Subject: Re: "Green Plug" electricity saver: what really is it?

From: [email-masked] (Tim Nye)
Date: Fri, 20 Jan 1995 19:32:15 GMT

In article <[email-masked]> [email-masked] (Mark Fraser) writes:

>There was a thread a year or so ago in sci.electronics. I recall
>that the device did ok on "older" refrigerators, did lousy
>on newer ones, and the folks speculated that it messed with the
>power factor.  If memory serves me [and it sometimes doesn't]
>the summary indicated a finite level of hype, but also some
>benefit.  The more ragged edges of this memory suggest that there
>was a problem with temperature rise in some motors, which
>could be more insidious.  

>If someone knows or recalls the thread, please post it,
>it's a very legitimate question.
>/mark

That's basically my recollection too.

An induction motor tends to force the AC voltage and current sine waves out 
of phase.  Power factor is how this is measured.  PF = 1 is in phase, 0 is 
90 degrees out of phase.

When lightly loaded, an induction motor tends to lower the power factor.  
Since AC power is volts X amps X power factor, and the volts and power is 
fixed at a given load, a lower power factor means more amps are required to 
do the same amount of work.

More amps means more heat generated in the wiring.  This is where the power 
loss comes in.

These gizmos sense the power factor and drop the voltage to the motor when 
it is lightly loaded.  With reduced voltage the motor thinks it is working 
near full load, so the power factor is better, amps go down, and less energy 
goes into heating the wiring.

If you have a motor which idles for long periods, this technology may make 
economic sense.  On the other hand, maybe you could just shut off the motor, 
and save even more energy (plus wear and tear).

Motors running at full load won't see much savings.  In fact, if I recall 
correctly, someone claimed a Consumers Reports story showed in some cases 
power use actually increased with this thing attached.

So, there may not be too much potential in a workshop where its easy to shut 
off idle machines.
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Tim Nye                            "Duct Tape: The handyman's secret weapon"
University of Waterloo                          - Steve Smith, aka Red Green