C/10 Chargers for NiCad and NiMH Batteries

 Typical Uses of C/10 Chargers:

• Applications where the battery can be recharged over night.
• Applications where the battery will not be left on the charger continuously charging.

C/10 Regulated Current Chargers	C/10 REGULATED CURRENT NiCad/NiMH chargers have output current which is fixed during the charge cycle as shown in FIGURE 1. Output power available from 0.1W to 18W. Units have Inputs of 120V 60Hz, 230V 50 Hz or input selection 115/230V 50/60 Hz.
C/10 Unregulated Current Chargers	C/10 UNREGULATED CURRENT NiCad/NiMH chargers have output current which varies during the charge cycle as shown in FIGURE 2. Output power available from 0.1W to 6.4W. Units have Inputs of 120V 60Hz, 230V 50 Hz or input selection 115/230V 50/60 Hz.

Often referred to as trickle chargers, C/10 chargers are quite economical due to the simplicity of design and the relatively low output power level. Users should be instructed to remove the battery from the charger after full charge is attained, since a permanent charging state will cause some loss in battery life. Standard NiMH batteries should not be exposed to C/10 charge rates continuously, however special NiMH cells from Varta and Energizer designed for power tools, are specifically designed to tolerate overcharge.

Regulated current designs are preferred for NiMH cells, since the current is more predictable, and less likely to cause overcharge. Using a C/20 rate instead of a C/10 rate for a NiMH charger may also be a good idea, if sufficient recharge time is available. Allow up to 26 hours to recharge.

Other techniques are available to reduce overcharge to NiMH batteries at the C/10 rate. An electronic timer circuit to switch back the charging rate from the C/10 rate to a C/40 rate is available for the regulated current version. Another option is a voltage level sensor set at 1.38V/cell which can switch the charge current from a high level to a lower level.