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Is this a clever gimmick or what? You just plug it in and it saves you money . . . Electricity– Saving Box by Mauro Grassi This all started out when a reader sent us a link to an item being offered on eBay. He wanted to know if the claims were true: could this little device really save money by reducing the amount of power used by your electrical appliances? Have Newton, Ohm, Kirchoff, Thevenin et al been wrong all along? I t’s called, quite simply, an “Electricity-Saving Box”. You simply plug it into the power outlet. . . and whenever you use any electrical/ electronic device on that circuit you start saving energy (and therefore money). But wait, there’s more: it would protect all the mains powered devices you used. And if that weren’t enough, it would even extend those device’s lives. Wow! We’d seen (and, we must admit, dismissed!) such claims before – but our reader wanted to know if somehow 22  Silicon Chip the supplier had rewritten the basic laws of physics. Could the claims possibly be true? “Reduce the amount of electricity used by your appliances”, they said. “Begins to save you money the second you plug it in” Wow again! “Save between 10% and 30% of the energy used depending on device” “Uses no power itself” “Prolong the life of your appliances” Really? Hmm! Our experience is that if something sounds too good to be true, then it invariably is. Therefore, we were dubious. Skeptical. Downright derisive, if you like. But hey, the price was only $25.00 including freight from China (where else, these days, on eBay?). So we hit the “Buy it Now” button and waited with bated breath for the magic device to arrive – which, in due course, it did. Even before we plugged it in, we attacked it with our trusty company screwdriver to see what was inside. (Oh dear. Have we voided the warranty?) The truth is, there’s not a great deal siliconchip.com.au inside ! Our photos and the circuit we’ve drawn (Fig.1) show what you get for your money. MAINS PLUG 100nF Fluoro clue One of the claims on eBay gave us at least some clue to the theory behind this product. “To test the device, fluorescent light tubes were used, however, please bear in mind that appliances used in the home may be different.” A fluorescent light is a common inductive load, as shown in Fig.2. When power is applied a bimetallic strip in the starter heats up closing the switch. When this happens, the filament at either end of the tube receive current through an inductor and eventually the potential difference reaches a point at which the gas inside the tube ionises. At this point, the tube fires and emits light and the starter opens again. This state will continue until the power is turned off. The large capacitor is not necessary for its operation (its purpose will be explained shortly). Sometimes it is omitted. Because fluorescent lights are common inductive loads, this suggested that the product was aimed at correcting the power factor of your household. Let us explain. The “power factor” of a load is the ratio between the real power (that which the load can use to do work, measured in Watts) and the power that is supplied, also known as the apparent power (measured in 6.2 µF 390V 330k 15 100µF Fig.1: there’s not much inside the Electricity-Saving Box – LED2 LED1 mainly a capacitor, a varistor and a power supply to light up a couple of LEDs. The claimed “intelligent and digital” circuitry (what else could that be but a microcontroller?) was obviously out to lunch on the day we opened up this can of worms! volt-amps, or the product of the voltage and current it consumes). The power factor is therefore a number between zero and one since the real power is at most equal to the apparent power that is supplied, by conservation of energy. The further from one the power factor is, the more power losses are involved in supplying electricity and transmitting it over the power grid. Now consider a sinusoidal voltage waveform. When the current waveform is in phase with the voltage waveform, the power factor is simply one. On the other hand, suppose the voltage waveform is 90° out of phase with the current waveform, as happens for an inductive load. Since power is the product of voltage and current, it will happen that the power waveform is symmetrical about the time axis. This means that the average power, which represents the real power transferred to the load, is zero, meaning that the power factor is also zero. As the phase difference between the voltage and current waveforms varies between these extremes, the power factor varies between zero and one. Fig.3 shows the derivation of an expression for the power factor in terms of the phase difference, for sinusoidal waveforms. The calculations are more complex for other types of waveforms. For a pure sine wave, it turns out that the power factor is the absolute value of the cosine of the phase difference between the voltage and current waveforms. Therefore, for an ideal inductive load, the power factor is zero, while for an ideal resistive load the power factor is one. Now back to Fig.1. The large 6.2mF capacitor across the mains confirmed our initial suspicion that it is there to correct the power factor. The term “power factor correc- Hey, we wuz ripped off! This more recent eBay page has exactly the same product, purportedly from Adelaide (but look at where the seller is located!) for less than $18.00 including postage. The claims are the same, though (we haven’t bored you with the rest of the page). And the good news is there is now a “2nd Generation” model. Hmmm – wonder what that has in it! siliconchip.com.au November 2007  23 BALLAST L1 AC 6-10 F The derivation of the power factor is as follows. Suppose we have sinusoidal voltage and current waveforms, which are out of phase by the angle φ, of amplitudes V0 and I0 respectively. Hence we may write the instantenous voltage and current as follows: V (t) = V0 cos(ωt) FLUORO TUBE I(t) = I0 cos(ωt + φ) = I0 (cos(ωt) cos(φ) − sin(ωt) sin(φ)) STARTER Fig 2: a simplified schematic of a typical fluorescent light, showing the in-built power factor correcting capacitor of around 6-10mF. The ballast inductor (L1) is typically around 10-15mH. It represents an inductive load, hence needs power factor correction. Let the instantenous apparent power be: P (t) = V (t)I(t) = V0 I0 cos(ωt)[cos(ωt) cos(φ) − sin(ωt) sin(φ)] The average real power is therefore: 1 2π  2π P (t).dt 0 Since: tion” refers to using a circuit, usually something as simple as a capacitor in parallel with the inductive load to correct the phase difference between the voltage and current waveforms, since for a capacitor the current leads the voltage. This is why sometimes you see a capacitor being used in fluorescent lights (in fact, in offices and factories where there are large numbers of fluorescent lights, there will always be a power-factor-correcting capacitor). Its purpose is to bring the current waveform closer into phase with the voltage waveform, thus increasing the power factor and minimising power losses. As can be seen from the schematic we traced out, this is one of the intentions of this product. The varistor in parallel with the mains is meant to provide surge protection, another claim of the manufacturer. The 330kW resistor is used to discharge the 6.2mF capacitor when the unit is unplugged. The bridge is  2π cos2 (ωt).dt = π 0 and:  2π sin(2ωt).dt = 0 0 It follows that the average real power is equal to:  2π V0 I0 cos(ωt) 1 P (t).dt = 2π 0 2 Since the RMS voltage is V0 √ 2 and the RMS current is it follows that the V0 I0 2 . The power factor is average apparent power is the product of these, or: the ratio of the average real power and the average apparent power, in other words it is: V0 I0 cos(ωt).2 = cos(ωt) V0 I0 .2 Fig 3: This shows a derivation from first principles of the power factor for a sinusoidal waveform. The power factor of the load turns out to be the cosine of the phase angle between the voltage and current waveforms. Here’s the back of the device showing the two mains plug pins (note two, not three – this circuit is not referenced to earth). They do give you the 3-pin international adaptor so you do actually get something usable for your money. Are we being a bit cynical? 24  Silicon Chip I0 √ , 2 solely there to rectify the mains, which is substantially stepped down by the 100nF capacitor, and then used to drive the two LEDs. Finally, the 15W resistor limits the current through the LEDs, which simply light up when 1 power is applied. It should now be clear that the claim that this device uses no power is false. Where’s the microcontroller? Another dubious claim of the manufacturer is that this product is a “new-type intelligent and digital electricity-saved (sic) device”. This suggests a microcontroller is being used, however, a look at the schematic reveals there is no intelligent or digital component there. The more appealing claim of the siliconchip.com.au advertising is that this device will reduce your electricity bill and save you money. Is this possible? The short answer is no, this product will not save you money. The long answer needs a little explanation. We need to go back to the concept of the power factor and what its real significance is. Since electricity suppliers charge you for Watts (ie real power) but since they supply voltage and current (VA), whenever your power factor is less than unity, there are losses that you are not strictly paying for, which the electricity supplier must foot the bill for. Hence, in certain cases, they charge extra whenever the total power factor is below a certain threshold. Because fluorescent lights are widespread in large commercial installations, potentially representing large power losses, most fluorescent lights now have “power factor correction” built in, usually in the form of a large capacitor of around 6 to 10mF, in parallel with the load. This has the effect of improving the overall power factor of the light. It is actually illegal in Australia not to have these for commercial installations, and the law is moving to make them mandatory in households. For household users, who seem to be the target audience for this product, we can say categorically that this product will not save you any money, against the claim of the manufacturer. This is because there is a logical flaw with this product. As mentioned previously, the electricity supplier bills you for real power, yet provides apparent power. If this product corrects the power factor, which is the ratio of these, it can only save them money, not your household. The only conceivable way that it could save you money is if you are being charged extra by the electricity supplier for having a low power factor, something that does not happen with domestic users in Australia. It does happen in industry, however but this product is not something that industry would seriously contemplate using. Much more sophisticated ways of correcting the power factor exist for industrial applications, like synchronous motors and banks of switched capacitors. To illustrate the effects of the electricity saving box on your electricity siliconchip.com.au The large black object at the back of the PC board is the 6.2mF capacitor while most of the other components are simply a power supply for the two green LEDs – which don’t show anything, except maybe that it’s plugged in and using power! bill we conducted a simple experiment. The results suggest that the Electicity Saving Box does not save you any power but actually consumes more power than what it saves, for an overall net gain in real power consumption and therefore an increase in the total of your electricity bill. We used the Energy Meter from our July 2004 issue, which measures real power consumption. We measured the real power consumption of the electricity saving box to be around 210mW. Table 1 lists the results of real power measurements that we made. This represents the real cost to you. We measured the power consumption of a fluorescent light without inbuilt power factor correction, with and without the electricity saving box. We then measured a fridge, another inductive load, in the same conditions. Ten measurements of instantaneous real power were made at 5-second intervals and the average was taken. We also measured the real power consumed in one hour for the fluorescent light, with and without the electricity saving box. The fluorescent light, without the electricity saving box, consumed 96Wh while the figure was slightly higher at 98Wh with the electricity saving box. Note that the fluorescent light we tested does not have a parallel capacitor to correct its power factor. Our tests show that your electricity bill will be slightly higher when using November 2007  25 Load/Time (minutes) 0 5 10 15 20 25 30 35 40 45 Average Fluorescent light 98.35W 98.62W 98.62W 98.71W 98.71W 98.50W 98.50W 98.50W 98.44W 98.44W 98.539W Fluorescent light + Electricity saving box 98.65W 98.86W 98.88W 98.88W 98.78W 98.65W 98.86W 98.88W 98.78W 98.56W 98.778W Fridge 142.61W 142.59W 142.83W 142.83W 142.34W 142.34W 142.35W 142.35W 141.64W 141.64W 142.352W Fridge + Electricity saving box 143.28W 143.28W 142.91W 143.19W 143.19W 142.33W 142.33W 142.94W 142.94W 142.94W 142.933W Table 1: the results of measurements of real power we made of two household inductive loads – a two-tube fluorescent batten and a domestic refrigerator. The table shows measurements of the instantaneous power consumption of the loads over ten consecutive 5-second intervals while the last column shows the average power consumption in watts. In every case, the real power consumption using the electricity saving box, representing the actual cost to you, is higher. the electricity saving box and hence that the claims of the manufacturer that this product will save you money are false. Given that it is clear that this device will not save you any money, the next question is whether it corrects the power factor. To answer this, we must look at the voltage and current waveforms through a load. We chose to use the same fluorescent light we used in the measurements of real power, which did not have power factor correction built in. To obtain the current waveform, we measured the voltages at either end of a resistor and subtracted the waveforms using the maths function of the scope. Fig.4 shows a scope grab of the mains voltage waveform (channel 3) and the mains current flowing through the fluorescent light (channel M). Note that the mains waveform is not a perfect sinusoid. Rather, it is an approximate sine wave with flattened peaks and troughs. This is because there are other appliances plugged into 1the Suppose we consider a typical fluorescent light without power factor correction. We think of the load as a resistance in series with an inductor. A typical value for the series resistance of the inductor is R = 1.8Ω and a typical value for the inductance is L = 10mH (these we measured using an LCR Analyzer). It turns out that the expression:   ωL θ = tan−1 = 60.18◦ R measures the phase difference in the voltage and current waveforms for this load, where ω = 2πf where f = 50Hz, the mains frequency. Now suppose we introduce a capacitor C = 6.2µF in parallel with this load (which represents a typical fluorescent light). Then it can be verified that the phase difference in this case will be:   ω(L − ω 2 CL2 − ωCR2 ) ′ −1 θ = tan = 32.34◦ R The corresponding power factors are the cosines of these angles or: cos(θ) = 0.497 and cos(θ′ ) = 0.845 Compare these values with the measured values in Figures 4 and 5. Fig 6: Theoretical calculation of phase difference between voltage and current waveforms, and hence power factor, for a typical inductive load with series resistance with and without a parallel capacitor. This setup roughly applies to the fluorescent light we used in our tests. 26  Silicon Chip same household circuit that perturb the mains waveform. The RMS voltage is as expected at 241.9V and the frequency is 50Hz. The current waveform is obtained by subtracting two voltage waveforms across a 4.4W resistor on the neutral side. The RMS voltage of the grey trace is measured to be 3.599V giving an RMS current of 818mA. The phase difference is shown to be around 59°. Note that the apparent power is therefore 0.818x240 = 196 W, roughly twice that of the measured real power of 98W. This makes sense because the power factor is given by the cosine of the phase difference and this is approximately 0.5. Fig 5 shows what happens when the electricity saving box is plugged in. Again, the mains voltage waveform and the mains current flowing through the fluorescent light are shown. In this case, the phase difference is shown to be around 37°. The RMS voltage of the grey trace is measured to be 2.063V giving an RMS current of 469mA. Note that the apparent power is therefore lower at 0.469x240 = 112.6W. This suggests that the electricity saving box does indeed correct the power factor of this load, also apparent from the lower value of the phase difference. In fact, all this is consistent with the theory. Fig 6 shows a calculation of the effect of adding a capacitor C in parallel with an inductive load L with series resistance R. The phase difference angles predicted from the equations are consistent with our measured values. Conclusion The Electricity-saving box will not save you any money. In fact, the opsiliconchip.com.au They have arrived! Fig 4: A scope grab of the mains voltage waveform (in purple) and the mains current (in grey) flowing through a fluorescent light (without power factor correction). The electricity saving box was not used. The RMS voltage is as expected at 241.9V and the frequency is 50Hz. Fuel Cells Off grid power for measurement, transportation, security and telecommunications industries Generate electricity without combustion, without sunlight or wind, without pollution. Fuel cells are small, lightweight and portable, quiet, have no major moving parts and require no maintenance. They have an expected operational life exceeding 8000 hours of run time. 5 litre and 10 litre fuel cartridges are available. For example, an off-grid video camera will operate for up to 8 weeks on a single 10 litre fuel cartridge. Technical data Model Charging capacity siliconchip.com.au 1600 1600Wh/day 130Ah/day 12V 12V 12V Nominal Power 25W 50W 65W Nominal Current 2.1A 4.2A 5.4A Fuel consumption 1.1 litres per kWh. 1.3 litres per 100Ah Weight 7.3kg Batteries posite is true – it will very slightly increase your electricity bill. However, it will have some effect on your household’s overall power factor. While this may benefit your energy provider, this effect will become negligible whenever many loads are connected in your household’s power circuit. This is because the value of the capacitor used (6.2mF) is simply too small for most households. This will be especially true when these loads already have power factor correction. Normally, switchmode supplies used in computer power supplies and other appliances have power factor correction, as do many fluorescent lights. In this case, the electricity saving box will have a negligible effect on your power factor. Many of the claims made in the advertising for this product are simply false. Since it will not save you any money and will have a negligible effect on your power factor, we see little reason to purchase this product. SC 1200 1200Wh/day 100Ah/day Nominal Voltage * Dimensions Fig 5: the mains voltage waveform shown in purple (with the electricity-saving box installed) and the mains current flowing through a fluorescent light without power factor correction is shown in grey. 600 600Wh/day 50Ah/day *24V available on request 7.5kg 7.6kg (L x W x H) 435mm x 200mm x 276mm 40 to 200AH recommended 100% availability Maintenance free and absolutely reliable. Even under extreme climate conditions it ensures 100% availability of your equipment. This is a decisive advantage, especially in hard-to-reach areas or with critical applications such as observation posts. Fully automatic Automatic charge control, continuously monitors battery status as it powers your electrical equipment. If the battery’s voltage sinks below the level pre-programmed by the user, the fuel cell activates, charges the battery, and then automatically shuts itself off. And it does so without any user intervention. Remote Control Each fuel cell can be connected by an interface adapter to any RS232 interface and serviced/monitored using a cellphone, laptop or PC from the office. Theft Proof Solar cells need to be placed out in the open where it is difficult to protect them against theft and vandalism. The compact fuel cell can be integrated into any standard cabinet or box. More Power With the control interface you can operate up to 5 fuel cells in parallel, giving you a capacity of up to 8000Wh per day. Siomar Battery Industries Ph: (08) 9302 5444 Email: mark<at>siomar.com Contact: November 2007  27