UM25C + HD35 set of USB doctor and electronic load.

Good day to all!
I want to offer to your court another review on a set of electronic load and usb tester. Anyone interested is welcome under the cat.
To begin with, let me write a few words about what these things are all about in the review and why they are needed.

USB tester (it is often called usb doctor)It is used to control the voltage and current passing through the cable at a specific time. It is used most often to test chargers, determine the maximum current that can be passed through the usb cable, and determine the battery capacity by counting the current consumed during charging the device or given out during discharge. At its core, this is a set of voltmeter, ammeter, and in this case an ohmmeter combined with a microcontroller that collects and processes information from devices.
In theory, if you do not have suchspecialized device, it can be replaced by the above-mentioned devices. If a pair of voltmeters, ammeters add a stopwatch and a person who will constantly record the readings, then the battery capacity can be calculated, but it will all be for a long time, and therefore inefficient. To facilitate such calculations, a usb tester is used, the user simply needs to connect it between the device under study and the current source or consumer and everything, the tester can do his own thing and record everything, the user only needs to correctly interpret the result.
The second device from the review is an electronic load, and it is very necessary for testing charging and power cans (PowerBank).
Load connected to powerbank or chargingallows you to set any current (from the range supported by the load) consumption and efficiently convert the current into heat by loading, say, charging in a way that no other consumer will load in real life.
At its core, the load is a variable resistor,which, in fact, it can be replaced. But the resistor is very smart, with its own temperature control and cooling system, and the HD35 also has a trigger that can make charging include fast charge technology.
And answering the question that most likely will be askedin comments. Yes, these are quite specialized devices, and yes they are very rarely needed by the simple user (at least the load is so rarely needed), but for those who are passionate about electronics, these two devices are very necessary.
On now to the perpetrators of the review.
The first thing that caught my eye when receiving a parcel is the quality of the packaging. The whole package was packed in a small box of solid foam and carefully wrapped in adhesive tape.

Yes, and the devices themselves are packed very well, and in the future there was definitely no question of how to store them and what to wear.


  • Model: UM25C
  • Screen: 1.44 inch color LCD display
  • Transmission Interface: Bluetooth
  • Voltage measurement range: 4-24,000 V Resolution: 0.001 V
  • Current measurement range: 0-5.0000A Resolution: 0.0001A
  • Capacity meter mAh: 0-99999 mAh measurement accuracy: ± (0.5 + 2 digits)
  • Capacity meter mW: 0-99999mWh accuracy measurement: ± (1 + 4 digits)
  • Load resistance: 0.8 ohm-9999.9 ohm
  • Measurement time: 0-99h59min59s
  • Temperature: -10 ~ 100 ℃ / 0 ℉ ~ 200 ℉ Temperature measurement error: ± 3 ℃ / ± 6
  • Adjusting the screen brightness: 0-5 levels Automatic screen shutdown: 0-9 min.
  • Refresh rate: 2 Hz
  • Charge Recognition Mode: QC2.0 、 QC3. 0 、 APPLE 2.4A / 2.1A / 1A / 0.5A 、 Android DCP 、 SAMSUNG
  • Size: 71.2 mm x 30.5 mm x 12.4 mm (UM25C)
  • Product weight: 23.74 g (UM25C) (unpacked); 54.56 g (UM25C) / 50.08 g with packaging


  • HD35 model
  • Rated operating voltage DC4-25.0V
  • Max power 35 W
  • Rated current 0.25-4.00A (when the fan is not working, Adjusting the current from 0.05a) 0.25-5.00A (when the fan is not working, Adjusting the current from 0.05A)
  • Fan speed up to 8000-10% rpm, regulated by a thermal sensor
  • Fast Charging Trigger: QC2.0 5V, 9V, 12V, 20V, QC3.0, FCP, AFC9V
  • Operating temperature -10 ℃ -40 ℃
  • LED display 4-seven-segment indicator
  • Ports: USB Type A, MicroUSB Type B, USB Type C
  • Weight 52 g
  • Size 84x41x28 mm

Appearance controls
To begin with, the tester itself is a UM25C.
Delivers the tester in a small aluminum boxinside filled with foam, inside which the doctor lies quite tightly. Almost all of its front part is occupied by a color display, the rest is hidden by blue plastic.

In addition to becoming standard for such devicesTwo USB Type A ports. This model of the tester has three additional usb ports to make it easier for the user to find them and figure out their purpose. On the back of the case there are hints.

In addition to the usb ports on the sides of the case are locatedFour buttons for selecting the operation mode and tester settings, and a microswitch allowing you to turn the Bluetooth module on and off. That is, in fact, all simple controls.

Now a few words about the load HD35.
Almost the entire upper part of the device takesradiator with fan. To connect the current source, the load has three ports compactly grouped on one side. The maximum current that can be passed through the load is 5 Amps for Type A / C ports and two Amps for a MicroUSB port.

On the opposite side of the ports to bea display of seven segment indicators, a variable resistor for setting the required current and three buttons for controlling the trigger for fast charging and information display.

On the reverse side of the board is the wholeelectronic filling loading. In the middle of the load board there is a hole through which voltage regulator LM317 and transistor TIP122 are screwed to the radiator. On the reverse side, the radiator is glued to the board so that the transistor with a stabilizer heats up the radiator, and already the radiator heats the rest of the electronics on the board, the solution is so-so, but what can you do in the fight for dimensions.

Charging does not have any case, and even there is no protection at the bottom of the board, so when placing it you should make sure once again that you don’t short the elements from the bottom.
About management
Tester UM25C
As I wrote above to control the tester serve 4buttons located at its corners. On the screen above / below each button it is written what it does by briefly pressing, by default the lower buttons serve to select one of six screens with information, and the upper ones are responsible for turning off the screen, calling for help, and with a long press allow you to turn the screen around axis.

When you rotate the screen, the control buttons rotate after it, on the one hand it is convenient, and on the other, if you want to rotate the screen by more than 90 degrees, you will have to do it with different buttons.
The tester has six working screens.
The main screen, shows the main parameters of the current,voltage, load resistance, power passing through the load at the moment and two storage counters in mA / h and mW / h. In addition, on the same screen, you can select one of nine groups in which the measurement data will be stored. Using groups allows, for example, to interrupt the PowerBank capacity check, switch to another group, check, say, charging, and then continue to suck the load, while new data will be added to the values ​​already stored in the group.

Screen check fast charging mode insteadData from the cumulative counters shows the current fast charging mode and the voltage values ​​that are fed to the D + / D- line to activate the fast charge mode.

Capacity counting screen, shows how muchthe test lasts, the value of current and watt counters, and also allows you to set the current consumption threshold after which the tester will stop calculating the current consumption. The last function is very necessary if you leave, say, a phone for charging through the tester unsupervised for a long time, in this case there is a possibility that, charging the battery, the phone will continue to work from charging by consuming current and introducing an error into the measurements. In this screen, you can set a threshold current value in the range from 0.01A to 0.26A, if the current through the tester falls below the specified test and stops adding it to the capacitance data and stops the test time timer.

Cable check screen. Allows you to test usb cable. For testing, it is necessary to connect the tester, ideally with a load or with a resistor, replacing it with charging and press and hold the lower right button until the cable icon flashes on the screen.

After that, you need to connect the tester to the sourcecurrent through the cable under study, after loading the tester, again press and hold the lower right button. In total, the screen will show the cable resistance and the values ​​of current and voltage when connected via cable and directly.
These are the values ​​that showed me a complete cable from PowerBank Xiaomi

This cable is from my phone THL

THL cable is definitely worse, although it is much longer.
A screen with a graph of current and voltage, so honestly II did not understand why it is needed, the time interval that fits in the window is less than a minute, so I personally didn’t see much practical use of this screen.

And the last sixth screen is responsible for generaldevice settings. Here you can set the time after which the screen will turn off, the backlight brightness, temperature measurement units and the background color for text and menus. To change one parameter or another, long-click the lower right button to set the cursor in the desired cell, and notice the left button to set the desired value, to save the set parameter, hold down and hold the lower right button again.

HD35 load
To control the load are three buttons and one variable resistor.
The resistor can be used to set the current that the load will consume, and the buttons serve to control the load and switch the fast charging trigger.
First, a few words about the use of the load in normal mode.
The current is set by turning the variable resistor,the manufacturer has installed a lot of reversal resistor so that you can fairly accurately set the required current, each turn of the resistor increases the load current by about 200 mA. By pressing the “OK” button you can disconnect and connect the load from the current source. The current can be regulated both when the current sources are connected and when it is disconnected, this mode allows you to find out not only the maximum current that the source can produce, but also the peak starting current. For example, my PowerBank in normal mode can deliver up to 2.6 A per port, but only if this current grows gradually during operation, but the peak current when the load is connected should not exceed 1.8A, otherwise the bank protection works and it turns off. In addition to the current value, the load can also display the current voltage supplied to its port and the power consumed, can be switched between the displayed values ​​by pressing the “Set” button.

Some tests
The first thing I wanted to know was how accurately the tester and the load display the current value. For the test, a USB cable was made into the gap, which can be connected to a multimeter.
In all tests, a resistor is connected to the second port of the bank, it does not directly participate in the test, but it is necessary that the bank did not turn off at a low consumption level.
The first test at load 0.01A multimeter shows 0.0229 And tester 0.0228 error in the fourth decimal place, to be honest, I thought that everything would be much worse. But with the accuracy of the installation of the current on the load, everything is sad, the displayed value of the current is half less than the real one.

On the load current 0.02A. On the tester, the value floats at 0.0329-0.0330A, the multimeter holds more consistently. The 0.0331A error is slightly higher, but again does not exceed the value of the fourth decimal place.

On the load of 0.05A. And again, all is well the error between the tester and the multimeter only in the fourth digit.

On a load of 0.10A. With the tester, everything is fine again, but the load has already begun to lie for as much as 10mA.

I conducted tests up to 2.2A, their photos can belook below. In all tests, the tester showed itself quite well, the difference in readings between it and the multimeter did not exceed ± 2 in the last digit of the displayed value, so we can hope for fairly accurate research results using this tester. But you shouldn’t fully rely on the load readings, at first it lowered the displayed current value, the difference between the real current and the displayed one gradually decreased and at a value of about 700mA the load finally showed the correct current value. But as they say, the music did not play for a long time and with a further increase in the current, the real value of the current again began to differ from the displayed one, but in a lower direction, with a current value of 2.2 And the difference reached 100mA. Such a deviation of readings is quite acceptable and affects perhaps the usability, but still unpleasant.
More photo tests here

Then I wanted to look at the graph of the current consumption of the load.
It was interesting she eats linearly or pulses. It is quite simple to do this using a shunt and an oscilloscope, in my case a multimeter in ammeter mode acted as a shunt. The consumption graph is smooth, without pulses, so the load works in a linear mode, small bursts on the graph are the noise of the can itself, this can be seen at the end after the load is disconnected, the ripple remains much less until the indicators on the can go out and it goes off.

Check trigger fast charging.
Again I allow myself a little explanation of what it is.
At first, the phones were charged through a separatethe connector and there the manufacturers did what they wanted, but over time, the USB connector became the standard for charging, but it was really limited to 5 volts and 500 mA, which was clearly not enough to charge the smartphone. The first attempt to improve the situation was the USB Battery Charging Revision standard, which increased the current to 1.5 amperes, then Quick Charge 1.0 with a current of 2 amps. It was good, but over time, this was not enough, and then they decided not to follow the path of further increasing the current, but to increase the voltage while maintaining the current value at 2-2.5A.
At the moment, the standard Quick Charge 3.0 allows you to change the charge voltage from 3.2 volts to 20 volts in increments of 0.2 volts.
But fast charging technology is not easyblindly increasing the supply voltage at the output of the charger, it is also a special protocol by which, for example, the phone can communicate with charging and agree on what kind of voltage and current it needs at a given time. The communication protocol between charging and the device was implemented quite interestingly, for communication, the D + and D- data wires inside the USB cable are used. To put it simply, in order for the fast charging mode to be activated, a consumer, for example, a telephone or in my case, the load must apply a certain level of voltage to these wires, by the presence of this voltage, the charging will understand that a device supporting the fast charge function is connected to it and set the required voltage value on its way out.
It is worth bearing in mind that due to the fact that forcommunication uses data cable wires, QC mode may not turn on when using cables with a detachable connector, or turn on only if the cable is connected to the phone. Understanding whether a QC will work on a cable or not is quite simple, if using this cable you can connect a phone to a computer and transfer files, then QC will most likely work.
And now the actual tests.
The first thing I tried to believe the fast charging mode was the power supply from the Meizu phone, judging by the description, he knows how to give out voltage up to 12 volts.
To activate the trigger for fast charging, you need to press and hold the trigger buttons until the red LED flashes.
Then by briefly pressing the trigger button you canselect the required protocol. Red LED QC2, green LED QC3, blue LED Huawei FCP and Samsung AFC 9V. After selecting the desired protocol, you must press the "OK" button and wait until the LED starts blinking. Then using the “Set / -” and “Ok / +” buttons you need to set the required voltage value. To confirm the selected value, you must again press and hold the trigger button. Also, the load has an AUTO mode, when the load automatically check all the fast charging protocols it supports in turn.

Unfortunately, it turned out that the load trigger is notable to work with such a charge so that the focus failed. Although the tester itself shows that the phone is charging in fast charging mode, the charging protocol really defines how Samsung, although in fact it uses the Meizu mCharge protocol.

I did not have anything else with support for fast charging, but my colleague found the PowerBank Xiaomi on which the load was tested.
The second attempt to start the trigger wassuccessful, the bank switched to QC 2.0 mode and issued 9 volts. As mentioned above, it is very convenient that the tester displays not only the protocol by which fast charging works, but also the voltage that is applied to the D + / D- cable.

And then 12 volts.

By the way, contrary to the instructions, fast charging is supported through the microUSB port and not only via USB and TypeC.

Check the trigger in QC 3.0 mode, unfortunately, there is nothing.
I think it’s worth completing the actual load tests and devoting a few words to the tester’s communication capabilities.
Model tester UM25C has a built-in modelBluetooth transmissions to communicate with both phones and a computer running Windows 7 and above. You can download the required applications by the QR code or by the url printed on the cardboard enclosed in the box with the device.
In the description of the application Android version 5.0 or higher is indicated. I tried to install it with Android 4.4, the application installs, but, unfortunately, it does not start, you need to take this into account when buying a tester.
The main and only screen of the application looks likelike this. It is very convenient that the programmers in the application refused to split into several screens and reduced the information from all the screens of the tester into one informative page. All tester settings can also be made on this page.

The buttons at the bottom of the screen are used to control the display of the tester itself.

On Windows, the application looks even more visually. When installing the application on a computer, it will ask you to restart the computer. On windows 7, everything worked without rebooting, but on windows 10, before rebooting, the data did not arrive.

Right-clicking on the chart allows you to export data as a picture or Excel file.

A bit of viscera.
In the load, there is nothing special to disassemble, there and so all the elements are in plain sight, but you should remove the protective panels from the tester. On the top there is only a screen.

All the main elements are on the bottom of the board. Bluetooth module is on a separate fee, with its own power stabilizer and a switch.

A small conclusion.
In general, that the load that the tester justifiedexpectations and will be a good help for people keen on electronics or reviews. As I wrote above, I consider that for a regular user such a set is superfluous and one can do without either just a tester, or even a simpler tester. It is a pity that the manufacturer has not provided the ability to connect to the tester via cable, but this is a small minus that you can put up with.
I apologize in advance for spelling andthe grammar of the text, all the mistakes made are not made on purpose, but only because of ignorance and in connection with the imperfection of automatic text-checking programs.