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Power saving device too good to be true?

  1. May 12, 2007 #1
    Hi,
    I'm not really into physics would would appreiciate any advice on a device which claims to save electricity.

    Take a look at this link on ebay -

    http://cgi.ebay.co.uk/ws/eBayISAPI....tToStoreCat&refwidgettype=cross_promot_widget

    I bought one of these on the off chance that it might be something revolutionary but I'm not at all sure it works...

    I have tried using it with a power monitor and the wattage reads 0w but the VA reading (apparent wattage) reads simething like 100w. I don't really understand what the VA reading is but does this mean it's giving me 100w back or does it mean that the device is total nonsense?

    Any feedback would be welcome.

    Thanks,
    Stacy
     
  2. jcsd
  3. May 12, 2007 #2

    AlephZero

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    The EBay description says
    "Power Save Device improves the power factor by reducing the amount of electricity that is used from our utility company."

    The test results they give look like snake oil. They tested fluorescent light tubes which (conveniently) are not a resistive load, so a device that changes the power factor will have a large apparent effect in the current.

    They don't quote the power used, they only quote current measurements, and they don't specify what they are measuring (peak? RMS?). They don't state the change in power factor, but assuming a device that says it changes the power factor actually DOES change it, there will be no direct read across from a reduction in current of 52% to the claimed "energy saved" of 52%.

    Apart from all that, there are legal limits to the power factor of equipment you can connect to public electricity supplies (in the UK, anyway), because large non-resistive loads are not good news for the power transmission network.

    That might be why they say "Please do not use this item for a factory or other business places" - factories are more likely to have the power factor of their usage monitored by the supply company than domestic consumers.

    Your own measurements (0 Watts and 100 VA) suggest it's just a box with a big capacitor inside. That isn't going to do anything much to save you money.

    Put it down to experience - something tells me you are going to have a hard time getting your money back, whatever it says on Ebay.

    If you want to save money, do the boring stuff like low energy light bulbs, don't leave equipment on standby, turn the heating thermostat down a couple of degrees, only run the washing machine when you have a full load of clothes to wash, etc, etc.
     
    Last edited: May 12, 2007
  4. May 12, 2007 #3
    Thanks for looking into this.
    I'm not worried about the money at all but I don't want to use something that's doing more harm than good.

    I really don't understand how it does what it is 'supposed' to do or what the 'apparent power' is but I guess it must be bogus or surely companies in the UK would be pushing them very agressively...

    Oh well, worth a try...

    Stacy
     
  5. May 12, 2007 #4
    First thing I saw from the website:

    the product came from China (not made in China, but shipped FROM China).


    this can't be good...(I'm a Chinese myself and this is my own experience)

    think about it... why would the product not be available in the USA if it is THAT good? why would it be stuck in China?
     
  6. May 12, 2007 #5
    "Power Saving" devices are somewhat of a misnomer, as they themselves must consume power.
    What is important here is that such devices seek to optimize the electrical flow to the end device.
    That general approach is not without merit, as some end devices respond more optimally with changes in input current parameters; be it alterations from AC to DC or even a modified AC sine wave or a pulsed DC.
    This is a difficult subject and entirely device dependent.
     
  7. May 13, 2007 #6

    chroot

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    The utility company doesn't charge residential customers by power-factor, anyway. Instead of trying to make consumers aware of their power-factor (good luck educating the public on that one!) they just build their own capacitor yards at substations to bring the power factor for an entire area close to one.

    The device is a waste of money.

    - Warren
     
  8. May 13, 2007 #7
    Not as such, but I've always understood it was possible to cheat the residential power meters by deliberately obtaining most power at unanticipated parts of the cycle (with the additional insult of adding extra noise to the rest of the local grid).

    Does anyone know exactly what type of motors are in those meters (so as to theoretically determine what the meter is actually sensitive to)?
     
  9. Mar 11, 2010 #8
    loooong time ago, I talked to a Navy Nucular power electrician... he said that he had created a large coil of wire (do not remember sizes but think the loops were over 1 ft in dia), and do not remember the load on the coil or if there were any electronics included) and hung it inside the house, right up against the spot where the meter was mounted outside.
    When energized, something about the field it was putting out, out of phase with incoming power, caused the meter to register a LOT less then was actually getting used
    Not entirely sure he was pulling my leg.
    Thoughts?
     
  10. Mar 11, 2010 #9
    Many years ago, I built a power factor controller, and it actually worked, on our refrigerator, which was the only item in our house with a large reactive (inductive) impedance. A few seconds after turning on, the voltage on the refrigerator dropped to ~95 volts, and the power factor increased to the regulator set-point. The I2R losses actually did decrease a little. These circuits are designed to be used on induction motors, where the power factor increases with decreased voltage and the motor RPM remains quasi-synchronous. DO NOT try one of these power factor regulators on appliances with microprocessors.

    Bob S
     
  11. Jul 20, 2010 #10
    I just purchased an energy saving device off Ebay. I had heard of the KVAR brand units but when I surfed the web and called the company, I couldn’t get specs for the product. So I went to Ebay and I ordered a unit out of Honk Kong with advertised good specs if you can believe what is stated on Ebay. The unit looks as good as any but on careful inspection after receipt, I noted it didn’t say where it was made. I decided to open the box to see how the electronics were configured and I was surprised by the simplicity of the device. It was clear to me that I would see a two capacitor device but I expected a circuit board with overload… What I found appears to be two capacitors hooked to a monitor light for the front of the box attached by a variety of wires and nothing else. I have pictures for your review if they will help. Here is what is advertised for specs that I have doubt the box will do but I don’t want to confront the seller or Ebay without a second and third reliable opinion.

    Advertised specs that I don’t see how are possible ( full list can be posted upon request ):

    1. double insulated

    2. Surge Suppression – 6500 Joules

    3. Let Through Voltage – 150V Line-To-Neutral

    4. Spike Protector: Utility Spike And Electrical / Lightning Storms

    5. Transient Noise Reduction: MOV (Metal Oxide Varistor)

    6. … Thermal & Overload Protection

    here is just a start of my concern: it says double insulated. There are three wires for the 220/240 VAC installation ( two red and one green wire ). As you would expect, one red wire goes to each 120vac leg of your electric panel and the green goes to the ground bus. Well in the box, the green wire comes into the all metal box and goes to a bolt that hold a flat metal crush clap over the two caps. So, when you look at #3 above to read 150V line to neutral, one would think that if the transient voltage stays too long over 150VAc on one of the legs, that energy will be diverted to the ground wire to protect what you have plugged in within your home. But as you can see, with the way it is designed, if that ground wire does not make a good contact with the home’s ground bus then the exterior of the box could be hot. But I don’t see how #3 is possible anyway with no circuit board to clap the voltage to the 150vac to start. So, how could this unit be double insulated? I need an elect engineers opinion so I know if I am looking at this list correctly. With no circuit board or other discrete component- where is the MOV of # 5 or how is #6 possible?
     
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