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Re: Newbie to the group with a problem

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    In general a resistor, variable or otherwise, is NOT the way to vary the speed of a motor. Resistors waste energy through heating and with any reasonable size
    Message 1 of 2 , Aug 17, 2004
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      In general a resistor, variable or otherwise, is NOT the way to vary
      the speed of a motor. Resistors waste energy through heating and with
      any reasonable size of motor the resistor gets quite large and
      expensive (and difficult to find). Also the motors tend to stall out
      especially when starting and at low speeds. A better way to vary the
      speed is to use a pulse width circuit, using a power transistor to
      make/break the circuit. This lets you vary the speed of the motor,
      maintains quite a bit of torque and lets the motor start even at low
      speeds. It is also much more efficient. You can make a simple pulse
      width controller from a 7556 or 7555 CMOS timer IC (see the "Files"
      section of this group for a data sheet for this timer IC) or there
      are dedicated motor control ICs available (do a search for motor
      control IC). Kits are also available at:
      http://www.electrokits.com/electronic-kits/motor-control/75.htm

      Regards
      xxxtoytech

      --- In home_electronics@yahoogroups.com, "Jay Stanley"
      <jaystanley@c...> wrote:
      > Greetings all,
      > Hope someone can lend a hand...I have a 12 volt DC motor .9amp this
      > runs from 110v household current to a switching power supply 110-
      12v
      > dc 3.25 amp...I need to put in a variable resisitor to slow the
      motor
      > down when needed (12v runs 44 rpm...9v 30rpm etc)...any ideas on
      > where to find this? I tried calling a company who sold a 12v 4amp
      dc
      > dimmer, but they claimed it would not work with a motor...I don't
      > know why.
      > Peace
      > Jay
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