1.2V NiMH battery

What is the principle of fast charging for electric vehicles? Will frequent use of fast charging damage the 1.2V NiMH battery?

At present, the mainstream charging methods for electric vehicles are divided into two types: AC slow charging and DC fast charging. If a low-power battery is regarded as a weak patient, then slow charging is like giving the patient steamed buns to eat, allowing him to digest the steamed buns and provide himself with energy; while fast charging is to inject glucose directly into the patient's veins to quickly restore his vitality. The basic principle of battery charging The battery on the electric vehicle is no different from our ordinary household dry batteries. Both output direct current. Charging the battery is a complicated process. It is not as simple as energizing the positive and negative poles. It involves professional current modulation issues, so a charger must be used to complete this part of the work. After obtaining electrical energy, the charger will modulate the appropriate current and voltage according to the current state of the battery, and then use it to charge the battery. The function of the charger is actually similar to the battery charger we used at home before. The speed of charging the same battery will be largely affected by the quality of the charger. What is AC slow charging? As we all know, the electricity used in cities is alternating current. In order to be able to use the city power supply directly for charging, each electric car will have its own on-board charger. It can convert AC into DC, modulate the appropriate current, and then charge the battery in three stages (similar to charging a mobile phone). In slow charging mode, the power supply or charging pile is just a simple power provider, without the need to undertake the task of modulating current and charging management, and the power is only treated as "raw materials" and handed over to the on-board charger for processing. Therefore, the structure of the slow charging pile is very simple and the volume is not large. In addition, many electric vehicles are equipped with household plugs, which can be directly plugged into household sockets for slow charging. AC slow charging can also make full use of charging during low power periods, reduce costs, and ensure stable voltage during charging periods. However, the disadvantages of slow charging are also obvious. That is, due to the limited capacity of the city's AC power supply and on-board charger, the charging current is very small, and it usually takes 5-10 hours to fully charge the battery. What is DC fast charging? We have learned before that there is an on-board charger on the electric car that is responsible for modulating the charging current, but unfortunately its efficiency is relatively low. So if we can bypass the on-board charger and directly charge the battery with a large current, wouldn't it be much faster? In fact, DC fast charging is achieved in this way. The DC fast charging pile itself is an off-board charger, and its current modulation capability is much stronger than that of the on-board charger. It can directly provide it with modulated high-current DC power according to the battery status. The fast charging pile will be connected to the car's CAN network. To put it simply, the charging pile makes itself temporarily part of the car's battery management system. Therefore, the fast charging pile not only provides power but also directly invades and takes over the charging management system on the car. Fast charging piles are often much larger in size, complex in structure, and more expensive, so their number is relatively small. However, fast charging is very fast, and charging can generally be completed within 12 minutes to 1 hour. The disadvantage of fast charging is that although the speed is fast, the utilization rate of electric energy is low (waste of electricity), and the high current will affect the life of the battery, and there are also certain safety hazards. Therefore, fast charging is often only used in emergency situations and cannot be used for a long time. This is like a person who still has to eat normally when he is not sick, instead of hanging glucose water every day to maintain life. In summary, the fast charging mode of electric vehicles is actually to temporarily replace the car's built-in charger with a powerful "plug-in", and directly provide the debugged high current to charge the battery according to the battery status. The advantage is fast speed, but the disadvantage is that it will affect the battery life and pose a safety hazard.

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