Theory of operation

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1.1.3

Maximum temperature detection method

With this method, if the temperature rises above a threshold, charging is stopped and trickle

charging is started.

1.1.4

dT/dt detection method

With an NiMH battery, as shown in Figure 1, there is an increase in the temperature vs. time

curve (approximately 1 to 2 °C/min) towards the end of charging. When a rise in the

temperature is detected by the thermistor or any other temperature sensor (NTC in this

case) during rapid charging, and the prescribed temperature increase is sensed, rapid

charging is stopped and trickle charging is started.

In the example implementation mentioned in Chapter 4, the zero delta voltage method is

used as the primary technique for terminating the charge. Time out, max voltage and max

temperature are used as the secondary or backup methods for ending the charge. Once the

battery is saturated, its voltage is still monitored to prevent the battery from discharging

completely and a saturation current is provided to compensate for the self-leakage.