Charger Nokoser DigiCharge D4u





Nokoser is a new charger brand and starts with some advanced chargers, this is a 4 cell charger that can handle 3 types of LiIon and NiMH and shows the capacity charged into the batteries, it us powered from usb and can also work as a power bank.





I got the charger in a envelope and the shipping did damage the box a bit, but not the charger.



The box contained the charger, a usb power supply, a usb cable and a instruction sheet.



The charger can only be supplied from usb power and can also work as a power bank.



During power on the charger will show all segments on the display.



Here I have loaded the charger with some batteries, the charger will automatic select NiMH/LiIon chemistry, but LiFePo4/3.7V/3.8V must be selected manually with the mode button. Default is 4.2 volt LiIon (3.7V on display).
The mAh display shows how many mAh is charged into the battery.
Note: The discrepancy on the display is my fault, not the charger!



When putting LiIon batteries into a unpowered charger, it will work as a power bank, this is also shown on the display.



There is two buttons, one to select battery chemistry (MODE) and one to select slot (SLOT).
When the charger is loaded with batteries the MODE button will select chemistry for all batteries at once. To select chemistry for individual batteries press the SLOT button (Very good functionality).
When the charger starts charging the selection is locked for that battery, to change it the battery must be removed and inserted again.



The charge uses the typical slider construction with a metal rail and it works very well from about 30mm to 71mm, i.e. the charger can handle just about any protected 18650 and 26650 cell.








The charger can handle 71 mm long batteries, including flat top cells.
The minimum charge current is 0.5A, this is on the high side for 10440 cells.



Measurements

• With only cells in slot #1 and #4 the charge current is 1A
• Any cell in either slot #2 or #3 will drop the charge current to 0.5A in all slots.
• Current will change between 0.5A and 1A as batteries are inserted and removed.
• A full cell in slot #2 or #3 will still reduce current in slot #1 and #4
• When not connected to power the batteries are drained with 3 to 5mA
• Below 0.6 volt the charger will assume empty batteries and charge with about 8mA.
• From about 1 volt the voltmeter will be precise (Within +/-0.03 volt).
• Above 2.0 volt the charger assumes LiIon batteries.
• Mode button is used to select LiIon chemistry.
• Slot button is used to select slot when selecting chemistry.
• With a full LiIon cell the charger will charge with 2mA
• When the battery is full the voltmeter will stop updating.
• The charger will not restart if battery voltage drops.
• Charge will restart charging after power loss, or battery insertion.
• After a bit over two minutes without button presses the display brightness is reduced.

Charging LiIon 4.2V



This is a sort of CC/CV charge curve with 100mA termination, but the power is limit, probably because of the usb power.
Display shows 3185mAh



The second slot only charges with 0.5A and uses the same 100mA termination. The lower charge current will make it slower, but also useful for smaller batteries.
Display shows 3174mAh



Slot #3 looks like slot #2
Display shows 3007mAh



Something goes wrong here, the charger do not terminate. I doubt the battery voltage will end up to high, but the high amount of mAh on the display shows that the charger has been charging for a lot more time.
Display shows 3506Ah



I did a second run to see if it was a single fluke.
Display shows 3455Ah




2600 and 3400mAh cells also looks fine.
Display shows 2661mAh and 3228mAh



This older 2600mAh cell also looks fine, but because of the higher resistance in the cell it requires more voltage, the charging current is reduced very early, i.e. charging time is longer.
Display shows 2320mAh



Another old cell, with a perfect charge curve..
Display shows 631mAh



Very nice charging for this cell, but I would have liked a lower termination current.
Display shows 722mAh



With four cells the charger also has some small trouble maintaining the full current during the full charge cycle, but the impact of that is minimal.
Display shows 3040mAh, 3080mAh, 3864mAh, 2909mAh



M1: 27,7°C, M2: 28,2°C, M3: 27,9°C, M4: 27,5°C, HS1: 30,2°C
There is not really any heat when charging LiIon batteries (Very good).



HS1: 32,4°C





When putting LiIon batteries in the charger it will always draw a small current until it is powered, due to the power bank functionality.
The charger is fairly slow to start because it waits for user input.



Charging LiIon 3.6V (LiFePo4)



A good LiFePo4 charging.
Display shows 1189mAh



Oops, the charger missed termination (This cell is an AA size LiFePO4 cell).
Display shows 732mAh



Charging LiIon 4.35V



The charger do a good job with 4.35V charging.
Display shows 2606mAh



Charging NiMH



This looks like a nice -dv/dt charging, the cell is definitely full.
Display shows 1747mAh



Something goes wrong here and the charger terminates way to early.
Display shows 1166mAh



This looks better, but it has problems terminating.
Display shows 1854mAh



With 1A charge current there is no problem with termination.
Display shows 1760mAh




Higher capacity with 1A charge current, the termination works perfectly.
Display shows 2258 and 2388mAh



It looks like the charger stops at the correct time with this cell, but it is not a -dv/dt termination.
Display shows 554mAh




Detecting a full cell depends on charge current, it is faster with 1A than with 0.5A.



NiMH needs less power and less voltage than LiIon, but it is not possible to see the charge current on the above chart.
Display shows 1940mAh, 1718mAh, 1919mAh, 1794mAh



Same as above, but with input current removed.



M1: 35,5°C, M2: 36,5°C, M3: 35,6°C, M4: 33,4°C, M5: 35,4°C, M6: 37,4°C, M7: 33,5°C, HS1: 49,8°C
With NiMH there is some heat, but not much.



M1: 34,7°C, M2: 35,4°C, M3: 34,7°C, M4: 33,0°C, M5: 38,1°C, M6: 34,8°C, HS1: 42,3°C




The charger is fairly slow to start because it waits for user input.




USB output

• When display is on usb output will drain the batteries with up to 55mA
• The display will turn off after 20 seconds without any load on usb output.
• Display light stays on when usb output is loaded.
• Brightness on display is unstable when the battery is low.
• USB output will turn off when charger is powered and on again when power to charger is removed.
• Output is coded as Apple 1A

With a single 18650 the charger can deliver up to 1.5A on the usb output, before the output voltage drops. The overload protection kicks in at 2.2A.



With 4 batteries the voltage is stable until the overload protection kicks in at 2.2A.



Using one cell and a light load (0.5A) the power bank function looks fine.



Increasing the load to 1A also works, except there is some problems when the battery is nearly empty.



Using 4 batteries and 2A load also works, except when the batteries are nearly empty.
The green area in the curve is because the charger is switching between batteries rather fast, I expect this to increase the output noise significantly. Another problem is the minimum battery voltage, with one cell it stops at around 3V, but with four cells some of them is discharged to 2.2V, this is bad.
The efficiency curve is invalid because I only measure on one battery.



With one 18650 cell and 10ohm load the noise is very low at 3mVrms and 50mVpp



Using four 18650 batteries and 2.5ohm load the noise increases to 12mVrms and 95mVpp, again very low.
This low noise is, of course, only valid with fresh batteries, as can be seen on the load test above the usb output does strange things when the battery voltage drops.



Supplied usb power supply



The charger was supplied with an unbranded usb power supply.

• Unloaded power consumption is 0.14 watt
• Power consumption with idle charger is 0.30 watt
• Output voltage is slightly above 5 volt.
• Output is coded as USB charger (DCP).

If it has a overload protection it is above 3A.



There is no problem maintaining the output voltage when loaded with 2A
The IR photos below are taken after 45 minutes.



M1: 52,7°C, M2: 59,0°C, HS1: 85,0°C



M1: 64,5°C, M2: 54,1°C, M3: 59,4°C, HS1: 73,4°C



M1: 57,9°C, M2: 42,4°C, HS1: 62,1°C


Testing the usb power supply with 2500 volt and 5000 volt between mains and low volt side, did not show any safety problems.



Conclusion

I like the functionality and display on the charger, but it has some issues.
The charger has some problems with LiIon termination, this can be seen above on the slot #4 curves. This is not dangerous, because the voltage will stay at about 4.2 volt, but it will wear the battery down faster.
The NiMH terminations is not perfect either, the curve from slot #2 stops early and from slot #3 has problems terminating.
The temperature of the batteries while charging is low, this is good.
Capacity display for LiIon looks fine, but for NiMH it looks a bit on the low side.
Usb output works fine with one cell and 1A load, but do not use 4 cells!

This charger gets an acceptable rating.



Notes

Here is an explanation on how I did the above charge curves: How do I test a charger
Read more about how I test USB power supplies/charger