal
filtering and varies the pulse frequency so they can go both above &
below the rated speed. AKA a 'VFD'


--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm


There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.
 
On Mon, 02 Feb 2009 08:39:55 -0500, "Michael A.
Terrell" <mike.terrell@earthlink.net> wrote:

Bob Masta wrote:

On Sat, 31 Jan 2009 14:04:43 -0500, "Michael A.
Terrell" <mike.terrell@earthlink.net> wrote:


Rich wrote:

But it would be PWM control if the "width" of a dc pulse was a function of a
sinusoid waveform.


If you use a sine wave, you lose efficiency, and raise the losses as
waste heat.


Industrial DC motors are often controlled via PWM
acting on the AC mains (in a rectifying
configuration). Switching losses are not a
problem.


What I've seen rectifies the AC with a full wave bridge, does minimal
filtering and varies the pulse frequency so they can go both above &
below the rated speed. AKA a 'VFD'
Click to expand...
The original post was in reference to DC motors,
which are not controlled by frequency but by
average voltage. The controllers are essentially
just fancy rectifying lamp dimmers. They vary the
duty cycle to control the power to the motor. The
one I own uses feedback to adjust the duty cycle
to maintain a given motor performance setpoint.

Best regards,



Bob Masta

DAQARTA v4.51
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!
 
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