Lithium-ion battery balance precautions

It takes a long time to balance lithium-ion battery during discharge. Because the discharge speed is related to the resistance of load resistance, the efficiency of balancing is low when the system is working. If the balance is carried out during the discharge and the balance time is expected to be short, a power transistor with smaller on resistance should be connected. Such transistors are very common, such as MOSFET or FET.

In order to reduce the power consumption of the power transistor, a low resistance resistor must be connected in series with the power transistor if the balance is to be fast during the discharge. Without the current limiting resistor, transistors would quickly consume the power of lithium-ion batteries.

It is not accurate to measure the voltage of lithium-ion battery during charging, and it will cause premature balance of lithium-ion battery. Therefore, the charging must be stopped periodically in order to measure the battery voltage. To balance the battery during charging, an external power transistor with low on resistance is required to achieve battery balance, which will have the same limitation as balance during discharge.

View on balance of lithium ion battery

1. Lithium ion battery capacity difference exists objectively. With the use of lithium-ion battery, this difference is expanding. Factory configuration can only delay the obvious difference time of lithium-ion battery, and eventually there will be capacity difference. The purpose of lithium-ion battery protection system and balance system is only to alleviate the difference and prevent the adverse effects brought by difference. It is impossible to achieve balance completely and should not be pursued as the goal of balance.

2. At present, there is a method of capacity compensation, which is to take out some power from the lithium-ion battery with high capacity to compensate the consumption of the battery with low capacity. There is no problem with this method in theory, but it is very troublesome in practice, especially it is difficult to achieve high efficiency.

3. It is necessary to balance the charging voltage, otherwise some batteries will be under charged in the later stage of charging. Some lithium-ion batteries are overcharged and undercharged, which will affect the life of the battery, and overcharge will lead to danger.

4. It is better to do the discharge balance than to do the under voltage protection, so that any single lithium-ion battery under voltage will be power-off protection to prevent the danger caused by over discharge.