Keweisi KWS-V20 - USB capacity meter from China - Not too precise

Hungarian version.

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Update: 2016.02.25 
Its power consumption is 3,82mA, because of the 5V it is around 0,02W.
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Welcome, I thought it would be a good idea to buy on Ebay from China an USB Capacity meter, so I can measure the capacity of my 18650 batteries. I planned to measure it when I charge something from the Soshine E3 power bank.

"Brand": KEWEISI
Model: KWS-V20
20030815 - I can assume this is the manufacturing date? It was on its case... Of course no manual or anything attached.

If I remember well this is also sold on Ebay under different brand names.

The product itself is looks nice with its "all the time" on white backlight. It has only one button which can reset the time counter. This thing does not do anything else than measure the current flowing through it in mAh. It shows the actual current and V . This works well, except that it is a bit inaccurate. It miscalculates easily with +- 0,2 Volts. Under 100mA the measured amount cannot be true. It fluctuates and sometimes it shows 0. On the picture below it shows 0 because nothing is connected to it, it is just plugged into an USB port. So it works but it’s too inaccurate to for example measure the consumption of my mouse or external sound card. However it seems to be accurate with higher currents. The power goes in on one side and it comes out on the other, as simple as that. I decided to build a capacity meter for the 18650s myself with my Arduino. This will be a new blog post.

DIY Universal USB charger

Hungarian version.

UPDATE 1: I had to put a diode into the cable, because it seems a Chinese battery charger can push the charge back to the Nokia power supply. I used a 1N4001 diode to the cable of the power supply's "+" side, which can withstand 3A and it has 50V Reverse voltage.

I was having trouble charging my Smartphone. I do not have a wall outlet AC charger for it, so I always had to charge it from my computer with an USB cable. But in this way the charging was a bit slow, since the computer only supplies 500mAh of current through the cable. The computer had to be turned on as well. I wanted to change this. I have an older 2007 Nokia phone charger, which charges the phone with 5V. It is funny that Nokia has been since bought by Microsoft. In the beginning of the 2000 years Nokia was a leader in the phone market. So the Nokia charger has only a pin connector as can be seen on the picture.

I have cut the charger cable in two. I took an USB extension cable, I cut it in half as well, then I soldered the USB mother connector to the charger side, the father connector to the other side. As it can be seen on the picture. Now I have a universal USB charger which can charge with 900mAh as written on the charger. I can connect any USB cable to it and as it is a quality charger I do not have to fear from cheap chargers from ebay.

One more interesting thing I would like to note. There are some smart things what do not charge themselves with all the available power from the charger, if the two data cable in the USB cable is not shorted. I have a handheld computer (PDA) from 2007. If the two data line is not shorted, it charges itself slower than if they are shorted. This PDA has a car charger which charges with 1A, but I have bought another car charger which does not charge it this fast. It turned out that this is because the data lines are not shorted here. I simply shorted them on the charger side, so the units charge themselves faster.