How to power 3 - 440V motor with 3 - 480V - Page 2
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  1. #21
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    Quote Originally Posted by iuctx View Post
    D'oh!

    What would be the proper way to lower the voltage to 440?

    Sent from my Pixel 2 XL using Tapatalk
    That chart just helped me understand why the induction motors in the shop I work at all draw less current when the line voltage drops. All of the motors are "dual rated" 208-230 so the actual lowest FLA is somewhere in between that.

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    Quote Originally Posted by Strostkovy View Post
    That chart just helped me understand why the induction motors in the shop I work at all draw less current when the line voltage drops. All of the motors are "dual rated" 208-230 so the actual lowest FLA is somewhere in between that.
    induction motors have an optimal voltage for every load. in addition to this, single phase capacitor run motors have both an optimum voltage and an optimum capacitance for every load.


    a very simple circuit that would pay for itself rather quickly is simply a current transformer, relay and a transformer. when the line current is low the transformer is engaged and you feed your refrigerator 90 volts instead of 120. when the current is high the relay trips and runs the compressor from 120. the hysteresis of the relay prevents chatter. (someone patented this in the 70's but it never took off)

    as you might know small induction motors are horribly inefficient. for example i have a 1/2 hp 8 pole induction motor that isn't efficient enough to re-generate power back to the grid. a typical 1 hp motor might be 300 watts no load losses and 70% efficient at full load, and if you were to backdrive it you would burn it up before you shoved 1 hp back into the grid, because you would have to push 1.5hp into the rotor to shove 1hp back into the grid. -much of this is simply that there are practical limits for how small the air gap can get.

    contrast that to a 5 hp 3 phase motor i have that has a 12.7 amp fla rating. (many are 14 amps for that size motor) i measured its no load losses on single phase at about 300 watts at 240v but only 250 watts at 230volts dropping to 200 watts at 200 volts perhaps. that drastic reduction is entirely the copper losses dropping as the wasted amp turns needed to magnetize the air gap dissappear as the volts drop. but that 200-300 watts is still less than a typical 1 hp single phase motor if you can believe it.

    at no load its optimal voltage is 20 vac single phase, cant remember the amps. at 16 vac single phase it draws 3 amps, and 44 watts.

  3. #23
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    Okay, so rather than bothering with bucking transformers, do this:

    --Plug it in, and go.

    IF you want 'room to grow', then just acquire a VFD, and place it immediately upstream of the motor, and immediately downstream of a power contactor. Remove the cooling fan from the drills' motor, and install a constant-speed cooling fan, wire the drill's controls to the VFD, put a foot-pedal on the floor (for foot-control, right?) and tell the VFD that it's a 440v motor.

    The VFD will handle the rest... and you'll get variable speed, dynamic braking, and low inrush current.

  4. #24
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    Quote Originally Posted by DaveKamp View Post
    IF you want 'room to grow', then just acquire a VFD, and place it immediately upstream of the motor, and immediately downstream of a power contactor. Remove the cooling fan from the drills' motor, and install a constant-speed cooling fan, wire the drill's controls to the VFD, put a foot-pedal on the floor (for foot-control, right?) and tell the VFD that it's a 440v motor.

    The VFD will handle the rest... and you'll get variable speed, dynamic braking, and low inrush current.
    I have yet to research VFDs. First off, what size VFD would I need for a 440V two speed motor that draws 2.8A on the high speed?

    thx

  5. #25
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    Look at the nameplate.
    It will say HP or kW somewhere.

    I very much feel sorry about posters using amps with anything regarding power tools.
    kW is power needed, and everything flows from that.

    kv/rpm is how many volts you need for a drive at x rpm, and the amps are the power it can use, max.

    At 3 amps 440V == 1.2 kW x nn probably around 1.5 kW power.
    The 3-phase fudge factor is around 1.3

    Quote Originally Posted by iuctx View Post
    I have yet to research VFDs. First off, what size VFD would I need for a 440V two speed motor that draws 2.8A on the high speed?

    thx

  6. #26
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    Quote Originally Posted by hanermo View Post
    Look at the nameplate.
    It will say HP or kW somewhere.

    I very much feel sorry about posters using amps with anything regarding power tools.
    kW is power needed, and everything flows from that.

    kv/rpm is how many volts you need for a drive at x rpm, and the amps are the power it can use, max.

    At 3 amps 440V == 1.2 kW x nn probably around 1.5 kW power.
    The 3-phase fudge factor is around 1.3
    Very close! See attached. Sorry, I should have asked the question based on P rather that I and E. img_20190212_104659.jpg


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