Charger 4Sevens Single Bay V1

This charger has been recalled

I have listed the differences between the recalled charger and the new charger





This charger was introduced in 2011 together with a new battery from 4Sevens. The charger has one bay and can only charge a single cell at a time, because the charge rate and voltage can be adjusted it can charge a large selection of different sizes can be charged.



The charger arrives in a white unmarked card board box.



Here the two switches can be seen. The voltage switch is used to select the correct charge voltage depending on chemistry, the current switch is used to select current, depending on cell size/capacity. The switches have a very short travel without any click.
The charger has connectors for 12 volt DC and for USB power.



The charger is supplied with leads for 3 different power sources. The mains power supply is universal voltage (100-240 VAC, 50/60 Hz). The car adapter needs a socket with 21 to 24 mm diameter. Using the usb power adapter the charger can not charge at 1 ampere, but at a lower rate.
The led is red when charging, both with 160 mA and 0.5A/1A and green at all other times.





The charger can handle 70 mm long batteries, and most flat top cells, short batteries (16340/18350) are a bit loose in the charger, more tension on the spring would have been nice.


Measurements

The charger does not start charging below 2.0 volt, i.e. it cannot turn tripped protection on again.
Between 2.0 volt and 3.0 volt it charges with 160 mA.
Between 3.0 volt and 3.6/4.2 volt the charger is applying regular charge current with constant current (either 500 mA or 1 A), when 4.2 volt is reached it uses a constant voltage charge.
The charger stops when the current has dropped to about 80mA.
When the battery goes above 3.6/4.2 volt or the charge stops the current is turned off (discharges with below 15 uA current).
The charger will not restart charging before the battery has been removed, the power cycled or the battery voltage goes below 2.5 volt.
When charger is disconnected from power, but with a battery in, it will draw below 20 uA from the battery.



Charging a 2000mAh cell with 0.5A takes about 5 hours, first 2½ hour with constant current and then 2½ hour with constant voltage.



Increasing the current to 1A reduces the charge time to a bit above 3 hours. Both CC and CV is faster. Here it can also be seen that the CC/CV regulation is done by a microprocessor and not with a analog chip. The steps is the processor adjusting, analog would have been smooth.



My old IMR cell is fast to charge on the 0.5A setting. This charge rate uses the same termination current as the 1A setting, but here it is a bit high, especially when charging 16340 cells. The cells will be charged fast, but with a bit lower capacity than possible.



Here I am using USB power to charge a cell, the current switch is in the 1A position. The charger starts with a charging current of 700mA and uses a little bit more from USB. After 10 to 15 minutes the current is down to 500mA. If I had uses the 0.5A ampere setting, the current would have started at 500mA.



The 4Sevens 26650 battery takes about 5½ hour to charge.



When charging a LiFePO4 cell with 3.6 volt termination voltage the charger also does a very fine CC/CV profile. It starts slowly, until the battery is raised to 3 volt, then it goes to full charge current.



Conclusion

This charger follows a CC/CV charging profile and also supports long 18650 cells and a lot of other cell types. This ought to make this charger a very good charger, with only a few small detail, that could have been better.
But that does not include the first series (i.e. all shipped before 2 Marts 2011) of the chargers, they has a problem that can lead to over current. 4Sevens is aware of the problem and will replace them.



Notes

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

When using the charger on USB I have not see the over current problem.