BMS Battery Management System also called lithium-ion battery protection board, is needed in the lithium-ion battery pack. While DIY your own battery pack, you may be confused about how to choose the suitable BMS. For example, shall I need the BMS with a common port or a separate port? In this article, we will share some tips.

The same port, charge, and discharge share a negative pole C-, only one lead wire is needed, the charging/discharging MOSs appear in pairs, and the charging current of the same port board is as large as the discharging current. It requires 2 wires out from the BMS.

The advantage of the common port BMS is that it has only 2 wires out, is easy to connect, and is much more commonly used while replacing the old BMS.

The disadvantage of the common port BMS is that the charge control and discharge control MOS on the protection board is required to be exactly the same, and the current will pass through the charge control MOS during discharge, which increases the cost, internal resistance, and heat.

Separate port, the charging and discharging negative poles are separated, each needs to lead out a line, the discharge terminal is connected to P-, the charging terminal is connected to C-, and the discharge circuit does not pass through the charging MOS. It requires 3 wires out from the BMS.

Since the charging current is small and the discharge current is large, the separate port can save the cost of the MOS that is used in the charging circuit, the MOS can be smaller. What’s more, the separate port can make the heat reduced while the BMS is working.

The disadvantage is that there is an extra wire, which is not suitable for use on some occasions.