Research on high frequency resonance lead-acid battery repair system

1 Introduction

Lead-acid batteries are widely used because of their simple structure, low price and reliable use. Due to problems such as improper use or maintenance of lead-acid batteries, white coarse grains of lead sulfide will be generated on the plates, referred to as sulfidation or polarization. The sulfidation of lead-acid batteries will increase the internal resistance of the battery and reduce the capacity, causing many lead-acid batteries to be scrapped prematurely. In fact, more than 80% of scrapped batteries can be repaired to extend their service life. With the continuous application of switching power supply technology, the method of using high-frequency harmonics to resonate with lead sulfate crystals and crushing lead sulfate crystals to achieve the purpose of repair is more promising and has important economic and social benefits.

2 Repair instrument main circuit

2.1 DC constant voltage power supply

The repair instrument adopts the method of superimposing high-frequency resonance with a constant voltage power supply. There is a 15 V DC constant voltage power supply in the front stage of the high-frequency resonance circuit. The repair instrument does not integrate it with the high-frequency resonance circuit. The current limiting circuit of the 15 V DC constant voltage power supply is shown in Figure 1. By controlling the opening and closing of switches K0, K1, and K2 to change the size of the current limiting resistor, the output current of the constant voltage source is changed. For lead-acid batteries of different capacities, different repair modes are set by controlling the states of the above three switches, making the repair instrument more intelligent.

2.2 High-frequency harmonics and discharge circuits

The high-frequency harmonic and discharge circuit is shown in Figure 2. The output of the 15 V DC power supply system is sent to the repair unit through the filter inductor. Each repair unit consists of 2 inductors, 1 capacitor, 1 diode and 1 switch tube. The high-frequency pulse controls the opening and closing of the switch tubes VT3 and VT4. The high-frequency harmonic signal generated by the resonance of the inductor and the capacitor can resonate with the lead sulfate crystal in the lead-acid battery to dissolve the lead sulfate crystal, thereby eliminating the sulfation of the lead-acid battery. The number of parallel repair units in the repair circuit is determined by the capacity range of the repair battery of the designed repair system. This repair instrument adopts two repair units in parallel. It is well known that timed discharge of the battery is beneficial to improve the repair effect of the lead-acid battery. The switch tube VT5 is connected in series with a small resistance resistor and connected to both ends of the battery. The purpose of discharging the battery is achieved by controlling the opening and closing of the switch tube.

3 Repair instrument control system

3.1 Composition of the control system

The repair instrument control system is shown in Figure 3.

The switch devices controlled by the switch tube control part include VT3, VT4, VT5 in the high-frequency harmonic and discharge circuits and K0, K1, K2 in the 15 V DC constant voltage power supply current limiting circuit. The output voltage and current detection part includes the output voltage and current detection of the repair instrument and the positive and reverse connection detection of the battery. The capacity keyboard selection part first adjusts the keyboard to send a signal to the microcontroller according to the capacity of the lead-acid battery to be repaired, and then controls K0, K1, K2 through the microcontroller to select different repair methods. The buzzer and indicator light control part includes the battery reverse connection alarm, the power-on indication of repair failure or completion, and the repair indication. The LCD display part includes the output voltage and current of the repair instrument, the repair time, the battery capacity, and the repair progress.

3.2 Switching tube control circuit

The switch control circuit is shown in Figure 4. SG3525 and its peripheral circuits generate a PWM signal with a frequency of 20 kHz and a duty cycle of 0.1. The oscillator frequency of SG3525 is determined by the external resistor R2 and capacitor CT1, f=1/[CT1(0.7R2+3RD)], where RD is very small and can be ignored. The duty cycle adjustment can be completed by sliding RP1. The PWM signal generated by SG3525 in Figure 4 is amplified by two PNP resistor-capacitor coupled common-emitter amplifier circuits to control the opening and closing of the switch tubes VT3 and VT4.

3.3 Positive and negative connection and voltage and current detection circuit

The positive and negative connection and voltage and current detection circuit is shown in Figure 5. When the battery is positively connected, the optocoupler A2 is turned on and outputs a positive connection detection signal to the microcontroller. The microcontroller controls the indicator light to indicate that the battery is connected correctly. The voltage signal represented by BATT+ flows through the diode and R3 and is transmitted to the microcontroller. After the microcontroller A/D conversion, the detection voltage value is displayed on the LCD display. The current signal represented by BATT- is amplified by the operational amplifier LM358 and transmitted to the microcontroller. After the microcontroller A/D conversion, the detection current value is displayed on the LCD display. When the battery is reversely connected, the optocoupler A1 is turned on and outputs a reverse connection detection signal to the microcontroller. The microcontroller controls the buzzer alarm to indicate that the battery is reversely connected. Figure 6 shows the microcontroller program workflow.

4 Experimental Results

The main circuit parameters of the high-frequency resonant repair instrument are: L1=350μH, L2=L4=6.75 mH, L3=L5=142μH, C1=C2=100μF. The AVR ATmega32 microcontroller is used as the main control device of the repair instrument control system. The switching frequency of MOSFET VT3 and VT4 is 20 kHz, and the duty cycle is 0.1. The driving waveforms of the switch tubes VT3 and VT4 are shown in Figure 7a. The output voltage and current waveforms measured by the current clamp when the high-frequency resonant lead-acid battery repair instrument is working are shown in Figure 7b. At the moment when VT3 and VT4 are turned on and off, the resonance of the inductor and capacitor produces rich high-frequency harmonic signals.

A lead-acid battery (120 Ah) scrapped due to sulfation was used as the experimental object. The repair cycle of the repair instrument was designed to be 23 h. During the repair process, the repair voltage and current, i.e., the RUN voltage, were recorded every half an hour. Based on the recorded data, the variable curve of the repair process was drawn using Matlab as shown in Figure 7c. After the lead-acid battery was repaired once, it was discharged for testing.

The above process lasted for about 9 hours, with an average discharge current of about 11 A. It can be calculated that the battery capacity was restored to about 100 Ah, reaching 80% of the total capacity. The experiment proved that the repair device studied has a good repair effect on lead-acid batteries scrapped due to plate sulfidation.

5 Conclusion

A high-frequency resonant lead-acid battery repair instrument has been developed. Experimental and operational results show that after one or several repairs of lead-acid batteries damaged by sulfation, their capacity can basically be restored to more than 80% of the total capacity, with a good repair effect, reducing the scrap rate of lead-acid batteries.