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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’re looking at meters designed to measure AC voltages and currents. Some of them can even 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 last month, 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 last month, 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. 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. 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 more safe 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 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. Current transformer basics One of the big advantages of AC 102 Silicon Chip 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, this means converting the DC voltage to AC, stepping it up or down, then rectifying and filtering it to turn it back into DC. That is 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, Australia’s electronics magazine siliconchip.com.au 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 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 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. 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 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 . 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. siliconchip.com.au Australia’s electronics magazine 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 the panel. It comes with a matching plastic ‘nut’ which 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. January 2021  103 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, shown at actual size, looks nearly identical to the DSN-VC288 shown in the last article. The DL69-2042 meter Apart from the separate CT, the DL69-2042 AC meter looks almost identical to the DSN-VC288 DC meter we checked out in the last article. It’s somewhat larger than the AD1622FVA 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 the price of the AD16-22FVA. It too 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 larger digits make the DL692042 significantly easier to read than the AD16-22FVA, while the 4-digit displays provide higher resolution. 104 Silicon Chip 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. You can even buy it online from the Dick Smith website which is owned by Kogan. Fig.3: as you might expect, like all the other panel meters described in this article, the DL69-2042 is very simple to operate. 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 Australia’s electronics magazine identical to the PZEM-051 DC meter module we described last month. 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 siliconchip.com.au 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. Fig.4: how to set up the PZEM-061 for measurement. ing 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, 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 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, the main digits being about 6.5mm high. In addition to the voltage and current readings, it also shows the corresponding power level and energy siliconchip.com.au consumed. All of these parameters are displayed using four digits (see the left-hand photo on page 102). 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 showAustralia’s electronics magazine 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 page 102). 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). January 2021  105 Silicon Chip Binders REAL VALUE AT $19.50 * PLUS P &P Are your copies of SILICON CHIP getting damaged or dog-eared just lying around in a cupboard or on a shelf? Can you quickly find a particular issue that you need to refer to? 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 page 102. Fig.5: how to use the D69-2058 meter. Keep your copies safe, secure and always available with these handy binders These binders will protect your copies of SILICON CHIP. They feature heavy-board covers, hold 12 issues & will look great on your bookshelf. H 80mm internal width H SILICON CHIP logo printed in gold-coloured lettering on spine & cover Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Order online from www. siliconchip.com.au/Shop/4 or call (02) 9939 3295 and quote your credit card number. *See website for delivery prices. 106 Silicon Chip The current range covers 0-99.99A, with a minimum resolution of 0.01A. 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. 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 Australia’s electronics magazine 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. Summary All of these AC panel meters work well and offer excellent value for money. But I think the one that impressed me most of all 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! SC siliconchip.com.au