VAC1100A ammeter-voltmeter with a measurement range up to 120 V and 100 A, and a little more

It's been a while since I picked up a shashka soldering iron. A little while ago, I received a very useful gadget, and today I plan not only to show it to you, but also to put it to work on a real project.
Warning: lots of photos, which may be a problem for users on expensive data plans.



I once reviewed a similar device, but with much more modest specs and capabilities: up to just 30 V and 3 A.
This time, I want to tell you about a small instrument that, according to the developer, can measure currents up to 100 A at voltages up to 120 V. I need it for another device, but I won't get ahead of myself; all in good time.

The ammeter-voltmeter comes in a neat, fairly large cardboard box. I have no complaints about the packaging, either as a retail package or as protection for the product itself; it's quite difficult to damage anything.


The package includes:
1. Measurement module
2. Display and control module
3. Power cable
4. Interface cable
5. Manual


1. There's no point showing the manual here; it's easier to download the more complete version in PDF format.
2. The cables aren't anything special either: a short wire with a two-pin connector and a standard USB extension cable.


According to the description, there are three versions of the meter: 100, 200, and 300 A. In my case, 50 A would have been enough, and even preferable, but unfortunately that version isn't available.
Below is the description from the product page in the store, which also lists the technical specifications. I'll check some of them during the review and explain the rest in more accessible terms as I go.


I'll start with the measurement module.
As you can see, the meter consists of two separate devices. The measurement module measures current and voltage, calculates power and capacity in Ah and Wh, and also provides a service for controlling the load.


1. The top board has a connector for connecting to the circuit under test, supplying power, and controlling an external relay. The LED to the right indicates that power is being supplied to the relay.
2. The module can be powered either from an external source or from the circuit being measured. In the first case, the range is 10–30 V; in the second, up to 120 V.
3. The board also has a shunt rated for currents up to 200 A, with a standard calibrated voltage drop of 75 mV at the rated current.
4. The power wires connect using large, hefty nuts. There is one small drawback, though: they spin, so it's best to hold them from underneath with a wrench or pliers.
The measurement circuit is connected properly, using a pair of separate wires.


Three connectors are used to connect the external board, which looks very neat to me. The measurement module itself is housed in a plastic box, which I also liked.


Undo four more screws and we can get inside.


The board itself is held in place by the same screws that join the two halves of the case, so once the cover is off, it's easy to remove. A pretty thoughtful design.
There's an LED on the board to indicate that power is present.


The meter's circuit board without the radio module.


The high-voltage regulator is built around a separate transistor mounted on a heatsink. In this case, it's a preregulator that "cuts off" most of the input voltage.
There's another transistor nearby. As far as I can tell, its purpose remains unclear.


1. As you may have noticed, the board has a radio module. The meter and display unit can "talk" to each other either over a cable or wirelessly. The connection works reliably at a distance of 8–10 m in an apartment, but obstacles significantly reduce the range.
2. The microcontroller, which handles all the control and measurements.
3. The RS485 interface transceiver. Yes, the wired connection isn't USB, as you might initially think from the type of cable and connectors used. The manufacturer simply chose convenient connectors, nothing more.
4. An operational amplifier that amplifies the signal from the shunt.
5. Input protection suppressors and the relay control transistor.
6. A switching voltage regulator; this is what the transistor-based preregulator supplies.


There’s nothing particularly interesting on the bottom, except that the entire lower part of the board is one large ground plane, split into two sections that are connected at just one point.


Display and control unit.
Yes, this unit is responsible only for those functions. Once the device is running, you can safely disconnect it; capacity counting will continue without it.


There’s a small cover on the back, with a connector for connecting to the measurement module. I have no complaints about the RS485 interface itself; it’s quite reliable. But the improvised connector ruins the whole thing—the connection is very unreliable.
By the way, the manufacturer’s logo and name are visible on the label underneath. I’ve already reviewed several of its devices: this power supply based on the 6005 board, as well as the more powerful 6020 version, and, at the other end of the scale, a very basic board with an 8 A output. A pretty good manufacturer, though it does have its “quirks.”


Under the cover is a small board with a radio module.


The board is held in the case by clips. The front panel is made of plexiglass, with a thin plastic overlay on the outside.


Unfortunately, the radio module is soldered in place, so I didn’t desolder it.


In any case, there’s no point desoldering it—there’s nothing underneath :)


1. Microcontroller
2. RS485 transceiver
3. Preregulator; it supports input voltages up to 30 V.
4. Additional 3.3 V regulator.


You can use the image from the product page to get an idea of its dimensions.
I’ll just say that, in my opinion, it’s quite compact, considering the operating currents of this device and the fact that it’s essentially two devices in one.


When operating over a cable, the corresponding icon appears in the upper left. When using the radio link, the antenna icon is shown if there’s a connection, or a crossed-out red rectangle if the connection is lost.
I didn’t notice any difference in operating speed between the cable and radio link; the readings update just as quickly.


The electronic version of the manual includes an image explaining the operating modes and the information shown on the screen. Curiously, this isn’t included in the printed version.
The screen displays:
1. Connection status
2. Lock mode (press and hold the OK button)
3. Output status (on/off), including protection trip information.
4. System address
5. Battery icon and charge percentage
6. Input voltage
7. Current
8. Power
9. Capacity in Ah
10. Capacity in Wh
11. Measurement module operating time
12. Operating mode menu items


But I’ll try to explain everything in my own words, since
a. the manual is in English and rather confusing
b. it doesn’t cover everything.

So, here goes.
1, 2. Since the device can measure current in both directions, it can count both discharged and charged capacity. The screen shows DIS for discharge and CHG (in red) for charging.
Now for the menu items.
3. NCP: negative current protection threshold. When the threshold is exceeded, a command is sent to the relay output. Set it to 0 to disable this function.
4. OCP: the same thing for positive current. Handy for overload protection.
5. LVP: protection against voltage dropping below a set level. All trips are sent to the relay output. This function is useful when measuring battery capacity.
6. OVP: the same as LVP, but for overvoltage. In all cases, 0 disables the protection.
7. OUT: toggles the relay output state, effectively switching it on or off.
8. CLR: resets the time and capacity counters.
9 BAT. Since the device can count both discharged and charged capacity, you can enter the battery capacity so that the battery’s charge percentage is calculated correctly.
10. This mode also lets you set the battery’s maximum capacity percentage. I didn’t quite understand this item.
11. SET. Sets whether the device powers up on or off.
12. Time delay. Initially, I thought this was the time during which the device would ignore an over-limit condition. It turned out to be a little different: this is the "restart" time, i.e. the interval before it tries to switch on again. At 0, protection operates in latching mode, i.e. until the user issues a command.


1. SET, output operating mode: active low or active high. This is needed for relays with different contact configurations.
2. Display timeout; at 0, the display stays on.
3, 4. ADR - device address in the system, from 1 to 99. Selecting a different address will break the connection.
5. Extended menu, opened by holding the "down" button. - Language; only English and Chinese are available.
6. Communication channel, used to avoid interference from similar devices located nearby.
7, 8. Screen brightness, 15 levels.

The calibration menu, however, wasn't documented anywhere, so I had to figure it out myself. The thing is, the device initially had a zero offset. With no load, it would sometimes show a current of 0.2 A. When measuring current, the positive reading was always 0.3 A too high, while the negative reading was 0.3 A too low. This was exactly what prompted me to look for this information.
By the way, although the device displays one decimal place, its resolution is not the expected 0.1 A, but about 0.15 A. So it may display, for example, 0.2 or 0.3, but skip 0.4 and jump straight to 0.5 A.

So, to open the calibration menu, go to the very top of the mode menu and hold the "up" button. This will give you access to the settings.
9. Voltage calibration menu. Apply a precisely known voltage to the input, then adjust the constant until the device display shows the same value.
10. Zero calibration. First, there is an automatic zero-setting mode; press the "up" or "down" button to use it.
11. Press OK once more to enter current calibration mode. The procedure is the same as for voltage calibration.
12. Reset all settings to their defaults.


The device supports several connection options.
Powered from the circuit being measured. In this mode, voltage is monitored only from 8–10 V.


Powered from a separate source. Essentially, everything is the same, but the voltage measurement range starts at zero.


The same setup, but with relay control. In this case, the relay breaks the power circuit when the specified parameter limits are exceeded.


Of course, I did a few tests.
I had no issues with voltage measurement. Well, almost none: even with the input disconnected and shorted, the display shows 0.05–0.09 V. It's not a big deal to me personally, but it did leave a bit of a bad taste.


Current measurement was a little worse. The zero was offset at first, but I quickly fixed that.


It's easier to view the rest of the results in a table, where I've marked the readings before and after setting zero.
On the other hand, the device supports calibration, so you can adjust it if needed. I should also note that, strictly speaking, it is within the stated error even as it is.



And now, why I actually needed it.
I already use three electronic loads, two all the time and one occasionally, and decided to add another. I gathered a number of different parts for it, and all I was really missing was an ammeter-voltmeter.


For the power module—the electronic load itself—I used the version I'd already shown, 300 W load.
The power supply, which I also reviewed, is 12 V, 0.5 A. The idea was that it would be enough to power the electronics and two fans.

I should probably make an important point here. Although I used a ready-made module, there's nothing stopping you from using a completely DIY version, like this one, just more powerful. There won't be much difference. The module shown offers little more than fan speed control, protection, and CV mode.


To avoid tiring the reader, I’ll keep things brief from here on, mostly with photos.

The first problem I ran into was that not everything fit very well in the Z2A case I’d chosen. But I like this case, so I ended up having to cut it.


I found a power cable connector at home, and the protective grilles I bought at a store.


This time I decided to use better terminal blocks. I liked the anti-rotation feature: a separate part keeps the clamped wire from twisting.


I wasn’t happy with the coarse adjustment using the supplied potentiometer, so I bought a multiturn potentiometer and a special knob for it.


1, 2. I chose a 2 kΩ potentiometer instead of a 5 kΩ one, figuring it would be less susceptible to interference picked up by the wires.
It’s a “million-turn” potentiometer, meaning it’s rated for a million knob turns. It’s fairly expensive, too—about $3.5—but I wanted something good: link. It’s also specified to have 0.25% linearity.
3, 4. The knob has an extra dial for finer adjustment, as well as a locking screw to prevent accidental rotation.
I bought it from the same place; it cost about $1.3.


The knob has the same diameter as the potentiometer—22 mm—and is easy to install.
Screw the plastic trim onto the potentiometer, fit the knob so the pin engages with the slot in the trim, tighten the locking screw with a hex key, and that’s it.


1. Illuminated power switch.
2. Relay for switching the power section.
3, 4. Control and indicator board for the load’s operating mode. Since it’s simple, I just cut the slots with a milling cutter instead of etching the board.

A separate note about the relay. Ideally, I should have used a high-power relay to switch the power circuit, but a relay rated for a guaranteed 40 A:
1. Is large, and space is limited.
2. Is very expensive.
3. Is very hard to find (the highest rating I could find was 30 A).

So I decided to use electronic switching instead. I’ll explain that later.


And, of course, wires, fasteners, and various odds and ends.


First, I covered the bottom of the heatsink using hardboard from the back of a piece of furniture. I once made some furniture for the house, so I had a few scraps left over. Two of them happened to be exactly the right width, so I only had to cut them to length.


I also made some extra spacers to raise the heatsink a little.


I cut out the unnecessary standoffs in the case, and had to sacrifice one of the mounting posts that holds the top cover, too.
But it actually holds together just fine without it.


On the meter board, I resoldered the wires to the shunt so they ran over the top of the board, then screwed mounting brackets onto both boards.
I also desoldered the USB connector because it was hitting the top cover. The load module is also a very tight fit, with about 1 mm between the shunts and the cover.


I measured and installed the wires to the shunt in advance.


To improve cooling, I widened the bottom ventilation slots from 3 mm to 4.5 mm. It looks a little worse, but since it’ll be on the bottom, I don’t care.


Install the measurement module board and the shunt boards.


Next up is the front panel. I didn’t reinvent the wheel here; I used a tried-and-true method.
Draw the panel and print both a “final” and a “draft” version. The draft has extra lines showing the dimensions of the front-panel components, as well as markings for the centers of the holes and the corners of the cutouts.


Transfer everything to the front panel.


Use a thin disc cutter to cut the openings, and a drill bit to make the holes. After that, trim off the excess with a utility knife and clean up everything we’ve done.


Test-fit the main components—that is, the ones that might not fit.


Lay down the “final” template and carefully stick a strip of ordinary wide tape over it, then cut out the holes. This is the most painstaking part of the job. It’s best to start with the small holes.
It’s best to use something smooth as a backing. I mistakenly stuck it to the back of the fiberboard, so some of the paper ended up stuck to the tape.


Before moving on to assembling the front panel, we first need to prepare everything that will be installed on it.
1. After some trial and error, I found that the button contains just an LED, not an LED and a resistor. By the way, my button switches 12 V, not mains voltage. This was done for safety reasons.
2. I soldered the connector from the board that came with the load to the variable resistor; I just didn’t want to cut the cable :)
3, 4. I assembled the control board. Nothing unusual: two LEDs, two buttons, and four 680 Ω resistors. I twisted the wires into bundles.


Now we can install everything on the front panel.


Some might think the controls are packed very tightly together. That was unavoidable: although the front panel is quite wide on the outside, the mounting posts limit the space inside, so I had to arrange everything as compactly as possible.


At the beginning, I showed that I raised the module with the heatsinks. I did this to leave enough plastic below the opening in the rear panel. But the most awkward part of working on the rear panel is cutting out the opening for the mains connector.


Overall, though, everything went fine, apart from one accidental scratch. To avoid scratches, do all the work from the back of the panel.


But I ran into a problem with the power supply. There was simply no way to secure it. It has no mounting holes, and I didn’t want to glue it in place, so I had to solder it directly to the input connector. The distance between the power supply’s input pads happened to match the distance between the connector terminals exactly.


Just to be safe, I insulated it with special tape. I know, it turned out pretty makeshift, but it was unavoidable.


And here I remembered the famous meme: “This is a disaster, bro.” I accidentally bought 60 mm grilles instead of 50 mm. :(
I had to use the grilles that came with the load module.


Unfortunately, they’re chrome-plated rather than black, so they look a bit sad. Never mind; I’ll pick up the right ones next time I’m at the store. They’re easy enough to replace.


Now we can solder all the wires to the front-panel components. Fortunately, there aren’t many.
1. Black wire from the shunt to the negative terminal
2. Red wire to the positive terminal.
3. Voltage-sense wire also to the positive terminal.
4. Wire from the power supply to the switch.
5. The power wires from the switch go to the electronic load and the control and display module.



I had three options for connecting the power module and the ammeter-voltmeter.
1. One power supply, with the shunt connected so that it also supplies power to the meter through the ground wire.
2. The meter is powered separately from the shunt, but measures the voltage including the drop across the shunt.
3. Two power supplies. Everything works correctly, but there’s nowhere to put an extra power supply.

I chose the first option for several reasons:
1. The measurement module draws only about 30 mA (the display is powered separately and draws 50 mA).
2. Only one power supply is needed.
3. The module’s current consumption can be subtracted with a single press of the zero-calibration button.


I couldn’t resist: here’s the first power-up, with everything still “held together by a thread.”


A little about connecting to the load board.
The display and button connections are very straightforward. Four wires go to each half:
1. Common
2. Button
3. Green LED
4. Red LED

I decided not to desolder either the original button or the LED, but to connect directly to the microcontroller outputs. The LED on the left is green, the one on the right is red, and figuring out the button is easy enough.


Here’s the overall wiring layout. To make the harnesses easier to tell apart, I used different wire colors for the button connection on each board.
Left: black, white, green, red.
Right: black, yellow, green, red.


I didn’t really trust the original power terminals to handle 40 A, so I connected the wires straight through without cutting them. I slit the insulation and stripped off a section. I bought some extra-flexible wire for jobs like this a long time ago; it’s much easier to work with than ordinary PV-3, ShVVP, or PVS wire. But the price...


While connecting the wires, I accidentally forgot about the electronic load module’s enable interlock.
I found a cluster of components on the board: five transistors (three MOSFETs and two bipolar transistors), plus two op-amps.
It turned out to be the circuit that selects CC/CV mode and switches on the power stage.


The principle is very simple: a command from the microcontroller turns on one amplifier or the other. But the schematic also showed a transistor supplying power to both circuits. This transistor isn’t controlled by anything, though. So I connected the relay contacts to it.

The schematic uses the relay’s normally closed contacts. I could have used the normally open contacts and changed the output logic in the volt-ammeter settings, but I wanted the relay to reliably disable the load as soon as power was applied. With the other option, there would always be a delay while the volt-ammeter started up and the relay switched.


The relay is small and light, so I simply glued it to the board.


Here’s the finished result. I routed all the wires so they wouldn’t get caught in the fans, while leaving as much free space as possible around the fans for airflow.




To keep the case from sliding around on the table or scratching it with any protruding fasteners, I glued on some feet.


The last step, and probably the trickiest, is removing the protective film from the display. And that’s about it.


I also drilled ventilation holes in the top cover so that air pockets wouldn’t form in areas the fans don’t reach.


Above, I mentioned the converter board and linked to my write-up on building a power supply around it. That was about 4.5 years ago, but I still use that power supply today. What’s more, the two units look and work pretty well together :)


Of all the cases, I like the Z2A best. They used to be made by Kradex, but as far as I can tell, they’re now made locally, so one costs only about 2.5 dollars.


A little more about current measurement accuracy. Above, I tested it at currents up to 5.1 A, but that’s very little for a meter with a range up to 100 A.
So I took a powerful 5 V power supply and loaded it to about 35 A.
My first thought was that the accuracy was terrible, but DC clamp meters are inherently not very accurate, unlike measurements made with a shunt.


So I decided to compare its readings with a more accurate meter.
I set the load current to about 10 A. With the current at 10.1 A, the clamp meter read 10.5.


Apparently, I shifted something while switching the wires, and the load current ended up at 10.2 A. But that’s not the main point: the readings match those of the more accurate meter. I’d guess the clamp meter itself reads a little high. I performed the zero adjustment.


Video.
Part 1: inspection of the ammeter-voltmeter and tests.


Part 2: an overview of electronic loads and how they work, plus a demonstration of the ammeter-voltmeter in operation.



So, what can I say in conclusion?
First, the positives: I liked the ammeter-voltmeter, mainly because of its convenient design, current measurement in both polarities, numerous service modes, high-quality display, reasonably good measurement accuracy and, importantly, calibration capability. It also offers both wired and wireless options for connecting the control and display panel.

There are some drawbacks, too. Current measurement is rather “coarse,” it displays a voltage of 0.05–0.09 V even with no input connected, and the buttons are very stiff. Oddly enough, the last issue is what annoys me most, since the others are much less critical to me.


That’s all for now. As always, I look forward to your questions and comments. I hope you found the review useful.