Datasheet

Rechargeable Button Cells
Intermittent Trickle Charge
NiMH Button Cells can also be charged with this
method. As the specified trickle charge is insufficient to
fully charge a discharged battery at high temperatures
and a constant overcharge at the specified rate or
higher limits the life, a modified charging method can
be adopted.
The following conditions must be observed:
■
Charging of the discharged battery should take place
time-controlled with a high rate possible, e.g. 0.2 CA, to
recharge the battery quickly after a mains failure
■
The following trickle charge should only cover the losses
due to self-discharge and stabilise the available capacity
For this purpose a two-step charge is applied, one to
fully charge the battery and a second for maintenance
charging the battery. The first charge is terminated by
a simple timer circuit.
After every discharge of the battery, regardless of the
duration, a full charge is applied, e.g. charging for 7 to 8
hours at 0.2 CA. The trickle charge is however different
from the previous methods and takes place at intervals.
It is recommended that the intervals last at least 1
minute per hour and are at the accelerated charge rate,
e.g. 0.1 to 0.2 CA.
In the interest of the life of the battery, however, no
more than 10% of the nominal capacity should be
recharged per day. This is sufficient to recover com-
pletely any losses due to self-discharge.
While the component cost for the electronic timing
con trol is not excessive, the necessary transformer
for full charge may not be available in every case.
Compromises are therefore necessary and may lead, for
example, to the reduction of the charge rate in the full
charge stage to 0.1 CA.
Note: Charging of cells connected in parallel must be avoided (if this cannot
be avoided blocking by diodes is recommended).