Table of Contents
Advertisement
4-1-5. 3-way overcharge protection system
Overcharge protection is ensured by a (A)
temperature sensors (thermostat and thermistor) and (C) a timer.
Ni-MH Battery
temperature
Ni-Cd Battery temperature
Fig. 7 Relationships of time, voltage, temperature and gas pressure while charging
(A) •
: This detects the increase in battery voltage at the end of charging using the value
charging.
dT/dt : This system is applicable to Ni-MH batteries. This detects the variation of Ni-MH battery temperature
by the value dT/dt at the end of charging and suspends charging.
(B) • Built-in battery temperature sensors : In the event the
the 40 ˚C thermostat or the 60 ˚C thermistor stops charging when battery temperatures reach their respective
values.
(C) • Timer : Should both the
stops charging within 30 --- 60 minutes from the beginning of charging.
(Note 2) The voltage of the battery increases during charging and begins to fall when further charging is not
possible. The
to protect the battery from overcharging.
(Note 3) The temperature rise during charging of a Ni-MH battery is higher than with a Ni-Cd battery, and a
sudden temperature rise occurs just before the battery is fully charged. The dT/dt system detects the
point where the temperature rises suddenly and suspends charging to minimize the temperature rise.
(Note 4) As shown in Fig. 7, the pressure of gas generated after a battery has become fully charged rises
rapidly to cause high temperature and high gas pressure that degrade the effectiveness of the
battery. If charging is allowed to continue, the pressure of the gas will activate the safety valve in the
battery, and the electrolyte will begin leaking.
system or dT/dt system (for Ni-MH battery), (B) built-in battery
2
V
Battery voltage
dT/dt
Charging time
system, dT/dt system and the temperature sensors fail, the timer automatically
system detects the point where the voltage begins to fall, and suspends charging
Overcharge range
Battery internal
gas pressure
system fails to detect the voltage change,
--- 5 ---
55˚C Thermistor
60˚C Thermistor
40˚C Thermostat
30~60-Minute timer
and suspends
Advertisement
Table of Contents
