Charging attachments for rechargeable batteries 6F22. Encyclopedia of radio electronics and electrical engineering

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

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To power small-sized electronic equipment, Ni-Cd and Ni-MH batteries of AA and AAA sizes are widely used today. Less common are batteries used instead of galvanic voltages of 9 V ("Krona", "Korund"): domestic Ni-Cd "Nika", 7D-0,125 and foreign Ni-MH size 6F22 from different manufacturers (the same size includes batteries GP17R8H, GP17R9H and others from GP). The capacity of these batteries is 0,1 ... 0,25 Ah, the nominal voltage is 8,4 ... 9,6 V, and their charging requires specialized chargers, which are extremely rare on sale (usually the ability to charge such batteries available only in rather expensive universal devices). The article below describes two attachments that allow you to charge nine-volt batteries from an existing power source.

You can make your own charger (charger) for batteries of size 6F22 based on a rectifier with a quenching capacitor, but due to the galvanic connection with the network, it can be unsafe to operate. A charger with a step-down transformer is safe, but, firstly, there may not be a suitable transformer either at home or in a store, and you will have to wind it yourself, and secondly, the dimensions of such a device will be larger. A possible way out is to make a charging attachment to an existing source, for example, to a laboratory power supply with an output voltage of 12 V or to a charger from a cell phone (5 V). The diagram of the charging attachment to a stabilized power supply with an output voltage of 12 V is shown in fig. one.

Fig. 1

The charging current of the battery battery connected to connector X1 is set with a trimming resistor R8. Transistors VT1, VT2 and resistors R4 - R7 form a charging current control unit. The VD1 diode prevents the battery from discharging through the set-top box and the power source if the latter is disconnected from the network or the voltage is lost in it. After connecting to the set-top box, a current I flows through the battery being charged._charge1, determined by its own voltage UB, the voltage of the power source Upit by the resistance of the resistor R3 and the input part R8 (the effect of the resistors R6 and R7 shunting it can be ignored) and, finally, the voltage drop UVD1 on the diode VD1: I_charge1 = (U_Pete - OR_Б - OR_VD1)/(R3+R8). When the battery is discharged to 7 V, this current does not exceed 2,5 mA, so the voltage drop across the resistor R8 is not enough to open transistors VT1, VT2, the HL1 LED does not light and the VT3 transistor is closed. When you press the SB1 ("Start") button, the transistor VT3 opens, and the charging current increases to the value I_charge2 = (U_Pete - OR_Б - OR_VD1 - OR_VT3)/R8, where U_VT3 - voltage drop in the emitter-collector section of the transistor VT3. In this case, the voltage on the engine of the tuning resistor R6 increases so much that the transistor VT1 opens, therefore, after the button is released, both of these transistors remain open and the battery starts charging with a current of 15 ... 50 mA (depending on the entered resistance of the tuned resistor R8).

LED HL1 indicates the progress of the process. As the battery is charged, the voltage of the battery rises, and the charging current and the voltage drop across resistor R8 decrease. When the battery voltage reaches approximately 10,5 V, the transistor VT1, followed by VT3, closes, the HL1 LED goes out and the battery charging {stops. From now on, only a small current I flows through it._charge3 (about 1 mA), determined mainly by the resistance of the resistor R3. If, due to a battery malfunction or a short circuit in the output of the set-top box, the current in the charging circuit exceeds 50 ... 60 mA, the transistor VT2 will open, the transistors VT1, VT3 will start to close and, as a result, the output current will be limited. The scheme of the attachment to the cell phone memory is shown in fig. 2.

Fig. 2

This device is an adjustable voltage boost converter. On inverters DD1.1-DD1.3, a master pulse generator with a repetition rate of about 30 kHz is assembled, and on DD1.4-DD1.6 and transistor VT1, a control pulse shaper for transistor VT2, which operates in the key mode. The impulse voltage generated on its collector is rectified by the VD1 diode, the capacitors C6, C7 are smoothing. After connecting to the X1 connector, the battery starts charging through the HL2 LED (it lights up) and the R7 resistor. If the charging current turns out to be more than 20 ... .25 mA, the voltage drop across this resistor will open the transistor VT1, it will bypass the resistor R4 and the duration of the control pulses will decrease, therefore, the rectified voltage and charging current will decrease. This ensures its stabilization during the charging process. When the battery is discharged, the transistor VT3 is closed and the HL1 LED does not light. As it charges, the current through the serial circuit VD2R9 increases, the voltage drop across the trimmer resistor R9 increases and there comes a moment when the transistor VT3 starts to open. As a result, part of the rectifier output current begins to flow through this transistor and the HL1 LED, and the charging current decreases. In other words, the brightness of the HL1 LED gradually increases, and the HL2 LED decreases. The latter continues to glow faintly even after charging is completed, since the current of the VD2 zener diode and a small (about 1 mA) charging current flows through it, which is safe for the battery (it can remain connected to the set-top box for an unlimited time). The printed circuit board drawing of the first attachment is shown on Fig. 3, and the second one in Fig. four.

Fig. 3

All parts are mounted on them, except for the connectors for connecting the battery and power source. Fixed resistors - P1 -4, C2-23, tuning resistors - SPZ-19a, oxide capacitors - imported (for example, the Jamicon TK series), the rest - K10-17. Transistors of the npn structure can be of the KT342, KT3102 series, and pnp - of the KT3107 series. LEDs - any with a direct voltage of 1,8 ... 2,5 V and a maximum allowable current of up to 25 mA. Possible replacement of the diode 1N5819 (see Fig. 1) - D310, D311, diode KD522B (see Fig. 2) - KD521A, 1N5819, zener diode KS162A - KS175A, KS182A. Choke L1 (see Fig. 2) - DM-0,2, button SB1 (see Fig. 1) - PKN-159. If the output current limiting mode in the first attachment is not needed, the elements VT2, R5, R7 are not installed. To connect a rechargeable battery to attachments, two-pin connectors are used (similar to the pads used in batteries of this type), which exclude incorrect connection, and to connect to a power source and a cell phone charger, the corresponding connectors are used. The author used a charger with an output voltage of 5 V, which is equipped with a USB-A socket. To dock with it, the charger was equipped with a cable with a USB-A plug, which made it possible to charge the battery from a computer. The appearance of the mounted attachments is shown in fig. 5 and 6.

Set up the first prefix in this sequence. By setting the sliders of the trimming resistors R6 - R8 to the lower (according to the diagram) position, a discharged battery is connected to the X1 connector and a milliammeter connected in series with it with a measurement limit of 100 mA. The power supply is turned on and, by pressing the SB1 button, the maximum (initial) charging current is set with the resistor R8 (no more than 50 ... 60 mA). Then the battery is replaced with a constant resistor with a resistance of 100 ohms and, by moving the slider of the resistor R7, the current is increased by 10 mA in relation to the previously set one. Next, a freshly charged battery is connected (without a milliammeter) and, slowly turning the trimmer resistor R6, the HL1 LED goes out. After that, several control charging cycles are carried out and, if necessary, adjustment is repeated.

Fig. 7

The second prefix is ​​adjusted as follows. By setting the slider of the resistor R9 to the lower (according to the diagram) position, the capacitor C5 is temporarily closed with a wire jumper. Then, as in setting up the first set-top box, a discharged battery and a milliammeter connected in series are connected to the output. Turning on the power supply, with a tuned resistor R2, a current is set in the charging circuit that exceeds the desired charging current by 10 ... 20%. After removing the jumper from the capacitor C5, it should decrease. The required value is set by selecting the resistor R7 (I_zar ~ 0.6/R7). Then a fully charged battery is connected and the charging current is set to about 9 mA with resistor R0,5. If desired, the indication of the end of battery charging in this memory can be made more clear. To do this, instead of the transistor VT3 and the zener diode VD2, a parallel voltage regulator KP142EN19 is installed (Fig. 7). Now only the charging current will flow through the HL2 LED. It should be noted that the nominal voltage of some batteries of this size, in particular GP17R9H, is 9,6 V, and when charged, the voltage on it reaches 12 V, so a 13,5 V power supply is required to charge it using the first set-top box.

Author: I. Nechaev, Moscow; Publication: cxem.net

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