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How much energy did you say you could save?

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Posted 19 August 2004 - 06:19 AM

Hi folks,

We have just completed an independant & detailed evaluation of one of the leading energy saver products and would like to present our findings to you.

- At 0% motor loading, a saving of less than 18% was achieved.

- At 25% motor loading, a saving of less than 3% was achieved.

- At 50% motor loading, a saving of less than 1% was achieved.

- At 75% motor loading, there was no energy saving to speak of.

- At 100% motor loading there was no energy saving, as you would expect.

As the above-mentioned results were achieved with a very small and inherently inefficient motor, we would expect savings potential to reduce as one moves up the kW spectrum ie where motors are generally far more efficient.

Note: The above results have not been posted in an attempt to dispute any claims made by manufacturers of this type of equipment and/or information presented by others who may have conducted similar performance appraisals. They have simply been posted to highlight that the overall performance one can expect from such devices is very much subject to variables (eg. motor design, efficiency, kW rating, number of poles & shaft loading) that are outside of our (and the product manufacturers) control. Identification of suitable applications prior to purchase is therefore strongly reccommended.


#2 marke


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Posted 19 August 2004 - 07:08 PM


Yes this is the typical pattern for a small motor. A larger motor would probably exhibit a profile skew further towards the no load end. i.e. the savings at 25% would be lower.

The real important factor here of course is, you are saving 18% at no load, but 18% of how much? and what is the cost of the unit?

As most machines have a residual mechanicla load that yeilds a shaft load in excess of 25%, the real energy savings are very small indeed except on machines where the motor spends a considerable period of time at virtually open shaft conditions, i.e. small punch press type machines.

Best regards,

#3 BigMax


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Posted 20 August 2004 - 02:44 AM

Hello GOSS,

That's good information ;d;

I too have recently been involved in evaluating an energy saving device and have noted results near identical to yours.

In addition, the other result I noted was the power factor improvement. For example;

0% Load, pf=0.24, energy saver enabled, pf=0.41, 71% improvement!

25% load, pf=0.55, energy saver enabled, pf=0.63, 15% improvement.

50% load, pf=0.71, energy saver enabled, pf=0.72, 1% improvement.

100% load, no improvement.

WOW, surely these pf improvements at low load are a good thing? (he says, tongue firmly planted in cheek.....)

Sure enough, these were displacement power factor measurements. Distortion power factor (the 'other' type of power factor, see previous posts on this forum) was not recorded but was noted......

Being an SCR based phase angle controlling energy saver (typical for such devices?), the energy savings were achieved by reducing motor terminal Voltage, by reducing SCR conduction below 360 degrees at low loads. The result? Harmonic current distortion and DECREASED distortion power factor!

Imagine a factory full of motors controlled by such energy savers, what effect would the resulting THD have on power quality? This effect has not been discussed on any energy saving device information that I have reviewed. Interesting.

These are my personal observations only, and are not necessarily those of my employer. Nor do I seek to discredit any claims by any energy saver manufacturer, 'cause I haven't seen any such claims!





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Posted 20 August 2004 - 07:18 AM

Hello Marke,

At no load the motor is not doing any useful work and therefore (to my way of thinking) it should be switched off if at all possible. I believe some of the enery saver products provide this functionality.

Your comment relating to payback periods are relevant, a quick calculation indicating that I would be very old and very grey before the cost of the product we evaluated could be recovered through a reduction in the energy bill.

BigMax appears to have taken a more detailed approach to his (I presume) studies. I wander if he is able to comment further on the THD aspect?


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Posted 13 October 2004 - 03:10 AM

Hello all,

Just to remind there is a theoretical max efficiency or power factor for a specific induction motor given the rotor speed. This max efficiency / pf is not a function of load directly, but the load and flux level or load and current level. And one cannot have both max efficiency and max pf at the same time usually.

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