Importance of BMS
With global new energy industry development, the lithium battery is a part of the new energy and has become a new focus for investment in manufacturing. A lithium battery is great, but it needs to be protected. To ensure the safety of lithium iron phosphate batteries, BMS for lithium ion battery appears to be the most important.
BMS functional
- Basic protection : overcharge protection, over-discharge protection.
- Enhanced protection : over current protection, high-temperature protection, low-temperature protection, short circuit protection, reverse connection protection.
- Extended requirements : good consistency, with small pressure and temperature differentials.
What are the consequences of overcharging and over-discharging lithium-ion batteries?
- Overcharge: there will have A large amount of gas in the battery, which will cause the internal pressure to rise rapidly and lead to the battery explosion.
- Over-discharge: shorten the battery life, direct damage to the battery scrap.
As different environments and applications, the lithium battery BMS needs more additional functions to meet your needs.
- Communication function – help you to know the operating status information of the battery pack, RS232 / RS485 / CAN, etc.
- SOC(State Of Charge) calculation / SOH estimation.
- Alarm function – to inform you when there is a problem with the battery.
- Logging function – Record the history of the battery pack, including alarm history data, etc.
- Fault diagnosis function – BMS can be diagnosed when there is a problem
- Display function – you can read information and set parameters directly through the display.
- Equalization function ……
With different demands, lithium battery protection has the following classifications.
- Simple BMS : Hardware BMS ; Software BMS（Communication BMS, startup power BMS etc.）
Hardware BMS: Use a special lithium-ion battery protection chip. When the battery voltage reaches the upper limit value or lower limit value, the switching device MOS tube will cut off the charging or discharge circuit. To protect the battery pack.
- Smart BMS
Simple BMS Features.
- Only overcharge and over-discharge protection. Part of them have overcurrent and reverse connection protection. But without other additional functions.
- Cannot change protection threshold. (general protection point is 3.9V and 2.0V)
- Cannot change equalization threshold. (the general equalization current is below 150mA)
Hardware BMS can be classified from the current direction as two types.
Split-port BMS : a total of three interfaces : charging port, discharge port, common terminal.
Common port BMS : a total of two interfaces : positive and negative interface.
Why we need the split port and the common port?
- According to the battery usage scenario, some charging and discharging ports share an interface, and some customers require charging and discharging ports can be wired separately.
- The MOS tube’s overcurrent capacity and qty determined the BMS’s overcurrent capacity. MOS tubes account for most of the BMS’s cost. Generally speaking, if the charging current is smaller than the discharging current, we will design the BMS with a split port to reduce the cost.
Precautions for BMS use
Can not be arbitrarily connected in series: the switch device of the BMS used the MOS tube. MOS tube price is proportional to its withstand voltage. When designing the BMS, the voltage withstands of MOS tubes will generally be higher than the battery pack voltage but not too much.
For example, for four series BMS, the maximum voltage of the battery pack will not exceed 16V, generally will select a 20V or 25V MOS tube.
If connected four series BMS in series, when the MOS tube is disconnected, the voltage of the whole battery pack will be applied to the MOS tube, resulting in MOS tube over-voltage breakdown damage.
The BMS balance function is also very important. if you want to know more, please pay attention to our website. we will update it in future.