AUTOMATED AZAT-2 UNIT FOR CHARGING AUTOMOTIVE BATTERIES

V. P. OBRUSNIK, A. V. KOBZEV, S. K. ZEMAN

(Presented by the Scientific and Technical Seminar
of the Department of Static Converters, Research Institute of AEM at TPI)

At present, the principal method for charging automotive storage batteries is group charging from low-power semiconductor rectifiers. In terms of their operating characteristics, the charging devices used in large motor-transport enterprises do not meet all the basic requirements imposed on devices of this type. They have low productivity, are bulky, and are unreliable in operation; most importantly, they do not provide automatic implementation of modern charging technology. Automation of this important process makes it possible to reduce its labor intensity, eliminate overheating, overcharging, and undercharging, which improves the operating properties of batteries and increases their service life. In addition, it becomes possible to obtain a specified law of variation of the charging current, shorten the duration of the cycle, and reduce gas evolution, which is especially important for enclosed premises.

In known circuits of charging units [4], either saturation chokes with an uncontrolled rectifier or a thyristor-controlled rectifier are used as the power regulating element. In the first case, the weight and overall dimensions of the unit become excessive; in the second, it is necessary to take careful measures to protect the unit against overloads and short circuits at the output, using special disconnecting devices in the power circuits.

A number of experimental and theoretical works carried out by the Gorky Polytechnic Institute, the Mordovian Research Institute, the Tbilisi Research Electrotechnical Institute, and others have also been devoted to the development and study of new charging devices. However, in our opinion, the devices developed by these institutions, despite their novelty and a number of significant positive qualities, do not take sufficiently full account of the highly specific requirements imposed by large motor-transport enterprises.

The task of developing simple and reliable automated charging units therefore remains urgent. At the request of a number of motor depots in Kemerovo Oblast, the converter group of the Tomsk Research Institute of Automation and Electromechanics developed, tested, and introduced the AZAT-2 charging unit (Automated Charging Unit, Tomsk—two-channel), which meets all the basic requirements imposed by large motor-transport enterprises. It is intended for automatic and semiautomatic two-stage charging with stabilized current of automo-

lead-acid automotive storage batteries of the types 3ST-70, 3ST-87, 3ST-98, 6ST-128, etc.; it has 2 channels operating independently of one another. The unit makes it possible to charge simultaneously on one channel from 6 to 20 six-volt batteries and half as many twelve-volt batteries in automatic mode, and from one to twenty-five six-volt batteries in semiautomatic mode.

The semiautomatic (manual) mode is used mainly for scheduled maintenance work and provides charging with stabilized current, in two stages, of any number of batteries within the indicated limits. In this case the switching on and off of the unit, as well as switching from stage to stage, is performed at the operator’s discretion.

The unit has the following technical data:

1. Mains voltage: \(220 \pm 15\%\) V.
2. Output voltage: \(0 \div 200\) V.
3. Output current of the first channel: \(9\text{ A} \pm 2\%\) at the first stage and \(4.5\text{ A} \pm 2\%\) at the second.
4. Output current of the second channel: \(16\text{ A} \pm 2\%\) at the first stage, \(8\text{ A} \pm 2\%\) at the second.
5. The steady short-circuit currents are equal to the rated current of the corresponding stage.
6. Efficiency: 85–90%.

A comparative analysis shows that AZAT-2 is the most successful device of this type. To a considerable extent this has been achieved by introducing a number of original circuit and basic design solutions.

The schematic diagram of the charging unit is shown in Fig. 1. As the power regulating element, a transformer regulated by biasing the shunts, TRPSh, is used. Since the range of voltage variation when stabilizing the charging current is large (from 0 to 200 V), and the power factor of the installation drops sharply when the voltage is lowered, in order to increase it and improve the quality of charging two levels of output voltage of the magnetic regulator are provided (\(0 \div 100\) V) and (\(100 \div 200\) V); for this purpose the secondary winding of TRPSh is made with taps. Switching is carried out by the manual power switch “P,” which is brought out to the front panel (Fig. 2).

The control unit BU is made on transistors \(T_1, T_2, T_3\). The sensing element of this unit is a magnetic modulator \(MM\) of transformer type, made on toroidal cores of permalloy 50NP. Power is supplied to the primary winding of \(MM\) through limiter D813 and ballast resistance \(R_{14}\). The variable resistor \(R_{10}\) sets the initial demagnetizing current in winding \(W_{\text{set}}\), which determines the maximum possible pulse width at the \(MM\) output. Winding \(W_{\text{fb}}\) is connected in opposition and, when the charging current increases, the current in winding \(W_{\text{fb}}\) increases and reduces the pulse width at the \(MM\) output. The BU implements the pulsed method of biasing the TRPSh [2]. The essence of this method is that the control voltage, in the form of narrow unipolar pulses adjustable in width, is fed to the bias winding at twice the mains frequency at the moments when the current in it is minimal. In this case, positive current feedback of the even harmonics is used effectively. The use of such a biasing method gives the following advantages:

1. The power gain of the TRPSh increases by a factor of 4–5 and, consequently, the power of the control unit is reduced by the same factor. The triodes of this unit operate in the most advantageous key—

Fig. 1. Schematic circuit diagram of the AZAT-2 charging unit

switching mode, as a result of which it has increased reliability and efficiency, and low weight and dimensions.

1. The power circuit of the TRPSh is extremely simplified, since there is only one control winding and there are no additional feedback and bias windings. This, in turn, leads to an additional reduction in the weight and dimensions of the TRPSh, and also to an increase in the efficiency of the power circuit.

2. The unit withstands overloads and short circuits at the output without damage, since the use of the pulse method provides the TRPSh with excavator-type external characteristics.

The PRZ charge-mode switch provides automatic switching of these modes from “high” current to “low.” It is made with Zener diodes \(KC_6\)—\(KC_{10}\), transistors \(T_4\) and \(T_5\), relay \(PH_1\), and wafer switch \(PK_1\). The latter is brought out to the front panel. The controlled voltage level is set discretely before charging begins. In accordance with this, a definite number of storage batteries must be connected for charging—6, 10, 16, 20 six-volt batteries, and half as many twelve-volt batteries.

The current sensor \(TPT\) is a magnetic amplifier operating in the forced-magnetization mode and, together with the \(MM\), largely determines the accuracy of current stabilization. The cutoff circuit \(CO\) is constructed in the same way as the PRZ circuit, but its output circuit is adjusted to the full charging voltage of the corresponding level. It is made with Zener diodes \(KC_{13}\div KC_{19}\), transistors \(T_6\) and \(T_7\), relay \(PH_1\), and wafer switch \(PK_1\).

The time-delay device \(UVZ\) is made with silicon transistors of reverse conductivity and, with a small number of elements, provides a stable delay (1 hour) [5].

Below, the operation of the circuit in automatic mode is considered for charging 10 six-volt batteries. They are connected in series and connected to the output terminals of one of the channels. Switch \(P_1\) is set to the lower voltage level, \(PK_1\) to the position corresponding to the number of batteries selected.

After circuit breaker \(A_1\) is switched on and the “Start” button is pressed, the unit is connected to the mains. Since at the beginning of charging the voltage on the batteries is below the breakdown voltage of \(KC_1\), transistor \(T_4\) is closed, \(T_5\) is open, relay \(PH\) is energized, and n.c. contact \(PH_1\) is open. The reference voltage taken from \(KC_{11}\), \(KC_{12}\) is at its maximum, the feedback signal is small, and at the output of the \(MM\) pulses of maximum width are modulated. Pulses of blocking polarity from the \(MM\) are fed to an amplifier stage built around transistor \(T_1\), where they are amplified and fed to a matching emitter follower on transistor \(T_2\), which in turn controls the operation of the output stage and ensures that transistor \(T_3\) operates in switching mode. The signal from the output stage is fed to the control winding, ensuring operation of the unit at the first stabilization step.

When the voltage on the batteries reaches the switching level, Zener diode \(KC_1\) breaks down and the Schmitt trigger flips. Relay \(PH\) is de-energized and, by its n.c. contact, shunts Zener diode \(KC_{11}\), thereby reducing the reference voltage. The feedback signal increases abruptly, and the unit switches to the second stabilization step. When the voltage on the batteries rises to the cutoff level, the Zener diodes of the cutoff circuit, \(KC_{14}\) and \(KC_{17}\), break down; the trigger flips, thereby de-energizing the winding of relay \(PH_2\), which, by opening its n.o. contact, starts the time relay. After the delay time has elapsed, \(PB\) disconnects the unit from the mains.

In the semiautomatic mode, charging may be carried out with either “high” or “low” current. For charging with high current, switch \(PK_1\) must be placed in the neutral position, disconnecting the input circuits \(PRZ\) and \(SO\) from the storage batteries. Toggle switch \(K\) is set to the “automatic” position (Fig. 2). The control circuit then operates analogously to operation in the automatic mode, except that switching of operating modes and disconnection of the unit in this case are performed manually.

Fig. 2. External view of the AZAT-2 charging unit

To operate in the low-current mode, toggle switch \(K\) is switched to the “manual” position and breaks the supply circuit of \(PRZ\) and \(SO\), shunts the \(KS\) Zener diode, and closes the supply circuit of relay \(RN_3\). By its normally open contact, \(RN_3\) shunts the normally closed contact \(RV\), since when relay \(RN_2\) drops out the time relay is started, which otherwise, after the delay has elapsed, would disconnect the unit from the mains.

Experience with introducing the completed AZAT-2 units at motor depots in the city of Kemerovo has shown their high operating characteristics. The productivity and quality of charging have increased significantly. All this gives reason to hope for an even wider dissemination of these units in large motor-transport enterprises.

REFERENCES

1. V. P. Obrusnik. Design features of TРPSh with combined magnetic circuits. Reports of the 5th Scientific and Technical Conference on Production Automation. Tomsk State University Press, Tomsk, 1967.

2. V. P. Obrusnik, A. V. Kobzev. Operating modes and characteristics of single-phase TРPSh under pulsed magnetization. Proceedings of the 6th Scientific and Technical Conference on Production Automation. Tomsk State University Press, Tomsk, 1969.

3. T. N. Kalayda. Chemical devices for electrical energy for aircraft. “Energiya,” Leningrad, 1967.

4. F. I. Kovalev, A. F. Mostkova, V. F. Sviridov. Marine static converters. “Sudostroenie,” 1965.

5. V. N. Platonov. Semiconducting time relays with long time delays. Mechanization and Automation of Production, No. 11, 1968.