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This is only a preview of the November 2007 issue of Silicon Chip. You can view 30 of the 104 pages in the full issue and the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Items relevant to "PICBased WaterTank Level Meter; Pt.1":
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Purchase a printed copy of this issue for $10.00. 
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 “ElectricitySaving 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 ElectricitySaving 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!
voltamps, 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
610 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 inbuilt power factor correcting
capacitor of around 610mF. The
ballast inductor (L1) is typically
around 1015mH. 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
powerfactorcorrecting 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
3pin 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 “newtype intelligent and digital
electricitysaved (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 5second 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 twotube fluorescent
batten and a domestic refrigerator. The table shows measurements of the instantaneous power consumption of the loads
over ten consecutive 5second 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 Electricitysaving 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 offgrid
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 electricitysaving 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 hardtoreach 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 preprogrammed 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
