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Arduino and Electric Motor

iseeall

I am new to the site. I have been having a blast with some projects with my arduino.  I do have a question that I am uncertain about.  I would like to control an external electric motor that already has its own power supply, such as a box fan.  I am not an electrical engineer by any means, just a tinkerer.   I would like to control the speed of the fan programatically.  But not sure if I can just interrupt the power flow to it and use something similar to like a dimmer.  Or if I need to use some sort of power regulating relay sheild. 

 

Any suggestions and help are appreciated!  Again, thanks for the great tutorials and I hope to be on the site more!

  • in reply to ntewinkel

    Nico teWinkel wrote:

     

    Thanks Mark!

     

    For the "cannot" line, are you referring to AC motors?

     

    Yes (I've edited the original to be clearer ...thks)

    Mains electric motors (110 or 230vac) cannot be controlled by transistors directly.

     

    There are some devices that use 10v dc to control a mains device.

    This was a common means to safely control stage lighting that wasn't using DMX.

    Some of the new dimmable lighting incorporate 10v control, either you supply the voltage, or connect a pot across the control line.

     

    The PN2222A datasheet I have says its 1A with a gain of anything from 35-75 but drops to 40 at 500mA (and that was pulsed not steady)

    generally the industry uses the same code, so a 2222 from xyz is likely to be the same as from abc.

     

    for your motor control

    The problem you start running into, is the voltage drop across the transistor tends to increase, then the heat increases, and its gain drops.

    The problem is not always the running current, but the start current, so using the car example...

    We have a big enough car, but we can't get moving as we don't have enough throttle and the brakes drag until it gets to speed.

     

    Personally I'd be using the TIP120 as I think your motors will draw more than 700mA.

    You can measure the maximum current by stalling the motor (stop) and seeing how much current it draws (1 or 2 secs ONLY as they get real hot, real quick)

     

     

    I sent you a link to the 300g bot I made ...

    I used the mosfet driver IC's and added the diodes across the outputs (the TIP120 has them, but others don't.)

    This gives a full bridge (ie backwards and forwards) without using a relay and well within the Arduino capabilities.

     

     

    Mark

  • in reply to mcb1

    So with the tip120 there is a chance of me being able to speed control a bigger electric motor that has its own power supply and requires more current than the arduino can supply? 

  • in reply to iseeall

    Jason Brunk wrote:

     

    So with the tip120 there is a chance of me being able to speed control a bigger electric motor that has its own power supply and requires more current than the arduino can supply? 

    Yes BUT we are talking a DC 'electric motor'

     

    Do you know how much current the motor draws (some have the stall current rating, others don't)?

     

    Mark