Stepped charger-discharge device. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Stepped charger-discharge device. 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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The operation of lead-acid batteries is always associated with an increase in the sulfation of the plates, the battery in the car eventually becomes unusable and is not able to give the starting current. since lead sulfate, creating a high internal resistance, prevents its exit from the inner layers of the plates.

Increasing the battery capacity to compensate for losses leads to an increase in its weight and dimensions. A good result for the electrochemical recovery of chronic sulfation is achieved by using a cyclic charge-discharge method with a "falling" characteristic of the charging current. The use of charge-discharge cycles with a current ratio of 1:10...1:20 allows you to restore the battery to a working state in 3.5 hours.

Diagnostics of batteries during recovery indicates a sharp decrease in their internal resistance after an hour. The disadvantage of this technology is that it is necessary to constantly monitor the charge current, which grows as the internal resistance of the batteries decreases, and, if necessary, reduce it, the automatic decrease in the charging current leads to a qualitative recovery of the batteries and simplifies charging. For such a process, a device has been developed, the scheme of which is shown in the figure. The device is structurally composed of several blocks:

multivibrator on the logic chip DD1;
time interval timer on a 14-bit counter DD2;
analog timer-comparator on the DA2 chip.

(click to enlarge)

The stepwise decrease in the charge current depends on the elapsed time since the beginning of the process and the code at the outputs of the counter DD2. The switching of the circuits that provide the charge and discharge currents is performed by switches on field effect transistors VT1 and VT2. Unlike switches based on bipolar transistors, they heat up less due to the low channel resistance. The only condition is that the gate voltage must not exceed the supply voltage. Key VT1 discharges the battery to the load in the form of a powerful resistor R17, VT2 supplies charging current from the mains rectifier to the battery. The sequence of switching modes, the duration of the pulses, their duty cycle and frequency depend on the parameters of the frequency-setting circuits of the DA2 timer. The parallel stabilizer on the "adjustable zener diode" DA1 sets the voltage at the input 5 DA2 depending on the current charge time and maintains a given level of charge-discharge current.

The modes are indicated on LEDs of different colors, and the total current is controlled by a measuring device. P1. The clock generator is made on the elements 2 OR NOT DD1.1, DD1.2, C1 and R1. The pulse frequency of the multivibrator is calculated by the approximate formula f=O.44/(R1 C1). It is set around 1 Hz. LED HL1, flashing, indicates the progress of the process. The battery charge time is set by resistor R1. After a high level appears at output 3 DD2, the generator on the DD1 chip stops working.

The counting pulses from the multivibrator are fed to the input. From the counter DD2 and change the state of its outputs. The levels from the outputs of the counter through resistors R4...R7 and diodes VD1.VD4 are summed up on the resistor R9. The more time has passed since the beginning of the cycle, the more voltage is obtained on R9. At the maximum voltage on R9, the adjustable zener diode DA1 opens with a control voltage at input 1, and the voltage at input 5 of DA2 decreases to the lower stabilization level of DA1 (2,5 V). This is below 1/3 of the DA2 supply voltage, so its output is set low and the battery stops charging.

Reducing the reference voltage at input 5 DA2 increases the generation frequency of the DA2 timer without changing the duty cycle of the pulses, which leads to a decrease in the charge current at this stage of the charge-discharge cycle. The maximum charge and discharge currents are set using the R11 "Charge" and R13 "Discharge" regulators. Resistor R9 sets the buffer current for charging the battery at high levels at all outputs of the counter and for the purpose of feedback (R8). The device can also provide for a decrease in the charge current with an increase in ambient temperature by replacing the resistor R10 with a thermistor (type MMT-1).

The diode VD5 in the discharge circuit of the capacitor C5 is installed to separate the charging (R10-R11) and discharge (R13) circuits. When charging capacitor C5 to a level of 2/3 Un, the internal timer trigger switches the upper comparator at input 6 DA2 to discharge the capacitor, and the voltage at pin 7 DA2 drops to zero. The transistor VT1 opens and the battery GB1 is discharged through the resistor R17 with a period of time T1=0?69R13C5. LED HL2 indicates the presence of discharge current. At the end of the discharge cycle, the internal transistor of the timer closes, and the charging cycle of the capacitor C5 resumes with an increase in voltage from 1/3Un to 2/3Un. At this time, the output 3 DA2 is high, the transistor VT2 is open, and the battery GB1 is being charged from the mains power source with a period of T2=0?69C5(R10+R11). Overload in the charging current circuit is indicated by the HL3 LED.

The microcircuits of the device are powered from the battery GB1 through the voltage regulator DA3. In the absence of a battery or its incorrect switching, the circuit remains without power and does not turn on.

To charge batteries with a capacity of up to 180 Ah, a current of 5 ... 8 A is sufficient. The power of the transformer T1 should be 150.200 W. You can use transformers such as TS-180, TN-55, TN-61. Field-effect transistor VT1 must be rated for current up to 5 A at a voltage of 100 V, VT2 - for a current of at least 20 A at a voltage of 150 V. Aluminum radiators with dimensions of 60x58x40 mm must be installed on the transistors to protect against overheating. Chips in the device - K561 or K176 series, controlled zener diode - KR142EN19A, analog timer - KR1006VI1.

Setting up the device begins with checking the supply voltages. It should be noted that the microcircuits and the discharge transistor VT1 are powered by the battery GB1, the charging circuit on the transistor VT2 is from the mains source at T1. To speed up the test, the capacitance of the capacitor C1 can be temporarily reduced to 0,01 uF. After pressing the SB1 "Start" button, the account will start, as indicated by the HL1 indicator.

Before checking the operation of the DA2 timer, the slider of the resistor R9 is moved to the lower position according to the diagram. In this case, the voltage at pin 5 DA2 is maximum. Resistor R11 sets the maximum charge current on the ammeter P1 in accordance with the capacity of the battery GB1 (Imax = 0,05C, where C is the battery capacity). The feedback circuit from the battery to the resistor R9 through R8 allows you to automatically reduce the charging current with an increase in battery voltage.

Authors: V.Konovalov, A.Vanteev

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Comments on the article:

Steranovich
How does vt2 lie if at its source plus 12 v relative to the case on the gate should be much more than 12v- plus the opening voltage. Even with the supply voltage dd3, pin 3 will never be more than 9v / 3 lead 7809. Radio amateur magazine 2007 number 5 pages .30 pulsating tooth. How to open vt2 if its base is less than 8v, according to the theory that on the base then on the emitter. Where is the mistake?

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