Universal charger-discharge device for small batteries. Scheme, description

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Universal charger-discharge device for small batteries. Encyclopedia of radio electronics and electrical engineering

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

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The proposed charger-discharge device is designed to service small batteries and can be used as a source of stabilized direct current.

This charger-discharge device differs from similar designs by increased stability of the charge-discharge current, the possibility of using a single circuit for charging and discharging, and an increased maximum current, which allows it to be used to charge batteries with a capacity of up to 20 Ah.

Specifications:

Maximum power consumption ....... 60 W
Maximum output current ......2 A
Current stabilization factor ....... 1000
Maximum battery voltage: when charging ....... 20 V
when discharging ....... 30 V

The functional diagram of the device is shown in Fig.1.

The power supply current passes through the current sensor, control element and load. The operation of the regulating element is affected by the control element, which receives the reference voltage signal and the signal from the current sensor. The control element affects the regulating element in such a way as to equalize the voltages of the current sensor and the reference. Thus, the stabilization of the current through the load is carried out.

The schematic diagram of the device is shown in Fig.2.

(click to enlarge)

The reference voltage source [3] is assembled on a field-effect transistor (FET) VT1 of the KP303E type and an operational amplifier (OU) DA1 of the K140UD7 type.

The bias voltage FET is formed on the resistor R1. Op-amp DA1 is connected according to the scheme of a non-inverting amplifier, its gain is set by the divider R2R3 included in the negative feedback circuit. Since an exemplary voltage Uob is applied to the non-inverting input DA1, then at its output there will be a voltage Uout.ob = (R3/R2 + 1) Uob.

The current sensor in the device is resistor R7. As a current source with an op amp, a classical circuit [2,3, 2] was used, assembled on an op amp DA140 of the K7UD2 type and a powerful composite transistor VT2 of the 827T2A type, which performs the functions of a regulating element. In this circuit, op amp DA5 compares the voltages at its inputs and regulates the current in the load so that the voltage at the inverting input becomes the same as at the non-inverting one (set by resistor R5). In this case, the current in the load In = Uout.rev / RXNUMX.

Using switch SA1, you can select three modes of operation of the device:

1) mode "1" (battery charging) allows charging with a final charging voltage of not more than 20,0 V and a current of 0 ... 2 A;

2) mode "2" (battery discharge without a power source) allows the battery to be discharged with an initial discharge voltage of not more than 20,0 V and a current of 0...2 A;

3) mode "3" (battery discharge without a power source) allows you to discharge the battery with an initial discharge voltage of not more than 30,0 V and a final voltage of at least 2,0 V and a current of 0 ... 2 A.

The power supply must provide two voltages: 22 ... 26 V at a current of 2,2 ... 2,5 A and 20 ... 24 V at a current of 0,1 ... 0,2 A. To control the current strength, use pointer devices RA1 and PV1 type M42100. There are no special requirements for them.

In the proposed scheme, it is possible to use almost any op amp with the appropriate correction circuits. PT type KP303E can be replaced by a similar one with indices V...D. The 2T827A type transistor can also be replaced with the same one with a different index. It must be installed on a radiator with a surface area of at least 800 cm2. Relay type RES-6 (passport RF0.452.112 or 113) can be replaced by any relay with two groups of normally open or switching contacts, a permissible current through the contacts of at least 2,5 A and an operating voltage of 20 ... 24 V. Switch SA1 type P2K can be replace with a PM type switch. Resistors of the MLT0,25 type, except for R8, R9 (MLT-1), R5 (SP3-33) and R7 (C5-16MV-5 W).

Setting. First you need to set the slider of the variable resistor R5 to the lower (according to the diagram) position. Switch SA1 set to position "1" and short-circuit the output terminals of the device with a jumper. Turn on the power. Measure the voltage at pin 6 of DA1, its value should be 5 ... 9 V. At a different voltage, replace VT1 with another one. After that, move the resistor slider to the upper position according to the diagram. By selecting the resistance of the resistor R4, achieve a maximum current of 2 A. If there are no errors in the installation, then the circuit setup ends here.

If desired, you can build a similar device for a higher current, while you need to select the resistor R7 and the regulating transistor (you may have to use two or three transistors).

References:

Fedichkin S. Micropower voltage stabilizers//Radio. - 1988. No. 2. -p.56-57.
Horowitz P., Hill W. The art of circuitry. - M.: Mir, 1984. Vol.1. - 599s.
Shilo V.L. Linear integrated circuits. - M.: Sov.radio, 1979. - 366s.

Author: V.Z. Jaskulka

See other articles Section Chargers, batteries, galvanic cells.

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