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jimbo
03-02-2009, 04:15 PM
There used to be a device...might have been called a "green plug" or something, that you plugged an appliance like an air conditioner or refrigerator, and by supposedly clipping the sine wave, you got the same performance at lower watts.


Now, I mostly heard that this was smoke and mirrors, and in fact may damage a motor. I would not use it. But I am now being asked to find such a device for the wall A/C in a hotel ( 240VAC, 20 amp units.)

My question is this: does anyone have a reference to a good technical article debunking the devices, or...???

Macman
03-02-2009, 04:43 PM
Don't need any articles to tell you this is bunk. The power available in a sine wave is based on the shape of the waveform. The moment you start clipping the wave is the moment that you start losing power. Some things wouldn't care much - a light bulb for example. It just wouldn't be as bright. But other electronics, and yes motors, aren't going to be very happy. You can't get something for nothing. BTW, clipping creates terrible harmonics that can fry electronics.

jadnashua
03-02-2009, 05:42 PM
Power factor adjusting things can confuse the power meter some and maybe help a little. Way back, Popular Science had an article on one and the schematic of how to build one. Normally, only used for big power users.

Scuba_Dave
03-02-2009, 05:48 PM
Green site I visit has one person who installed one & claims 10% savings:

http://forums.treehugger.com/viewtopic.php?f=1&t=6271

hcbflash
03-02-2009, 07:42 PM
I used to take money from a guy that sold them ("energy saving" transient clipping do-dads) to folks he sold them to. I still feel bad about it, but I went back and installed more at one site where the "customer" said that it worked well and saved energy and the connected equipment.

I'll be dog-goned if I can remember the name of the device or its manufacturer. The guy I dealt with is probably dead, as I haven't seen him in 20 yrs, and he was an old man then.

If it could work, it could only by a couple "games", that can shunt a voltage spike to ground without the utility meter being able to detect the power flow. Since I'm no expert on the operation or electronics of utility power meters I don't know how it could be done. I do know that whatever is shunted to ground at the device would simply be "grounded" in essence through the load otherwise and both conditions are metered.

Another very, very slight possibility is that a users power supply has so much "noise" imposed on it by a local source, that motors suffer additional electrical heating in their windings, and that heating is enough to do damage to those windings, resulting in the use of the power required to destroy the motor fully or trip the protective devices. Of course the new unit might offer higher efficiency......

What I'd like to find out is how the inventor explains it!

hcbflash
03-02-2009, 08:02 PM
I should have also mentioned that "surge suppressors", "noise filters" and "power factor" are all very different things. In fact, the single thing that they may have most in common is that none of them effect a residential electrical bill.

:p

Bill Arden
03-04-2009, 02:12 AM
jimbo:

The main concept is not that it affects the meter, but that older units tend to have a overbuilt compressor motor so that it can start at lower line voltages.

As you increase the voltage you increase eddy current losses. I use variacs and transformers to get the same effect on some of my larger pieces of equipment. I was able to reduce my line current from 6 amps to 4 amps on one blower fan by lowering the voltage to 90 volts AC. The actual wattage was lowered even more since watts = volts * amps.

The problem is that if you lower the voltage too much OR if the line voltage sags you could damage the unit.

jadnashua: Sorry. Jimbo is looking for a voltage reducer. not a PFC device.

Macman: Clipping the top might actually be better for a motor since it reduces the peak flux density. Older motors tend to magnetically saturate parts of the armature at some voltage.

Scuba_Dave: Sorry that is something else.

Macman
03-04-2009, 06:26 AM
Bill, I'm not sure what you mean by "better" but when it comes to motors the obvious thing is that if you start taking away parts of the waveform you're going to reduce power. If the motor is already overpowered for the application then yes, it could work. But it could also be playing with fire (literally). If it can't keep up the rpms then it becomes a big problem. "Might" is indeed the key word here.

jimbo
03-04-2009, 06:42 AM
I have taken the 'safe' route and advised the hotel to get approval from the PTAC mfg ( GE ) before modifying the power in any way. This is really an electrical engineering issue, and they should forget about trying something on their own, or on the recommedation of a well-intenioned technician or wholesaler.

alternety
03-04-2009, 10:27 AM
If the hotel is large enough for the power company to bill for use of out of phase current, a power factor corrector (probably just a capacitor in a cheap plugin but can be more elaborate) could reduce bills by getting the overall load closer to a power factor of 1. If they are not billed that way, PF correction gets the user nothing. Generally speaking, PF correction in consumer products is for the benefit of the power company and grid capacity. For example, most any decent new computer power supply has PF correction built in.

If PF correction is what they are after, they might look into buying an industrial device and deal with the building as a single load.

jimbo
03-04-2009, 03:08 PM
They are not that big, and are completely clueless. "somebody" at another hotel told them they should look into it!

dx
03-05-2009, 05:05 PM
Bill Arden:

Programmer is spelled with 2 m's.