What is used to measure

Discussion in 'General Electronics Chat' started by bwd111, Aug 23, 2013.

  1. bwd111

    Thread Starter Member

    Jul 24, 2013
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    the true power of a motor? well when power is applied to motor Is it a wattmeter or voltmeter. I want to get the true reading of power
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Traditionally a Dynomometer is used to measure Power (HP).
    Max.
     
  3. bwd111

    Thread Starter Member

    Jul 24, 2013
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    What about a wattmeter?
     
  4. wayneh

    Expert

    Sep 9, 2010
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    The wattmeter determines input. The dynamometer determines output. They will not be the same. :(

    Note that the load is important, since the motor performance will vary with the load. "Power" is not an abstract, one point measurement.
     
  5. bwd111

    Thread Starter Member

    Jul 24, 2013
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    We dont have dynamoteter here. All we have is a ammeter,wattmeter or voltmeter in the shop so what other meter would be close to get the true power. A wattmeter is a device that is used for measuring electrical power. They measure in terms of watts. This can tell you if an electrical device is working properly
     
  6. wayneh

    Expert

    Sep 9, 2010
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    I guess it comes down to what the OP means by "true power". It could mean annual electricity cost or it might mean instantaneous, peak transient.
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    A wattmeter CANNOT measure the mechanical output of a motor.

    None of the things you mentioned can measure the mechanical output power of a motor. You either have to get a dynamometer or go without the measurement.

    If you couple the motor to a generator, then accounting for another set of losses you'll have an idea of the power output for a given load. Not a very complete picture, but better than nothing.

    PS -- why are you asking such questions without the equipment or the budget to get the answer?
     
  8. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Actually, if pushed to measure the output of a motor in some remote corner of the earth, I might consider Joule's orignal method.
    Connect the motor to drive a paddle inserted in an insulated drum of water and measure the temperature rise for a given measured electrical input.
     
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  9. bwd111

    Thread Starter Member

    Jul 24, 2013
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    Why not? Its not the extensive of a test that warrents such equipment to buy. I did not vote for obama so with watching spending you use what you have. And those were the choices we have to use. But I will pass your thoughts on to management and will see what happens. Thanks
     
  10. wayneh

    Expert

    Sep 9, 2010
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    It makes as much sense as "measuring" the swimming speed of Michael Phelps by looking at the plate of food he eats. Electrical power in does not give you the shaft-work power output.

    As I mentioned above, the answer to your question depends on your definition of "true power". If management wants to know what the motor consumes, a wattmeter is a good device to start with. If they want to know how much water it will pump in an hour, that's something quite different. If they want to know how big the mounting platform needs to be, that's another issue (more torque related).
     
  11. Papabravo

    Expert

    Feb 24, 2006
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    Proper names are supposed to be capitalized. I don't care who you voted for and neither does the motor. You still can't use what you have to measure the power output of the motor. So quit your whining. You either spend the money or go without the measurement -- which one hurts worse?
     
  12. Shagas

    Active Member

    May 13, 2013
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    A good motor will usually have its efficiency published in the datasheet .
    Would it be reliable to measure the Electrical power input using a wattmeter and to multiply it by the efficiency to get an ouput power reading?

    I guess the question is ... How accurate of a reading do you really need?

    A good datasheet will have an rpm/load versus efficiency curve
     
  13. bwd111

    Thread Starter Member

    Jul 24, 2013
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    Temp + prssure as in superheat and subcooling. Man I sure asked a hard question my bad soory to make everyone think so hard for a friday. Theres 5 min I wont get back
     
  14. bwd111

    Thread Starter Member

    Jul 24, 2013
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    Datasheet is not readable and no manufacture either. Its like following a wiring diagram with no schematics. Also need to find the cfm and think this is the right calc cfm2=rpm2 x cfm1/rpm1
     
    Last edited: Aug 23, 2013
  15. studiot

    AAC Fanatic!

    Nov 9, 2007
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    What on earth does this mean?
     
  16. bwd111

    Thread Starter Member

    Jul 24, 2013
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    This hurts worse Obama cant do it obama with no caps I feel better and the wattmeter worked for what we needed.
     
  17. bwd111

    Thread Starter Member

    Jul 24, 2013
    117
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    That was a little hvac terminology I thought I would throw in. Pressure/temp relation. Where pressure = temp and temp=pressure
     
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