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Condenser fan motor?

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Robert O'Brien
Robert O'Brien Member Posts: 3,541
in A-C, Heat Pumps & Refrigeration
1075 RPM motor,has 2 speed taps,hi and low. What is the hi and lo RPM?
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  • Ironman
    Ironman Member Posts: 7,376
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    RPM

    Look on the data plate of the motor. The low is usually about 70% of the high. It is actually a horsepower tap more than a speed tap. With no load, the motor would run at the same speed on either tap. With a load attached (the fan), the motor slows down on the lower horsepower tap. This is why you should not increase the horsepower when replacing a multi speed motor.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Techman
    Techman Member Posts: 2,144
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    SPEED

    HI Robert, usually it's 850 rpm w/ 1075 as the hi
  • Eugene_Silberstein
    Eugene_Silberstein Member Posts: 349
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    Right On!

    Lo speed will typically be between 750 and 850 on that motor. When in doubt, use a tachometer on the shaft to measure accurately, as all motors will vary somewhat.

    There was an error rendering this rich post.

  • Robert O'Brien
    Robert O'Brien Member Posts: 3,541
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    Thanks!!

    Long story short,had a job yesterday with a bad condenser fan motor. All I had was a 1075  rescue motor,existing was 1/3 horse 825 RPM. At high speed,the new motor goes into overload fairly quickly. I assumed the fan was overloading the motor at the higher RPM,at set it to low speed with same result. Coil is clean and voltage good out of contactor. 
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  • Techman
    Techman Member Posts: 2,144
    edited July 2011
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    Motor

    Is the rotation  of the motorcorrect and the cond fan blade?What HP is the new motor at 825 rpm?
  • don_9
    don_9 Member Posts: 395
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    Over load

    I dont see how the new motor could go into over load just bc u change the hp.Sound more like a bad run capacitor to me.

    Is this a three or four wire motor?
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,541
    edited July 2011
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    Right

    Right rotation,new cap. Can a fan designed for 825 overload a 1075 motor?
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  • Techman
    Techman Member Posts: 2,144
    edited July 2011
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    RPM

    The new 1075 rpm motor is still running at 1075 rpm even on the lower hp tap,so the fan blade will overload the new motor.  Plus the cap size changes 208v vs. 230v You need the Rescue motor #5464 @ 825rpm
  • Techman
    Techman Member Posts: 2,144
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    Rescue motors

    How does one motor do it all? At pretty much the same speed [  hi 3/4 hp = 1110 rpm ,lo 1/5 hp=  1140 rpm ] Why not just use a 3/4 hp in all lower hp applications ?
  • Techman
    Techman Member Posts: 2,144
    edited July 2011
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    Inverse Porportionality

    is the words the Emerson Motor Engineer used to describe what would happen to a 3/4 hp motor used in a 1/5 or 1/4 hp application.My motor repair shop guy said "The damn thing will overheat on you " The Rescue  condensor motor line has a "special" winding w/ two taps ,both @ 1075rpm ,but different HP's
  • sasman
    sasman Member Posts: 32
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    just a little read

    from Fasco Motor Facts



    FACT Modern multi-speed motors are really not multi-speed,

    but multi-horsepower. The speeds are simply taps at different

    points in the coil. The higher speeds are tapped at a point with

    fewer turns as compared to where the subsequent speeds are

    tapped in the same coil. The more turns that are wound before a

    tap is brought out, the lower the horsepower will be each time.

    Obviously, the lowest speed lead is connected to the end of the

    last turn on the coil. These added turns weaken the motor. This

    field weakening allows the load to slow the motor down each

    time a slower speed is selected. With no load mounted on the

    shaft, as with a bench test, no difference between speeds will be

    seen. If too strong a replacement motor is used on a unit, there

    may be no appreciable difference when the speed is changed in

    the unit. Remember, the motor relies on the load to slow it down

    between the speeds. As an example, if a 1/2 HP three speed

    motor is used instead of a 1/4 HP three speed, there might not be

    any noticeable difference between Hi, Med, and Low.

    NOTE: A motor nameplate showing 1350 RPM is a special design

    and must be replaced with an OEM direct replacement. This is a

    high slip 4 pole motor, which is not generally available in a general

    line of motors. If one is available, it would be marketed as an OEM

    direct replacement motor for a specific piece of equipment. These

    motors are specially designed for a very specific load.
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,541
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    The correct motor

    solved the issue,the 1075 was pulling over 5 amps at low speed,the motor is rated at 2.1 amps. I didn't realize a prop fan could be that different?
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  • Robert O'Brien
    Robert O'Brien Member Posts: 3,541
    Options
    The correct motor

    solved the issue,the 1075 was pulling over 5 amps at low speed,the motor is rated at 2.1 amps. I didn't realize a prop fan could be that different?
    To learn more about this professional, click here to visit their ad in Find A Contractor.
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