Charger for starter batteries. Encyclopedia of radio electronics and electrical engineering

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

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The simplest charger for automotive and motorcycle batteries, as a rule, consists of a step-down transformer and a full-wave rectifier connected to its secondary winding. A powerful rheostat is connected in series with the battery to set the required charging current. However, such a design turns out to be very cumbersome and unnecessarily energy-intensive, and other ways of regulating the charging current usually complicate it significantly.

In industrial chargers, trinistors are sometimes used to rectify the charging current and change its value. KU202G. It should be noted here that the direct voltage on the included SCRs at a high charging current can reach 1,5 V. Because of this, they heat up a lot, and according to the passport, the SCR case temperature should not exceed + 85 ° C. In such devices, it is necessary to take measures to limit and stabilize the temperature of the charging current, which leads to their further complication and increase in cost.

The relatively simple charger described below has a wide range of charging current regulation - practically from zero to 10 A - and can be used to charge various 12 V starter batteries.

Fig.1. Charger circuit (click to enlarge)

The device is based on a triac controller with an additionally introduced low-power diode bridge VD1 ... VD4 and resistors R3 and R5.

After connecting the device to the network with its positive half-cycle (plus on the upper wire according to the circuit), the capacitor C2 begins to charge through the resistor R3, the diode VD1 and the series-connected resistors R1 and R2. With a negative half-cycle of the network, this capacitor is charged through the same resistors R2 and R1, the diode VD2 and the resistor R5. In both cases, the capacitor is charged to the same voltage, only the charging polarity changes.

As soon as the voltage on the capacitor reaches the ignition threshold of the neon lamp HL1, it lights up and the capacitor quickly discharges through the lamp and the control electrode of the triac VS1. In this case, the triac opens. At the end of the half cycle, the triac closes. The described process is repeated in each half-cycle of the network.

It is well known that the control of a thyristor by a short pulse has the disadvantage that with an inductive or high-resistance active load, the anode current of the device may not have time to reach the holding current during the control pulse. One of the measures to eliminate this drawback is the inclusion of a resistor in parallel with the load.

In the described charger, after turning on the triac VS1, its main current flows not only through the primary winding of the transformer T1, but also through one of the resistors - R3 or R5, which, depending on the polarity of the half-cycle of the mains voltage, are alternately connected in parallel to the primary winding of the transformer by diodes VD4 and VD3, respectively . The same purpose is served by a powerful resistor R6, which is the load of the rectifier VD5, VD6. Resistor R6, in addition, generates discharge current pulses that prolong battery life.

The main node of the device is the transformer T1. It can be made on the basis of a laboratory transformer. LATR-2M, insulating its winding (it will be primary) with three layers of varnished fabric and winding the secondary winding, consisting of 80 turns of insulated copper wire with a cross section of at least 3 mm2, with a tap from the middle.

Capacitors C1 and C2 - MBM or others for a voltage of at least 400 and 160 V, respectively. Resistors R1 and R2 - SP 1-1 and SPZ-45, respectively. Diodes VD1-VD4 -D226, D226B or KD105B. Neon lamp HL1 - IN-3, IN-3A; it is highly desirable to use a lamp with electrodes of the same design and size - this will ensure the symmetry of the current pulses through the primary winding of the transformer.

Diodes KD202A can be replaced with any of this series, as well as with. D242, D242A or others with an average direct tone of at least 5 A. The diode is placed on a duralumin heat sink plate with a useful surface area. dispersion not less than 120 cm2. The triac should also be mounted on a heat sink plate with about half the surface area. Resistor R6 - PEV-10; it can be replaced by five MLT-2 resistors connected in parallel with a resistance of 110 ohms.

The device is assembled in a strong box made of insulating material (plywood, textolite, etc.). Ventilation holes should be drilled in its upper wall and in the bottom. The placement of parts in the box is arbitrary. Resistor R1 ("Charging current") is mounted on the front panel, a small arrow is attached to the handle, and under it is a scale. Circuits carrying a load current must be made with a wire of the MGShV brand with a cross section of 2,5 ... 3 mm2.

When setting up the device, first set the required charging current limit (but not more than 10 A) with resistor R2. To do this, a battery of batteries is connected to the output of the device through a 10 A ammeter, strictly observing the polarity. The engine of the resistor R1 is transferred to the uppermost position according to the scheme, the resistor R2 - to the lowest position, and the device is connected to the network. By moving the slider of the resistor R2, set the required value of the maximum charging current.

The final operation is the calibration of the scale of the resistor R1 in amperes using a reference ammeter.

During charging, the current through the battery changes, decreasing by about 20% towards the end. Therefore, before charging, the initial battery current is set slightly higher than the nominal value (by about 10%). The end of charging is sent according to the density of the electrolyte or with a voltmeter - the voltage of the disconnected battery should be in the range of 13,8 ... 14,2 V.

Instead of resistor R6, you can install an incandescent lamp for a voltage of 12 V with a power of about 10 W, placing it outside the case. It would indicate the connection of the charger to the battery and at the same time illuminate the workplace.

Author: Semyan A.P.

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