Charger for sealed lead-acid batteries. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Charger for sealed lead-acid 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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Many of us use imported lanterns and lamps for lighting in the event of a power outage. The power source in them is sealed lead-acid batteries of small capacity, for charging which they use built-in primitive chargers that do not provide a normal mode. As a result, battery life is significantly reduced. Therefore, it is necessary to use more advanced chargers that exclude the possibility of overcharging the battery.

The vast majority of industrial chargers are designed to operate in conjunction with car batteries, so their use for charging low-capacity batteries is impractical. The use of specialized imported microcircuits is economically unprofitable, since the cost of such a microcircuit is sometimes several times higher than the cost of the battery itself.

The author offers his own version of the charger for such batteries (Fig. 1).

Rice. 1 (click to enlarge)

The power dissipated by these resistors is

P \u2d R.Izar7,5 \u0,16d 1,2. XNUMX = XNUMX watts.

To reduce the degree of heating in the memory, two resistors of 15 ohms with a power of 2 W are used, connected in parallel.

Calculate the resistance of the resistor R9:

R9=Urev VT2 . R10 / (Izar. R - Uobr VT2) \u0,6d 200. 0,4 / (7,5 . 0.6 - 50) = XNUMX ohms.

We select a resistor with the closest resistance to the calculated resistance of 51 ohms.

The device uses imported oxide capacitors Relay JZC-20F with a response voltage of 12 V. You can use another relay that is available, but in this case you will have to correct the printed circuit board. Diodes 1N4007 (VD1 - VD5) are replaceable by any that can withstand a current at least twice the charger. It is permissible to replace the transistors indicated in the diagram with any of the KT503 (VT1) and KT3102 (VT2) series. Instead of the KR142EN12A chip, you can use an imported analogue of the LM317T.

In any case, it must be placed on a heat sink, the area of \u1b\u60bwhich depends on the charging current, the voltage on the capacitor C80 and AB. In the author's version, a heat sink with dimensions of 1x14 mm was used. Transformer T17 must provide an alternating voltage of 0,5 ... 1 V on the secondary winding at a load current of about 2 A. It is possible to use a transformer with a high output voltage, but this will lead to excessive heating of the microcircuit, which will require an increase in the size of the heat sink. LEDs of green (HLXNUMX) and red (HLXNUMX) glow colors can be replaced by any existing ones that provide sufficient brightness for indication.

All parts, with the exception of the mains transformer, microcircuit and LEDs, are mounted on a printed circuit board made of one-sided foil fiberglass 1,5 mm thick, 55x60 mm in size. Its drawing is shown in Fig. 2.

Charger for sealed lead-acid batteries

A properly calculated and assembled device requires minimal adjustment. When the battery is off, power is supplied and, selecting resistor R6, a voltage of 6,75 V is set at the output of the memory. To check the operation of the current limiting unit, instead of the battery, a 2 W resistor with a resistance of about 10 0 m is briefly connected and the current flowing through it is measured. It should not exceed 0,4 ... 0,45 A. On this, the adjustment of the device can be considered complete.

The board together with the transformer can be mounted inside the case of the device powered by the battery. If there is not enough space inside, a suitable connector is installed on the case and connected directly to the battery. The memory in this case is assembled in a separate plastic case.

LEDs and a power switch are mounted on its front panel (not shown in the diagram). To improve cooling, it is desirable to place the heat sink outside the device case. The connecting wires leading to the battery must be of minimum length and with a cross section of at least 1mm2.

Author: V.Pedyash, Odessa, Ukraine

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