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sharath4
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India - Member - Proud to be INDIAN Engineering Fields - Power Engineering - New Member

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Location: Bengaluru, India
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How to Calculate back EMF of a Motor?

03/02/2012 7:26 AM

How to calculate back emf of a 8 pole 7500 RPM 55Volts 0.25Nm 1.2Amps, single layer winding, 50 turns with 5 parallel paths BLDC motor?

Thanks

Sharath

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Horrible Old Bat
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#1

Re: how to calculate back emf of a motor?

03/02/2012 7:48 AM

Well, correct me if I'm wrong, but doesn't it depend on how much mechanical load is on the motor at any instant, and hence how much slower than 7500rpm it's spinning? Not a sausage on that. If so, then one of the ways of doing it is to measure the current at load, measure the current at no load, measure the resistance across the terminals when the motor is stopped, and bung the numbers through some algebra based upon Ohm's Law.

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sharath4
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India - Member - Proud to be INDIAN Engineering Fields - Power Engineering - New Member

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Location: Bengaluru, India
Posts: 91
#2
In reply to #1

Re: how to calculate back emf of a motor?

03/03/2012 12:33 AM

Yes, it doesn't depend on mech. load, i have just mentioned if somebody asks about the load. Lets take 7500 rpm at no load.

You are telling me to measure current and resistance, even i can measure back emf directly by mounting the motor shaft to some rotating part and running at 7500 rpm.

But i want to calculate rather than measuring, i wish to measure and clarify after i know it!!!

Hope i am correct

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