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Question about using a micro-motor and voltages

Discussion in 'Sensors and Actuators' started by NickGuy, Oct 2, 2012.

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  1. NickGuy

    NickGuy

    4
    0
    Oct 2, 2012
    So I'm building a small device that will be powered by a 8.4v power source.

    The problem is I want to add in a micro-vibrating motor but the motor I want to use runs off of 0.9v -1.6V. And I would like to run the motor slow. I believe the motor runs at 65ma typically.

    Here is the motor I will be using:
    http://www.elept.com/4mm-x-8mm-vibration-pager-vibrating-vibrator-motor_p2532.html

    Space is extremely limited so I can only use a single resister or diode to drop the voltage/current.

    I would appreciate any help that anyone could give me on this matter.
     
  2. GreenGiant

    GreenGiant

    842
    6
    Feb 9, 2012
    depending on the final voltage that you want I would say use one of the 1N4000 series diodes (1N4007 is a good one)
     
  3. NickGuy

    NickGuy

    4
    0
    Oct 2, 2012
    Well I would need about 6-7 of those in series in order to drop the voltage enough right? (at 1.1v drop)
     
  4. GreenGiant

    GreenGiant

    842
    6
    Feb 9, 2012
    nope, you use its forward voltage (1V)
     
  5. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Actually more than that. At 60ma the forward voltage is only about 0.7V, so more like 9 or 10 to drop the voltage to 1.6. A single resistor of about 120 Ohms, 1 Watt should work.

    Bob
     
  6. NickGuy

    NickGuy

    4
    0
    Oct 2, 2012
    That definitely sounds more like it, but I can't fit that many diodes in the space I have to work with...

    So would just a resister work?

    At my desired running speed the motor would run at: 35ma/0.8v which would be 28mW.

    Could I put a ~2500ohm resister in series with the motor so that the total power getting to the motor would be 28mW?

    Or would the voltage still be high when it got to the motor and screw things up?
     
  7. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    If you want 35ma at 0.8V, all the rest of the voltage goes to the drop in the resistor. Use Ohm's law:

    E = I R

    (8.4-0.8) = 0.035 R

    217 = R

    So probably start with a 220 Ohm resistor.

    Then calculate the power requirement for the resistor:

    P = V I = (8.4-0.8) * 0.035 = 0.266 Watts. So a 1/2 Watt resistor will give you a good safety margin.

    Bob
     
  8. NickGuy

    NickGuy

    4
    0
    Oct 2, 2012
    Well I did that calculation earlier but for some reason I was thinking that would give me 35ma at 8.4v.

    Thanks for your help Bob!
     
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