Battery Management System – BMS is a core important part people can’t ignore while building their own lithium battery pack. Some people maybe confused about how to choose the right BMS for a lithium battery pack. Below are some tips:

Different lithium battery cells have different nominal voltages. 例えば, ternary lithium nominal 3.6V, lithium iron phosphate nominal 3.2V, and lithium titanate nominal 2.0V. Depending on the type, the protection IC of the BMS is also different.

例えば, a ternary lithium battery, a conventional protection IC, the overvoltage of the single cell will be around 4.25V, and the undervoltage of the single cell will be around 2.8V. The IC of lithium iron phosphate generally sets the overvoltage of the cell to about 3.7V and the undervoltage of the cell to about 2.5V.

The number of lithium battery series is directly related to the voltage. 例えば, ternary lithium 20 number of lithium batteries series, the nominal voltage is 72V, and the voltage range is 60V~84V.

The selected BMS MOS tube and TVS must withstand a voltage value of more than 100V. Otherwise, the lithium battery will damage the BMS under abnormal conditions.

The current value of the lithium battery pack is also very important for the selection of the BMS. Including charging current and discharging current, continuous current, pulse current, 等.

Only in this way can the matching BMS be selected. 例えば, a continuous current of 20A requires a MOS tube of 4pcs, and a MOS tube with lower internal resistance can be used with 3pcs. For charging and discharging circuits, the number of MOS tubes should be separated.

The interface mode of the load wiring device, the outlet mode of the split port, or the same port, is also more important for the battery pack.

Assuming that the battery pack needs to charge 10A and discharge 50A, you can choose a BMS with separate ports, which will be much cheaper and smaller in size than directly using a 50A BMS with the same port.

According to the structural design of the lithium battery pack, you need to choose the size of the BMS accordingly to fix it in, also you need to consider whether it is necessary to develop a specific size, integrated BMS.

Including IIC SMBUS RS485 RS23 CAN UART LIN and so on. Specific communication protocol content, also need to customize a specific BMS.

例えば, whether you need a current limiting module, equalization function, pre-charging function, 等.

If you still have doubt about how to choose the right BMS for your DIY lithium battery pack, welcome to contact us or leave us comments below.