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Mohamed Akram Khan
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Induction Motor No-Load Current

11/14/2012 3:36 AM

Apart from getting the data from the motor manufacturer or from actual measurement, is there a way to calculate the motor no-load current of an induction motor?
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PWSlack
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#1

Re: Induction Motor No-Load Current

11/14/2012 3:41 AM

As it's just a phone call, why bother <rhetorical question>?

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Joshi
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#2

Re: Induction Motor No-Load Current

11/14/2012 4:21 AM

Yes.
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PWSlack
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#7
In reply to #2

Re: Induction Motor No-Load Current

11/14/2012 8:49 AM

Indeed there is. Supply voltage minus motor back-EMF all divided by winding resistance springs to mind. The challenge is to measure the back-EMF...

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user-deleted-1105
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#3

Re: Induction Motor No-Load Current

11/14/2012 4:39 AM

If you really want a meaningful figure then measure it or contact the manufacturer.
You can do reams and reams of calculation which will probably bear no relation to reality.
I just don't understand why some people would rather believe pages of calculation rather than actual measurement.

I had a rep in the other day who was trying to estimate the torque I needed on my pump by working backwards from the torque provided by an overengineered motor gearbox fitted by someone else. The result was over 50% out.
It took me 15 minutes to screw a bar onto the pump rotor, add weights until it turned and come up with a real world result.
What is calculated and written on paper doesn't necessarilly effect reality.
Del

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PWSlack
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#4
In reply to #3

Re: Induction Motor No-Load Current

11/14/2012 4:49 AM

Absolutely amazing, isn't it?

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lyn
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#5

Re: Induction Motor No-Load Current

11/14/2012 7:39 AM

Certain types of people seem to think that there should be formulas and calculations for everything.

Electric motors is a fine example of this mindset.
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Codemaster
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#6

Re: Induction Motor No-Load Current

11/14/2012 8:30 AM

Not sure whether you'd call it a calculation, but I think it's about 20 - 25% FLC. (that's from memory, somebody might say it's wrong %). No-load current is higher than you might expect as the power factor is much lower on no load.

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Yuri B.
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#8
In reply to #6

Re: Induction Motor No-Load Current

11/14/2012 11:44 AM

I would put it 8-80% of the FLC, depending on an induction motor type, size, etc.
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JRaef
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#9

Re: Induction Motor No-Load Current

11/14/2012 11:54 AM

What I find interesting is that this question comes up quite a bit in this and other forums I frequent. I keep wondering why people seem to think this data is remotely important to know in advance (as opposed to measuring it after the fact). I see no value in it as advanced data, only empirical data, i.e. to know if a shaft or belt is broken maybe.

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lyn
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#10
In reply to #9

Re: Induction Motor No-Load Current

11/14/2012 12:06 PM

We are dealing with the mindset that everything in the world can be put into a formula and calculated, regardless of the real world practicality of the calculations.

In that world, logic does not apply.
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user-deleted-1105
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#11
In reply to #10

Re: Induction Motor No-Load Current

11/14/2012 1:10 PM

Yup, I'd love to know if that sort of mind simply stalls when confronted by a boomerang.
Mind if it whacks 'em on the head it will certainly stall.
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SHOCKISCAN
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#12

Re: Induction Motor No-Load Current

11/15/2012 8:57 AM

http://www.engineeringtoolbox.com/electrical-motor-calculator-d_832.html
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msamad
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#13

Re: Induction Motor No-Load Current

11/15/2012 5:52 PM

Here is some information:

No Load current: 1/3 of full load (Thumb rule), generally between 20% and 40%
No Load Power: Almost 8% of the Motor Capacity
No Load Power Factor: 0.2 - 0.3

Locked rotor current: 4 - 6 times of full load current
Locked rotor Power Factor: 0.2 - 0.4

-MS

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Mohamed Akram Khan
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#14
In reply to #13

Re: Induction Motor No-Load Current

11/16/2012 12:20 AM

Thanks for your answer.
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user-deleted-1105
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#15
In reply to #13

Re: Induction Motor No-Load Current

11/16/2012 3:02 AM

I find the concept of 'No Load Power' a tad confusing...
A bit like those supermarket special offers you see when there's no product on the shelf.
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Codemaster
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#16
In reply to #15

Re: Induction Motor No-Load Current

11/16/2012 7:21 AM

No-load power is the power drawn from the mains. Obviously the output shaft power is zero at no load. Can't see anything confusing.

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Users who posted comments:

Codemaster (2); Joshi (1); JRaef (1); lyn (2); Mohamed Akram Khan (1); msamad (1); PWSlack (3); SHOCKISCAN (1); user-deleted-1105 (3); Yuri B. (1)

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