Exploring PWM

[Ardent]

X-No-Archive: yes

Hi all

I have been trying to play with driving a motor with PWM using
different circuits off the web, using 555, OpAmps.However I could not
get satisfactory results with a motor that needed 6 amps at12 volts..

I finally made a good PWM system using a microcontroller and just 38
bytes of code.

The part I want to tell about is the control of the motor.I used a
decade switch which gave me no rotation at 0 setting and then 9
speeds, at 9 at the decade switch I got 90% speed. This has made the
whole thing very simple

Hope this helps someone.

 

[Winfield Hill]

Ardent wrote...

I have been trying to play with driving a motor with PWM using
different circuits off the web, using 555, OpAmps. However I could
not get satisfactory results with a motor that needed 6 amps at 12
volts.

I finally made a good PWM system using a microcontroller and just
38 bytes of code.

The part I want to tell about is the control of the motor. I used
a decade switch which gave me no rotation at 0 setting and then 9
speeds, at 9 at the decade switch I got 90% speed. This has made
the whole thing very simple .... [snip]

Thanks for the story, Sandy, it sounds like you're enjoying yourself
exploring power electronics. I do have a comment, or question.

Are you just using the microprocessor to make a simple pulse-width
modulator that can supply 10 different power levels to the motor?

Most of the effort in industrial power electronics PWM circuitry is
aimed at the issue of feedback control. For example, in your case
these would set 10 different motor speeds that start up and quickly
servo to the correct final speed, and then remain at constant speed
despite differing load or power supply conditions.

You can expand the code in your microprocessor to include this type
of capability. There's a great deal written about servo control on
the web. You will discover that it's even possible to well control
the speed of a motor without a position or speed sensor on the shaft.

BTW, I have one other comment. Why do you set "X-No-Archive: yes"
for your posting? Do you really want it to disappear? Why should
people engage in discussions with you if they promptly disappear?

Thanks,
- Win

whill_at_picovolt-dot-com

 

[Ardent]

Thanks for the story, Sandy, it sounds like you're enjoying yourself
exploring power electronics.

Well, my cousin is building a TIG welder and he wanted a motor to move
the head with speed control. I just keep electronics as a hobby and
the opportunity to do something was nice. And,thank you, I really
enjoyed doing it.

I do have a comment, or question.
Are you just using the microprocessor to make a simple pulse-width
modulator that can supply 10 different power levels to the motor?
Yes.

Most of the effort in industrial power electronics PWM circuitry is
aimed at the issue of feedback control. For example, in your case
these would set 10 different motor speeds that start up and quickly
servo to the correct final speed, and then remain at constant speed
despite differing load or power supply conditions.

Since it was just a welding head that was to be moved any feedback
control was not even considered.

You can expand the code in your microprocessor to include this type
of capability. There's a great deal written about servo control on
the web. You will discover that it's even possible to well control
the speed of a motor without a position or speed sensor on the shaft.

Yes, I may soon take up making an X-Y coordinate table - there I will
get the opportunity to do all this. And thanks for the suggestion.

BTW, I have one other comment. Why do you set "X-No-Archive: yes"
for your posting? Do you really want it to disappear? Why should
people engage in discussions with you if they promptly disappear?

Sorry, not intentional.It is part of my signature and I clean forgot
to remove it.

 

[Winfield Hill]

Ardent wrote...

Well, my cousin is building a TIG welder and he wanted a motor to move
the head with speed control. I just keep electronics as a hobby and
the opportunity to do something was nice. And,thank you, I really
enjoyed doing it.


Since it was just a welding head that was to be moved any feedback
control was not even considered.

Aha! What you expect is really welding-head position control, with
a slowly changing position. Instead what you'll get will be closer
to torque control, which translates into rotary-mass acceleration.
Integrate once for speed and a second time for position. Because
the speed is very slow, it's quite likely that you'll need a servo
system. On the other hand, it you choose a stepping motor...

Yes, I may soon take up making an X-Y coordinate table - there I will
get the opportunity to do all this. And thanks for the suggestion.

Hmm, right up the same alley.

Thanks,
- Win

whill_at_picovolt-dot-com