Charger for four nickel-cadmium batteries
Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells
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Often there is a need to simultaneously charge several nickel-cadmium batteries. Charging a battery from batteries connected in series is in most cases ineffective due to their varying degrees of discharge. Best results can be achieved by charging each cell separately.
The figure shows a diagram of a simple charger (charger) for four nickel-cadmium batteries with a nominal capacity of 500 mAh. They are charged with a stable current of 50 mA for about 10 hours. An LED indicates the charging process. When the battery voltage reaches the set value, its charging will automatically stop and the LED will turn off.
(click to enlarge)
The charger contains a bipolar stabilized power supply ±12 V on microcircuit stabilizers DA1 and DA2. an exemplary voltage generation node on the VD5 zener diode and four identical nodes, each of which includes a comparator on one of the op-amps of the DA3 microcircuit and a charging current key on the transistor (VT2 - VT5).
The charger is fed from a network transformer having a secondary winding with an average output, which provides an alternating voltage of 2x15 V.
On the zener diode VD5 and the current amplifier on the transistor VT1, an additional voltage regulator of +6,2 V is assembled, loaded on resistors R2 and R3. The variable resistor R3 sets the voltage to which the batteries are charged.
Consider the operation of one of the cells on the op amp DA3.1 and the transistor VT2. From the engine of the resistor R3, part of the reference voltage is applied to the inverting input of the op-amp. The non-inverting input is supplied with voltage from the battery through resistors R4. Resistor R5 forms a small hysteresis (50 mV) for switching the comparator. If the voltage on the battery (non-inverting input of the op-amp) is less than the reference voltage (at the inverting input of the op-amp), the output of the comparator is a low-level voltage close to -10.2 V. Circuit VD7. VD8 stabilizes the voltage at the connection point of resistors R5. R6 and R7 at the level of - 6,2 V. Charging current flows through the collector-emitter section of the open transistor VT2 and resistor R9. Diode VD6 prevents the connected battery from discharging when the charger is off.
When the voltage on the battery being charged exceeds the reference voltage, the comparator will switch. A high level voltage close to +10.2 V will be established at its output. Transistor VT2 will close and charging will stop.
Domestic elements are applicable in the device: DA1 microcircuits - KR142EN8B. KR142EN8D: DA2 - KR1162EN12A. Crib2EN12B. KR1179EN12; DA3 - K1401UD2A; transistors VT1 - KT943A, VT2 - KT3W7A, KT3107B; diodes VD1-VD4, VD6, VD8, VD9, VD11, VD13, VD14, VD15, VD17 - any rectifier silicon: zener diodes VD5 - KS168A, VD7, VD10, VD13, VD16 - KC156A; LEDs - any red glow, for example AL336B.
The transistor VT1 dissipates more than 1 W of power, so it should be placed on a heat sink.
Author: S.Constantin
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