How does the battery charger work?

The simple charger can automatically charge the battery below 24V, the maximum charging current can reach 2.5A, and it has constant current charging and full self-stop function. Figure 4-9 shows the schematic diagram of the automatic charger. The 220V mains voltage is stepped down by the transformer T to obtain the secondary voltage U2. The VD1~VD4 format is used to rectify and output the DC ripple voltage. The positive A point passes through the relay normally closed contacts K1-2, R4, ammeter PA, VT1, and passes through the battery GB. VT2 to the negative B point to charge GB, adjust the size of RP1, that is, adjust the base potential of VT1, VT2, thereby adjusting the Icb of VT2, that is the charging current. Since the battery terminal voltage can reflect its charging condition, the battery with a nominal voltage of 12V is taken as an example. When the battery voltage rises to (12/2)*2.5=15V, the VT3 is saturated and the K1 is electrically connected. The closed contact K1-2 is turned off, the charging circuit is cut off, and the charger stops charging. Adjust RP2 to set the upper limit of the battery full self-stop. LED1 is the power indicator, LED2 is the charging indication, the larger the charging current, the brighter LED2, and the darker. The charging current of the battery is the product of the battery's ampere-hour value and the charging rate. If a battery is 24V, 6Ah, then its charging current is about = (6/10) x (1 + 20%) = 0.72A. The stop limit is (24/2) x 2.5 = 30V.

The battery charger is divided into a high frequency machine and a power frequency machine: the power frequency machine is mainly realized by transformer. The high frequency mainly changes the frequency through VMOS and IGBT, and the transformer changes the voltage. According to different power principles, it is mainly divided into single tube forward, double tube forward, half bridge, full bridge, chopping, etc.

In the mid-1960s, American scientist Mass made a lot of experimental research on the charging process of open batteries, and proposed an acceptable charging curve for batteries with the minimum outgas rate, as shown in Figure 1. Experiments have shown that if the charging current changes according to this curve, the charging time can be greatly shortened and the battery capacity and life are not affected. In principle, this curve is called the optimal charging curve.

After the battery is discharged, it is returned to the working capacity by direct current through the battery in the opposite direction to the discharge current. This process is called battery charging. When the battery is charged, the positive pole of the battery is connected with the positive pole of the power supply, the negative pole of the battery is connected with the negative pole of the power supply, and the voltage of the charging power supply must be higher than the total electromotive force of the battery. There are two types of charging methods: constant current charging and constant voltage charging.

Battery charger principle

There is a large amount of sulfuric acid and other solutions that can be supplied from the battery. When the power is plugged in, the current is ionized through the lead plate inside (some batteries are not lead), thus converting the electrical energy into chemical energy; if it is used, the solution will be It is converted into electrical energy and sent out through the electrode. This is a description of the principle. In fact, the real situation is very complicated. Please refer to relevant professional books.

Charging method system

The conventional charging system was designed based on internationally accepted rules of thumb before 1940. The most famous of these is the "Ampere Hours Rule": the charging current amperage should not exceed the number of hours the battery is to be charged. In fact, the speed of conventional charging is limited by the temperature rise of the battery during charging and the generation of gas. This phenomenon is important for the shortest time necessary to charge the battery.

Constant current charging method

The constant current charging method is a charging method in which the output voltage of the charging device is adjusted or the resistance in series with the battery is changed to maintain the charging current intensity. The control method is simple, but since the acceptable current capability of the battery is gradually decreased as the charging process progresses, the charging current is mostly used to electrolyze water and generate gas to make the gas out too late. Therefore, the stage charging method is often used.

Constant voltage charging method

The voltage of the charging power source maintains a constant value throughout the charging time, and the current gradually decreases as the voltage at the battery terminal gradually increases. Compared with the constant current charging method, the charging process is closer to the optimal charging curve. Fast charging with a constant voltage, because the battery electromotive force is low at the initial stage of charging, the charging current is large, and the current will gradually decrease as the charging progresses, so only a simple control system is needed.

This charging method seldom electrolyzes water and avoids overcharging of the battery. However, in the initial stage of charging, the current is too large, which has a great influence on the battery life, and it is easy to bend the battery plate and cause the battery to be scrapped. In view of this drawback, constant voltage charging is rarely used, and is only used when the charging power supply voltage is low and the current is large. For example, during the operation of a car, the battery is charged by a constant voltage charging method.

Stage charging method

This method includes a two-stage charging method and a three-stage charging method.

The two-stage method employs a fast charging method in which a constant current and a constant voltage are combined. First, charging with a constant current to a predetermined voltage value, and then changing to a constant voltage to complete the remaining charging. Generally, the conversion voltage between the two phases is the constant voltage of the second phase.

The two-stage charging method uses constant current charging at the beginning and end of charging, and is charged with a constant voltage in the middle. When the current decays to a predetermined value, the second phase is switched to the third phase. This method can minimize the amount of gas output, but it is limited as a fast charging method.

Fast charging method

1 pulse charging method, this charging method not only follows the inherent charging acceptance rate of the battery, but also can improve the battery charging acceptance rate, thereby breaking the limitation of the battery index charging acceptance curve, which is also a new development of the battery charging theory. The pulse charging method first charges the battery with a pulse current, then stops the battery for a period of time, and so on, as shown in FIG. The charging pulse charges the battery to a full charge, and the intermittent period causes the oxygen and hydrogen generated by the chemical reaction of the battery to be recombined and absorbed, so that the concentration polarization and the ohmic polarization are naturally eliminated, thereby reducing the internal pressure of the battery. The next round of constant current charging can be carried out more smoothly, so that the battery can absorb more power. The intermittent pulse makes the battery have a sufficient reaction time, reduces the gassing amount, and improves the charging current acceptance rate of the battery.

22REFLEXTM fast charging method, which is a patented technology in the United States, it mainly faces the charging of nickel-cadmium batteries. Because it adopts a new charging method, it solves the memory effect of the nickel-cadmium battery, thus greatly reducing the time for rapid charging of the battery. The charging method of the lead-acid battery and the detection method of the charging state are very different from those of the nickel-cadmium battery, but one working cycle of the REFLEXTM charging method can be used for each other, including a forward charging pulse, a reverse instantaneous discharging pulse, and stopping. Charge to maintain 3 stages.

3 variable current intermittent charging methods, this charging method is based on constant current charging and pulse charging, as shown in Figure 7. It is characterized by changing the constant current charging section to a voltage limiting variable current intermittent charging section. In the early stage of charging, the method of variable current intermittent charging is adopted to ensure that the charging current is increased and most of the charging amount is obtained. In the later stage of charging, a constant voltage charging section is used to obtain an overcharge amount, and the battery is restored to a fully charged state. By intermittently stopping the charging, the oxygen and hydrogen generated by the chemical reaction of the battery are recombined and absorbed, and the concentration polarization and the ohmic polarization are naturally eliminated, thereby reducing the internal pressure of the battery and enabling the next round. The constant current charging can be performed more smoothly, so that the battery can absorb more power.

4 variable voltage intermittent charging method, based on the variable current intermittent charging method, a variable voltage intermittent charging method has been proposed, as shown in FIG. The difference from the variable current intermittent charging method is that the first stage is not intermittent constant current but intermittent constant pressure. In each constant voltage charging phase, due to the constant voltage charging, the charging current naturally decreases exponentially, which is consistent with the characteristics that the battery current acceptability decreases gradually with the charging.

5 variable voltage variable current wave type intermittent positive and negative zero pulse fast charging method, combined with pulse charging method, Reflex TM fast charging method, variable current intermittent charging method and variable voltage intermittent charging method, variable voltage variable current wave positive and negative zero pulse The intermittent fast charging method has been developed and applied. There are two types of control for the charging circuit of the pulse charging method:

1) The amplitude of the pulse current is variable.

2) The pulse current amplitude is fixed.

The amplitude of the pulse current and the frequency of the PWM signal are fixed, and the PWM duty ratio is adjustable. On this basis, the intermittent charging and charging phase is added, which can charge more power in a shorter time and improve the charging acceptance of the battery.

Lead-acid battery is a kind of chemical power source widely used in the world at present. The product has the advantages of good reversibility stable voltage characteristics, long service life, wide application range, abundant (and renewable use) raw materials and low cost. Mainly used in transportation, communications, power, railways, mines, ports and other sectors of the national economy, is an indispensable product in social production and business activities, with broad prospects for development.

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