Two common balancing methods for lithium batteries, and precautions for balancing lithium batteries!
The most important step in the charging and discharging process of lithium battery packs is the balancing step, which requires protection against charging overvoltage, discharging undervoltage, overcurrent, and short circuit. Because you need to ensure that the output of the lithium battery is reasonable for each battery, the two most common balancing methods for lithium batteries currently are energy consuming balancing and energy conversion balancing.
Several opinions on balancing lithium batteries
In order to provide sufficient voltage to the device, lithium battery packs are usually composed of multiple batteries connected in series, but if there is a capacity mismatch between the lithium batteries, it will affect the capacity of the entire battery pack. For this, we need to balance the mismatched lithium batteries.
1. The capacity error of lithium batteries is absolute, and with the use of lithium batteries, this error is expanding. The factory assembly can only delay the significant error time of lithium batteries, and ultimately serious capacity errors will still occur. So, the error is absolute, and the purpose of making lithium battery protection and balancing systems is only to alleviate this error and avoid the danger it brings. Capacity balancing is impossible and should not be pursued as the goal of balancing.
2. At present, there is a method of capacity compensation, which is to extract some power from high-capacity lithium batteries to compensate for the consumption of low capacity batteries. This method is theoretically feasible, but in practice it is very cumbersome, especially with difficulty in achieving high efficiency.
3. Balancing the charging voltage is necessary, otherwise some lithium batteries may experience undercharging in the later stages of charging. Overcharging and undercharging of some lithium batteries can affect their lifespan, and overcharging can lead to danger.
4. Undervoltage protection is better than discharge balancing. Any single lithium battery that experiences undervoltage should be protected by power-off to prevent the danger caused by over discharge.
Precautions for lithium battery balance
The time required for lithium battery balancing during discharge is relatively long. Due to the correlation between discharge speed and load resistance, balancing efficiency is low during system operation. If balancing is performed during discharge and a shorter balancing time is desired, an external power transistor with lower on resistance is needed, which is very common, such as MOSFET or FET.
If rapid balancing is desired during discharge, a low resistance resistor must be connected in series with the power transistor to reduce its power consumption. If there were no current limiting resistor, the transistor would quickly consume the power of the lithium battery.
Measuring the voltage of lithium batteries during charging is not accurate and can cause premature lithium battery balancing. Therefore, it is necessary to periodically stop charging in order to measure the battery voltage. Balancing during charging also requires an external power transistor with low on resistance to achieve battery balancing, which will result in the same limitations as balancing during discharging.
The design of balanced management process is crucial in any lithium battery system. Nowadays, balanced management is indispensable in both electric forklift lithium battery systems and new energy vehicle lithium battery systems. In the internal balanced management of battery assembly, whether it is traditional lead-acid batteries or popular lithium batteries, the performance is not determined by the performance of individual cells, but more by the overall balanced management performance of the lithium battery pack.
Summary: Lithium battery balancing management technology, as one of the key technologies for lithium battery power management, has important practical and economic significance for studying energy issues. At present, the balance of lithium batteries cannot be well improved, and the technology in this area still needs improvement.
