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Why does the charging speed drop off after the battery is charged to 90%?
294 2023-09-25
Battery after years of application and development, from the practical application, battery technology engineers basically agree that the battery in charging, when the battery is nearly full charge, through the control of the charging circuit, the charging current becomes smaller, to protect the battery and extend the battery life requirements.
In general, most of the current battery charging schemes are in accordance with the following formula to set the charging circuit and charger:
1, start: pre-charge stage (small current floating charge);
2, middle: fast charging stage (set maximum current charging stage);
3, finally: slow charge to trickle charge (fast full charge stage to full charge).
Here is a brief introduction to the internal reasons for these three stages of charging:
1, start: pre-charge stage (small current floating charge)
This stage is the first stage of insertion and charging, which will use a small current to slowly increase the charging method, because at this time the chemical substances inside the battery will have a reverse reaction, and at this time, the battery will preheat, that is, the small current will slowly heat up the battery, which can make the internal reaction of the battery more reasonable, and will not suddenly react violently and cause internal particles to decay. Prevent acceleration of battery back and forth, shorten battery life.
2, middle: fast charging stage (set maximum current charging stage)
At this stage, the battery is ready to accept the high current fast charging, you can use the set maximum charging current to charge, which is why we can obviously feel the battery charging speed is relatively fast at this stage.
3, finally: slow charge to trickle charge (fast full charge stage to full charge)
After entering this stage, the battery after a long time of high current charging, the temperature of the battery has begun to become warm (heat), coupled with the case of energy near saturation (battery internal chemical reaction activity is relatively high), continue to charge with high current, it will lead to such a chain reaction: the temperature rises, the internal resistance rises, the temperature will become higher.
In the end, this will lead to the following consequences:
At high temperatures, the internal chemical structure of the battery is prone to cracking, decomposition will occur to produce gas, and then we often say that the battery will bulge, and spontaneous combustion or explosion will occur under the aggravation.
At this stage, if the charging current continues to become smaller (or cliff drop), into the trickle charging, so that you can very well avoid the above situation.
Through the above analysis, after fast charging to 90% of the power, the purpose of charging speed will be reduced by a cliff is to ensure battery safety and service life.