Fnirsi FNC88 USB Tester

At last, the FNC88 USB tester has made its way to me. It’s been reviewed many times already, and it’s made by a company with the very strange name Fnirsi.
Inspection, description, tests, conclusions—as usual.


I don’t know how many reviews of this tester there have been, but I agreed to write one only because I was interested in its relatively low price and decent claimed specs.
Why do I think its price is just right? Basically, it’s positioned as an alternative to the TC66 from RuiDeng, which costs about one and a half times as much, so I’ll inevitably compare the two from time to time.

To be fair, I’d already forgotten that this tester was supposed to arrive, and was even surprised to get a text from the post office. But when I opened the package at home, it all came back to me. They really had sent it to me, but that was more than two months ago....


And the first comparison is the box. Here, I think I have to give the edge to the FNC88, because the box for the RuiDeng tester is a bit more basic.


Claimed specifications
Voltage measurement range: 4–24 V, or 0–24 V with external power.
Voltage measurement resolution: 0.0001 V
Voltage measurement accuracy: ± (0.5 ‰ + 2 LSB) @ 25℃
Current measurement range: 0–5 A
Current measurement resolution: 0.0001 A
Current measurement accuracy: ± (1‰ + 2 LSB) @ 25℃
Power measurement range: up to 120 W
Power measurement resolution: 0.01 W
Capacity measurement range: 0-> 99999.9 mAh (5 groups)
Energy measurement range: 0-> 9999.99 Wh (5 groups)
Timer range: 0-> 999 h: 59 m: 59 s
USB HID interface: 5 V
D+/D− data line voltage: up to 3.3 V
CC1/CC2 line voltage: up to 3.3 V
Temperature measurement range: 0-> 65 ℃



The tester is slightly larger than the RuiDeng model, and its somewhat angular case makes it feel even bigger. Both models are clearly smaller than my two main testers, though.


1. A 0.96-inch color LCD is on top.
2. The voltage and current measurement ranges are printed on the bottom, along with the button labels and the power mode switch.
3, 4. Type-C connectors are used to connect to a source or load, exactly as on the RuiDeng tester. Both testers also support data transfer in USB 3.0 mode.
5. There are three control buttons, rather than two as on the RuiDeng model. The outer buttons move up and down through the menus and modes; the middle one selects a mode and changes a setting. The power mode switch is to the right, with standard and Power Delivery modes.
6. There’s also a microUSB socket on the side, which can be used to power the tester or update its firmware when connected to a computer.

Key differences from the TC66:
It has three buttons, but I wouldn’t say that makes it much easier to use—you can still get confused sometimes.
There’s just one power mode switch, which I think is better.


Like many testers of this kind, the case is semi-open: the top and bottom are covered, but the sides are completely open. I don’t like this design either, so it’s best to keep it in the box to prevent small conductive objects from accidentally getting inside.
Speaking of the case, it’s noticeably thicker than the TC66—almost 11 mm versus 8 mm—which can sometimes make it less convenient to use.


I also wasn’t too keen on some aspects of this design, since it’s a little different from other testers. The front "glass" is very thin, and the screws have countersunk heads, so the underside of each head isn’t flat. The result: chipped corners on the "glass". One had already chipped before I took it apart; another (top right) is about to go, and I think the same will happen to the others. During normal use, you’ll inevitably put pressure on the case, so it’s only a matter of time.


Inside, I found an S3M diode rated for up to 3 A. My first thought was that it was a TVS diode; then I noticed it was just a regular diode and thought, well, at least it provides reverse-polarity protection. As it turns out, though, it isn’t connected to anything at all—it’s only there to hold the USB plug in place.
There are no components under the display.


The internals are almost identical to the TC66.
On the left is a 24 V TVS diode; to the right is a 10 mΩ current-sense shunt. The TC66 had a 15 mΩ shunt, which is better for measurement accuracy but worse in terms of the voltage drop across the meter itself. Both testers have the shunt in the power line rather than the ground line, which is an advantage.
It uses the same microcontroller, the same INA226 ADC, the same 256 Kbit (32 KB) EEPROM, and also has a chip for controlling Power Delivery functions. Basically, this is the same TC66, just with a slightly different PCB layout and more buttons.


When power is applied, a splash screen appears, gradually fades out, and the tester then switches to normal operation.


The screen is bright, but in my opinion it feels a bit cramped—not because of its physical size, but because it’s overloaded with information, which means the current and voltage readings are shown in tiny digits. The TC66, for example, has a better-optimized layout in this respect.

There are several modes, which you cycle through using the left and right buttons.
1. Main screen 1 — time, current direction, temperature, voltage, current, power, equivalent load resistance, memory slot, capacity in mAh and mWh.
2. Main screen 2 — time, current direction, temperature, voltage, current, power, data-line voltages, and charging protocol. As you can see, only the last three items differ from the previous mode.
3, 4. Automatic detection of fast-charging protocols. This is where I figured out how this and other testers behave. If you connect the tester directly to the charger’s output, not all available protocols are shown. For example, SCP and AFC are highlighted in red here, but turn green when connected directly.
5, 6. Manual protocol control, meaning you can force the charger into a particular operating mode.
7. Power Delivery mode control. I found no problems; it changes the voltage.
8, 9. Settings for brightness, automatic dimming, image rotation (2 options), temperature units (Celsius/Fahrenheit), language, and factory reset.

There are clearly fewer settings than on the TC66, and the controls aren’t entirely intuitive either: in some modes the middle button changes a value, while in others it switches between menu items.


The different display modes of the charger-control trigger.


And the same thing in practice.
At first I had problems with AFC and FCP modes. It later turned out that the tester doesn’t always control these modes when the charger is connected to the tester’s output.


A brief overview of the main display and control modes—and here I should add a small note about ergonomics.
By default, the tester starts in display-only mode. To start measuring capacity, you have to press the OK button. So when power is connected or disconnected, the device will continue charging or discharging, but it won’t measure capacity.
The TC66 starts measuring capacity automatically, but resets to zero after power is connected or disconnected, so it’s a tie here—both options are inconvenient.
My main ZY1276 handles this better: measurement starts automatically, and after a power interruption it simply resumes from the readings recorded when power was lost.


The tester supports firmware updates. It does complain when connected to a computer, but you can ignore that.


Go to the repository and download the new firmware, the update utility, and even a video tutorial if you need one.
The rest is simple: connect the tester to the computer via microUSB while holding down the OK button. The current firmware version appears on the screen (mine was 1.00). Run the update utility and flash the new version (the latest is 1.02).


Tester power consumption in different modes
1. Full brightness
2. Minimum brightness
3. In addition to all the modes shown earlier, there’s also an option to turn off the screen, but power consumption is almost the same as at minimum brightness.
4. When external power is connected, power drawn from the measured circuit drops to zero.


Measurement accuracy check
Modes are all well and good, but this tester is still a measuring instrument, albeit a basic one, so in my opinion it’s important that it measures correctly. There are a lot of photos below, but for the most part they simply confirm my conclusions and are included as supplementary material.

The specifications state that the minimum supply voltage is 4 V. In reality, the tester starts up at 3.35 V, and at 3.5 V it can already read measurements quite reliably; in both cases, the readings match the actual values.
Across the 4–27 V range, the error was about 0.1%, compared with the specified 0.5%, which is excellent in my opinion. The tester also worked normally with an input voltage of 27 V.


In current measurement mode, the specified error is 1%. In reality, I got about 0.4–0.6% across the 50 mA–5 A range. That’s not quite as good as my ZY1276, but still very good and well within the stated specifications.


Although the current-sense shunt dissipates only 0.25 W at maximum current, there is still a small amount of drift. For example, while I was running the test, the reading “drifted” from 5.0007 to 5.0016 with the input current unchanged.



Conclusions, starting with the objective ones:
1. Hardware-wise, this is almost the same as the TC66, which is good because its circuit design was quite sound.
2. The measurement accuracy is excellent and better than specified.
3. It can display and control various protocols (QC 2.0/3.0, PD, Huawei SCP/FCP, Samsung AFC). I did have questions about the AFC and Huawei FCP modes, but it turned out that the tester is picky about controlling these modes when a charger is connected to its output.
4. The shunt is 10 mΩ, compared with 15 mΩ in the TC66. This reduces measurement accuracy somewhat, but has less effect on the circuit being measured. The ZY1276 has a 12 mΩ shunt, but it comes from a more reputable manufacturer.

And the subjective ones:
1. I like the design less than the TC66, both in terms of size (especially thickness) and mechanical strength. It’s simply flimsy.
2. Although it has three buttons, I didn’t find it any more convenient to use than the TC66.
3. The software is noticeably simpler and more “rough around the edges.” Unfortunately, although firmware updates are supported, version 1.02 has been on the website for a long time.
4. Both the FNC88 and the TC66 have quirks when power is disconnected: the FNC88 will pass current but won’t count capacity until you press a button, while the TC66 will count, but starts from zero.

All in all, there’s no miracle here. The FNC88 costs about one and a half times less than the TC66, and you get about one and a half times less in return (roughly speaking). Also, don’t forget that the TC66 can send data to a computer and is available in a Bluetooth version.
But if you need a decent, relatively inexpensive tester with support for modern fast-charging protocols and good measurement accuracy, the FNC88 is a solid option. It currently costs $13, but discounts come around from time to time, bringing the price down to $11. I think that’s a reasonable price for an instrument in this class.

That’s all from me. I hope you found this information useful.