Now, with the common use of common small household appliances such as watches, smartphones, phones, televisions, video players, video recorders, and mobile communication products, the charger has naturally become a must-have for every family. Cadmium batteries have also been reused. The function of the charger is to restore the discharged capacity of the discharged battery. There are many types of chargers, including civilian and industrial ones; nickel-cadmium battery chargers and lead-acid battery chargers.
The general working process of a charger is to change alternating current into pulsating direct current, that is, the current varies but the direction does not change. Proper charging is one of the important conditions to ensure battery life and performance. The commonly used charging methods are constant current charging and constant voltage charging. A combination of the two methods can also be used, that is, improved constant voltage charging or current limiting constant voltage charging. Actually, it starts with constant current charging and then constant voltage charging.
Constant current charging refers to charging in which the current is maintained at a constant value. Is a widely used charging method. The initial charge of the battery, the capacity check of the battery during operation, the charging of the traction battery during operation, and the formation charge of the battery plate are mostly constant current or staged constant current charging. The advantage of this method is that it can determine the charging current value according to the capacity of the battery, directly calculate the charging amount and determine the time to complete the charging. That is, the method of keeping the charging current constant during the charging process. It has the following types:
(1) Slip-flow charging, a charging method that maintains the fully charged state of the battery, which can exactly offset the self-discharge of the battery. Such a charging rate is not harmful for long-term charging of a fully charged battery, but the current is too high for a fully discharged battery small.
(2) Minimal charging. On the premise that a deep-discharged battery can effectively restore the battery capacity, the charging current is minimized as much as possible.
(3) Standard charging, using standard rate charging, charging time is 14 hours or overnight.
(4) High-rate charging, a method of fully charging the battery within 3 hours. This charging method requires an automatic control circuit to protect the battery.
Before charging , adjust the voltage of the charger to a certain value according to the number of batteries connected in series. During the charging process, keep the charger voltage constant, and the charging current starts to be large. As the charging time increases, it gradually decreases and finally becomes zero. This charging method is called constant voltage charging. The voltage and time selected for the common constant voltage charging method are as follows:
(1) Buffered charging, used to maintain the fully charged state of the battery to offset the self-discharge of the battery
Charging voltage: 1.55V (per battery)
(2) Floating charging. The battery is connected in parallel with the load. On the one hand, the battery discharges the load and on the other hand it accepts the charger to charge.
Charging voltage: 1.35V (per battery)
(3) Constant voltage charging to charge fully discharged batteries.
Charging voltage: 1.40—1.42V (per battery)
Time: 80% battery capacity in 40 minutes, 120% battery capacity in 2 hours.
High charger voltage will cause serious battery overcharging, and low charger voltage will cause insufficient battery charging. In order to prevent the current from being too large at the moment of charging, the improvement of constant voltage charging is called current limiting and constant voltage charging.
Charging voltage: 1.65V (maximum for each battery)
Time gate 2 hours charge 120% battery capacity
General charger circuits are divided into direct charging and automatic chargers with over-voltage and under-voltage protection circuits and reverse battery protection circuits. There are two forms of step-down circuit: capacitor step-down and transformer step-down. The rectifier circuit has several forms such as unidirectional half-wave, full-wave, bridge full-wave rectification, and half-controlled bridge rectification. The components used in the charging switch control circuit and various protection circuits are various, including transistors, field effect transistors, single junction transistors, Darlingtons, thyristors, high-power switching integrated circuits TWH8751, TWH8778, and time base circuits. 555, programmable control regulator TL431, op amp bi-stable comparator LM358 and charge control special integrated circuit LZll0 and so on. Each charger has its own characteristics, and the unit circuit used is different.
The circuit structure of the pulse charger is composed of the following parts: circuit filtering, primary rectification filtering, PWM conversion, secondary rectification filtering, pulse circuit, charge and discharge circuit and feedback control. Compared with ordinary switching power supply circuit, this circuit has more pulse generating circuit and charging and discharging circuit. In order to improve the conversion efficiency of this circuit, the PWM control uses an integrated control device specially developed by Guisheng Power; the pulse generation circuit uses a 555 time base circuit and a decimal counter / frequency division circuit. The DC / DC conversion part is a flyback circuit specially developed by Guisheng Power. Except for the characteristics of the PWM control itself, such as working in quasi-resonant mode, no-load frequency reduction, dynamic self-power supply, low no-load power consumption, etc., they are similar to conventional flyback circuits.
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