Datasheet

Rechargeable Button Cells
3.5 CHARGING METHODS FOR POWERFUL FAMILY
CHARGING METHODS
1. Standard Charge
The method to fully charge sealed NiMH cells is to
charge at nominal constant current (0.1 CA) with time
limited charge termination. The timer should be adjusted
to terminate charging after having reached 150–160%
capacity input (15–16 h) to avoid extended overcharge.
This charging method may be used in the temperature
range of 0 to +65°C. The cells should not be over-
charged for more than 1000 hours at room temperature
at a maximum rate of 0.1 CA.
2. Accelerated Charge
An alternative method to fully charge NiMH cells in a
shorter time is to charge at a constant current of 0.3 CA
with time limited charge termination. The timer should
be set to terminate charging after 4 hours, which is
equivalent to 120% charge input. This charging method
may be used in the temperature range of +10 to +45°C.
3. Fast Charge
Another method to fully charge NiMH cells
V450–V600 HR or batteries in an even shorter time
is to charge at a constant current of 0.5–1 CA. Use
of a timer control circuit alone is not sufficient for fast
charge termination. In order to achieve the best cycle
life we recommend the fast charge termination by
dT/dt. For dT/dt control a temperature increase rate
of 0.7°C/min should be used.
As shown in Fig. 24 the temperature rise as well as the
voltage decrease can be used for charge termination.
–∆V
1)
charge termination may be used.
Reference value for –∆V termination should be 5–10
mV/cell. An additional TCO
2)
device should be used
to interrupt charging if these switch-off methods fail to
respond. After the fast charge termination it is possible
to switch to trickle charge at a rate of 0.01–0.03 CA.
4. Trickle Charge
A large number of applications require the use of cells
and batteries which are maintained in a fully charged
condition. In order to compensate the loss of capacity
due to self-discharge it is recommended to maintain a
trickle charge current of between 0.01–0.03 CA. The
preferred temperature range for trickle charge is in
the range of +10 to +35°C. Trickle charge may be used
following any of the previous charging methods.
1)
For dT/dt and/or –∆V cut off applications please consult us for more detailed
information.
2)
TCO = Temperature cut off.
FIG. 24
Charging characteristics
(Charging current > 0.5 CA)
Charg ing recommended and methods
refer to single cells. For batteries there
may be different conditions requir ing other
means of charge or control.