voltage or current divider?

Discussion in 'General Electronics Chat' started by ale2121, May 28, 2009.

  1. ale2121

    Thread Starter Active Member

    Mar 20, 2009
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    I've got a motor that i bought from electronics goldmine. it was rated at 9v DC, not sure what the current is. here's the info:

    Tiny pager motor made for Motorola Products - This tiny pager motor body is only .44" L x .18" Dia. It has a weight attached to its shaft. These make great motion generators to cause movement in tiny robots, and are also useful in making silent alert alarms, timers etc. Has 2 flexible terminals for power connection. Will operate from 1VDC up to 9VDC. Resistance of the motor is 10 ohms. This pager motor has a black rubberized boot that can be removed to reduce its size even further. It is one of the smallest and best quality pager motors we have ever offered.
    G13566

    When i hook it up to a 9v battery it burns up and stops working in less than a minute. So, my question is, am i giving it too much voltage or too much current? and would a voltage or current divider work to fix this problem?
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    If it is rated at 9V and you supply it with 9V it will draw as much current as needed to work safely unless it stalls and draws much more current. In this case it will overheat and burn.

    Is there a link which can provide more information about the motor?
     
  3. ale2121

    Thread Starter Active Member

    Mar 20, 2009
    71
    0
    here's the link, but there isn't any more information available.

    http://www.goldmine-elec-products.com/prodinfo.asp?number=G13566

    there is no load on this motor, i just want it to vibrate. I believe i measured the current flowing through it at about 300 mA. i hooked it up to 6v (coin cell batteries) and it ran much slower, did not overheat, however, when i measured the current, it dropped, and the motor kept slowing down, perhaps i already burned it out? I've got more, but this is the 3rd one I've destroyed.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    Pagers don't generally have 9 volts present. That may have been a misprint. 3 - 4 volts is more like it.
     
  5. ale2121

    Thread Starter Active Member

    Mar 20, 2009
    71
    0
    that was my guess. the strange thing was I bought a bunch for a project thinking great they will shake even more! ugh.

    so can i use a voltage divider?
     
  6. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Better to use a voltage regulator.
     
  7. ale2121

    Thread Starter Active Member

    Mar 20, 2009
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    oh wait! but i also wanted to add an LED in there... it will take care of some of the voltage right? and, if i use a voltage divider anyway, as opposed to a voltage regulator, will it still work?
     
  8. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    I agree with Mik3 that a voltage regulator is the way to go.

    hgmjr
     
  9. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    A voltage divider will give you a specific voltage at a specific drawn current. Also, power will be wasted as heat on the resistors.

    Are you planning you put a LED in series with the motor?

    If yes, forget it. A typical LED draws about 20mA to work properly. The motor needs much more and it will burn the LED. Put the LED in parallel with the motor via a current limiting resistor.
     
  10. ale2121

    Thread Starter Active Member

    Mar 20, 2009
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    but the LED won't help reduce the voltage going to the motor then?
     
  11. beenthere

    Retired Moderator

    Apr 20, 2004
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    Not usefully. It will drop some voltage before it conducts, but some current limiting device will be necessary if the motor current can go over 10 - 20 ma. Put in a resistor to save the LED and the motor may not do much.
     
  12. radiohead

    Active Member

    May 28, 2009
    474
    31
    With the motor in the first entry, you have the voltage, you have the resistance. Now use ohm's law to figure out the current. There is an excellent ohm's law example that includes P (power in watts) in the tips and tricks thread (post #8). If your circuit is small, you can breadboard it and record your voltage and resistance measurements to verify your math.
     
    Last edited: May 29, 2009
  13. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    The LED will act like a low current fuse, with extra special effects. In addition to light, you might get smoke, and possibly flame! You are thinking of a high wattage zener, which is a close cousin of a voltage regulator. PWM is much better for motors though.
     
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