Using Cheap Asian Electronic Modules
By Jim Rowe
Mini Digital
AC Panel Meters
In this follow-up article on low-cost digital panel meters, we look at meters
designed to measure AC voltages and currents. Some of them can calculate
and display power, energy consumption and frequency. As usual, we’ll give
you an idea of how they work, how they perform and how easy they are to use.
A
s promised in December
2021’s issue, this second article describes some small meters
designed to measure AC voltages and
currents. The AC models are even more
interesting than those we described last
time. For a start, they vary more significantly in both size and price.
Like the DC meters we looked at in
the first article, these AC meters are all
designed to be powered from the same
source used for voltage measurements.
So no separate power source is needed.
It’s important to make sure all connections are properly insulated when
taking measurements.
As explained in December, DC meters measure currents by measuring
the voltage drop across a very low resistance current shunt. In contrast, AC
meters typically measure currents by
using a special kind of transformer: a
‘current transformer’ or ‘CT’. This steps
down the current to a much lower level,
as well as providing galvanic isolation
for improved safety.
Current transformer basics
One of the big advantages of AC compared with DC, as Nikola Tesla and
George Westinghouse stressed over
120 years ago, is that with AC you can
use transformers to step the voltage up
or down to whatever level best suits
your purposes.
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This means that AC power can be
stepped up to hundreds of thousands
of volts to reduce losses when conveyed
over long distances, then stepped down
to much lower voltages like 230V or
115V, for somewhat safer use in houses,
factories and offices.
Of course, when a transformer steps
up the voltage, it also steps down the
current, and vice versa. This is due
to the conservation of energy (ie, the
product of voltage and current at the
output must be similar to that at the input). So if the voltage is stepped up by
a factor N, the current is stepped down
by the same factor, and if the voltage
is stepped down by N, the current is
stepped up by the same factor. (This is
much harder to do with DC; generally,
it means converting the DC voltage to
AC, stepping it up/down, then rectifying and filtering it to turn it back into
DC – not easy to do efficiently!)
The current transformer works on
the same principle, as shown in Fig.1.
It consists of a toroidal magnetic core,
usually made from either silicon steel
or ferrite, through which passes the wire
carrying the current to be measured. The
wire effectively forms the transformer’s
single-turn primary ‘winding’.
Many turns of much lighter wire are
wound around the toroidal core to form
the transformer’s secondary winding.
So the turns ratio is 1:N, where N is the
number of secondary turns.
When a relatively heavy alternating
current is flowing through the wire
forming the CT’s primary, this produces an alternating magnetic field in
its core. And as a result, an AC voltage is induced in the CT’s secondary
winding, which can provide an alternating current N times smaller than
that flowing through the single-turn
primary (assuming that it’s connected
Fig.1: how the current
transformer (CT) operates.
The CT secondary should
be terminated with a low
impedance, otherwise it will
generate a very high voltage
if any significant AC current
is flowing in the primary.
Make sure to connect the
secondary leads of the CT to
the panel meter before any
current is allowed to flow
through the primary.
Practical Electronics | February | 2022
The AD16-22FVA is the smallest AC panel meter out of the three but has the
highest measurement range of 60-500V. The current transformer (CT) is shown
adjacent and is rated at 0-100A.
The AD16-22FVA meter shown at
actual size.
to a low-impedance load or ‘burden’).
This is illustrated by the expression at
upper right in Fig.1, relating secondary
current IS to primary current IP .
So, for example, if the CT has a secondary winding of 1000 turns and the
current flowing in the primary wire
is 50A, the secondary current will be
50mA (50A ÷ 1000).
The advantages of using a CT includes a stable transformation ratio,
which helps ensure measurement
accuracy, as well as a high degree of
electrical isolation. The main disadvantage is that the ‘primary’ wire must be
passed through the centre of the transformer core.
One way around this is to have the
core in two halves. But this adds significantly to the cost, as well as reducing
its conversion efficiency a little (due to
the inevitable air gaps).
The AD16-22FVA meter
The AD16-22FVA is both the physically
smallest meter that we will describe in
this article, and also the lowest in cost.
As you can see from the photos,
it’s quite tiny, measuring only 31mm
wide, 31mm high and 56mm deep.
Behind the front square display section, the body is cylindrical so it can
pass through a 22mm diameter hole
in a panel. It comes with a matching
Fig.2: the AD16-22FVA meter is easy to use. One of the power leads from the AC
source to the load passes through the CT (polarity connections do not matter),
while the other two leads connect across the source.
Practical Electronics | February | 2022
plastic ‘nut’ that allows the meter to
be attached firmly to the panel.
The CT is separate and is connected to
the meter via a light two-wire lead. The
CT lead is close to 180mm long, while
the meter’s own lead is 100mm long.
The AD16-22FVA has two 3-digit
7-segment LED displays, one above
the other, with both sets of digits
7mm high. And the meter is available in five versions, with red, blue,
green, yellow or white displays. It’s
hard to be sure, but I suspect that all
these versions differ only by having
different colour filters in front of the
same white LED displays. The voltage measurement range of all versions
is 60-500V AC, while their current
range is 0-100A.
The AD16-22FVA meter is very easy
to set up and use, as you can see from
Fig.2. All you have to do is pass one
of the load power leads through the
centre of the CT, and then connect the
power terminals of the meter to the
same source of AC power.
I found the AD16-22FVA advertised
on AliExpress by the supplier Sevenstar Tools at $4.58 plus 78¢ for delivery
(including the CT). The ‘white display’
version I ordered arrived about 30 days
later, in good condition.
I checked its performance with my
reference instruments, using a finned
oil heater as the load. It gave voltage
readings that were 0.2% low and current readings that were 0.94% low,
compared with my Agilent U1251B
DMM. So the AD16-22FVA may be tiny,
but its performance is quite respectable.
I admit that I found the small 3-digit
displays a little hard to read. But for
less than $5.50, it still represents excellent value.
The DL69-2042 meter
Apart from the separate CT, the DL692042 AC meter looks almost identical to
the DSN-VC288 DC meter we checked
out in the last article. It’s somewhat
larger than the AD16-22FVA at 80mm
wide, 42mm high and 48mm deep. It
clips into a 75 x 39mm rectangular hole
in a panel.
The DL69-2042 sports two 4-digit
7-segment LED displays, both with digits 10mm high. The volts display is at
the top, with a red filter, while the current display is below with a green filter.
This meter has a voltage range of 80300V, although it is also available with
a range of 200-450V. In both cases, the
current range is 0-100A. The rated accuracy is ±1%, ±2 digits for both voltage and current.
I found the DL69-2042 advertised
on the Banggood website for $17.00
plus $3.73 air parcel shipping (again,
including the CT), ie, about four times
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(Above) the DL69-2042 looks nearly identical to the
DSN-VC288 shown in the last article.
Fig.3: (Below) as you might expect, like all the other
panel meters described in this article, the DL69-2042
is very simple to operate.
the price of the AD16-22FVA. It also
arrived safely about 30 days later.
When I checked it out using the same
test setup as before, the voltage readings
were only 0.2% high while the current
readings were 2% high. This was just
within spec at the current level concerned (about 6A).
Like the AD16-22FVA, the DL692042 is quite easy to use, as you can see
from Fig.3. Again all you need to do is
thread one of the wires connecting to
the load through the centre of the CT
core, then connect the meter’s voltage
input terminals to the same source of
AC power.
Both the CT and VIN terminal blocks
are on the rear of the meter’s case;
they’re only shown on the front in Fig.3
for clarity.
The DL69-2042 has a measurement range of 80-300V and
0-100A. There are also some versions with a voltage range
of 200-450V.
The larger digits make the DL692042 significantly easier to read than
the AD16-22FVA, while the 4-digit displays provide higher resolution. So this
meter is good value for money even at
its higher price. If you only need readings for both voltage and current, it is
a good choice.
The PZEM-061 meter
If the PZEM-061 AC meter looks a bit
familiar, that’s because apart from the
accompanying CT, it looks almost identical to the PZEM-051 DC meter module we described in December. That’s
because it is manufactured by the same
firm, Ningbo Peacefair Electronic Technology, in China’s Zhejiang province.
Like the Peacefair DC meter, it comes
in a rectangular case measuring 90mm
wide, 50mm high and 25mm deep,
designed to clip inside a rectangular
panel opening 87 x 46mm. Like the DC
meter, it also features an LCD window
measuring 50 x 30mm with blue LED
backlighting, and the main digits are
about 6.5mm high.
In addition to the voltage and current
readings, it also shows the corresponding power level and energy consumed.
All of these parameters are displayed
using four digits (see the left-hand
photo on the first page).
The voltage measurement range is
80-260V and the current range 0-100A.
The power range is 0-22kW, with readings for power levels below 1kW showing as 0.0-999.9W, readings for power
levels between 1kW and 10kW showing as 1000-9999W and readings for
power levels above 10kW showing as
10.0-22.0kW.
The energy consumed range is
0-9999kWh (kilowatt-hours), with
readings below 10kWh showing as
0-9999Wh and readings above 10kWh
showing as 10-9999kWh.
It has a small recessed button at centre right on the front panel, allowing
you to switch the backlighting on or off,
reset the energy consumption level to
zero to start a new set of measurements,
The rear and internals of the PZEM-061. It has a
measurement range of 80-260V and 0-100A in addition
to reading power levels from 0-22kW (power factor is
taken into account). The front of the meter is pictured
on page 102 and has a bright blue backlight.
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Practical Electronics | February | 2022
Fig.4: set up of the PZEM-061
for measurement.
The rated accuracy of the D69-2058
for voltage and current is ±1%, ±2 LSDs
(least-significant digits).
I found the D69-2058 on offer at AliExpress from a supplier called Cooperate Electric Store, for $19.65 plus 81¢
for airmail shipping. It arrived in good
condition about 40 days later.
The D69-2058 is just as easy to use
as each of the other AC meters, as you
can see from Fig.5. I found that the voltage readings were 0.22% high, while
the current readings were 0.22% low.
So the power readings should be very
close to spot-on.
Reproduced by arrangement with
SILICON CHIP magazine 2022.
www.siliconchip.com.au
or set a power level alarm threshold to
a level between 0.0 and 22.0kW.
The PZEM-061 is again quite easy to
use, as you can see from Fig.4. You simply need to pass one of the load power
leads through the centre of the CT, and
then connect the meter’s own power
leads to the same source of power. The
four-way terminal block is at the rear of
the meter, but is shown in Fig.4 at the
front, for clarity.
I found the PZEM-061 advertised on
the Banggood website for $19.22 plus
$3.73 for air parcel delivery. Again, it
arrived about 30 days after I ordered it.
The rated measurement accuracy
of the PZEM-061 is ±1%, and when I
checked it out, I found the voltage readings to be 0.21% high while the current
readings were 0.05% high. That is not
only well within spec, but quite respectable. The power and energy readings were accurate too; not surprising as
these are calculated from the measured
voltage and current.
Although the display digits are only
6.5mm high, the blue LED backlighting
makes them quite easy to read. So all in
all, the PZEM-061 represents excellent
value for money.
The D69-2058 meter
The last AC meter we’re describing is
the D69-2058 multi-function meter.
This one is slightly smaller than the
PZEM-061 at 80mm wide, 42mm high
and 47mm deep, but it displays a total
of six measurement parameters: voltage,
current, power, mains frequency, energy consumption and power factor (see
the right-hand photo on the first page).
The D69-2058 has an LCD screen
with digits about 6.5mm high, and it
is quite bright, so all the parameters
are easy to read. The voltage display
has four digits and covers the range
of 80-300V (although the meter can
alternatively be ordered with a range
of 200-450V).
The current range covers 0-99.99A,
with a minimum resolution of 0.01A.
Practical Electronics | February | 2022
Power can be displayed over the range
0-9999.9W, with a claimed accuracy
of 0.1W. Mains frequency can be displayed over the range 45-65Hz, which
should cover all countries outside of
odd situations.
Energy consumption can be calculated and displayed over the range
from 0-999999kWh, with a resolution
of 0.01kWh for values below 1000kWh,
a resolution of 0.1kWh for values up to
9999.9kWh, and 1kWh for values up to
999,999kWh. Finally, the power factor
is shown as 0.00-1.00.
Summary
All of these AC panel meters work well
and offer excellent value for money, but
the one that impressed me the most was
the D69-2058, which not only has the
largest number of measurement parameters, but also the most readable display.
So, if you need a multi-function AC meter for checking the operation of household appliances or workshop machines,
it would make an excellent choice.
It’s important to make sure that,
regardless of what meter you use, all
your mains wiring is properly insulated, and the meter is housed in an
appropriate, sturdy case.
Shown above are the internals of the D69-2058 AC panel meter. Compared to
the previous three meters, this one offers a lot more features, displaying voltage,
current, power, mains frequency, energy consumption and power factor. The
front view can be seen on the first page of this article.
Fig.5: how to use the D69-2058 meter.
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