Charger Xtar MC0





Xtar makes many LiIon chargers, this is their smallest chargers. The charger is small and light weight and only smaller batteries fits in the charger. The two current settings makes it possible to have fairly fast charging of the larger supported cells, but not using to high current on the small AAA (10440) sized liIon. Note: Some of the larger Xtar charger can charge with the same low current.



I got the charger in a small cardboard box with the specifications printed on it.



The box contains the charger, a usb cable and a instruction manual.



There is no power supply included with the charger, you must supply your own usb power supply/charger. With a maximum charger current of 0.5A the charger can run will most usb supplies (Some of the cheaper ones does not supply specificed current: See my test).



The charger has one button to select between 0.25A and 0.5A charge current and two blue leds to show the switch position. I would have prefered a larger more visible marking of the two leds.
There is also a red/green led that shows red while charging and green at all other times.



The charger can handle both button top and flat top batteries.
The slider moves smoothly and can hand cells from 31mm to 52.5 mm long.






The charger can handle 52.5 mm long batteries, including flat top cells. (See my small LiIon comparison for length of different brands).



Measurements charger

• Below 2.85 volt the charger charges with about 40 mA or 80 mA, depending on current selection.
• Above 2.85 volt the charger applies regular charge current.
• When the charge is finished the charger is charging with a few uA.
• The charger will restart if the voltage drops below 4.07 volt.
• Power cycling or battery reinsertion will not restart charging.
• When charger is disconnected from power, but with a battery in, it will draw below 1 uA from the battery.

This is a very good CC/CV charge curve. The input current and the output current is the same, meaning the charger uses a linear charge controller chip.



The cell does also charge perfectly.



No problems with my old 16340 cell.



Lets try a charge with 0.5A. It is still a good CC/CV charge curve, but there is a step during the CV phase, where the charger says the cell is full. Looking at the blue curve it can be seen that this is not the case, it is missing some percent yet. This capacity is also charged into the cell, but after the charger shows a green light.



It is the same with the 18350 cell.



And it is much worse with my old 16340 cell. Note: It will not be this bad in real usage, my 16340 cell is well past its best time.

What is happening? My guess is that the charger has two charge controllers, each supplying 250mA (This is a good solution for heat distribution), but the led is only connected to one of them and in this case it was the charge controller with the lowest charge voltage. This means that when the battery reaches the setpoint for the first charge controller, the charger will say ready, but the second charger controller will continue to charge until the CV phase is finished.
Due to the random nature of the controller voltage, it could just as easily have been the other way round, i.e. the charger would finish before turning the green light on (Probably half the MC0 will do that).


M1: 30,4°C, M2: 38,9°C, HS1: 45,3°C

With only 0.5A charge current, not much heat gets to the battery.



Conclusion

The charger is a very good charger at 0.25A, but on some of the chargers the led showing charging finised too early when using 0.5A current.
Of course it is always possible to wait an hour extra or charger at 0.25A to get the full capacity into a cell.



Notes

The charger was supplied by XTAR for a review.

Here is an explanation on how I did the above charge curves: How do I test a charger