In order to meet the power demand of the electrical appliances on the vehicle, traditional gasoline vehicles can only use the engine to drive the generator to achieve energy conversion from gasoline to electricity, and provide power for the lights, windows, audio and even the power assist system on the vehicle. At the same time, gasoline vehicles also have an electric starter motor to ensure that the engine can still run again after it is turned off. Therefore, both the power of the power supply and the power consumption of the starter motor will be temporarily stored in a small battery.
In the era of electric vehicles, any electric vehicle is equipped with a large battery with a capacity of dozens of degrees, and the electrical appliances on the vehicle are also powered by large batteries. In theory, electric vehicles no longer need 12V small batteries. But in fact, even pure electric vehicles with dozens or even hundreds of batteries still have 12V small batteries hidden in the car. Why do new energy vehicles still have 12V small batteries?
First of all, everyone must be curious, why is the battery of the car 12V, instead of 8V, 18V or 20V, which has to mention the type of car battery-lead-acid battery. Compared with the lithium batteries that everyone is familiar with now, lead-acid batteries are not only low-cost, but also very mature in technology, and are particularly safe. They are not affected by ambient temperature. More importantly, they also support large current discharge, which is enough to drive the “electrical appliances” such as starters that require instantaneous high power.
As for why it is 12V, it is because the positive and negative electrodes of the lead-acid battery are lead dioxide and lead respectively. In sulfuric acid solution, the electromotive force difference between the two is just a little more than 2V. At present, the mainstream lead-acid batteries all use a design of 6 groups of batteries in series, and the total voltage is 12V. Of course, for trucks with higher power consumption, the voltage is increased to 24V by connecting 12 groups in series.
The reason why new energy vehicles still retain 12V small batteries is essentially a supply chain problem. Since fuel vehicles have been developed for dozens or hundreds of years, 12V car batteries are already very mature, so almost all electrical devices on the car work with 12V voltage, including but not limited to windows, central locks, car machines, speakers, brake assist and other electrical equipment. As a latecomer, electric vehicles use ready-made 12V electronic devices to reduce R&D and supply chain costs. After all, the cost of redesigning the voltage of all the electrical appliances in the vehicle is too high, and it is difficult for different car companies to unify, and the pressure on suppliers will be great.
However, friends who are familiar with circuits should know that the 400V and 800V power batteries can actually be reduced to 12V through the DC-DC (direct current to direct current) step-down module to work the electronic and electrical components on the vehicle. So this time we are back to the question at the beginning, why do we need batteries? In fact, the essence of small batteries is to be used when the vehicle is powered off after parking. Compared with 12V lead-acid batteries, the stability of lithium batteries with high energy density is naturally slightly inferior. When there is no one in the car, it is impossible to deal with the danger caused by battery out of control in the first time. And more importantly, if the voltage of more than 400V leaks, it is too dangerous to face the human body, and basically you can start the meal directly.
Because of this, new energy vehicles with large batteries must also use small batteries to meet the power support of some electrical systems on the vehicle. The power inside the 12V small battery is “charged” or transferred to the 12V small battery through the DC-DC buck module mentioned above when the vehicle is started. In addition, when charging new energy vehicles, the DC-DC buck module will also use external energy to replenish the power of the 12V small battery.
Another very important function of the small battery is to ensure that the various electronic systems of the vehicle can still work normally in the event of an accident. Whether it is a lithium iron phosphate battery or a ternary lithium battery, there is a certain probability of thermal runaway due to deformation after a major collision. In order to prevent this from happening, the vehicle will quickly cut off the power to the large battery after detecting a collision. At this time, things like door unlocking, double flash, and automatic call for rescue are all powered by the small battery, which is a bit similar to the emergency lights in the fire passage that are not lit when plugged in and lit when the power is off, playing a backup role.
Although according to the above article, we know that new energy vehicles still need small batteries to power the car when large batteries are hung below, but not all new energy vehicles currently use 12V lead-acid small batteries. Among them, the voltage of Tesla’s small battery, which has always been unique, is different from that of general models. It uses a 16V lithium battery as the small battery of the whole vehicle. However, although the voltage is different, its function is still the same as that of a 12V small battery. As for how to determine whether your Tesla is a 16V lithium battery, you only need to determine the central control screen processor. As long as it is an AMD version, it has been replaced with a 16V lithium battery.
In addition to Tesla, BYD, which has a large shipment of new energy vehicles, has also begun to make changes to the 12V small battery. However, it did not reset a new voltage standard like Tesla, but used its own lithium iron phosphate battery to replace the original lead-acid battery. Calculated by the voltage of a single lithium iron phosphate battery of about 3.2V, BYD’s small battery should just operate at around 12.6V, which is very close to the voltage of the lead-acid battery.
Although new energy vehicles have not yet abandoned the 12V small battery, its role is indeed gradually decreasing with the progress of the times. For example, the exclusive function of many new energy vehicles now-the sentinel mode, has actually begun to be separated from the small battery. As a car camera, in theory, it needs to work at a voltage of 12V, which is the responsibility of the small battery. However, friends who have driven a car know that the power stored in the small battery is not only precious, but also not abundant. Then 24-hour non-stop monitoring is likely to “dry” the small battery, and then it will be an expensive rescue fee.
Why do new energy vehicles still have 12V small batteries? For this reason, in today’s new energy vehicles, functions similar to the sentinel mode are usually driven by power batteries, that is, large batteries to reduce voltage. That’s why after turning on the sentinel mode, the power will be reduced the next day. As for why the small battery is not used, it is mainly because all batteries cannot be discharged while charging!
Although the rapid development of new energy vehicles in recent years has driven the rapid progress of the entire automotive industry, as a mature industrial product that has been around for more than 100 years, automobiles will not completely overturn everything in the past due to changes in energy forms.
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