minus delta U cutoff

To prevent damage to batteries during charging due to overcharging or excessive temperatures, chargers are equipped with shutdown mechanisms. The cut-off procedures depend on the battery characteristics and monitor certain parameters during charging.

In most charging methods, the charging current and voltage are continuously monitored during the charging process and interrupted in case of strong deviations. Other chargers operate with temperature cut-off.

The different batteries show certain behavioral patterns during the charging process by which one can recognize that the charging process must be terminated. For example, NiCd batteries and NiMH batteries show a slight voltage drop of only a few millivolts when fully charged. The charge voltage then drops slightly, despite further supplied charge energy. As soon as this voltage drop (delta-U) occurs, the charging process is switched off. This process is therefore called minus-delta-U disconnection. The voltage drop can be detected via differentiators, and the switch-off can be performed via a microprocessor.