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uday_pr
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Motor Efficiency

07/21/2019 2:27 AM

What is the meaning of motor efficiency and how to use it in different formula for doing some calculations

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7anoter4
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#1

Re: Motor Efficiency

07/21/2019 9:19 AM

I'll try to explain this in a very simple way.

If you calculate the incoming [ active] power - or measure it by a wattmeter, you'll get always more than the power measured –or calculated at the outgoing shaft. The difference are the losses-electrical [resistance heating and magnetic losses] ,mechanical [friction and ventilation] and other. Then, the ratio of ouput power to intput power is called efficiency. For a shaft [load] power different than rated the efficiency is different[usually less].

You may use it in order to calculate the rated current -for instance: Irated=Prated/Vrated/cos(fi)/efficiency.

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JRaef
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#2

Re: Motor Efficiency

07/21/2019 10:25 AM

Good answer. Shorter version is that motor efficiency is the difference between the energy involved in the work that the motor does and the losses ensued in making it into a motor instead of just a mass of dissimilar metals.

I once had a student ask me if there was any way that a motor can be 100% efficient, and I answered yes, when it is turned off! It’s not doing any work, but there are no losses involved in that process.

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PWSlack
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#3

Re: Motor Efficiency

07/22/2019 3:53 AM

<...motor efficiency...> is the shaft output power at any instant divided by the electrical input power at the same instant, which will always be less than 100% in this universe.

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67model
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#4

Re: Motor Efficiency

07/22/2019 8:37 AM

Formulae are useful, but only as good as the ingoing data. Motor efficiency varies much with type, supply voltage/frequency, rating, shaft speed and actual loading.

The following will help as typical for usual industrial AC motors.....

http://www.brookcrompton.com/upload/20113E_W_Cast%20Iron_issue3.pdf

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gutmonarch
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#5

Re: Motor Efficiency

07/22/2019 12:57 PM

It's how much you enjoy the ride with the money it cost you to get the ride. Yeah, if its a big bike, yeah like that.
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