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Thread: a horse a horse is a horse of course of course

  1. #1

    a horse a horse is a horse of course of course

    Over the years people have told me 3 HP is 3HP.

    Ive said my SCM 3 HP is stronger the past General Leeson motored (1981 new) 3 HP planer. I had a few questions to a compressor guy about compressors and below was his answer as I said im not sure i see a 5HP compressor on a rotophase compared to single phase as its a machine that cycles on and off rather than machines you run constant.

    There can be other things going on I know like flywheels etc in the planer but the feed rate is faster and it just had more power even with that.




    Response: I personally would recommend 3 phase power for compressors over 3 HP as a 3 phase motor has a much higher starting and running torque which reduces load on the motor in the long term. Newer single phase motors are not made to the same quality as they did a few generations back and are prone to capacitor failures on frequent start/stop situations.

  2. #2
    Join Date
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    "...a 3 phase motor has a much higher starting and running torque....". That is very true - even on a RPC setup. Always two phases powered when the third coils goes to zero. The coils on the 1ph motor are always hotter and for longer.

    That being said, a one man shop is not damaging a 2021 Quincy Baldor equipped 3hp 1ph compressor no matter what he believes about the quality of todays quality motors. Baldor, WEG, Champion, Leeson - you are not wrecking them in a hobby shop. Their lack of quality is still way outside the failure rate of a one man shop. They can run 24X7 and you cannot. I'd question the pump on a cheaper compressor before one with a quality 1ph motor.
    Glad its my shop I am responsible for - I only have to make me happy.

  3. #3
    not a hobby guy and my 5 HP was likely worked harder than most shops As far as 24/7 its how much they run in whatever time period. If your compressor runs more than 40 percent of your work time you need a larger one. Sandblasting, Dynabrades take big air, I overworked it tons, motor is still fine. Bearings not so.
    Last edited by Warren Lake; 03-02-2021 at 5:56 PM.

  4. #4
    Join Date
    Aug 2017
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    Arlington, TX
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    401
    If you have 3 phase line power to the shop (not a phase converter or VFD) then yes a three phase motor is more reliable than a single phase motor (centrifugal switch, start/run capacitor(s), etc.)

    But if you have to add a phase converter or VFD to create your own 3 phase power, then you have to factor in the reliability of that along with the reliability of the three phase motor, compared to a good quality single phase motor.

    Another thing to think about, though perhaps not that important in woodworking, is the additional vibration created by the torque ripple in a single phase motor. A three phase motor has no torque ripple, and torque is constant (at a given motor speed and load).

    -- Andy - Arlington TX

  5. #5
    Join Date
    Jan 2008
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    4,139
    Quote Originally Posted by Mike Heidrick View Post
    "...a 3 phase motor has a much higher starting and running torque....". That is very true - even on a RPC setup. Always two phases powered when the third coils goes to zero. The coils on the 1ph motor are always hotter and for longer.

    That being said, a one man shop is not damaging a 2021 Quincy Baldor equipped 3hp 1ph compressor no matter what he believes about the quality of todays quality motors. Baldor, WEG, Champion, Leeson - you are not wrecking them in a hobby shop. Their lack of quality is still way outside the failure rate of a one man shop. They can run 24X7 and you cannot. I'd question the pump on a cheaper compressor before one with a quality 1ph motor.
    Hadn't thought about why, but had noticed in a few ag situations. The three phase stuff always had more startup torque, makes sense now.

  6. #6
    Quote Originally Posted by Warren Lake View Post
    not a hobby guy and my 5 HP was likely worked harder than most shops As far as 24/7 its how much they run in whatever time period. If your compressor runs more than 40 percent of your work time you need a larger one. Sandblasting, Dynabrades take big air, I overworked it tons, motor is still fine. Bearings not so.
    I've run 75 to 150hp air compressors fully loaded for weeks on end in a 24/7 operation. They did fine. ...Drying all that air got to be problematic, but that's another tale.

    One often overlooked spec for a motor is the service factor ("SF" on the data plate). For a high-cycle, recip air compressor, I'd look for a 1.25 or maybe even a 1.5 SF rating. Especially if in a pro environment. If the motor is for a centrifugal pump on you pool, SF=1 is probably plenty.

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