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  1. #1
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    Default 240v electric motor

    This motor was off the bench saw project which i scrap. $20

    Resize of IMG_6592.jpgResize of IMG_6591.jpg

  2. #2
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    I’ll take it, subject to HP and pick up location.
    Cheers.
    …..Live a Quiet Life & Work with your Hands

  3. #3
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    Quote Originally Posted by DSEL74 View Post
    I’ll take it, subject to HP and pick up location.
    Cheers.
    Pick up north croydon, as for hp will need to have a look at it tomorrow.

  4. #4
    BobL is offline Member: Blue and white apron brigade
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    5A @ 240V = 1200W -20% for efficiencies = 1080W = ~1.5HP

  5. #5
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    Bob, I would be surprised if the motor shown is more than 1HP. I think your assumption of 20% losses for inefficiencies is being rather conservative, given the class of motor and the fact that it is four pole. On the practical side I have a similar CP 1.5HP motor which is rated at 7.1 amps. I would expect a similar four pole motor to draw 7.5 to 8 amps.

    Chas.

  6. #6
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Chas View Post
    Bob, I would be surprised if the motor shown is more than 1HP. I think your assumption of 20% losses for inefficiencies is being rather conservative, given the class of motor and the fact that it is four pole. On the practical side I have a similar CP 1.5HP motor which is rated at 7.1 amps. I would expect a similar four pole motor to draw 7.5 to 8 amps.

    Chas.
    You are right my calc above is wrong
    It should be 5A @ 240V = 1200W -20% for efficiencies = 960W = ~1.29 HP

    Working backwards from your motor 240V @7.1A = 1.7kW = 2.28HP rated at 1.5HP = 65% efficient which is on the low side, more like a low class 1/2 HP motor. I've measured the actual HP and efficiencies of a few 4 pole motors (including some relatively elderly ones) around the 1kW output level at the rated current and never seen one with that low an efficiency.

    The usual efficiency I measure is around 80% which is consistent with this chart.
    Screen Shot 2018-09-03 at 8.07.40 pm.png

    My experience is that HP output ratings printed on motors are fairly nominal - and on small motors often stated to the nearest and higher 1/2 HP. interestingly none of the cheap chinese motors I have measured have output less than their stated HP.

  7. #7
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    Quote Originally Posted by BobL View Post

    Working backwards from your motor 240V @7.1A = 1.7kW = 2.28HP rated at 1.5HP = 65% efficient which is on the low side, more like a low class 1/2 HP motor. I've measured the actual HP and efficiencies of a few 4 pole motors (including some relatively elderly ones) around the 1kW output level at the rated current and never seen one with that low an efficiency.


    Bob
    Are you comparing 3 phase motors to the OP's single phase unit?
    John

  8. #8
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by GuzziJohn View Post
    Bob
    Are you comparing 3 phase motors to the OP's single phase unit?
    John
    Good point.
    I have only tested 2 newish (chinese) SP nominally 2HP 4 pole motors.
    I didn't record their class but they drew 7.5A to generate 2HP and this makes them 80% efficient.
    An older motor like that in the OP could easily be 65% efficient.

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