Charger Woyum ZK4




This charger supports NiMH and LiIon batteries, has adjustable charge current and is flexible with length.



It arrived in a cardboard box with a lot of specification on it.



The box contained the charger, power supply, car adapter and instruction sheet.



The charger is powered from 12V and do also have a usb charger output.



The power supply is a standard 12V plug pack with a Woyum label on it.



The charger also includes a car adapter.



The charger has a LCD display on the front, but no buttons.



There is a button hidden on the side of the charger, it will change between the 3 charger currents.



Display during power on.



No batteries in the charger, the missing 0.5A text is because it is flashing to signal it is selected. It can be changed at any time by pressing the button.



Charging two LiIon batteries and one NiMH battery, the pie chart shows the charge status.



The specifications are on the bottom of the charger.



The charger uses the classic slider construction and will handle batteries from 33mm to 77mm, this will handle even the longest protected cells.










The charger can handle up to 70mm long batteries. Some small cells can be charger, but only if they are rated for 1A or more in charge current.



Measurements

• Power consumption when idle with no batteries is 0.5 watt
• Charger will discharge a full LiIon battery with less then 0.15mA when not powered.
• Below 0.6V the charger will not detect a battery
• Between 0.6V and 2V the charger will assume NiMH
• Between 2V and 3V the charge assumes LiIon and chargers with about 150mA.
• Above 3V the charger use selected charge current.
• Voltmeter is within 0.04V (All readings are slightly low).
• Voltmeter is will not show above 4.20V
• Will restart charging it voltage drops below 4.1V.
• Will restart charging if battery is inserted or power cycled.

Charging LiIon

LiIon can be charger with 0.5A, 1A or 2A. The 2A only works for 1 or 2 cells.



The charger uses a CC/CV profile with a termination current of about 200mA.





The 3 other slots are about the same, but I would have liked slot #3 to better match the other slots in voltage.







Thse cells are handled fairly nice, but the high termination current means a significant voltage drop when finished with older cells.



At the lower charge current the steps in the current regulation is very obvious (It is fine).



No problem charging with 2A, but this cell is not the best for this.



This is a newer high current cell that is much better suited for 2A charging.



The same with this larger cell.



A old and very worn down cell is hopeless to charge here, it gets lots of restarts.



The 14500 is handled fine.



The charger can handle 4 LiIon at 1A.



For that it need about 1.7A from the 12V power supply.



M1: 35.3°C, M2: 36.6°C, M3: 36.8°C, M4: 34.8°C, M5: 38.4°C, HS1: 50.0°C



M1: 40.7°C, HS1: 51.4°C



The charger needs some seconds to start.



The charger pauses the charge current at regular intervals.



Current can be changed at any time between 0.5A, 1A and 2A, 2A is only possible with one or two batteries.



Charging NiMH

NiMH can be charger with 0.5A or 1A.



The eneloop cells is charged nicely, it looks like a -dv/dt termination and no top-off or trickle charge.





The other 3 slots looks similar.



With the eneloopPro it looks like voltage termination and it is fully charged.



The leise is stopped on -dv/dt.



The termination also works at 0.5A.



The AAA cell was definitly stopped on -dv/dt.



The charger needs about 10 minutes to detect a full eneloop.



The charger maintain the 1A charge rate with 4 NiMH.



And need a bit below 1A from 12V when doing it.



M1: 37.3°C, M2: 38.5°C, M3: 38.8°C, M4: 38.2°C, HS1: 48.2°C



The charger needs a some to start.



And as usual with NiMH chargers it pauses to check voltage.



With NiMH the current can be changed between 0.5A and 1A at any time.



USB charger output

• Usb output is coded as Apple 1A

The charger output is rated for 1A and can deliver about 1.3A, this is fine, but not a very powerful usb charger.



Charging battery at the same time as using the usb output do not affect the usb output, but the efficiency is, of course, much lower, due to the power used to charge the batteries.



The usb charger has no problem delivering 1A for 1 hour and as can be seen below stays cool.
The temperature photos below are taken between 30 minutes and 60 minutes into the one hour test.



M1: 31.6°C, HS1: 34.7°C



M1: 34.2°C, HS1: 37.4°C



HS1: 35.9°C



At 0.5A the noise is 25mV rms and 423mVpp.



At 1A the noise is 36mV rms and 657mVpp.


The charger passed the 2830 volt and 4242 volt test, this means it is it is fairly safe.



Conclusion

The charger works fairly well with LiIon batteries, but due to the high termination current it is not perfect for older or small cell.
The charger works well with NiMH batteries.
The usb output is only 1A and coded with a older code.

All in all a good charger.



Notes

The charger was supplied by Woyum for review.

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