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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Car battery charger. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Automobile. Batteries, chargers The version of the charger proposed by the author is assembled on an accessible element base, practically does not need to be adjusted and is quite simple to repeat. Setting the charging current in the range of 0 ... 10 A is done by turning the variable resistor knob on the front panel. The operation of the charger is based on the well-known method of vertical control of the regulating element - the trinistor. At the inputs of the comparator, the sawtooth voltage is compared with a constant reference voltage. At the moment when their values become equal and then their difference changes sign, a control pulse is formed. The charging current depends on the phase of the pulse, which can be adjusted manually by changing the reference voltage. As a comparator, a general purpose op amp was used. A distinctive feature of this device is that the control takes place not in a high-current output circuit, but in a relatively low-current input - the primary winding of a step-down network transformer. This reduces power losses in the form of heat generation on the control element, which has a positive effect on the reliability of the device. In addition, there is no need to install a regulating element on the heat sink. The device is capable of delivering current up to 10 A to the load. The circuit is shown in fig. 1.
The voltage from the secondary winding of a powerful network transformer T1 is supplied to a rectifier bridge assembled on diodes VD2-VD5, to the output of which a rechargeable battery is connected through a fuse-link FU2, an ammeter PA1 and connecting wires in the appropriate polarity. On a low-power network transformer T2, rectifier bridges VD6, VD7, smoothing capacitors C2-C4 and an integrated voltage regulator DA1, a power supply is assembled for the control units of the control element - the trinistor VS1. The dual op-amp on the DA2 chip is powered by +14 V from the positive terminal of capacitor C2 and -7 V from the negative terminal of C3. These values can be in the range +12...16 V and -3...12 V respectively, depending on the voltage of the secondary windings of the existing transformer (see below). On the load resistor R3, synchronizing pulses are generated for the control unit, for which a separating diode VD6 is connected between the positive terminals of the VD2 bridge and the capacitor C8. The pulses have the usual form of half-sine waves with a repetition rate of 100 Hz. The sawtooth voltage (PN) forms a generator consisting of two nodes: a source of stable charging current for the capacitor C5, assembled on a transistor VT2, resistors R12-R14, and a node for its fast discharge on the op-amp DA2.1, included as a comparator. As long as the voltage of the next clock pulse with a frequency of 100 Hz coming from the resistor R3 to the non-inverting input (pin 3) of the op-amp is greater than the level specified by the divider R6 R7, the output (pin 1) of the op-amp is about +13 V and the voltage across the capacitor C5 increases linearly. The charging current is set by resistor R12 so that when the capacitor reaches +8,5 V, the falling voltage of the next synchronization pulse becomes less than the level set by the divider. At this moment, at the output of the op-amp, the voltage changes polarity and the capacitor C5 is quickly recharged to -0,7 V through the circuit: the output of the op-amp, VD9, R9, the power line is 0 V. When the next pulse reaches the voltage level set by the divider, the process repeats. The signal from the output of the PN generator is fed to the comparison unit, where it is compared with the reference control voltage set by the variable resistor R4. The comparison node also works as a comparator and is assembled on the op-amp DA2.2. With a linear increase in the PN at the moment of its equality with the control one, an increasing voltage drop occurs at the output of the op-amp, and with a sharp drop in the PN, a falling voltage drop occurs. The moment of decline practically coincides with the moment when the mains voltage passes through zero. A positive pulse from the output of the op-amp opens the transistor VT1 and the control element - the trinistor VS1. The pulse acts on its control electrode until the end of each half-cycle of the mains voltage. The trinistor controls the state of the switch, assembled on a diode bridge VD1, connected in series with the primary winding of a powerful network transformer T1. With a change in the control voltage, the time (angle) of connecting the primary winding to the network in each of its half-cycles changes, and hence the average value of the charging current. The device uses a transformer T1 - OSM1-0,16, which can be replaced by another with a power of at least 160 VA and a secondary winding voltage of 12 ... 18 V. With a lower maximum charging current, you can install a transformer of lower output power. T2 - any low-power network with two secondary windings. The voltage of winding II should be 12.16 V with a load current of 0,3 A, and winding III - 3.12 V without load. It is desirable to use capacitor C5 with a low leakage current, for example, polyethylene terephthalate K73-16. Variable multi-turn resistor - SP5-44-01, SP5-39 or imported 3540S-1 4,7.100 kOhm. According to the author, domestic resistors are superior to imported counterparts in terms of reliability. Transistor VT1 should be selected with the highest current transfer ratio available. Neon lamp - any. Switch SA1 is a toggle switch for an operating voltage of 250 V, current 5 A. An ammeter PA1 with a DC current measurement limit of 10 A, and a voltmeter PU1 - a constant voltage of 25 V. Two high-current alligator clips are used to connect to the battery. Connecting wire - brand PVS, four-wire with a cross section of 2 mm2 for each core. Two wires, one from each terminal, are power, and the other two are connected to the PU1 voltmeter. This measure eliminates the error in measuring the charging voltage when the charging current flows through the wires. For ease of carrying, the connecting wires to the device are connected through the RP10-7 connector (not shown in the diagram). The appearance of the device is shown in fig. 2. The case is taken from the old pop power amplifier "Rainbow".
A properly assembled device does not require adjustment. When you first turn on, instead of the battery, you should connect a halogen lamp with a power of 50 W at 12 V. When you turn the knob of the variable resistor R4, the brightness of the lamp should change smoothly, and the arrows of the ammeter and voltmeter deviate following the rotation of the knob. If there is no proper brightness control or there is another sign of inoperability, before troubleshooting, disconnect the T1 transformer and the VD1 diode bridge from the network. Further, by turning on the device in the network, they check the presence of the above voltages on the capacitors C2 and C3 and +9 V at the output of the stabilizer DA1. Further search is carried out using an oscilloscope. Oscillograms are taken relative to pin 2 of the DA1 chip. First you need to check for the presence of clock pulses on the resistor R3. Their amplitude must be at least 11 V. Otherwise, the number of turns of the secondary winding II of the transformer T2 should be increased or replaced with another one. At the output of the op-amp DA2.1, rectangular bipolar pulses with a frequency of 100 Hz and amplitudes less than 1.1,5 V of the supply voltage should be observed. Next, they check for the presence of sawtooth pulses with an amplitude of about +8,5 V on the collector of the transistor VT2. For measurement reliability, an external divider with an input resistance of 10 MΩ should be used. Rotating the knob of the variable resistor, check the operation of the comparison unit. When moving the resistor slider up the circuit at the output of Oy DA2.2, positive polarity pulses with a period of 10 ms should decrease in duration to a certain minimum value, and down should increase up to a duty cycle equal to 1. Observe the pulses on the collector and emitter of the transistor VT1: they must be antiphase. Next, you need to restore the disconnected connections and check (replace) the trinistor and the diode bridge VD1. If the trinistor is not turned on, the resistance of the resistor R100 should be slightly reduced (up to 11 ohms). When charging the battery, do not allow the charging voltage to increase above the value specified in the instructions attached to it or in the manufacturer's recommendations. In case of exceeding, it is necessary to set it at the recommended level with the variable resistor knob. When the charging current decreases to 0,2.0,5A, the battery is considered fully charged. Of course, the device can be supplemented with a node for automatically limiting voltage and turning off charging. The output circuits are galvanically isolated from the network, but the remaining elements and nodes are under its voltage, which is a disadvantage of the circuit solution during the adjustment process. However, in operation, this disadvantage is easy to neutralize structurally. The device has been working flawlessly for several years. Author: D. Chernyansky
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