Introduction to Lithium Battery Protection Board

The lithium battery protection board is a protection for the charging and discharging of the series lithium battery pack; when fully charged, it can ensure that the voltage difference between the individual cells is less than the set value (generally ±20mV), and realize the equal charge of the individual cells of the battery pack , Which effectively improves the charging effect in the series charging mode; at the same time, it detects the overvoltage, undervoltage, overcurrent, short circuit, and overtemperature status of each single cell in the battery pack to protect and extend the battery life; undervoltage protection makes every A single-cell battery is used to prevent damage to the battery due to over-discharge.

The working principle of lithium battery protection board

The IC is powered by a battery, and the voltage is between 2v and 5v to ensure reliable operation.

1. Overcharge protection and overcharge protection recovery

When the battery is charged and the voltage exceeds the set value VC (4.25-4.35V, the specific overcharge protection voltage depends on the IC), VD1 reverses to make Cout go low, T1 ends, and charging stops. When the battery voltage drops to VCR (3.8-4.1V, the specific overcharge protection recovery voltage depends on IC), Cout becomes high, T1 is turned on and charging continues, VCR must be less than a fixed value of VC to prevent frequent jumps .

2. Over-discharge protection and over-discharge protection recovery

When the battery voltage drops to the set value VD (2.3-2.5V, the specific overcharge protection voltage depends on the IC) due to discharge, VD2 reverses, after a short time delay, Dout becomes low and T2 ends. Discharge stops. When the battery is placed in charge, the internal OR gate is flipped to make T2 turn on again to prepare for the next discharge.

3. Over current and short circuit protection

When the charging and discharging loop current of the circuit exceeds the set value or is short-circuited, the short-circuit detection circuit acts to turn off the MOS tube and the current is cut off.

Common faults of lithium battery protection board

1. No display, low output voltage, no load

2. No charging

3. No internal resistance, large internal resistance

4. No resistance

5. Large overcurrent

6. No decoding

Lithium battery protection board quality inspection

Make sure that the sampling line (flat line) is connected correctly.

Take 7 battery 8pin line as an example

B- wire is connected to the battery total negative

Connect the B1 line to the positive pole of the first battery

Connect the B2 line to the positive pole of the second battery

Connect the B3 line to the positive pole of the third battery

Connect the B4 line to the positive electrode of the fourth string of batteries

Connect the B5 line to the positive pole of the fifth battery

Connect the B6 line to the positive pole of the 6th battery

Connect the B7 line to the positive pole of the seventh battery

Tips: The positive electrode of the seventh string of 7-string batteries is also the total positive electrode, and the same can be applied to any string battery pack.

Use a multimeter to make sure that the battery cable is connected correctly

1. By pressing the B-line terminal with the black test pen of the multimeter and the B1 line terminal with the red test pen of the multimeter, the voltage of the first battery string is 3.584V.

2. By pressing the B1 line terminal with the black test pen of the multimeter and the B2 line terminal with the red test pen of the multimeter, the voltage of the second battery string is 3.584V.

Measured by this method, we get:

The first battery voltage: 3.584V

The second battery voltage: 3.584V

The third string of battery voltage: 3.585V

The fourth string of battery voltage: 3.585V

The fifth string battery voltage: 3.583V

The 6th string battery voltage: 3.583V

The seventh battery voltage: 3.584V

The voltages of these 7 strings are all 3.58V, the cable wiring is correct, and the battery voltage difference is less than 0.002V, and the battery consistency is good. pS: The voltage of each battery string should be: ternary lithium voltage is 3.0-4.2V; lithium iron phosphate voltage is about 2.0-3.6V; lithium titanate is about 1.5-2.75V. If the voltage difference of any string exceeds 2V, it indicates that the cable is connected incorrectly and needs to be re-wired.

After the measured voltage is normal, plug the cable into the protection board and measure the resistance between the protection board B- and p-. The resistance is 0, which means that they are unimpeded before and the protection board is good.

Or you can connect the B- line to measure the voltage of B- and the total positive electrode of the battery and the voltage of p- and the total positive electrode of the battery. The voltage is consistent, indicating that the protection board is normal (the protection board is equivalent to a switch, the switch has been opened, and the current can be passed safely). Example test results: B-to the battery total positive voltage is 25.11Vp-to the battery total positive voltage is 25.11V. If the two voltages are consistent, the protection board is normal. If p- is discharged through a large current, there will be a slight voltage drop and the protection board will heat up (about 50 degrees), which is a normal phenomenon.

Precautions for testing lithium battery protection board

1. When measuring the voltage of each string, the test leads are placed correctly, and they will short-circuit and smoke when they touch each other.

2. When connecting the protection board, be sure to connect the cable first and then plug the protection board. Inserting the protection board may cause the protection board to burn out.