Somehow before I already reviewed a similar device, but the main distinguishing feature of this model is its ability to work with current up to 3 A, voltage up to 9 V. But first things first.
So, the order was made on eBay, since at the time of the purchase it was the cheapest lot, even cheaper than on Aliexpress. :) The seller turned out to be quite prompt and sent the parcel the next day after payment. She spent about 3 weeks on the road, after which she was safely found in a mailbox (apparently, postmen now deliver very small parcels to homes). The tester is supplied in a shiny bag with a plastic zipper.
Unlike the previous model, this is no longer an anonymous Chinese-made creation, but quite a branded product. The manufacturer's name is indicated on the front side of the tester, in the upper left part - Keweisi. The same brand is indicated on the sticker that is on the bag, so it is logical to assume that in this case the bag is the original factory packaging :) 
The tester has 2 standard USB connectors - mother and father. Male is the input connector, female is the output connector. Indications of what and where to connect are also on the plastic body of the device. On the right side of the upper end there is a data reset button (also labeled). 
The reverse side of the tester looks like this: 
The case is assembled very well - no cracks, gaps, play, creaks or other unpleasant flaws were found. So the assembly gets a solid 5, the plastic also has no unpleasant odor.
In principle, there is nothing else interesting in the appearance of the device, and therefore you can move on to practical tests, but before doing this, I will introduce you to the characteristics of the tester:
Model: KWS-V20
Housing material: Plastic
Color: Blue
Operating voltage: 3-9V+/-1%
Current: 0-3A+/-1%
Time counter: 0-99 H
Dimensions: 59*23*13.5 millimeters
Weight: 19 grams
So the designation “V20” present in the model name is purely a marketing ploy, which the Chinese use very often. :)
And this is what the Keweisi KWS-V20 looks like next to the world-famous white tester: 
Here the first obvious advantage of the new model immediately catches your eye - with fairly similar body sizes, the screen of the new product is much larger, which means that reading information from it should be much faster and easier, but this is not the case. The fact is that the data from the large screen of the Keweisi KWS-V20 is clearly readable only from a certain angle and you have to twist it to make out what is written there :(
Okay, let's get back to our tester and its testing. Here it is in a calm state, connected to the network: 
Just for fun, I connected two testers into one circuit to look at the data they display (sorry that the new product is upside down, but there’s no other way:(): 
As you can see, the Keweisi KWS-V20 shows 5.14 V versus 5.12 V for the old friend. And here the second disadvantage of the new product immediately opens - it has a stationary USB connector that does not spin, does not rotate, does not move, that is, the tester can be connected in one specific position, it cannot be installed the way you want. This drawback is especially visible if the socket is located in a narrow opening between some furniture elements (I have one) - then you can’t see what is shown on the tester: (Well, it doesn’t have a microUSB connector, so you can “hang” the tester on another the end of the cable is impossible: (And since it turns out that this paragraph is devoted to the shortcomings of the tester under review, then I will point out one more thing - it does not have memory cells. The tester can only count one value and if there is a need to make a new measurement, then the old values will have to be reset when using the Reset button (and the white tester has as many as 10 memory cells).
Let's connect some device to our tester. 
He thinks everything is very good. The display displays information about the current voltage, current strength, received capacity and the time during which the tester is working (it’s a pity that the total time while the tester is online is counted, and not the time during which the connected device is charging). When the tester is disconnected from the network, the received data is saved.
During operation, it was discovered that the Keweisi KWS-V20 also does not have an indication of too high or low voltage. The white tester notified us about this using a flashing screen and a corresponding icon on the display. For example, it’s only 3.99 V, but the tester doesn’t react to it in any way. 
I can say that during the test, all measurements obtained using the Keweisi KWS-V20 were compared with the data obtained using the old white tester. We can say that the data were identical and differed within 0.01-0.03.
To sum up everything that was written above, I can say that the Keweisi KWS-V20 turned out to be quite a working tester; the main advantage of this model is the presence of a time counter. But in general, for me the white tester turned out to be much more convenient and practical due to the normal screen, the presence of a cable with a USB connector and a microUSB connector. The Keweisi KWS-V20 can operate at higher voltages and pass more current through itself, but this is not necessary for measuring the capacities of batteries and batteries. :) And also, a charger for all kinds of VariCore V10 batteries should arrive soon - there we’ll check this tester more seriously.
Basically, that's all. Thank you for your attention and your time.
ROCK SX-Q1U2
USB-microUSB cable with tester
The USB-microUSB cable with a tester is designed to measure the supply voltage and current consumption of devices connected with it.
When the cable is connected to any USB output without load, the indicator lights up V(voltage) is green and the tester display shows the USB output voltage for 10 seconds. When any load is connected to the microUSB connector (phone, tablet, etc.), the indicator lights up A(current) blue, for 10 seconds. The current/voltage readings alternately light up on the display, after which the current consumption value is constantly displayed.
Measured voltage: 3- 9V
Measured current: 0 -3000mA
Measurement error: ±1%
Cable length 1m
Price 300 rub. IN STOCK BUY
USB-microUSB cable with tester
DT-1
The DT-1 tester is designed to measure the voltage and current consumption of devices connected to the USB connector. To measure parameters, the DT-1 tester can easily be connected to the power cable. The display alternates between current and voltage values.
Measured voltage: 3.5 - 7V
Measured current: 0 -3000mA
Measurement error: 1%
Price 250 rub. IN STOCK BUY
USB tester XTAR VI01
USB tester XTAR VI01
The XTAR VI01 tester is designed to measure the supply voltage and current consumption of devices connected to the USB connector.
XTAR VI01 USB Detector is designed as a USB flash drive with two USB connectors (input and output). To measure parameters, the XTAR VI01 tester can easily be connected to the power cable. The display alternates between current and voltage values.
Measured voltage: 4.5 - 6V
Measured current: 0 -2500mA
Measurement error: ±0.02V, ±0.02A
NOT AVAILABLE
USB tester XTAR VI01
USB tester XTAR VI01
USB Tester KWS-10VA
USB Tester KWS-10VA
The KWS-10VA USB tester with two USB outputs is designed to measure the voltage and current consumption of devices connected to the USB connector. To measure parameters, the tester can be easily connected to the power cable. The display simultaneously shows the following readings:
- current (A)
- voltage (V)
Measured voltage: 3 - 9V
Measured current: 0 - 3000mA
Measurement error: ±1%
Price 290 rub. IN STOCK BUY
USB Tester KWS-10VA
USB Tester KWS-10VA
USB tester KWS-A16
USB tester KWS-A16
The KWS-A16 USB tester is designed to measure the voltage, capacitance and current consumption of devices connected to a USB connector, as well as for testing micro USB cables. The device has a 24-hour timer to automatically turn off connected devices. The display shows the following readings:
- voltage (V)
- current (A)
- capacity (mAh)
- timer
Measured voltage: 4 - 30V
Measured current: 0 - 3000mA
Measurement error: ±1%
The MENU button is used to view and reset capacity values and set the shutdown timer.
Price 400 rub. IN STOCK BUY
USB tester KWS-A16
USB tester KWS-A16
USB Tester KWS-V20
USB Tester KWS-V20
The KWS-V20 USB tester is designed to measure the voltage, capacitance and current consumption of devices connected to the USB connector. To measure parameters, the tester can be easily connected to the power cable. The display simultaneously shows the following readings:
- voltage (V)
- current (A)
- capacity (mAh)
- time
Measured voltage: 4 - 20V
Measured current: 0 - 3000mA
Measured capacity 0 - 99999mAh
Measurement error: ±1%
The RESET button (long press) is designed to reset the capacity and time values.
Price 380 rub. IN STOCK BUY
USB tester KWS-V20
USB Tester KWS-V20
USB tester J7-F (JW-D2LCDS-35W) 1 -25 volts
USB tester J7-F with adjustable electronic load
designed for measuring voltage, current, and other parameters of devices connected to the USB connector.
You can also use the device to test USB cables with connectors:
- micro USB,
- mini USB,
- apple Lightning 8pin,
- type C,
- It is also possible to connect via a DIY terminal block.
Two resistors allow you to smoothly regulate the load current up to 4A. The built-in cooler provides constant cooling and has automatic speed control. When measuring voltage below 3V, it is possible to connect additional power to the display via a special micro USB input (4-30V).
The J7-F USB tester measures many parameters and has three switchable screens to display them. To switch between different screens of the J7-F USB tester, simply press the control button once.
voltage (V)
current (A)
capacity (mAh)
energy (Wh)
power (W)
load resistance
voltage on contacts V+, V-, D+, D-
working hours
temperature inside the tester (C)
enable/disable timer
The tester has memory cells in which all calculated values are stored, such as capacity in Ah, energy in Wh, and operating time with load. When the tester is disconnected from the power supply and then turned on, the calculation of all values continues from the previously recorded values. These values can be reset either all at once or individually.
- 6 clicks – switch the language Chinese/English.
Full reset - with the tester turned off, hold down the control button. Turn it on. Release the button and press it again until RESET appears on the display.
After five clicks, the tester is switched to the power-off timer setting mode. By default it is disabled and in OFF mode. After entering the mode, one short press switches the timer to “A0” mode. In this mode, the load power will be turned off when the current drops significantly when the power consumption drops below 2 W in 1 hour. In the following mode, you can set the operating time in hours from 1 to 24 hours. A single short press decreases the value. If you then hold down the button, the values will automatically decrease quickly. Pressing twice briefly will increase the value. If you then hold down the button, this will lead to an automatic rapid increase in values. To disable the timer you need to set it to “OFF”. Setting a value greater than 24 hours will set the timer to “A0” mode. If you hold down the button during installation, all modes will change in a circle.
Characteristics of the J7-F tester:
- input voltage 1V – 25V with an accuracy of 0.01V;
- measured current up to 4A with an accuracy of 0.01A;
- charge counting range 0-999.99 Ah with an accuracy of 0.001 Ah;
- energy counting range 0-999.999 Wh with an accuracy of 0.001 Wh;
- measured power range 0-299.999 W with an accuracy of 0.001 W;
- counted time range 0-999 hours 59 minutes 59 seconds
PRICE 1350 rub. IN STOCK BUY
USB tester J7-F (JW-D2LCDS-35W)
USB tester J7-F (JW-D2LCDS-35W)
USB tester J7-T 3 -30 volts
USB tester J7-T
The USB J7-T tester is designed to measure voltage, current consumption, and other parameters of devices connected to the USB connector. To measure parameters, the tester can be easily connected to the power cable. The tester has a universal USB connector, which allows you to connect it face down without turning the connected device over. The J7-T USB tester measures many parameters and has three switchable screens to display them. To switch between different screens of the J7-T USB tester, simply press the control button once.
The display shows the following readings:
- voltage (V)
- current (A)
- capacity (mAh)
- energy (Wh)
- power (W)
- load resistance
- voltage on contacts V+, V-, D+, D-
- working hours
- temperature inside the tester
- enable/disable the tester
The tester has memory cells in which all calculated values are stored, such as capacity in Ah, energy in Wh, and operating time with load. When the tester is disconnected from the power supply and then turned on, the calculation of all values continues from the previously recorded values. These values can be reset either all at once or individually.
Instructions for operating the tester:
- 1 click – switch between screens;
- 1 long press – reset of all calculated values;
- 2 presses – reset the capacity value in Ah;
- 3 presses – reset the calculated energy value in Wh;
- 4 clicks – reset operating time under load;
- 5 clicks – setting the power off timer;
After five clicks, the tester is switched to the power-off timer setting mode. By default it is disabled and in OFF mode. After entering the mode, one short press switches the timer to “A0” mode. In this mode, the load power will be turned off when the current drops significantly when the power consumption drops below 2 W in 1 hour. In the following mode, you can set the operating time in hours from 1 to 24 hours. A single short press decreases the value. If you then hold down the button, the values will automatically decrease quickly. Pressing twice briefly will increase the value. If you then hold down the button, this will lead to an automatic rapid increase in values. Disabling the timer - “OFF”. Setting a value greater than 24 hours will set the timer to “A0” mode.
Information on the screens:
ATTENTION! A quick double press of the button increases the reading, a triple press decreases it. Holding the button for a long time also increases or decreases the screen readings.
BL:ON- Adjustable screen backlight time from 5 to 60 seconds. The ON backlight is constantly on.
AAA- Flip screen readings. Press the button twice, the screen display will be reversed.
>35.0v- Threshold value of overload protection 0-35V. If the voltage exceeds the set threshold value, a sound signal will sound.
<0.00v
- Threshold value of low voltage protection 35-0V. If the voltage is below the set threshold value, a sound signal will sound.
>10.0A- Overcurrent protection threshold 0.20-15A. If the current exceeds the set threshold value, a sound signal will sound.
J7-T tester specifications:
support Qualcomm Quick Charge 2.0 / Qualcomm Quick Charge 3.0
- input voltage 3V – 30V with an accuracy of 0.01V;
- measured current up to 5.1A with an accuracy of 0.01A;
- charge counting range 0-999.99 Ah with an accuracy of 0.001 Ah;
- energy counting range 0-999.999 Wh with an accuracy of 0.001 Wh;
- measured power range 0-299.999 W with an accuracy of 0.001 W;
- the range of calculated time is 0-999 hours 59 minutes 59 seconds.
Price 450 rub. IN STOCK BUY
USB tester J7-T
USB tester J7-T
USB tester KCX-017 3 -7 volts
USB tester KCX-017 3 - 7V
- voltage (V)
- current (A)
- capacity (mAh)
- memory cell number (0-9)
Measured voltage: 3 - 7V
Measured current: 50 - 3500mA
Measurement error: ±1%
Price 400 rub. IN STOCK BUY
USB tester KCX-017 3 - 7V
USB tester KCX-017 3 - 7V
USB tester KCX-017 3 - 7V
USB tester KCX-017 3 -15 volts
USB tester KCX-017 3 - 15V
The KCX-017 USB tester is designed to measure the supply voltage and current consumption of devices connected to the USB connector, as well as for testing micro USB cables.
To measure parameters, the tester can be easily connected to the power cable. The display simultaneously shows the following readings:
- voltage (V)
- current (A)
- capacity (mAh)
- memory cell number (0-9)
Measured voltage: 3 - 15V
Measured current: 50 - 3500mA
Measured capacity 0 - 19999mAh
Measurement error: ±1%
Price 450 rub. IN STOCK BUY
USB tester KCX-017 4 -30 volts
USB tester KCX-017 4 - 30V
The KCX-017 USB tester is designed to measure the supply voltage and current consumption of devices connected to the USB connector, as well as for testing micro USB cables.
To measure parameters, the tester can be easily connected to the power cable. The display simultaneously shows the following readings:
- voltage (V)
- current (A)
- capacity (mAh)
- memory cell number (0-9)
Measured voltage: 4 - 30V
Measured current: 50 - 3000mA
Measured capacity 0 - 19999mAh
Measurement error: ±1%
Price 480 rub. IN STOCK BUY
USB tester KCX-017 4 - 30V
LOAD RESISTOR R2
with USB connector and current switch 1A-2A
Load resistor
The load resistor is designed to supply load to connected devices via the USB connector. Has a current switch (1A-2A) and a two-color LED.
Price 150 rub. 100 rub. IN STOCK BUY
Load resistor
Load resistor
LOAD RESISTOR R3
1A-2A-3A
Load resistor 1-3A
The load resistor is designed to supply load to connected devices via the USB connector. Has two current switches (1A-2A-3A) and three LEDs.
When connecting a resistor to a USB tester, you can check the real voltage and current of various USB chargers, and when connecting to a KCX-017 tester, you can find out the real capacity of Power Banks and check the quality of micro-USB cables.
Price 150 rub. IN STOCK BUY
1A - turn on the 1A resistor
2A - turn off 1A and turn on 2A
3A - turn on both resistors.
Load resistor 3A
Load resistor 3A
LOAD RESISTOR R4
with USB connector and current switches 0.25A-0.5A-1A-2A
The load resistor is designed to supply load to connected devices via the USB connector. It has four current switches (0.25A-0.5A-1A-2A) and a cooler with a toggle switch (on/off) for cooling the resistors.
When connecting the resistor to a USB tester, you can check the real voltage and current of various USB chargers, and when connecting to the tester KCX-017 You can find out the real capacity of Power banks and check the quality of micro-USB cables.
Price 350 rub. IN STOCK BUY
Load resistor 0.25A-0.5A-1A-2A
Load resistor 0.25A-0.5A-1A-2A
LOAD RESISTOR R5
with USB connector and current regulation 0.15A-3A
Load resistor with continuously adjustable current
The load resistor is designed to supply load to connected devices via the USB connector. It has a tuning resistor for smoothly changing the load from 0.15 to 3A and a cooler for cooling the device. The cooler automatically turns on when the temperature reaches above 40C.
When connecting the resistor to a USB tester, you can check the real voltage and current of various USB chargers, and when connecting to the tester
‘s videos about a power bank. As someone had mentioned in a comment on the prior articles, the products have evolved over time and “integrating” mAh display units are now available.
I suppose it would only be right for me to go and grab one for myself and test it. A quick trip to eBay, AU$10 and a month later, I had a new toy to test.
Unboxing
Rather uninspiringly, the unit came in a zip-lock anti-static ESD shielding bag and that was it. On the front, the label claims the unit to meter voltage from 4-20V (+/- 1%), meter current from 0-3A (+/- 1%), count time up to 99 hours and integrate capacity up to 99,999 mAh.
Aside from this, there was nothing – no manual, no leaflet. I suppose that’s fine – it’s a pretty straightforward device.
Once extracted from the packaging, it was a little disappointing to see that it was just “plopped” inside without any love, so the plastic outer has some fine-scratches.
Of course, the scratches are purely cosmetic and don’t affect the functioning of the device at all. Keweisi is not a brand I’ve heard of, but it seems the meters are somewhat popular. It has an USB A-M connector on one side, and an A-F connector on the other, with no wires to add resistance. The translucent case allows you to see inside (so a teardown isn’t really needed) and see the LCD display which is an “inverted” type.
Aside from that, there is a reset button that is used to clear the integrated time/mAh values. This is accessed from the top and needs to be held for a few seconds to clear the values.
The rear shows a 0.05 ohm shunt resistance, an unmarked microcontroller and a gob-top chip next to it, along with a three terminal device which is probably a voltage regulator of some sort.
The casing is simply clipped together. The USB connector was a bit crooked on this sample, and bending it is not advisable as the LCD is mounted to the board and shows strain when pressure is applied.
Teardown
There's really nothing to it. A careful poke at the case with a good fingernail and it comes apart.
Inside, the backlit LCD glass is directly soldered onto the PCB. The amount of solder used on the joints are highly variable, and seem to be a little on the low side since they haven’t nicely flowed through the vias and all over all the pads (especially for the USB connectors). It’s not entirely necessary to do that, and it’s probably still fine as it is. I suppose in the case of the LCD, there’s a good reason why the soldering is done so casually, as applying excessive heat is likely to damage the glass-seal that keeps the crystal in and would destroy the LCD altogether. This type of pin arrangement as opposed to elastomeric connector leaves the LCD is vulnerable to stress being conducted through the board, so bending the USB connections can potentially strain or break the display.
The underside shows exactly what I mentioned earlier – U1 appears to be a microcontroller with its markings rubbed off. U3 is a gob-top chip mounted directly on the board, and is probably the LCD display controller. U2 is probably a voltage regulator, but it was not confirmed. S1 is a 24C02S 256 byte EEPROM, which is probably used to store the integrated data values.
One thing I did notice is that D1, which is supposed to be a diode, was replaced with a 0-ohm resistor. I didn’t carefully check if this was in series with the actual USB output, but if it was, it may have been replaced to avoid voltage-drop contribution from the diode. However, this alteration may mean that the unit is not going to survive being plugged into a USB port with reversed polarity.
In Use and Testing
It's extremely simple to use. Plug it in, and basically off it goes. When the current reading is 0.01A or higher, the integration will run to accumulate charge time (blinking colon indicates it is running) and charge (in mAh). Once the current falls below the threshold, the time and integration stops. The last value is stored in the unit itself, and is shown when power is re-applied unless reset. Resetting the unit involves pressing and holding the reset button for about five seconds.
On the whole, I found it quite a nice unit. Although the LCD characters are a little small, the backlight is extremely efficient and the display reads quite well. The viewing angle is somewhat limited though. The display features two decimal places for voltage (under 10V) and current. Above 10V, only one decimal place for voltage is shown. The display updates about twice a second, and is sometimes jumpy especially for rapidly changing spiky loads.
The wide voltage range of 4-20V allows for compatibility with the latest Qualcomm Quick Charge capable power adapters which can output up to 20V in some rare cases, making diagnosis of quick charge issues more efficient.
Integrated Charge
I decided to see how good its charge integration was by testing it with my torch. I drained it and went through a full charge with it. Testing with the Keysight U1461A and the modified USB Charger Doctor shunt produced a result of 2499.82mAh and 5h 55m 29s charge time.
As we can see from this result, the Keweisi has an integrated current of 146.82mAh less, although the charge time is less as well. This may be because the discharge/charge termination may have been slightly different between runs. However, it still does seem to indicate that the unit’s charge integration ability is quite good as an indicator.
I also tested it with an power bank in Qualcomm Quick Charge 2.0 mode. The power bank was run down to flat, and then recharged with the meter integrating the charge.
It's important to remember that mAh is not a measure of energy. It is a measure of current-flow integrated across time, and to derive energy requires the voltage as well.
As a result, we can see 5130mAh was fed into the power bank over 4 h 41m, but at 9V. This is a total of 46.17Wh which at 3.7v is equivalent to 12,478mAh. Note that the value is higher than the 10,050mAh of the power bank due to conversion losses and losses in display/control/etc. Assuming the cells are 10,050mAh, the charging efficiency was 80.5%.
Note that different types of charging circuitry exist. Switching converter chargers such as that in the Anker power bank will convert the energy with ~85% efficiency to charge the battery. Linear chargers simply drop and lose the excess voltage (e.g. in the MH10), so the displayed figure corresponds to the mAh of charge going into the battery (except for losses in indicator lights etc) and are lower energy efficiency (~74% efficient). Unfortunately, it’s not always easy to know what is in use unless you’ve peeked inside or the figures are obvious.
One of the biggest failures is that the unit only integrates charge and not energy. It appears that they have everything they would need to do it for energy and record mWh by multiplying voltage and current pairs, as this would be helpful as the supply voltage may change during the charge (e.g. for Qualcomm Quick Charge 3.0 where devices can select voltages at 0.2V granularity and step up and down on demand). This would make the delivered energy unambiguous (and potentially make it very handy for things like metering solar energy charge into a battery for a small scale system). It would be nicer if the unit had some way of storing multiple results for recall and more extensive data logging features but I suppose that might be asking for too much.
I did have a think of just how long such a unit might last, because flash memory has a limited endurance and storing these figures in anticipation of the power being removed at any time is likely to be quite burdensome. As a result, I made some back of the envelope calculations:
Data to be Stored: Time - 99h99m -> convert to 2475m -> can be stored in 12 bits Charge - 99999mAh -> can be stored in 17 bits Total amount of data to be stored = 29 bits (assuming efficient packed storage) Storage medium : Flash chip = 256 byte capacity, 8 bit words. Round up data to be stored to 32 bits (4 bytes). Endurance: Data storage frequency = 2Hz (equal to display update frequency) Flash endurance = 1,000,000 writes (ATMEL datasheet) Storage slots (assuming levelling) = 256/4 = 64 locations Time to expiry = 32,000,000 seconds = 370 days of operation
It seems that this is somewhat adequate for a diagnostic tool that’s not designed to be always plugged in. However, it does assume that the storage is efficient and that the storage location is rotated. If the storage is not rotated, the lifetime is only around 6 days. That being said, failure of the flash is likely only to impact the retention time or integrity of the integrated time and charge figures if power is removed, so the loss of the flash may not be critical to the operation of the unit. In fact, the presence of the EEPROM might make for a potential point to tap for data logging purposes if someone is bothered to sniff the bus.
Voltage Range
The unit is specified to operate up to 20V, so I decided to see if that was the case. Rather surprisingly, it did manage 20V, and even higher.
At around 26V, the unit was still rather happy, with a good display and ~0.3V error.
At 28V, the unit became rather unhappy, showing phantom current readings and making a strange whistling noise. I suspect maybe the internal inverter that generates the AC drive for the LCD is not happy, or the regulator itself was somehow over-stressed.
With such a wide voltage range, it could make for a good unit to modify to act as a general voltage/current indicator (e.g. for 12v systems).
Self-Consumption
When you're powering yourself off the supply that you're measuring, any amount of current you consume can change the result and is current that is not otherwise available for the device.
Checking the self-consumption using the front panel metering of a bench-top supply shows a very impressive result. The display first kicks in at about 2.8V. Below 4.2V, the LED backlight on the screen is not fully running and the current consumption is hence increasing with voltage. Above that, the unit regulates its current well with respect to increasing voltage, and consumed about 4.2mA at the most. This is an absolutely miniscule amount of current, which makes this a rather efficient meter.
Running the same experiment with the previous favorite – the Blue USB Charger Doctor shows the stark contrast –
Due to its “shunt” regulation scheme, it’s got a linearly increasing current consumption with respect to voltage over its limited operating range. Due to the consumption of the LED display, the unit draws up to around 55mA at 7.5V, which is an order of magnitude higher. Overall, a positive result for the Keweisi.
The shunt resistance of 0.05 ohms will contribute a voltage loss of about 0.15v at 3A. Slightly more loss is to be expected due to resistance in the PCB traces and connectors, but this is probably a good trade-off between accuracy and burden voltage.
Voltage Accuracy
Voltage accuracy was tested with the output of the Keysight E36103A power supply. Given the program to output voltage accuracy was established to be at most a few millivolts (an order of magnitude below the smallest digit displayed which is 10’s of millivolts), the programmed voltage is taken as the actual output voltage.
Voltage accuracy was tested open circuit under no load, with voltage supplied at 0.1V steps throughout, except for 0.01V steps between 4.75V and 5.25V which is the nominal USB power range.
A comparison was made with the previous favorite “Blue USB Charger Doctor”, but owing to the new test protocol, a different sample was re-tested under the new protocol, so the results may vary from previous report.
The voltage accuracy was shown as the absolute value of the absolute difference in displayed voltage and actual supplied voltage. In the case of the Keweisi KWS-V20, the error was always positive (indicating the display overestimated the voltage). Above about 4.2V, the error is seen to increase linearly with voltage, indicating a “gain” error. Below 4.1V, the indicated voltage is severely out of line with actual voltage. Compared with the “Blue USB Charger Doctor”, the Keweisi has fairly similar error magnitudes within their common operating range. The difference is that the Blue unit seemed to start off high and cross over to under-reporting voltage at 4.85V or so, thus while the magnitude of the errors above 4.85V are the same, they are in the opposite direction.
Based on this, within the nominal USB power range, the “Blue” unit is still a hair more accurate. However, it seems the Keweisi was off by 3 to 4 counts, so in terms of absolute value, the last digit is only really a “third of a digit”.
However, since the accuracy is given as a percentage on the package, if we plot it on a semi-log plot, we can see how the errors are even in the under-voltage area. On the whole, within the operating range above 4.2V, the unit mostly meets the 1% claim with the exception of some blips near 19V. At 4.0V, it doesn’t meet the specification, either, but I suppose it can be forgiven. The “Blue” unit has poor performance below 4.5V, but otherwise good performance until it reaches full scale at 7.5V.
Current Accuracy
As I don't have an electronic continually variable load, I tested the current accuracy based on the old protocol by using my configurable power-bank test rig load consisting of wire wound resistors, a benchtop power supply set to 5V, and a Keithley 2110 5.5-digit DMM providing the “actual” current values.
When it came to current error, both meters didn’t seem to have particularly clear trends based on the small number of samples. The “Blue” unit was, again, better somewhat keeping within 2-counts of error, but the Keweisi was within 3-counts with the exception of the final 2.38A current reading.
Percentage-wise, to call the error within 1% would be quite optimistic, as it was within 3%. It’s likely to be much worse at the low end of the scale, as I have observed loads of 100mA registering as 30mA, as if there is a little bit of non-linearity near zero to ensure low loads don’t keep the integrator running. It’s still accurate enough for comparison testing, which is probably its main function anyway.
Conclusion
For AU$10, it’s not the cheapest USB diagnostic tool out there, but it’s definitely affordable and quite featureful. With the wide voltage range, it’s prepared for all manner of Qualcomm Quick Charge 3.0 capable devices, and its integration feature allows you to roughly determine the capacity of power banks, and batteries being charged.
On the whole, accuracy was acceptable, although the 1% figure is not particularly ambitious, it was a bit optimistic at the ends of the ranges for voltage, and across the board for current. It wasn’t quite as accurate as the “Blue” unit I had on hand, but it was still fairly close. For the intended purpose of relative comparisons of chargers, cables and power banks, it’s accurate enough. Of course, I tested only one sample of this unit, and it’s quite likely there will be some sample to sample variation especially because there will be tolerances in resistors which is probably where the 1% figure came from.
Not having energy integration (mWh) and only charge integration (mAh) can make for some ambiguity where the voltage varies significantly during charge/discharge. The limited endurance of the flash memory is also a potential drawback, but doesn’t seem likely to be a major one in realistic use.
Its low self-consumption was excellent, and the wide voltage range makes it amenable to modification and use in unconventional non-USB monitoring scenarios as a generalized voltage/current meter. There is a potential that the data flowing to the EEPROM chip may also be useful for data logging purposes if the format of the data is determined.
Price: $3.33
A USB tester for measuring battery capacity, monitoring charge current, voltage and charge time is a “must have!” I just couldn’t “pass by” when I saw the price. Buy It Now clicked instantly. The seller sent the goods the next day, delivery time was exactly 3 weeks.
There was no packaging at all, not even a plastic box: they simply wrapped it in bubble wrap and sent it in a standard white envelope. The device works without problems. The case is assembled from transparent plastic neatly, without flaws.
The body is non-separable.
The numbers on the display are large and easy to read. There is backlighting around the perimeter of the display.
Why is such a device needed?
A microprocessor meter allows you to determine the true battery capacity of a tablet, phone, or external portable charger. That is, if there are problems with battery life, you can find out for sure whether the battery is alive, or whether it’s time to prepare to buy a new one.
Measuring range 1 – 99,999 mAh. Measuring range of current passing through the device: 0 - 3 amperes.
The built-in timer allows you to control the charging time of the connected device. Measuring range: 1 minute – 99 hours 59 minutes.
How to accurately measure the actual battery capacity?
Connect a completely discharged phone (tablet) to the charger in series via a USB tester.
Press the Reset button for a few seconds and release. In this case, the indicators are reset to zero, and a new countdown according to the parameters begins.
After charging is complete, the timer stops and the screen displays the charging time and the actual battery capacity. The last measurement data is retained in memory when the device is turned off.
Using a tester, you can easily check whether the capacity declared by the manufacturer matches the actual capacity of a new battery or the battery of a purchased phone.
Useful device or not? Definitely not an essential item, but it will come in handy if there are several phones, tablets, and other battery-powered devices in the house. An indispensable thing for everyone who often changes smartphones, sells/buys tablets (will save money on battery replacement).
The best clothes and shoes on "
Monitoring the network voltage is always necessary: during installation of electrical wiring, replacement or repair of electrical equipment, and checking circuit continuity. The surest way to do this is to use a voltage tester, which is popularly called a probe. Such a device is much cheaper than a multifunctional multimeter. How to use the tester? More on this below.
Voltage tester
An electricity tester is a device that can be used to measure voltage and determine its presence or absence in the network. The tester is much simpler in design than a multimeter, it is not difficult to use, you can carry out work quickly, in uncomfortable conditions, for example, hold yourself at a height with one hand and take measurements with the other.
How to use a voltage tester? They can measure the electricity of sockets on the contacts of electrical appliances and the output of generators. More complex devices display information digitally, while simpler ones display information using an indicator light.
Types of Voltage Testers
There are many types of testers - from the simplest devices to complex instruments. All of them allow you to analyze stress, but the degree of analysis will naturally vary. Voltage testers are made as:
How to use a screwdriver probe
The network voltage monitoring device - the probe - is not able to determine the level of electricity. Its main task is to detect the phase. This is very important to know, since during repairs, when disconnecting the plugs, you need to be sure that the phase is missing. It is she who, closing through the human body to the ground, produces an electric shock.
How to use the probe tester:
- Make sure it is in good working order visually. The insulating material on the device must not be damaged.
- Hold the screwdriver by the insulating handle with one hand so that one finger is free.
- Insert the device into any hole in the socket and touch the contact on the end of the handle with your thumb.
- If the light does not light, move the screwdriver to another hole in the socket. A burning light indicates the presence of a phase on the contact.
It is also easy to understand how to use a screwdriver tester to test the continuity of wires, for example in a carrier. To do this, you need to determine the phase contact in a specific outlet. Next, insert the plug of the carrier being tested and find the phase at the output. By changing the location of the plug, determine which wire the phase does not go through - there is a break there.
How to measure with a screwdriver tester
This indicator device is similar in form to the one discussed above, but its functionality allows you to determine significantly more parameters. Such an electrical tester is used as an indicator of the presence of electrical voltage in the line, checks batteries for discharge status, determines the polarity of the leads, finds the point of wire break in the circuit, and records the presence of electromagnetic and microwave radiation.
The screwdriver tester has the following technical parameters:
- Possibility of measuring DC and AC voltage in the range: 220, 110, 55, 36, 12 volts with information displayed on a digital display.
- Determination of the polarity of the terminals of constant power supplies and the phase of an alternating network.
- Finding the break point in an electrical wire in the resistance range from zero to 50 MOhm.
- Detection of the presence of radiation in the frequency range from 50 to 500 Hz.
- The input current is less than 0.25 milliamps, the voltage is no more than 250 volts.
- Compliance with European standard requirements and approvals DINVDE 0680 Teil 6/04.77.
How to use the screwdriver tester:
1. Contact testing method. Using this method, voltage measurements are taken within the permissible range. Actions:
- The device probe is used to touch a connector in a socket, a bare wire, or a contact of a live electrical device.
- Use your finger to press the sensor button labeled Directtest located on the device.
- Take readings from the tester display.
2. Non-contact testing method. In this way, you can find the wiring of an alternating line hidden under a layer of plaster, if current flows in it, electromagnetic and microwave radiation, check the integrity of the electrical wire. Actions:
- Use your finger to press the sensor button labeled InductanceBreak-pointtest.
- The device is brought to the approximate location of the wiring and carefully moved along and across.
- The appearance of a Z lightning bolt icon on the screen indicates that the device has detected a weak magnetic field created by the conductor.
- Checking the wire for a break, move along it until the Z icon disappears.
How to use a voltage tester when working with batteries and chemical batteries?
- By pressing the Directtest sensor button with your finger, the contact with the slot touches any pole of the battery.
- The second hand touches the other pole of the battery.
- The Z lightning bolt display on the indicator confirms the functionality of the power supply element.
- The polarity is shown by the LED, which lights up on the positive side and does not light up on the negative side of the contact.
How to use a multimeter tester
The multimeter is quite easy to operate, it is multi-functional, with a user-friendly interface. But you still need to be extremely careful, since due to the many operating modes and measurement limits, it is quite possible to get confused and burn the device. For cheap Chinese meters, it is better to immediately replace the test lead wires with more reliable ones.
How to use the tester correctly when measuring DC voltage:
- The red test lead is inserted into the VΩmA socket, the black one into the COM socket.
- The circular measurement mode switching knob is moved to the DCV position at the highest measurement limit.
- The probes are connected to a source of electricity to plus and minus. Polarity reversal in this case is not terrible. If allowed, it will simply be displayed as a “-” sign on the screen display.
- Record the instrument readings.
If the voltage is approximately known, then it is better to set the measurement limit a little more than what is obviously expected to increase the measurement accuracy.
How to use a multimeter tester when measuring AC voltage:
- The probes remain connected in the same place.
- The mode switch is moved to the ACV position to a limit of over 220 volts for a single-phase network, over 380 volts for a three-phase network.
- Very carefully, without touching the exposed areas of the probes with your hands, connect the probes to the contacts of the socket. It doesn't matter where you connect which test lead.
- Record the instrument readings.
What is Keweisi tester
The KWS-V20 USB tester is designed to measure the electrical parameters of USB chargers, devices connected to them, as well as the capacity received and released when charging and discharging the power bank. Technical specifications:
- The measured DC voltage is from 3 to 9 volts.
- Measured direct current up to 3 amperes.
- Measured capacity up to 99999 milliamp-hours.
How to use the Keweisi tester
How to operate the device:
- Connect the measured charge to the USB port and press the reset button.
- Take voltage measurements displayed on the screen.
- To measure the current consumed by any device, insert its cord into the Keweisi USB connector.
- Take readings on the device.
- To determine the output capacity of the power bank, connect a tester to the output of a fully charged device, and a load to the output of the tester.
- As soon as the power bank is completely discharged, the tester is switched to some voltage source and the readings recorded in the device’s memory are taken.
Conclusion
If you don’t have a single tester or even a screwdriver probe at hand, and you urgently need to check whether there is voltage in the outlet, the easiest way is to use an ordinary incandescent light bulb. To do this, connect a wire with a plug to it through a cartridge and plug it into the socket being tested. How to use this type of tester correctly? You need to be extremely sure that there is no overvoltage in the network. Otherwise, the light bulb may explode and cause harm.