Charger on a half-wave rectifier. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Charger on a half-wave rectifier. 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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An easy-to-make charger allows you to restore the technical condition of a car battery overnight.

Characteristics of the device

Mains voltage, V ...... 180-230
Transformer power, W ...... 30-100
Battery voltage, V ...... 6/12
Charge current max, average, A......2
Charge current pulse max, A ...... 5
Discharge current, mA......30-50
Recovery time, h ...... 6-12
Accumulator ...... a) open type; b) closed type; c) helium
Battery capacity, Ah ...... from 10 to 240

Long-term storage or operation of car batteries leads to the formation of crystalline lead sulfate on the plates and terminals, which prevents the battery from normal operation. In case of poor contact, the battery terminals covered with sulfate can be cleaned with a coarse file or sandpaper, but it is impossible to remove sulfate from the battery plates using this method. Due to the high internal resistance created by the poor conductivity of the sulfate crystals, the car will probably start, but not more than once.

In winter, with increased viscosity of oils, starting the engine is almost impossible.

High internal resistance reduces the voltage at the battery terminals, when the load is connected - below the permissible limits, the starter at such a voltage of the current source is not able to turn the engine shaft. Hoping that the battery will recover on the way, with such a state of the plates is unrealistic. If we consider the car's generator as a power source, it is possible to charge the battery, but it will not be able to fully remove the crystallization of the plates due to the insufficient voltage of the generator and the constant current of the three-phase generator.

The surface (working) sulfation of the plates is removed at an operating battery charging voltage of 13,8-14,2 V, and the internal crystallization of the porous structure of the plates reacts poorly to such a voltage due to the high resistance of the crystals and the low charge voltage.

To restore the plates - to remove crystallization - a non-standard voltage of the charge current source with the possibility of regenerating the plates is required.

In no case should you add voltage to the car's generator - because of the danger of damage to the electrical and electronic equipment of the car by non-standard voltage.

The solution is simple - restore the battery with an external charger with an increased voltage of the current source. These devices include pulse chargers.

The presence of a discharge current component with a value not exceeding 10% of the charging current accelerates the recovery of battery plates well.

The average charge current when removing the sulfation of the plates does not exceed that recommended for charging by the manufacturer, and the charge voltage per pulse is almost twice the standard one, which accelerates the conversion of lead sulfate crystals to amorphous lead. The pulse time is short and such charging with recovery does not lead to excessive heating of the battery and warping of the plates.

Pulse recovery allows you to extend the life of the battery and restore it to a working condition. Elimination of macrocrystalline sulfation of battery cells reduces internal resistance to a working state, eliminates self-discharge and interelectrode short circuits, increases voltage under load, which makes it easier to start the car.

The proposed charger allows you to meet these conditions. This device is not designed to power electronic devices.

Schematic diagram

Schematic diagram of the charger (Fig. 1) consists of a power transformer T1 with external switching circuits SA1 and overload protection FU1.

(click to enlarge)

The output windings of the transformer are switched by switch SA2 depending on the voltage of the battery being charged GB1. The pulse current rectifier VD1 is made on a single diode to perform the required technology for restoring battery plates.

A discharge current of small amplitude is created by a circuit consisting of a diode VD2, reverse polarity and a limiting resistor R1, the purpose of which is to accelerate the recovery of the battery plates.

The second purpose of this circuit in the circuit is to eliminate the magnetization reversal of the iron of the transformer T1 from the action of a half-wave rectifier on the diode VD1.

This reduces the need to install an increased power transformer in the circuit, eliminates overheating, and increases efficiency.

Full-wave diode bridges used in factory chargers, due to the absence of a time gap between charging current pulses, do not allow recrystallization of the plates, which leads to premature electrolysis of the electrolyte, boiling and heating of the battery. When using batteries with a helium filler or the absence of air pockets (closed type), this is unacceptable, due to the possible depressurization of the case.

The one-half-wave pulse recovery circuit, with intervals between pulses equal in time to the period of a positive current pulse, lowers the electrolyte temperature and increases the time for recombination (rebuilding) of electrolyte ions. The discharge component of the recovery current allows electrolyte ions to accumulate potential energy aimed at melting "old" lead sulfate crystals.

Charging current control is performed on a PA1 galvanic device with an internal shunt. The power-on indication is made on the HL1 red LED, by its brightness one can also judge the charge voltage and the presence of current in the charge circuit. Capacitor C1 in the primary circuit of the transformer winding and capacitor C2 in the load circuit reduce the level of interference that occurs when the current is switched by the rectifier diode VD1, VD2.

The GB1 battery is connected to the charger using crocodile clips.

Restoring the battery can be done without removing it from the car; the positive terminal of the car's power supply must first be disconnected.

Device details

In the charger circuit on a half-wave rectifier, there are no purchased radio components, they are used from electronic devices that have expired.

The power transformer T1 is used from tube radios: the iron is pre-disassembled, the mains winding is used unchanged, the step-up and filament are carefully removed in layers - by biting the turns with wire cutters, instead of them a new winding is wound with a wire with a cross section of 0,5-0,6 mm until it is filled with a tap (approximately ) from the middle. The iron is being reassembled. Several W-shaped sheets will not fit due to the lack of a tie - this will not affect the characteristics of the transformer. When the mains voltage is connected, the secondary voltage on the taps must be between 8-10 V and 16-20 V.

Switching switches SA1, SA2 are used from network toggle switches for a current of 3 A. The pulse diode VD1 is KD202-248 diodes. Diode VD2 - D7, D226, KD226. In extreme cases, silicon rectifier diodes from computer power supplies are used. Capacitor C1 type K17 with a voltage of 250-400 V. The indication LED HL1 can be set to any glow. In the absence of an ammeter of the specified current, any galvanometer from tape recorders is used (indication of the output signal) with an artificial shunt in the form of a spiral of wire with a diameter of 0,6-1 mm - 10 turns on a frame with a diameter of 1,6 cm. Into the gap of the positive bus of the charging current the tester is temporarily connected and the readings of the charging current are checked. The number of turns of the shunt winding must be adjusted according to the readings of the current ammeter.

Accumulator charging

The presence of an ammeter allows you to track the process of recrystallization of the plates - at the initial moment, the charge current has a minimum value, then as the electrode plates are cleaned from crystallization, the current will increase to a maximum value and after a time determined by the state of the battery, the current will begin to drop to almost zero, which will be an indication completion of battery recovery.

If the polarity of the GB1 battery is connected incorrectly, the LED will not light, the ammeter needle will turn to the left - to discharge. For a long time, in the wrong connection, the battery cannot be kept, an uncharged state can lead to polarity reversal of the electrodes and the complete impossibility of further use of the battery.

After several hours of restoring the battery capacity, the circuit elements are checked for heating, with satisfactory results, the restoration is continued.

Due to the small number of elements, the circuit is assembled in a case from a computer power supply or type BP-1 by surface mounting with the installation of toggle switches, an HL1 LED, a RA1 galvanometer on the front panel, a fuse is mounted on the rear wall. Diode VD1 is mounted on a radiator with dimensions of 50 * 30 * 20 mm.

The charger is connected to the battery with a stranded wire in vinyl insulation with a cross section of 2,5 mm.

At the end of charging, the network is first turned off, then the clamps are removed from the battery terminals.

Authors: V.Konovalov, A.Vanteev, Irkutsk-43, PO Box 380

See other articles Section Chargers, batteries, galvanic cells.

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