A technical method and application for optimal charging of li ion 18650 battery pack

　　A friend has greatly shortened the service life of the battery due to improper charging methods. He would like to announce that I designed a normal charger circuit many years ago and have been using it. Genuine batteries can be used once a day and charged once, and they can be used for more than a year and a half. There are two models in total, one will be announced today, and the data is absolutely true.

　　1. Working principle: Based on the research results of the optimal battery charging technology by American battery expert Maas in the mid-1960s, he proposed an acceptable charging current curve for the battery based on the lowest gas evolution rate, which is an exponential curve The regular charging current gradually decreases the curve. That is, the current is very large at the beginning of charging. As the battery voltage continues to rise, the charging current continues to decrease until it is fully charged, at which time the charging current approaches zero. Then it automatically switches to constant voltage charging to prevent battery self-discharge loss. No matter how long you charge it, it will never be overcharged. This charging method can greatly extend the service life of the battery and shorten the charging time.

　　2. R8 is used to adjust the charging current. I used two 0.15/2W resistors and connected them together. After 36AH is discharged, the battery voltage is 10.8V at this time. The initial charging current is about 6A. Adjust RW so that the no-load voltage is 16.3V. When fully charged, the battery online voltage is 16V to 16.1V.

　　3. The working mode is flyback and the working frequency is 100KHz. The transformer is made of sandwich bread type, that is, the secondary pole is wrapped between two layers of primary to reduce leakage inductance and increase the coupling strength between primary and secondary. . Masters, don’t laugh at this crude work!

　　4. The 75W of this machine is suitable for charging li ion 18650 battery pack from 12AH to 60AH. Changing R8 can adjust the initial charging current within a certain range. If you are charging a battery from 60AH to 120AH, you need to replace it with a larger magnetic core, and the high-frequency transformer also needs to be redesigned, otherwise the charging time will be much longer. For example, if you switch to pQ3230, EE40 and EC40, you can achieve 150W under the premise of an input voltage of 220V to 230V. Enlarge the heat sink of the switch IC and output rectifier diode, and reduce R8. No other changes are required.

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