PWM Controller for DC Motor

Discussion in 'The Projects Forum' started by james211, Aug 17, 2013.

  1. james211

    Thread Starter Member

    May 29, 2012
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    So I have two diaphragm air pumps that I need to test out and both use DC motors. I need to control the speed of them and the company suggested I use a PWM controller. What I don't know is if I need to build a specific PWM controller based on the specs of each motor. Here are the specs for each motor:

    #1 Current Range (mA) 34 mA to 104 mA Motor Voltage 3.3 VDC
    #2 Current Range (mA) 50 mA - 675 mA Motor Voltage 12 VDC

    Is it possible to build one PWM that would work for both? And can anyone recommend a good circuit diagram for building this? I do have soldering and breadboard layout experience. I just need to find the right diagram as I really don't know how to do the appropriate calculations.

    Also, if its easier and more cost effective to just purchase a PWM module I'm fine with that. Although not as much fun, it might just be easier.

    Any help would be GREATLY appreciated.
     
    Last edited: Aug 17, 2013
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You can get both off ebay for <$10.00 P.Paid.
    Max.
     
  3. james211

    Thread Starter Member

    May 29, 2012
    210
    2
    Would this work? Seems to be the smallest one. http://bit.ly/148DeJz
    I couldn't find any for a 3.3v motor.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I see it Comes as a Kit so you could modify as needed for the motors.
    Although with a PWM controller the P.S. should be at least 10% higher than motor rated voltage.
    Within reason, the P.S. voltage can be much higher than the motor rated, it is only if you were to apply the higher voltage and overspeed the motor, with PWM, the RPM can be controlled as needed.
    You could modify the Transistor supply to be lower than the required logic supply, possibly, to customize it for the lower motor.
    Max.
     
  5. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Another mod for 3.3 volt motor:
    If the speed pot is connected as a typical voltage divider with one end to gnd, other end to V+, you could add a 10k resistor (value equal to pot value), in series with the pot to limit the pulse width to 50% at max setting (assuming linear operation of the circuit)
     
    Last edited: Aug 17, 2013
  6. james211

    Thread Starter Member

    May 29, 2012
    210
    2
    So if I buy two of those modules from eBay is it safe to say one can be modified to work with the lower voltage motor?
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I would say you should be able to, the logic/control section may need the proper voltage.
    Max.
     
  8. james211

    Thread Starter Member

    May 29, 2012
    210
    2
    Ok, so here is what I bought...definitely over kill but I wanted enough options to make this work. What I'm really looking to do currently is control the speed of a 3.3V motor (34mA-104mA). In addition to the motor, I have a 12V fan that needs to be powered. So my assumption is I would need a power supply that is at least 16-18V is that correct?

    So here's the list:
    12V 60 Watt Digital PWM DC Motor Variable Speed Control Kit ( I bought 2)
    - Here is the link for the build guide - dpwm.pdf

    LM2596 DC-DC Buck Converter Step Down Module Power Supply Output 1.23V-30V

    DROK PWM 12V-40V DC Electric Pump/Motor Speed Controller Stepless 10%-100% 10A

    PWM DC Converter 12V-36V 10A DC Motor Speed Controller Adjuster DC Motor Driver

    In an idea world I would modify the first option that is a kit where I can just change out some of the components. But if I need to use the buck converter thats fine.

    Any dummy help you can offer would be appreciated. Thank you.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I assume you want to control the fan off the same supply?
    It sounds like what you suggest will work, I prefer to put a IC socket in just in case for any reason the IC needs replacing?
    Max.
     
  10. james211

    Thread Starter Member

    May 29, 2012
    210
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    Well the IC is the only piece that comes soldered for me on that kit.

    So how can I mod that dpwm kit to work with a 3.3V motor?
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It would be a good idea to reverse engineer the circuit, at least up to the PIC, there does not seem alot to it.
    The board appears to have a 5v regulator, you may be able to remove it and supply the whole board and motor supply with 5v, the rev's can be controlled so you do not overspeed the motor.
    Max.
     
  12. james211

    Thread Starter Member

    May 29, 2012
    210
    2
    I like where you are going with this, except I have no clue how to go about that. Figuring out the details with resistors, etc is not my specialty.

    Also, I would like to use one power supply that will power the 12V fan, and the 3.3V motor. I do have the buck converter that I purchased and I was able to dial the voltage down from 12V's to 3.3V. So I could probably use that to convert the voltage.
     
    Last edited: Aug 24, 2013
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It is very useful to be able to trace a circuit or reverse engineer, other wise it is a bit of guess work.
    It looks like the circuit takes 5v according to the on board regulator, so If you used the Buck Conv. to bring it down to 5v and feed the board and the motor, as I said, you are not feeding the motor direct with a full 5v, but a mean voltage signal via PWM.
    After the FET device there will not even be 5v peak anyway.
    Max.
     
  14. james211

    Thread Starter Member

    May 29, 2012
    210
    2
    So I'm trying to re-engineer my design to a simpler setup. I've attached a drawing of my current setup.

    What I'd like to do is build a PCB from scratch that has everything contained on one board. I've been looking at sketch software, and its a bit over my head, so I thought I'd start with the overall design, then work with someone ($$) to help me create the eagle file to have a custom PCB made.

    I figure I can take the design from the current PWM controller and incorporate that into the design and use the circuit attached for the voltage conversion. What I don't know is if I need any additional components between the LM7812 and the fan.
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    As long as you remain within the power capability of the 7812, then you should not need anything between that and the fan.
    Max.
     
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