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thingmaker3

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Posts posted by thingmaker3

  1. While an SCR-type light-dimmer or a rheostat might work fine & dandy on a "universal" motor, they don't do so good with an "induction" (aka "squirrel cage") motor. With an induction motor, there will be a fairly big range where the motor just sits there and gets hot. It is not good for motors to just sit there and get hot.

    Speed controllers for induction motors are quite complicated, and therefore expensive.

    Note also: some motors are "self-cooled" and must be run at full speed to avoid over-heating.

  2. Thanks, Gaylan.
    I'm still surprised that no one has asked why I use scroll jigs that can make a C-scroll that will touch.
    Hey, Brian... why do you use scroll jigs that can make a C-scroll that will touch? I remember these jigs from the Tips & Tricks thread, but the "why" part is indeed an interesting question.
  3. I have a question concerning this chart. Doesn't amperage also vary with efficiency? So could an electric motor produce more power ( in the form of HP) with less amps if the motor is more efficient since amperage is how much the motor is drawing?
    "Horsepower" and "watts" are both measures of "power." "Power" is the rate at which energy is converted from one form to another. Electric motors will be anywhere from 20% efficient to 60% efficient, so 746 watts of electricity might get converted to a fifth hp or more than a half hp. (746 watts = 1 hp). Any electrical energy which does not get converted into mechanical energy gets converted into waste heat, waste noise, waste electromagnetism, and such.

    The chart from Richter and Schwan's book is a good rule of thumb.
    When shopping for anything that uses a motor should you base how strong the motor is based off of amp's? For instance I know that 230 is more efficient than 115, but uses half the amperage.
    Power (in watts) is equal to voltage (in volts) multiplied by current (in amperes). 230 V is not actually "more efficient" than 115 V, but it does let us use smaller wires because we use half the current for the same power. Smaler wires means less weight and less cost.

    And just to remind us how complicated life can get, any electric motor will draw more current when it bogs down. The "stall current" is the high current drawn by the motor when the shaft is unable to turn - this is used to calculate the artificially inflated "max hp" rating.

    -Lee Cordochorea, IBEW Local 48
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