Donnerstag, 28. Mai 2015

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.

Keine Kommentare: