Common faults of lithium battery BMS

Under What Circumstances Does a Lithium Battery Protection Board Lose Its Charging/Discharge Protection?

First, let's look at the typical parameters for common chemistries: NMC (often around 2.8V ~ 4.25V per cell) and LiFePO4 (around 2.5V ~ 3.65V per cell).

Potential Causes for Loss of Protection:

1. Protection triggered due to conditions like over-voltage (overcharge), under-voltage (over-discharge), over-current, short circuit, or overtemperature.

2. Open circuit in the charge/discharge MOSFETs. This can be checked with a multimeter.

3. If the lithium battery protection board is equipped with an LED indicator, the LED may flash at 0.5-second intervals as an alarm when charging/discharging is disabled.

4. If the protection board is paired with host software/PC, connecting to it can allow you to check the current protection status.

5. Some lithium battery protection boards include a "weak current" switch or enable pin. Please check if this switch is in the correct (ON/closed) position.

In these situations, you can attempt the following recovery methods:

1. For protections triggered by overcharge, over-discharge, over-current, or short circuit, inserting a charger can often reset the protection state.

2. For over-current protection, simply disconnecting the load may allow recovery.

What is a Lithium Battery Protection Board?
A Lithium Battery Protection Board (PCM/BMS Protection Circuit Module) is designed to provide charge and discharge protection for series-connected lithium battery packs. After fully charging, it ensures the voltage difference between individual cells remains below a set value, allowing all cells in the pack to charge uniformly. This effectively improves charging efficiency in series charging configurations. Simultaneously, it monitors each cell in the pack for over-voltage, under-voltage, over-current, short circuit, and overtemperature conditions to protect and extend the battery's lifespan. Under-voltage protection prevents damage to individual cells from being over-discharged during use.

The protective functions of a lithium battery are typically achieved through the combined operation of a protection circuit board and current-sensitive devices like PTCs. The protection board consists of electronic circuits that can accurately monitor cell voltage and charge/discharge loop current within an environment of -40°C to +85°C, promptly controlling the connection or disconnection of the current loop. A PTC (Positive Temperature Coefficient) device helps prevent severe battery damage under high-temperature conditions.

A common lithium battery protection board usually includes a control IC, MOSFET switches, resistors, capacitors, and auxiliary components such as fuses, PTCs, NTCs (for temperature sensing), ID chips, memory, etc. Among these, the control IC normally keeps the MOSFET switches in the ON state, connecting the cell to the external circuit. When the cell voltage or loop current exceeds specified limits, it immediately commands the MOSFET switches to turn OFF, safeguarding the cell.

Principle of the Lithium Battery Protection Board:
The need for protection in rechargeable lithium batteries stems from their inherent characteristics. Due to the nature of the materials used in lithium batteries, they must not be over-charged, over-discharged, subjected to over-current, short-circuited, or charged/discharged at ultra-high temperatures. Therefore, a well-designed protection board and often a current fuse are essential components in a lithium battery pack.

The protective functions are typically a collaboration between the protection circuit board and current-sensitive devices like PTCs. The protection board comprises electronic circuits that operate within a -40°C to +85°C range, constantly and accurately monitoring cell voltage and the charge/discharge loop current, and timely controlling the circuit's continuity. The PTC acts to prevent severe damage to the battery under high-temperature environmental conditions.

A standard lithium battery protection board generally contains a control IC, MOSFET switches, resistors, capacitors, and auxiliary components like fuses, PTCs, NTCs, ID chips, memory, etc. Here, the control IC manages the MOSFET switches, keeping them conductive under all normal conditions to connect the cell to the external circuit. It instantly switches the MOSFETs off to protect the cell's safety whenever the cell voltage or loop current surpasses predetermined values.