Complete set of battery charging methods
There are three charging methods for lead-acid batteries: constant voltage charging, constant current charging and pulse fast charging.
1. Constant voltage charging
Constant voltage charging refers to the charging method in which the charging power supply voltage is kept constant during the charging process. In the car, the battery uses this charging method. The connection method of constant voltage charging is shown in Figure 1-12, and the charging characteristic curve is shown in Figure 1-13.
When charging at constant voltage, according to Icu003d(U-E)/R, it can be known that as the electromotive force E of the battery increases, the charging current Ic gradually decreases. If the charging voltage is adjusted properly, the charging current is zero when fully charged, that is, the charging is completed.
When charging at constant voltage, the battery to be charged is connected in parallel with the charging power source, the number of cells in each branch should be equal, and the appropriate charging voltage must be selected. If the charging voltage is too high, it will cause overcharging, the plate will bend, the active material will fall off, and the temperature will be too high; if the charging voltage is too low, the battery will not be fully charged. Generally, the charging voltage of a single cell battery is 2.5V.
In the initial stage of constant voltage charging, the charging current is relatively large, 90%-95% of the rated capacity can be reached within 4～5h, so the charging time is short, and there is no need to take care of and adjust the charging current. For supplementary charging. Since the charging current cannot be adjusted, constant voltage charging is not suitable for initial charging and desulfurization charging.
2. Constant current charging
Constant current charging refers to a charging method in which the charging current is kept constant during the charging process. It is widely used in initial charging, supplementary charging, and desulfurization charging. The connection method of constant current charging is shown in Figure 1-14, and the charging characteristic curve is shown in Figure 1-15.
When charging with constant current, the battery to be charged is connected in series. Each cell battery needs 2.7V when it is fully charged, so the number of cell batteries in series u003d the rated voltage of the charger / 2.7 (pcs). The charging current should be selected according to the small-capacity battery. When it is sufficient, it should be removed in time, and then continue to charge the large-capacity battery.
In order to shorten the charging time, the charging process is usually divided into two stages. The first stage uses a larger charging current to quickly restore the capacity of the battery. When the battery power is basically sufficient, the single cell battery voltage reaches 2.4V, and the water starts to electrolyze water to produce bubbles, transfer to the second stage and reduce the charging current by half until the electrolyte density and battery terminal voltage reach the maximum value and are within 2~ It does not rise within 3h and there are violent bubbles in the battery.
3. Pulse fast charging
The pulse fast charging must be carried out with a pulse fast charger, and the charging current waveform is shown in Figure 1-16. The process of pulse fast charging is: first use a large current of 80% to 100% of the rated capacity for constant current charging, so that the battery can be charged to 50% to 60% of the rated capacity in a short time. When the single cell battery voltage rises to 2.4V and starts to bubble, it is automatically controlled by the control circuit of the charger to start pulse fast charging, first stop charging for 25ms (called pre-stop charging), and then discharge or reverse charge to make The battery reversely passes a larger pulse current (the pulse depth is generally 1.5 to 3 times the charging current, and the pulse width is 150 to 1000 μs), and then stops charging for 40ms (called post-stop charging). The subsequent process is Positive pulse charging→front stop charging→negative pulse instantaneous discharge→post stop charging→positive pulse charging...This process is repeated until fully charged.
The advantage of pulse fast charging is that the charging time can be greatly shortened (new battery charging takes 5h, supplementary charging takes 1h); the disadvantage is that it has a certain impact on the life of the battery, and the pulse fast charger has a complex structure, The price is expensive, and it is suitable for the occasions where the battery is concentrated, the charging is frequent, and the emergency requirements are required.
Precautions for battery charging
1. Strictly abide by the charging specifications of various charging methods.
2. Pay attention to the measurement of the voltage and electrolyte density of each single cell battery during the charging process, and judge its charging degree and technical status in time.
3. Pay attention to the temperature rise of each cell during the charging process to prevent excessive temperature from affecting the performance of the battery. If necessary, air cooling or water cooling can be used to cool down.
4. The initial charging work should be carried out continuously, and should not be interrupted for a long time.
5. When preparing and filling the electrolyte, strictly abide by the safety operation regulations and the rules for the use of utensils.
6. When charging, prepare cold water and 10% soda water or 10% ammonia water to deal with the splashed electrolyte.
7. When charging, open the filling hole cover of the battery to allow hydrogen and oxygen to escape smoothly to avoid accidents.
8. The charging place should be equipped with ventilation equipment, and it is strictly forbidden to use open flames for lighting or heating.
9. When charging, you should first connect the battery cable, and when you stop charging, you should cut off the charging power supply; the wire connection should be reliable, and prevent the occurrence of sparks.