Soshine T2 - measurements

The Soshine T2 serves me well for some months now already. As I built a low side shunt voltage and current logger, I wanted to take a closer look at the charger again.

Here's a photo of the battery dummy to feed the charger output to the shunt+opamp PCB, measurements are done with ATmega328 10Bit ADC (Arduino Nano in this case).

Some chargers have problems when there is additional resistance between the battery and ground, even if it's only 0.03 Ohms. But from the results I got, the Soshine T2 seems to work properly even with this data logger in place.
















The Soshine T2 shows some remarkable behaviour: It charges for roundabout 14 seconds, then switches off for 3 seconds - this seems to be a mechanism to measure battery voltage without load. This leads to a prolongued charging cycle, though.

Update 13.07.2015: Soshine T2 LiIon charging plot

The charger constantly drops the current over the whole charge cycle, so it delivers no real Constant Current phase. This is not the recommended charging scheme for LiIons, but no real problem as it only leads to a longer charge cycle.
What I deem problematic is that the charger doesn't really end the charging cycle even when it shows "FULL" on the display. After the charging ends, with different equipment I can see small current spikes. The voltage didn't rise anymore even when I left the battery in place for more than half an hour, even contrary, the voltage dropped as the cell discharged a few mV after charge end as usual. These spikes seem just to be very short and without real energy to detect if a battery is inserted.




So for rare occasions / not everyday usage the Soshine T2 is useable, but users should remember to take out the batteries after charging ends with a "FULL" display. It is not the best charger, but still ok. Especially considering that it can handle not only LiIon and LiFePos, but also NiMHs batteries (which is what I use it for).

Update 13.07.2015: Soshine T2 NiMH charging plot

Update 13.07.2015: With my improved Shunt and ADC setup (replaced the first plot of a charging curve), I can see that the current spikes at the end don't deliver measurable real current. Those seem to be for detecting an inserted battery; so all-in-all no bad feelings here. The charger seems to work correctly. The battery had exactly 4.200V when the charge ended, dropping a few mA (5-10) after that - the usual fast self discharge shortly after ending a charge cycle.

Also the NiMH charging is working correctly as you can see in the NiMH charge cycle plot to the left. The -dV charge termination detection can be clearly seen - and that there is some trickle charging, contrary to what happens in the LiIon charge program.

Another charging graph with even improved measurement and setup:

It's better visible that the charge current drops continuously - and when "switching to constant voltage" mode, a small increase in current occurs shortly before charging ends. To get an idea what this charging behaviour means in practice: Charging ~2500mAh into the battery took nearly 5 hours. Better chargers with real 1A current do this in 3 1/2 to 4 hours.

DIY LiIon-Charger

There are plenty of readily built chargers for LiIon batteries available on the market, and many are even quite cheap. But they all are usually limited to a form factor like 18650 cells, special for certain LiPo batteries like for quadcopters, mobile phones or digital cameras. Also, you never really know what you get technically, and sometimes it's not even worth being called a charger.

DIY battery holder with TP4057 DIY charger.

For example, I ordered a chinese wall-plug-charger with sliding connectors so I could charge all kind of flat batteries. One problem though, this charger showed "ready" when the battery had 4.4V - the limit is 4.2V +/- 0.05V, so correct result should have been 4.15-4.25V. Other chargers behave like LiIons are NiMH/NiCd batteries and don't stop charging, but continue to trickle-charge with a few mA; unfortunately the one I bought as universal charger with changeable cradles is one of these. LiIons have very little self discharge, so this will overcharge and damage the battery. Other chargers like the Trustfire TR-001 and TR-002 have electrical problems and also don't work properly with many produced lots; it's like playing the lottery to get a good charger.

"Damage the battery" doesn't sound as bad as it possibly is. Cheap NiCd/NiMH can blow up and leave an ugly mess with the acidic electrolyte. LiIons not only can produce fire and a hydrogen explosion, they also contain Lithium which is one of the most reactive alcaline metals which burns by itself. Destabilizing such a battery with a cheap or simply broken-by-design charger is something you certainly want to avoid. Just remember the Boeing Dreamliner LiIon issues.

TP4056 IC on the eBay/Aliexpress PCBs - original.

This was the reason I was looking around for alternatives. The first thing I stumbled upon a few years ago were TP4056 boards which received quite good feedback. They are small, extremely cheap (less than a buck per board on Aliexpress) and reliable.

These boards use the original TP4056 charger IC (datasheet). There seem to be a few knock-offs or clones around, which nearly all seem not to work well like the original ICs (WARNING!). But this shows that you always need to check at least one charge cycle to verify that your charger is working correctly.









I ordered a few handful of these chips for about 2 Euros including shipping and today finally built my own PCB with it. It is a bit smaller than those boards from eBay/Aliexpress.

Size comparison: DIY board vs. eBay PCB.

On the picture you can see that it is possible to save some space. But it was a challenge to get that on a perfboard without shorts and solder bridges. The LEDs are in the usual colours - red and green, instead of blue (charging) and red (ready/stand by) on the properly manufactured boards.

Finally it worked correctly. Using my improvised battery holder I had a decent CC CV charging cycle with very little thermal throttling. During the constant current phase, close to 1A current were flowing. The battery came out with 4.175V, the charger completely stopped charging the battery. So the IC works like wanted and expected. This was only a random result though, see the newer article about fake and clone TP4056 ICs.

Close-up view of the DIY TP4056 PCB.

Knock-off TP4056 - the logo is missing.

I also ordered a few different ICs which I wanted to test for building my own (universal) chargers .

The LTC4054 DIY PCB.

There is a small SOT-23-5 chip available called LTC4054 (datasheet). It is dirt cheap on Aliexpress, I got 50 pieces for less than 3 Euros. That again includes shipping fees. It can charge with up to 800mA.

At least in theory. At that rate the IC gets quite hot and thus runs into thermal throttling. This not only prolongs the charging cycle, it also leads to a premature end of the CV phase. My batteries had only around 4.15V after charging with this IC.

The LTC4054 only supports one status LED. With a capacitor for the battery connection, without a battery attached it shows a dimmed light with bright pulses at a frequency depending on the capacitance. During charge, it shines bright; when finished, it is in the dimmed state again - without flashing.

It is reliable and doing a good job, but it is hard to cool down due to its small footprint. I like it anyways. Not charging a LiIon battery to the full 4.20V is putting less stress on the cell, leading to a longer life span.

Another charging IC I recently found is the TP4057 (datasheet). The datasheet is only available in chinese, but Google Translate delivers a sufficient translation.

A TP4057 DIY charger board.

The SOT-23-6 IC is also hard to put on a perfboard. But it works fine after all.

The TP4057 delivers up to 500mA charge current. As the other ICs I tested, it properly stops the charging cycle at the end. The final cell voltage was exactly within the datasheet specs of 4.20V +/- 1% with the batteries having 4.158V after the charge cycle.

The TP4057 also has a very good reputation and as noticeable special feature a reverse-battery protection. It got used on some Miller ML-102 versions, where two of the ICs were used in parallel for increasing the charge current up to 1A. The LEDs are connected to only one of the ICs then, which is why those ML-102 versions continue charging a bit longer even when their green LED lights up already.


With these ICs it is quite easy and fun to build your own LiIon charger. The result is a reliable charger which does a proper job without overcharging or trickling the battery. For very little money as well!

Some more measurements on the Soshine T2 charger

I finally had my VC97 multimeter at hands and could take a closer look at the Soshine T2 charger (read the full review here). While reading reviews for the old Soshine H2 / H2V2 chargers I was afraid the charger may be not too good - but the values I got are indeed great!

The charger stops charging of LiIon correctly, slightly below 4.2V (my 14500 LiIon had 4.192V without load). The Soshine T2 properly stops charging and draws 5mA from the battery then; as it will start recharging at a certain threshold voltage, the battery cell will always stay "ready to use". When unplugging the charger, it seems like a good idea to remove the batteries, though.

Soshine T2 USB Charger for NiMH and LiIon

This post just redirects to the proper article - the permalink got broken.
The review is here:
http://blog.koepi.info/2015/02/soshine-t2-usb-charger-for-nimh-liion.html

Soshine T2 USB charger for NiMH, LiIon and LiFePO - Short Review / Test

(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! :) )

Usage

First tests show that the charger works well for NiMH and LiIon cells. For a few seconds after plugging in new batteries, the chemistry is checked based upon the cell voltage.

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.

The charger monitors the cell voltage which it shows on the display during charging. And of course the current: It can display the mAh charged into the battery, also the time it needed and a fourth position which just shows "----" for me; during charging LiIons or LiFePO, the percentage is shown here.

A LiIon cell gets detected correctly, too.









Technical details

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.



Insights


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.

Bottom line

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.