Would this really save electricity?

[Andy Champ]

Would you trust any gadget sold by someone who thinks electricity comes from a nucula power station?

Andy

[Bob Smith]

The devices would still need the same amount of power - they would draw more current at the lower voltage. You would probably get more transmission losses - there is a reason the national grid transmits at

40,000V - your house wiring would be warmer with the higher current flowing through it.

How much energy is used to make the damned thing - refining all the metals and plastics - vs how much it actually saves (which I would guess is 0 anyway)?

And would you buy something from someone who says "nucyuller"? And refilling it every month with snake oil would be expensive.

Bob

[Anthony R. Gold]

By suspending Ohm's law?

Tony

[John Rumm]

Yup, for that to be true it would be required (at least for the majority of domestic loads). ;-)

About the only obvious occasions I can think of where true power consumption will remain the same (and hence a drop in voltage will correspond to an increase in current), is when driving an induction motor, or a switched mode power supply.

[Anthony R. Gold]

The true snake oil devices (such as those claiming cost savings through power-factor correction for domestic power customers) could have made Bob so cynical that when something with sound theory behind it arrives, his automatic reaction is not just skepticism but automatic disbelief.

Tony

[Bernard Peek]

If the device does what it says on the tin then there would be some saving. Incandescent lamps would use less power, but would also produce less light. Most other devices would just draw more current.

[Anthony R. Gold]

For some unusual value of "most". The theory is that European consumer devices are designed to operate satisfactorily on 220V and so there is a power saving opportunity in reducing supplies to that figure. Of course there will always be some differences in performance. As you say, incandescent lights will be dimmer and redder. Also electric kettles and hot water heaters will simply run longer to use roughly the same energy.

Tony

[Bernard Peek]

As will fridges, freezers and anything else controlled by a thermostat. That just leaves CFL lamps as possible sources for savings.

[Bill Wright]

So what not just fit lower wattage bulbs and have done with it?

Bill

[John Rumm]

Alas the light output of the lamp will fall off much faster than the power input. So you only gain so long as you don't need to turn on more lights to compensate.

"Most" other devices will draw less rather that more current. For resistive loads I = V/R. So where R is fixed, and V has been reduced, I must also reduce. In most cases that will simply lower the performance a little. Your vacuum cleaner will lose some suction, your toaster or kettle will take longer to do its job (hence the total energy use will remain about the same for them). Anything with a thermostatically controlled heater will heat slower and longer etc.

The place you may gain is with small appliances using linear regulated power supplies, they will dissipate a little less heat. Whether that

[John Stumbles]

CFLs are also switched power supplies and pretty independent of supply voltage. I once saw an incandescent and a CFL on a single lighting cct with a dimmer switch: the CFL stayed on at the same brightness while the incandescent got dimmer, until you got to a point where the CFL suddenly went out.

[mark]

Agreed that this is fine in a purely resistive environment, but in a home, the domestic load is largely inductive so we need to factor in the phase change between current and voltage which is determined by the inductance. An inductive load (thinking back 20 years) will make the current lag the voltage in phase. The greater the inductance, the greater the phase change and the greater the current consumption needed to develop the required power.

It's interesting that the company is called VPhase and that the patent shows that the design includes "a phase angle or pulse width modulation (PWM) switching". So, my thought is that they are deploying Power Factor Correction on certain loads in the home and adjust the power factor correction based on the current phase mistmatch to reduce overall current draw whilst maintaining the same power at each device.

That said, I've not seen the video (as at work) :(

Cheers, Mark

[The Natural Philosopher]

Sklight correction. An inductor is always a 90 degrees phase lag. Its not the inductance value per se, its the ratio of the inductance to the resistance. Or other in phase components (like a load on a motor).

A dimmer is a "a phase angle or pulse width modulation (PWM) switching" device..

It may be no more than that dressed up fancy..

[mark]

Thanks ... there is much I have forgotten :)

Agreed.

[John Rumm]

Woah there...! How do you figure that?

I would estimate most loads in a house are largely resistive. It might even be the case with the ever increasing number of switched mode supplies and CFLs etc that the bias is toward the capacitive. Yes there will be small reactive components in input filters, and a little from any coil in a heater element, but nothing significant. Fridge / Freezers with their induction motors will be one source (although modern ones already have complicated power management technologies in front of the compressor load anyway).

By the vector sum of the reactive elements plus the resistive. A pure capacitive load will lead 90 degrees, and a pure inductive will lag 90.

I would be a little wary of phrases like "current consumption" though ;-)

While common in industrial environments where the billing is based (at least partly) on VA loading and peak requirements, its not going to do anything useful (from a cost saving point of view) in a domestic environment. IIUC, a domestic meter just sums the instantaneous product of I and V and hence does not really care about the phase angle - it just records the real power component.

It did not give you any technical detail really, other than to suggest it dropped the voltage.

[Anthony R. Gold]

A power meter does indeed record power (what you call "real power"), but that is not generally the instantaneous product of I and V but rather what is variously known as their dot, scalar or inner product.

Tony

[Andrew Gabriel]

John is right (and it's a "true power" meter). It is done by multiplying the instantaneous product of I and V as scalers (not vectors). It's actually done by integrating the instantaneous product of I and V (as scalers) to give energy, and (typically) repeating every second to give energy/second, or Watt readings. (Yes, I built one back around 1980;-)

[The Natural Philosopher]

well I don't see the difference actually.

At any given instant the power is the product of both..of their instantaneous values. If you allow for negative results when one is positive and the other negative.

The meter merely integrates that lot to provide an energy reading over time.,

[Anthony R. Gold]

Ah, yes - I hadn't though through "instantaneous" and was thinking of longer periods. Of course, for "instantaneous" periods each sample is essentially direct current and direct voltage, there is no phase angle involved and so each product is true power. My apology to John.

Tony

[John Rumm]

Tis ok, none needed! ;-)