Drawing power from an AC Unit

Discussion in 'The Projects Forum' started by Lucyfur1, Jul 16, 2015.

  1. Lucyfur1

    Thread Starter New Member

    Jul 16, 2015
    Hello all!

    I am building a project with an AC/Heater Unit and a PMDC motor. I have 208 VAC going into the AC/Heater Unit and the motor is rated at 130VDC.

    Right now, they (AC and motor) are separate from each other. I salvaged the motors from old treadmills and plan to use them to move conveyor belts, so they won't require a lot of power. I measured the slowest, smoothest speed the motor will rotate at is with 1.2 V and .3 amps, which is 3.6 Watts (I used a power supply unit directly connected to the motor's + and - terminals).

    Now, I am assuming I will need to build an AC->DC converter circuit that will then feed into a PWM circuit to control the speed of the motor. Note: there will be a step down transformer before the converter circuit.

    So my question is this, because this is my first time doing a big project like this: can I "feed" off of the voltage going into the AC Unit to supply the motors since they won't require much power or is this a big no-no? I would assume that I could run +, - and ground lines from the AC unit to the transformer, etc.

    I appreciate any help!! I've included a beautiful picture of what I have in mind, in case my description wasn't clear. Thanks!!
  2. #12


    Nov 30, 2010
    Your picture shows that you are not feeding off the AC unit. You are feeding off the wall outlet. You are only imagining a problem which does not exist.
  3. MaxHeadRoom


    Jul 18, 2013
    If you check out the KB DC motor controller site, you will find many SCR and PWM controllers for these motors that run directly off of the mains input, both 120/240.
    The SCR type is just a controlled bridge, no Caps, the PWM require a capacitor smoothed PS.
    The above units come included with each.
  4. Lucyfur1

    Thread Starter New Member

    Jul 16, 2015
    You are completely right! Silly me....connecting the AC->DC converter to the AC unit power supply would just be the same as connecting to the wall. I am just worried about blowing something up, I don't want to damage the AC unit.

    Wow, thanks a bunch!