Cm8 V20 Battery Votage Capacity Checker Review Instructions

It's almost been one year since I've looked at "USB charger doctor" mode devices, but having opposite engineered, tested and modified ane, I didn't retrieve I'd ever carp with them over again. That was, until I saw the Keweisi KWS-V20 USB Tester in one of bigclivedotcom's videos about a ability depository financial institution. As someone had mentioned in a annotate on the prior articles, the products have evolved over time and "integrating" mAh brandish units are now bachelor.

I suppose it would just be right for me to go and grab one for myself and exam it. A quick trip to eBay, AU$10 and a month afterwards, 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 information technology. On the front end, the characterization claims the unit to meter voltage from 4-20V (+/- i%), meter current from 0-3A (+/- 1%), count time upwards to 99 hours and integrate capacity up to 99,999mAh.

Bated from this, there was zilch – no manual, no leaflet. I suppose that's fine – it's a pretty straightforward device.

Once extracted from the packaging, information technology was a little disappointing to see that it was but "plopped" within without any love, so the plastic outer has some fine-scratches.

Of class, the scratches are purely cosmetic and don't touch on the functioning of the device at all. Keweisi is not a brand I've heard of, but it seems the meters are somewhat pop. It has an USB A-M connector on one side, and an A-F connector on the other, with no wires to add together resistance. The translucent case allows you to run into inside (so a teardown isn't actually needed) and come across the LCD display which is an "inverted" type.

Aside from that, there is a reset push button that is used to articulate the integrated time/mAh values. This is accessed from the meridian 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 fleck side by side to it, along with a three final 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 equally the LCD is mounted to the board and shows strain when pressure is applied.

Teardown

There's actually goose egg to information technology. 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 corporeality 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'due south not entirely necessary to do that, and it'southward probably however fine every bit it is. I suppose in the case of the LCD, in that location's a skillful reason why the soldering is done and so casually, as applying excessive heat is likely to damage the glass-seal that keeps the crystal in and would destroy the LCD birthday. This type of pin arrangement as opposed to elastomeric connector leaves the LCD vulnerable to stress beingness conducted through the lath, so bending the USB connections can potentially strain or break the brandish.

The underside shows exactly what I mentioned earlier – U1 appears to exist a microcontroller with its markings rubbed off. U3 is a gob-peak chip mounted directly on the board, and is probably the LCD brandish controller. U2 is probably a voltage regulator, just it was not confirmed. S1 is a 24C02S 256 byte EEPROM, which is probably used to store the integrated information values.

I matter 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 serial with the bodily USB output, simply if it was, information technology may accept been replaced to avoid voltage-drop contribution from the diode. Withal, 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'south extremely unproblematic to use. Plug information technology in, and basically off information technology goes. When the current reading is 0.01A or higher, the integration volition run to accrue accuse 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 of measurement involves pressing and holding the reset button for almost five seconds.

On the whole, I establish it quite a squeamish 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 express though. The display features two decimal places for voltage (under 10V) and electric current. Higher up 10V, only ane decimal place for voltage is shown. The display updates about twice a 2d, and is sometimes jumpy particularly for rapidly changing spiky loads.

The broad voltage range of 4-20V allows for compatibility with the latest Qualcomm Quick Accuse capable power adapters which tin can output up to 20V in some rare cases, making diagnosis of quick accuse bug more efficient.

Integrated Accuse

I decided to see how good its charge integration was by testing it with my Nitecore MH10 torch. I drained it and went through a full accuse with information technology. Testing with the Keysight U1461A and the modified USB Charger Medico shunt produced a outcome of 2499.82mAh and 5h 55m 29s accuse time.

As we can come across from this result, the Keweisi has an integrated current of 146.82mAh less, although the charge fourth dimension is less likewise. This may be considering the discharge/charge termination may have been slightly different between runs. However, it still does seem to indicate that the unit'due south charge integration ability is quite good as an indicator.

I also tested it with an Anker Powercore+ 10050 power bank in Qualcomm Quick Charge 2.0 mode. The power depository financial institution was run down to flat, and then recharged with the meter integrating the charge.

It'southward of import to recall that mAh is not a measure of energy. It is a measure out of current-flow integrated across time, and to derive free energy requires the voltage likewise.

As a effect, we can run across 5130mAh was fed into the ability bank over four h 41m, only at 9V. This is a total of 46.17Wh which at three.7v is equivalent to 12,478mAh. Notation that the value is higher than the x,050mAh of the power bank due to conversion losses and losses in brandish/control/etc. Assuming the cells are 10,050mAh, the charging efficiency was 80.five%.

Note that different types of charging circuitry exist. Switching converter chargers such equally that in the Anker ability bank will catechumen the energy with ~85% efficiency to charge the battery. Linear chargers merely drop and lose the excess voltage (e.g. in the MH10), so the displayed figure corresponds to the mAh of charge going into the bombardment (except for losses in indicator lights etc) and are lower energy efficiency (~74% efficient). Unfortunately, it's non always easy to know what is in use unless y'all've peeked inside or the figures are obvious.

1 of the biggest failures is that the unit of measurement only integrates accuse and non energy. Information technology appears that they have everything they would demand to practise it for energy and record mWh by multiplying voltage and current pairs, every bit this would be helpful every bit the supply voltage may modify during the charge (e.g. for Qualcomm Quick Charge 3.0 where devices can select voltages at 0.2V granularity and footstep up and downward on demand). This would make the delivered energy unambiguous (and potentially make it very handy for things like metering solar free energy charge into a battery for a pocket-size scale system). Information technology would be nicer if the unit had some fashion of storing multiple results for recall and more extensive data logging features but I suppose that might exist asking for too much.

I did accept a recollect of just how long such a unit of measurement 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 crushing. Equally a result, I fabricated some back of the envelope calculations:

Information to be Stored: Time - 99h99m -> convert to 2475m -> can be stored in 12 bits Accuse - 99999mAh -> tin can be stored in 17 bits Total corporeality of data to exist stored = 29 bits (assuming efficient packed storage)  Storage medium: Flash scrap = 256 byte capacity, 8 fleck words. Circular up data to be stored to 32 bits (iv bytes).  Endurance: Data storage frequency = 2Hz (equal to display update frequency) Flash endurance = 1,000,000 writes (ATMEL datasheet) Storage slots (bold levelling) = 256/4 = 64 locations  Time to expiry = 32,000,000 seconds = 370 days of operation

Information technology seems that this is somewhat acceptable for a diagnostic tool that's non designed to be always plugged in. Nevertheless, it does assume that the storage is efficient and that the storage location is rotated. If the storage is non rotated, the lifetime is but around 6 days. That being said, failure of the flash is probable but to touch on the memory time or integrity of the integrated fourth dimension and accuse 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 indicate to tap for data logging purposes if someone is bothered to sniff the double-decker.

Voltage Range

The unit of measurement is specified to operate upwardly to 20V, and so I decided to run into if that was the case. Rather surprisingly, information technology did manage 20V, and even higher.

At around 26V, the unit of measurement was however rather happy, with a good display and ~0.3V mistake.

At 28V, the unit of measurement became rather unhappy, showing phantom current readings and making a strange whistling noise. I suspect perhaps 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 broad voltage range, information technology could make for a adept unit to modify to act as a general voltage/electric current indicator (e.g. for 12v systems).

Cocky-Consumption

When you lot're powering yourself off the supply that you're measuring, whatever amount of electric 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 Keysight E36103A bench-height supply shows a very impressive result. The display first kicks in at about ii.8V. Below 4.2V, the LED backlight on the screen is non fully running and the current consumption is hence increasing with voltage. To a higher place that, the unit regulates its current well with respect to increasing voltage, and consumed about 4.2mA at the most. This is an admittedly miniscule amount of electric current, which makes this a rather efficient meter.

Running the aforementioned experiment with the previous favourite – the Blue USB Charger Doc shows the stark contrast –

Due to its "shunt" regulation scheme, information technology's got a linearly increasing current consumption with respect to voltage over its express operating range. Due to the consumption of the LED display, the unit draws upwardly to around 55mA at 7.5V, which is an lodge 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 than loss is to be expected due to resistance in the PCB traces and connectors, but this is probably a good merchandise-off between accuracy and brunt voltage.

Voltage Accuracy

Voltage accurateness was tested with the output of the Keysight E36103A power supply. Given the program to output voltage accurateness was established to be at most a few millivolts (an guild 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 excursion nether no load, with voltage supplied at 0.1V steps throughout, except for 0.01V steps between 4.75V and five.25V which is the nominal USB power range.

A comparison was made with the previous favourite "Blue USB Charger Md", only owing to the new examination protocol, a unlike sample was re-tested under the new protocol, and so the results may vary from previous written 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" fault. Beneath 4.1V, the indicated voltage is severely out of line with actual voltage. Compared with the "Blueish USB Charger Doctor", the Keweisi has fairly like error magnitudes within their common operating range. The difference is that the Blue unit of measurement seemed to kickoff off high and cross over to under-reporting voltage at 4.85V or so, thus while the magnitude of the errors in a higher place 4.85V are the aforementioned, they are in the opposite direction.

Based on this, inside the nominal USB power range, the "Blue" unit is still a pilus more than accurate. However, it seems the Keweisi was off past iii to four counts, so in terms of absolute value, the terminal 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, nosotros tin can encounter how the errors are even in the under-voltage area. On the whole, inside the operating range to a higher place 4.2V, the unit of measurement mostly meets the 1% claim with the exception of some blips near 19V. At 4.0V, it doesn't run across the specification, either, only I suppose information technology tin be forgiven. The "Bluish" unit has poor performance beneath iv.5V, but otherwise good performance until it reaches full scale at 7.5V.

Current Accuracy

Every bit I don't take an electronic continually variable load, I tested the current accurateness based on the old protocol past using my configurable power-banking company examination rig load comprising of wire wound resistors, a benchtop power supply ready to 5V, and a Keithley 2110 5.5-digit DMM providing the "actual" current values.

When information technology came to current error, both meters didn't seem to accept especially clear trends based on the small number of samples. The "Blue" unit was, again, better somewhat keeping within ii-counts of error, only the Keweisi was inside iii-counts with the exception of the final two.38A current reading.

Percentage-wise, to call the error within 1% would exist quite optimistic, as it was within 3%. It's likely to exist much worse at the low end of the scale, as I have observed loads of 100mA registering as 30mA, equally if there is a little chip 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 principal office anyway.

Determination

For AU$10, it's non the cheapest USB diagnostic tool out there, simply it'southward definitely affordable and quite featureful. With the broad voltage range, it's prepared for all style of Qualcomm Quick Charge 3.0 capable devices, and its integration feature allows you to roughly decide the capacity of power banks, and batteries existence charged.

On the whole, accuracy was acceptable, although the 1% figure is non particularly ambitious, information technology was a bit optimistic at the ends of the ranges for voltage, and across the board for current. Information technology wasn't quite every bit accurate equally 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 plenty. Of course, I only tested 1 sample of this unit, and information technology'southward quite likely there will be some sample to sample variation specially considering there will be tolerances in resistors which is probably where the i% figure came from.

Not having energy integration (mWh) and only accuse integration (mAh) can make for some ambivalence where the voltage varies significantly during accuse/belch. The limited endurance of the flash memory is likewise a potential drawback, but doesn't seem likely to be a major one in realistic utilise.

Its low self-consumption was excellent, and the wide voltage range makes it amenable to modification and utilize in unconventional non-USB monitoring scenarios as a generalized voltage/current meter. There is a potential that the data flowing to the EEPROM scrap may also be useful for data logging purposes if the format of the data is determined.

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Source: https://goughlui.com/2016/08/20/review-teardown-keweisi-kws-v20-usb-tester/