Looking for informative notes about reduced voltage motor contollers.

Discussion in 'The Projects Forum' started by alphacat, Jun 6, 2009.

  1. alphacat

    Thread Starter Active Member

    Jun 6, 2009
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    Hello.
    I'd like to build a circuit that reduces the voltage supplied to the motor to the minimal voltage it needs in order to drive its load.

    Can anyone refer me please to an application note or anything else that is helpful and will give me something to start off with?

    Thank you.
     
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Try googling for the LM317 datasheet, that is a 3-pin device that gives you a lower voltage very easily. It's good for about 1 amp, if your motor needs more than 1 amp there are larger devices that do a similar job.
     
  3. alphacat

    Thread Starter Active Member

    Jun 6, 2009
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    Thank you very much.
    Do you (maybe) also know about schematics/app. notes that can be found about that?
    I was hoping to build it from scratch.
     
  4. alphacat

    Thread Starter Active Member

    Jun 6, 2009
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    anyone please?
     
  5. THE_RB

    AAC Fanatic!

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    The datasheet shows how to setup the LM317 with just 2 resistors to give a low voltage. If you change one of the resistors to a pot you can adjust the voltage and find the point where the motor starts turning. There's info on that in the datasheet too.
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    What kind of motor is it, and what voltage and current does it need?
     
  7. alphacat

    Thread Starter Active Member

    Jun 6, 2009
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    The RB,
    Thanks.
    I mean if you know of any schematics of this controllers that do not use ICs, but "regular" components?
    I'd like to build it without using ICs.

    BeenThere,
    Its for single phase motors.
    I assume the controller receives the power line voltage (110Vac/220Vac) and the current is what the motor draws from the power line.
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    AC motors require a certain amount of power to start and run. That power is the product of the line voltage times the current draw. If you reduce the starting voltage, the consequence will be increased current. In a very real sense, the motor is already running under the minimum practical voltage conditions.

    If your motor starts under no load conditions, you may get away with some current limiting to hold down starting current, but that can get you into trouble if you load the motor later. Startup surge is very transient, and normally presents no problems with operation.
     
  9. alphacat

    Thread Starter Active Member

    Jun 6, 2009
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    Thank you very much :)

    As far as I know, it is possible to reduce the motor's input voltage during normal operation (not just on start-off) and by that saving true power during all the time the motor works.

    I searched through alot of places in the web but couldnt find even one schematic of such device.
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
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    I was not aware that input voltage to a motor and true power savings were related. When a device wishes to use a certain amount of power, it will do so. As power is the product of voltage and current, reducing one means increasing the other so the product stays the same.

    Let's say your motor runs on 115 VAC and 2 amps, meaning a power consumption of 230 watts. If we reduce the voltage to 90, for the power to remain the same, the current goes up to 2.55 amps. How does this save true power?
     
    Last edited: Jun 8, 2009
  11. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    My apolgies alphacat, I just assumed it was the most common type ie a little DC motor.

    Re an AC motor, some types can be used with a "triac drill speed controller" this will reduce the motor speed and power consumed, generally they work ok with hand tools but won't work on most big motors (like lathes) or fans etc.
     
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