Charge termination methods

AN417

6/21

Doc ID 2074 Rev 2

Figure 2.

The negative delta voltage method fast charge is terminated at point A

In fact, a NiCd battery charged with the [-

shows that the battery temperature has substantially increased at point A when charge is

terminated, which may decrease the life-time of the battery. More precisely in Figure 3, most

of the current fed to the battery between point B and the negative voltage drop A is not

directly converted into active battery charge, but into heat. This can be seen in the

temperature curve shown in Figure 3. The point B corresponds to the inflexion point of the

battery voltage curve versus time.

The [-

the NiMH charging reaction is permanently exothermic (releases heat), so the battery

temperature would become excessive in its [-

Another characteristic of the NiMH batteries makes the [-

types of NiMH batteries do not exhibit a significant voltage drop as NiCd batteries do when

reaching their full capacity.

charging time

cell voltage

battery voltage

battery temperature

temperature

1.2

1.3

1.4

1.5

1.6

20

30

40

50

60

-dV

deg C

V

A