Pulsed DC

  • #1

Main Question or Discussion Point

How would one go about creating a speed control circuit for a brushless DC motor? I need two circuits to pulse DC in one direction, pause, reverse polarity, pause, and repeat. And I need the two circuits to be synchronized. I also need them to be opposite of each other in there polarity.(when one circuit is pulsed Neg. the other is pulsed Pos.) Ineed to control the speed at which this is happening. Does anyone have any information on this or a link to a site that explains it clearly?
 

Answers and Replies

  • #2
My mistake, I just need one circuit that can do what I described from 1 DC source(battery bank) So I need to pulse DC in one direction, pause, Pulse DC in opposite direction, pause and repeat. And I need to control the speed at which this is happening. Thanks for any help. And I need to do this without brushes.
 
  • #3
berkeman
Mentor
56,657
6,559
My mistake, I just need one circuit that can do what I described from 1 DC source(battery bank) So I need to pulse DC in one direction, pause, Pulse DC in opposite direction, pause and repeat. And I need to control the speed at which this is happening. Thanks for any help. And I need to do this without brushes.
Traditionally you do it with an H-bridge circuit, and you use PWM for speed (and direction) control:

http://www.google.com/search?sourceid=navclient&aq=1&oq=h-bridge+pwm&ie=UTF-8&rlz=1T4GGLL_enUS301US302&q=h-bridge+pwm+motor+driver
 
  • #4
Thanks Berkeman. So I found some diagrams but they are way over my head at the moment. Learning how a transistor works is probably a good start. My problem right now with understanding complicated circuit diagrams is that they don't really show how a current moves through it and why. I get inductors,capacitors and resistors but transistors not so much. What do you think would be a good start in understanding this stuff?Ifthere was only an animation showing the path of the current and why, that would be great, but I haven't been able to find anything like that. Also the speed controller in not so obvious. I would imagine there would be some kind of 'lever' in the diagram that you would move to increase the frequency of the current in the circuit increasing the speed of the motor.
 
  • #5
berkeman
Mentor
56,657
6,559
Thanks Berkeman. So I found some diagrams but they are way over my head at the moment. Learning how a transistor works is probably a good start. My problem right now with understanding complicated circuit diagrams is that they don't really show how a current moves through it and why. I get inductors,capacitors and resistors but transistors not so much. What do you think would be a good start in understanding this stuff?Ifthere was only an animation showing the path of the current and why, that would be great, but I haven't been able to find anything like that. Also the speed controller in not so obvious. I would imagine there would be some kind of 'lever' in the diagram that you would move to increase the frequency of the current in the circuit increasing the speed of the motor.
I googled h-bridge tutorial, and got lots of hits that look like they might help you:

http://www.google.com/search?sourceid=navclient&ie=UTF-8&rlz=1T4GGLL_enUS301US302&q=h-bridge+tutorial

BTW, there are h-bridge ICs available that package up the transistors for you. They would be the easiest way to start a project.

http://www.google.com/images?rlz=1T4GGLL_enUS301US302&q=h-bridge+ics&um=1&ie=UTF-8&source=univ&ei=buE0TajZIYL2swPky8SBBg&sa=X&oi=image_result_group&ct=title&resnum=2&ved=0CC4QsAQwAQ

.
 
  • #6
Yea I guess this is something not easily answered but thanks for the tip. I know what direction to look now in understanding how that circuit works, but I have a little studying to do. Thanks again
 
  • #7
4,239
1
If your intent is not to roll-your-own speed controller but utilize one, you might find one available at the ratings you need. They come under the name electronic speed control or ESC for three phase brushless DC motors. Those I am aware of are for model airplanes and cars running up to 80 VDC input and perhaps 30 amps. The speed control is via pulse width.

For both forward and reverse control you would have to find one that specifically does this--if you try to use two in anti-parallel their microcontrollers will get confused.
 
Last edited:
  • #8
13
0
Dear BilPrestonEsq,
My friend is working on this project. He has designed a speed control circuit of Brushless DC motor. I have seen his designed circuit once, it includes two push buttons that increase and decrease the speed of Brushless DC motor, one LCD that displays motor's current speed.
If you need some technical assistance from him than i may provide his email address to you.
 
  • #9
Dear BilPrestonEsq,
My friend is working on this project. He has designed a speed control circuit of Brushless DC motor. I have seen his designed circuit once, it includes two push buttons that increase and decrease the speed of Brushless DC motor, one LCD that displays motor's current speed.
If you need some technical assistance from him than i may provide his email address to you.
Hmm...Thank you, sure if he won't mind. I definetely need some technical assistance!:biggrin:
I can't use buttons on my project but it would definetely help me out.
I still don't even know what I designed...really.
I understand how it works but not what it is called!
First I thought I designed a BLDC motor then a syncronous ac motor then I got real confused and called it a induction motor(WRONG) so then I read that a BLDC motor is essentially the same as synchronous ac motor. What I do know is it would work and how it works. I just don't know what kind of circuit I need to power it exactly.
Anyways.....probably didn't need to get into all that....Yeah let me know. Thanks again.
 

Related Threads for: Pulsed DC

  • Last Post
Replies
7
Views
957
  • Last Post
2
Replies
42
Views
14K
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
11
Views
1K
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
5
Views
5K
Top