(First Blog post after 4 years of absence - wow! Let's see if I fill it with more electronics and µC stuff in the near future! :) )
The display shows LiIon, which is a bit terrifying - will it blow up the 1.2V battery with 4.2V? But after short time, no chemistry is shown on the LC display which means the NiMH charging program with -dV detection is used. During this detection phase you can push the buttons below the LCD to switch between LiIon and LiFePO charging parameters.
A LiIon cell gets detected correctly, too.
The build quality is actually quite nice, I don't see bad soldering, everything seems clean. The negative contacts for the batteries are sliding smooth. The display is easy to read.
Flat top cells can make contact with the positive tabs due to a small bump. The charger delivers 500mA to each cell when charged in pairs; 1A for a single cell. Which seems to be one of the major differences to a Soshine H2 charger. The NiMH charging program uses a constant current and switches off either with a -dV detection or a timer based time-out.
For LiIon I currently can only measure the load on the USB port. It is 0.63A at 4.8V. A few millivolts later, the load decreases to 0.55A at 4.8V, the battery has 3.9V and the charger shows 70 percent. It seems that the current is jumping around between 2.25W and 2.75W on the USB port most of the times. Overall, slowly decreasing until dropping fast in the CV phase. (This seems to be usual for USB chargers, by the way.)
This is no real problem, but it unnecessarily prolongs the charging process. The charger uses a 'good enough' approximation of a CC-CV charging scheme. After the charger shows 4.2V /FULL for the LiIon battery, the input current drops down to 0.7-1.0W. Removing the battery then lets the current drop down to 30mW. The Soshine T2 silently continues with the CV charging without increasing the counters. It silently charges a little more; this is also the behaviour of the charger when it restarts due to the cell dropping below the threshold voltage for recharging. After a short time, the current decreases to 30mW on the USB port with the LiIon battery still inserted in the Soshine T2. This will be the idle power from the microcontroller and additional circuits.
Further measurements: A 14500 LiIon cell gets charged up to 4.192V (cell voltage without load). At that time I could measure -5mA load while the charger shows "full". It switches off charging and immediately draws 5mA from the cell afterwards. As it will restart charging if the voltage drops below a certain threshold the cell doesn't get drained empty, thus no problem here. Just remember to take out the batteries when unplugging the Soshine T2. In conclusion, it works properly for LiIons. :)
Update: Here are results from a deeper look at this charger with real current and voltage plots.
The used Holtek µC in a SSOP16 housing offers plenty of IOs, 12 bit ADC, LCD driver, an internal 12 MHz oscillator, 128 Bytes of RAM; in short it is cheap and powerful enough for controlling a Buck topology for constant current and constant voltage. Though as can be seen, only one inductor is used for two otherwise independant channels and there are two 56 Ohm high-power resistors in place. It'll step down by limiting the current and then burn energy with resistors and transistors.
The LC display has its own controller or even just a shift register (sealed with a tar blob), by the way. It is connected via 6 lines, from which 3 seem to be power supply as they lead to thicker lanes on the PCB.
LiIon tests are still going on, but so far they are as well as the NiMH tests very promising. The charger does what I need it for - it properly fast charges my AAA batteries for the mouse at the computer at work.
Prominent parts on the Soshine T2 PCB:
- Holtek HT46R066 8-Bit MCU w/ enhanced AD
- Holtek 46R066 Datasheet
(Holtek also has an AppNote for a Holtek µC based charger - the Soshine T2 seems like an improved version of this.)
- APM9435 SOIC8 P-Channel MOSFET: -30V, -5.3A, less than 90mOhm @ Vgs=4.5V
- Diodes, SOT23 transistors, ceramic capacitors, heaps of SMD resistors.
Backside of the PCB:
- Display, Inductor/Coil, electrolyte capacitors, MicroUSB connector.
So far for my fast first-look at this charger.