Dual mode charger

Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells

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Today, nickel-cadmium and nickel-metal hydride batteries are widely used to power various household equipment (radios, players, remote controls, etc.), since their price is relatively low and does not exceed the cost of several galvanic cells. Economically, it turns out to be much more profitable. However, a charger is required to charge the batteries.

Despite the fact that a lot of various chargers have already been described in Radio - from very simple to very complex - interest in this topic has not waned. For the attention of readers, we offer a variant of a dual-mode charger with a timer that limits the charging time of the batteries.

The proposed charger (charger) has two charging modes - standard, with a current of 0,1C (C is the nominal capacity of the battery) for 14 hours, and accelerated, with a current of 0.25C for 5 hours. It is equipped with a timer that switches the battery after the time has elapsed. for recharging with a current of about 0,01 C, compensating for its self-discharge. The battery can remain in this state for a long time. So if you accidentally forget to unplug the charger, don't worry, the battery won't recharge.

However, this memory has one negative property: if during the charging process the voltage in the network disappears for a while and then recovers, the countdown will start over and eventually the battery will be recharged. Therefore, if power outages are not uncommon in your area, you should take appropriate measures to prevent the battery from overcharging, such as monitoring the end of charging time. If after its expiration the memory did not turn off automatically, you should do it manually.

The memory circuit is shown in fig. one.

The cell ratings are given for the case of charging 600 mAh AA nickel-cadmium batteries in standard mode with a current of 60 mA for about 14 hours or 150 mA for 5 hours. However, the cell ratings of this charger can be recalculated for charging other batteries.

Functionally, the memory consists of a timer and current-setting circuits. The timer is assembled on a K176IE5 (DD1) microcircuit. The power supply of the microcircuit is stabilized by a parametric stabilizer R4VD3VD4. The frequency of the clock generator is determined by the values ​​of the elements R10 and C5 when the SA2.2 switch is open, and the elements R10, C5-C7 when the switch is closed. At the same time, the SA2.1 switch connects different charging circuits to the battery being charged: VD5R5R6 and R7HL4, if the charging time is 5 hours (the SA2.2 switch is open); VD2R3R5R6 and R2HL2 when charged for 14 hours (switch SA2.2 closed). The HL2 and HL4 LEDs indicate the standard and accelerated charging modes, respectively.

Resistors R3, R5 and R6 are specially selected with a power dissipation margin to reduce their heat generation.

The memory works as follows. After turning on the power switch SA1, the counters of the DD1 chip are reset to zero by a high-level pulse passing through the capacitor C4. The clock generator turns on, and the countdown begins. Pulses from the generator through the resistor R14 are fed to the base of the transistor VT3 and periodically open it. In time with the pulses, the HL5 LED starts flashing, clearly indicating the frequency of the master oscillator and the operation of the memory.

Another R9VT1 circuit with an HL13 LED is connected to output 2 of the DD3 microcircuit, with which it is convenient to control the total operating time of the timer, since its glow time is equal to 1/64 of the charging time.

After the timer has expired, a high level will appear at output 15 of the DD1 chip, which will open transistors VT1 and VT4. The first one will stop the clock generator, and the second one will turn on the relay K1, which, with the contacts K1.1, will switch the battery to recharge with a low current through the R1HL1 circuit. At the same time, the HL1 LED indicates that the battery is fully charged.

The device, the appearance of which is shown in Fig. 2, assembled on a double-sided PCB.

The drawing of the board is shown in fig. 3.

(click to enlarge)

The board is designed for the use of capacitors K73-17 (C5-C7), oxide capacitors K50-29 (C2-C4) and imported (C1), PEV resistors (R3, R5, R6) and MLT - the rest, of the corresponding power, relay RES59B version HP4.500.020 .48 or RES4.590.202B version RS1. However, in the latter case, the DA15 stabilizer will have to be installed on the heat sink. Resistor R7 and capacitor CXNUMX are mounted on the board first.

It is permissible to use almost any low-power npn transistors in the memory, for example, the KT315, KT3102 series. Zener diodes KS147A (VD3, VD4) are replaceable by one with a stabilization voltage of 9 V, for example, D814B1. Diodes KD208A (VD2, VD5) can be replaced by any with a permissible forward current of at least the battery charging current, respectively, standard and accelerated

Network transformer T1 used ready. It is chosen based on the required charging current and the number of simultaneously charged batteries. The transformer must provide a voltage on the secondary winding of 14 ... 16 V at maximum current for one rechargeable battery, 20 ... 23 V for two, 30 ... 33 V for three or four. In addition, it should be remembered that in idle (recharging) mode, the voltage at the input of the DA1 stabilizer should not exceed 35 V.

If it is necessary to charge batteries of a different capacity, by selecting resistors R5, R6, you should set the accelerated current, and then, by selecting resistor R3, the current of the standard charging mode.

Author: A. Trapeznikov, Severodvinsk, Arkhangelsk region.

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