At present, there are more and more articles promoting the fast charging of power batteries. Some manufacturers' propaganda is too much. Some experts also follow the trend and say that 30 minutes or 15 minutes can complete the charging of electric vehicles, which is even more ridiculous. , said that the charging task can be completed within 5 minutes. The author expresses concern that these propaganda will be detrimental to the development of the industry. People engaged in engineering understand that "it is impossible in principle and impossible in engineering". The principle of lithium-ion batteries has already told people that they cannot be charged quickly.
- What is fast and slow charging?
Vehicle batteries all have positive and negative poles. To charge the battery, it must be a DC power supply with positive and negative poles. What does it mean? The AC power from the grid cannot directly charge the vehicle battery.
But to charge electric vehicles, it is all 220V for civilian use, or 380V AC for factory use. Why is this? This is what engineers use an "AC to DC (AC/DC)" device to convert alternating current into direct current. Remember for ordinary users:
① The power supply for charging the vehicle battery must be a DC power supply, and an AC power supply cannot "directly" charge the lithium-ion battery.
②Where is the DC power supply? At present, the electricity in the grid is AC. The direct current for charging electric vehicles is converted by an "AC to DC (AC/DC)" device.Also read：lifepo4 10kwh manufacturer
③ "AC to DC (AC/DC)" is a device that meets the standard requirements. If the device is installed on the car, the car and charging interface is the AC charging interface; if the device is installed under the car (ground), the car and charging interface is the AC and DC interface.
④The AC to DC (AC/DC) device can be made into high power on the ground (Note: the greater the power, the larger the volume and the heavier the mass; and the car has insulation requirements, volume and weight restrictions, so the on-board AC transformer Direct current (AC/DC) is small in power.
The first level of "fast and slow" concept. The charging speed of the DC interface is faster than that of the AC charging interface. In principle, the charging speed of the DC interface is 3 hours to 4 hours, and the AC charging interface is 6 hours to 8 hours. (Note: The power grid can guarantee the supply, 220V for civil use, or 380V for factory use)
The second level is the concept of "fast and slow". The current theoretical charging speed of the DC interface is 3 hours to 4 hours, compared with 5 minutes for fuel vehicles. Due to the limitation in principle, some experts put forward the concept of "charging to 80% in 30 minutes (or 15)", there is still 20% space, and the charging time is ignored. In other words, the entire charging process is segmented.Also read：eve lifepo4
The third level is the concept of "fast and slow". The DC interface cannot be fast charged, which means 3% to 99% of the entire process, which is fully charged; the DC interface can be quickly charged, basically referring to 20% to 80% of the entire space. This is part of the charge (discharge) curve of a Li-Ion battery. Some manufacturers have made some optimizations to this curve. In principle, there is no substantial innovation.
- It is a comprehensive conclusion that the DC interface cannot be fast charged, and there are many preconditions for fast charging.
Let’s look at an example from our daily life. The wooden barrel is used to store water, and the faucet fills the empty wooden barrel with water. The barrel has a volume (similar to the amount of the car battery), and the maximum water output of the faucet is also certain (similar to the charging interface). analyse as below:
① To add water to the wooden bucket whose volume has been determined, if it is fast, you can turn on the faucet to the maximum.
②The water output of the faucet is determined. If you want to add water quickly, you can make the volume of the wooden barrel smaller.
③ To add water to the barrel whose volume has been determined, the water output from the faucet is also determined, and there is an average (rated) speed when adding water. The average speed comes from the fastest and the lowest speed.
Logic analysis of the fast charging of the power battery:
① The capacity of the on-board battery has been clarified. If you want to charge quickly, the physical approach is to add one (or two) charging ports. The current 12-meter pure electric bus is this way.
②The specification of the charging interface is the national standard (already clarified). If you want to charge quickly, the basic method is to make the capacity of the vehicle battery small, and the charging of lithium titanate is faster than that of lithium iron phosphate. This is the principle.
- Lithium-ion batteries cannot be charged quickly in principle
At present, the battery that can be quickly charged is lithium titanate, but the specific energy of lithium titanate battery is too far from that of lithium iron phosphate and ternary battery. In other words, the car lithium titanate battery, its cruising range is too short. Running the same mileage, the on-board lithium titanate battery is charged more times. The vehicle lithium titanate battery with multiple fast charging takes longer than the one slow charging lithium iron phosphate and ternary battery. For users, there is no advantage. Is it possible to change the battery? No. Replacing the battery also requires charging, which is technically more difficult and more expensive than charging.Also read：48v 400ah lithium battery
Electric vehicle power supply is too slow to refuel than fuel vehicles, which is an objective shortcoming. Everyone is trying to make up for it. How to do it? The author's point of view is that engineering technology (process) must find a solution with correct principles, and then integrate resources (conditions), and do not always try and try again with ideas that are not correct in principle.
The best way is to increase the specific energy of the power battery, that is, a slow charge, the car mileage can exceed one day (two days, three days) of operating mileage. At present, the research and development progress of power batteries is faster than that of energy, and everyone's mileage anxiety will gradually disappear.