Recovery of acid batteries with alternating current. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Automobile. Batteries, chargers

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AC mains voltage is an oscillogram in the form of a sinusoid with positive and negative half-cycles.

When charging batteries, the positive part of the sinusoid is used in half-wave and full-wave DC rectifiers.

It is possible to speed up the process of restoring the battery plates without deteriorating the condition if an additional negative half-cycle of a low power current is used.

Due to the low speed of the chemical process in the electrolyte, not all electrons reach the lead sulfate crystals in the allotted time of ten milliseconds, moreover, based on the shape of the sinusoid, the voltage is zero at the beginning, and then grows and reaches a maximum after five milliseconds, in the next 5 ms it drops and goes through zero into the negative half-cycle of the sinusoid. The electrons of the middle part of the sinusoid have the highest energy potential and are able to melt the lead sulfate crystal with its transfer to the amorphous state. The electrons of the rest of the sinusoid, having insufficient energy, do not reach the surface of the battery plates, or inefficiently affect their recovery. Accumulating in molecular compounds on the surface of the plates, they prevent recovery, converting the chemical process into water electrolysis.

The negative half-cycle of the sinusoid "retracts" electrons from the surface of the plates to their original positions with the total energy unused in the initial attempt to melt the lead sulfate crystal and return energy. There is a swing of energy power with its growth, which in the end allows you to melt insoluble crystals.

The voltage amplitude value of the negative half-cycle does not exceed 1/10... 1/20 of the charge current and is sufficient to return the electrons before the next cycle of applying a positive pulse aimed at melting the lead sulfate crystal. With such a current, there is no possibility of polarity reversal of the battery plates with negative polarity.

In practice, several recovery technologies are used, depending on the technical condition of the batteries and the conditions of previous operation. The technical condition can be determined using a diagnostic tool or a simple load plug, with a high internal resistance, the voltage under load is noticeably lower than without it - this means that the surface of the plates and the internal spongy structure are covered with lead sulfate crystals, which prevents the discharge current.

Previously used recovery technologies have positive and negative qualities: long recovery time, high power consumption, work with acid, large gas emissions, which include an explosive mixture of hydrogen and oxygen, the need for powerful forced ventilation and acid transfusion protection during recovery work. The end result is positive.

The technology for restoring atf-batteries with a long-term charge with a low current was developed in the last century and was used with slight electrode sulfation, the charge was carried out before the onset of gas formation, the current decreased stepwise with short interruptions. This method is still used to restore the plates of powerful industrial batteries for low voltage and current up to tens of thousands of amperes. Recovery time is at least fifteen days.

The second method is the restoration of plates in distilled water, it is also long in time and is associated with the replacement of acid with water, followed by a charge, as in the first variant. At the end of the reduction, the density is leveled by the addition of an electrolyte.

It is possible to restore the plates by short-term supply of a large charging current for 1 ... 3 hours. The disadvantage of this method is a sharp reduction in the battery life, excessive heating of the plates and their warping, increased self-discharge, abundant gas evolution of oxygen and hydrogen.

The technology of recovery of lead batteries with alternating current allows to reduce the internal resistance to the factory value in the shortest possible time, with a slight heating of the electrolyte.

The positive half-cycle of the current is used completely when charging batteries with a slight operating sulfation, when the power of the charging current pulse is sufficient to restore the plates.

When restoring batteries with a long post-warranty period, it is necessary to use both half-periods of current in comparable quantities: at a charge current of 0,05C (C - capacity), the discharge current is recommended within 1/10 ... 1/20 of the charge outflow. The time interval of the charge current should not exceed 5 ms, that is, the recovery should proceed at the highest possible voltage level of a positive sinusoid, at which the pulse energy is sufficient to transfer lead sulfate to an amorphous state. The released acid residue SO4 increases the density of the electrolyte until all the lead sulfate crystals are reduced and the increase in density ends, at the same time, due to the electrolysis that has occurred, the battery voltage will increase. When charging and restoring work, it is necessary to use the maximum amplitude of the current with a minimum time of its action. The steep leading edge of the charge current pulse freely melts sulfate crystals when other methods fail. The time between charge and discharge is additionally used for plate cooling and electron recombination in the electrolyte. A smooth decrease in current in the second half of the sinusoid creates conditions for the deceleration of electrons at the end of the charging time with a further reversal when the current passes into the negative half-cycle of the sinusoid through zero.

To create recovery conditions, a thyristor-diode circuit for setting and regulating the current synchronized with the frequency of the mains was used. The thyristor during switching allows you to create a steep leading edge of the current and is less susceptible to heat during operation than the transistor version. Synchronization of the charging current pulse with the mains reduces the level of interference generated by the device.

Fig. 1

The moment of increasing the voltage on the battery is controlled by introducing a negative voltage feedback into the circuit, from the battery to the standby multivibrator on the DA1 analog timer (Fig. 1).

A temperature sensor is also introduced into the circuit to protect against overheating of power components. The charge current regulator allows you to set the initial recovery current based on the value of the battery capacity.

The average charge current is controlled by a galvanic device - an ammeter with a linear scale and an internal shunt. In the ammeter readings, the currents are algebraically summed, so the readings of the average charging current, taking into account the simultaneous supply of a negative half-cycle from the positive current, will be underestimated.

Do not apply only a negative half-period of current to the battery for a long time - this will lead to the discharge of the battery with a polarity reversal of the plates.

In a charged battery, self-discharge always occurs due to the different density of the upper and lower electrolyte levels in the bank and other factors; being in the buffer charging mode keeps the battery in working condition.

The alternating current battery recovery circuit (Fig. 1) contains a small number of radio components.

The circuit includes a waiting multivibrator - a shaper of pulses synchronized with the mains on an analog timer DA1 type KR1006VI1, a pulse amplitude amplifier on a bipolar reverse conductance transistor VT1, a temperature sensor and a negative feedback voltage amplifier VT2, a power supply unit and a thyristor charging current controller. The synchronization voltage is removed from the full-wave rectifier on diodes VD3, VD4 and fed through the voltage divider R13, R14 to input 2 of the lower comparator of the DA1 chip.

The pulse frequency of the waiting multivibrator depends on the values ​​​​of resistors R1, R2 and capacitor C1.

In the initial state, there is a high voltage level at output 3 DA1 if there is no voltage above 2 / 1Up at input 1 DA3, after it appears, the microcircuit operates with a threshold set by resistor R14, a pulse appears at the output with a period of 10 ms and a duration depending on the position of the regulator R2 , - the charge time of the capacitor C1. Resistor R1 determines the minimum duration of the output pulses.

Pin 5 of the microcircuit has direct access to the 2/3Un point of the internal voltage divider. As the voltage on the battery increases at the end of the charge, the transistor VT2 of the negative feedback circuit opens and reduces the voltage at pin 5 of DA1, a modification of the circuit is created and the pulse duration decreases, the time the thyristor is in the open state decreases. The pulse from the output 3 of the timer through the resistor R5 is fed to the input of the amplifier on the transistor VT1. The pulse amplified by the transistor VT1 through the optocoupler U1 supplies the triggering voltage synchronized with the network to the control electrode of the thyristor VS1, the thyristor opens and supplies a pulse of a full-wave charging current to the battery circuit with a duration depending on the position of the current regulator R2. Resistors R9, R10 protect the optocoupler from overloads.

The temperature of the power elements is controlled by a thermistor R11 installed in the voltage divider of the negative feedback circuit.

An increase in temperature causes a decrease in the resistance of the thermistor and shunting transistor VT2 output 5 DA1, the pulse duration is reduced - the current decreases.

The power supply of the timer and the RC circuit in the circuit is stabilized by the Zener diode VD1.

The electronic circuit is powered from the secondary winding of the power transformer through the diodes VD2 ... VD4, the ripples are smoothed out by the capacitor C3. Diode VD2 separates the pulsating voltage of the rectifier on the diodes VD3, VD4 from the supply voltage of the timer and amplifier on the transistor VT1.

The thyristor is powered by a full-wave pulsating voltage and acts as a key with an adjustable turn-on time of positive current pulses, a negative pulse is supplied to the battery from a half-wave rectifier on the VD5 diode.

The radio components in the circuit are installed for general use: a timer chip of the 555, 7555 series. Resistors MLT 0,12, R15 - 5 watts. Variable resistors type SP. The transformer can be used of the CCI type 2 * 18 V / 5 A. Small-sized diodes for a current of up to 5 A. A thyristor with a battery capacity of up to 50 A * h is suitable for the KU202B ... N type with a radiator.

The adjustment of the device circuit begins with a voltage check of +18 V, small discrepancies do not affect the operation of the device.

Having temporarily installed a capacitance of 1 μF in parallel with capacitor C0,1, the operation of the timer is clarified by the flashes of the LED.

To control its operation, a 12 V light bulb and a power of 50 ... 60 W are included in the thyristor cathode circuit to control its operation. The flashing of the light bulb confirms that the thyristor is in good condition and that it is operating in an acceptable thermal regime. By rotating the shaft of the setting resistor R14, the threshold for the operation of the microcircuit is set. After connecting the battery to the charging circuit, it is necessary to set the charging current with resistor R2 at the middle position of the tuning resistor R12. When the thermistor R11 is heated, the charge current should decrease.

Fig. 2

Circuit elements, except for the switch, charge current regulator, ammeter and fuse, are installed on the printed circuit board (Fig. 2), the rest is mounted in the charger case.

The battery recovery technology with alternating current was developed in 1999 and made into a product in a small batch for a patent experiment.

Literature

1. I.P. Shelestov "For radio amateurs - useful schemes". Solon-Press. Moscow. 2003
2. V. Konovalov. "Charger and recovery device for Ni-Cd batteries". - "Radio", No. 3/2006, p. 53.
3. V. Konovalov. "Meter Rbh AB". - "Radiomir", No. 8/2004, p. 14.
4. V. Konovalov., A. Razgildeev. "Battery Recovery" - "Radiomir", No. 3/2005, p. 7.
5. V. Konovalov. "Pulsating charger - recovery device". - "Radio Amateur", No. 5/2007, p. 30.

Author: Vladimir Konovalov; Publication: radioradar.net

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