Why does a lithium battery have three wires and what is the function of each wire?

Two possibilities!

(1) If your battery doesn't have a protection board, the three wires are as follows: the red wire is the positive pole, the black wire is the negative pole, and the wire of another color is the middle pole of the battery. These three wires are connected to the mainboard of your product. The middle pole is for the mainboard of your product to monitor the voltage of the lithium battery.

(2) If your battery has a protection board, the three wires are: the red wire is the positive terminal of the battery, the black wire is the negative terminal of the battery, and the wire of other colors is the NTC (thermistor) of the protection board. The thermistor is used for the main board to detect the temperature of the lithium battery or to distinguish the type of battery. Of course, you know this best yourself. Asking others will result in a lot of explanations because your question leaves much room for speculation. Of course, apart from these two possibilities, there are many, many more possibilities. For example, one wire could be the battery's balance charging wire or data signal wire, etc. If you know exactly what the three wires do, please tell me where each wire should be connected?

With the decline in the price of lithium batteries, many fields in the market are now beginning to use lithium batteries to replace the original lead-acid batteries, nickel-metal-hydride batteries, etc. Due to the high reactivity of lithium ions, it is essential to use a protection board when using lithium batteries to prevent overcharging, overdischarging and overcurrent.

Wiring principle diagram

1. Wiring sequence for connecting the protection board to the battery: ☆ Special note: The flat cables from different manufacturers are not interchangeable. Please ensure to use the matching flat cable:

Before connecting the ribbon cable, make sure it is not inserted into the protection board.

② Solder the B- line (the thick blue wire) of the protection board to the total negative terminal of the battery.

③ The wiring starts from the thin black wire connected to B-, and the second wire (thin red wire) is connected to the positive terminal of the first battery string. Then, it is successively connected to the positive terminals of each battery string until the last one, B+.

After the wires are properly connected, do not directly insert the plug into the protection board. Measure the voltage between each pair of adjacent metal terminals on the back of the plug. For a ternary polymer battery, the voltage should be between 2.8 and 4.2V; for an iron lithium battery, it should be between 2.5 and 3.65V; and for a lithium titanate battery, it should be between 1.6 and 2.8V.

After confirming the wiring sequence and voltage of the wire harness are correct, insert it into the socket of the protection board.

After the wiring is completed: Measure whether the voltage of battery B+ and B- is equal to that of P+ and P-. If they are equal, the protection board is working normally and can be used. If not, please check the wiring sequence above again. PS: The method of connecting this row of wires for the same port and separate port is the same. The difference lies in the way they are discharged (load, motor) and charged. For the same port charging and discharging, the negative pole is connected to the P- line; for the separate port, the charging line is connected to the C- line and the discharging is connected to the P- line.

By pressing the black probe of the multimeter against the B- terminal and the red probe against the B1 terminal, the voltage of the first battery string was measured to be 3.584V.

By pressing the black probe of the multimeter against the terminal of B1 wire and the red probe against the terminal of B2 wire, the voltage of the second battery string was measured to be 3.584V.

3. Through this method of measurement, the following results were obtained:

Voltage of the first battery string: 3.584V

Voltage of the second battery string: 3.584V

The voltage of the third battery string: 3.585V

Voltage of the 4th battery string: 3.585V

Battery voltage of the 5th string: 3.583V

Battery voltage of the 6th string: 3.583V

Voltage of the 7th battery string: 3.584V

All the 7 strings of voltage are 3.58V. The ribbon cable is connected correctly, and the voltage difference between the batteries is less than 0.002V, indicating good battery consistency.

By connecting the B- line, measure the voltage between B- and the battery's total positive terminal, as well as the voltage between P- and the battery's total positive terminal.

Consistent voltage indicates that the protection board is functioning properly. (The protection board is like a switch; the switch is already open, allowing current to pass safely.)

Sample test result:

The voltage from B- to the positive terminal of the battery pack is 25.11V.

The voltage from P- to the positive terminal of the battery is 25.11V.

Two consistent voltages indicate that the protection board is normal. If P- discharges through a large current, there will be a slight voltage drop and the protection board will heat up (around 50 degrees), which is a normal phenomenon.

The connection of the wires must be correct. Connecting the wires wrongly will burn out the protection board. Therefore, check the voltage again and again to ensure that the voltage of each battery string is correct to guarantee that the wire harness is not connected wrongly.

If the batteries are old, and the voltage difference between each string of batteries is greater than 0.1V, the battery strings with significant differences are likely to have false voltage, with changes in capacity and resistance. This will create a "short plank effect" in a "barrel", leading to rapid charging and overcharge protection, as well as rapid discharging and overdischarge protection. In simple terms, the battery's service life will be short, and the application scenarios such as electric vehicles will have a short usage time.

The protection board is designed to safeguard each battery string. If any string overcharges or overdischarges, it will trigger protection. For a 4S lithium battery, there are five different voltages: 0, 3.7, 7.4, 11.1, and 14.8. If it comes with a protection board, the two red wires and the two black wires should be internally short-circuited, and the two additional wires are for increasing current. The white wire is the indicator of the protection chip. It is at a high voltage when protection is activated and at a low voltage when it is not. A lithium battery has five wires: two red, two black, and one white. What do they represent?

Unstable three-phase voltage can cause heating and even burn out the motor. This is because a three-phase motor is a balanced three-phase load, meaning the impedance of each phase load is equal. When the power supply is a symmetrical three-phase voltage, the current flowing through each phase load is equal. However, when the power supply is an asymmetrical three-phase voltage, the current flowing through each phase load is unequal, and the current in one phase load will increase (possibly far exceeding the rated value), thus resulting in the phenomenon you described.

Two-wire DC motors have their circuits internally connected (such as shunt motors) or only require two wires (such as toy motors); for three-wire DC motors, one wire is the common wire, and the other two are the armature and field wires respectively (such as series motors in electric tricycles).

Firstly, nickel-metal-hydride battery chargers use pulse charging! The voltage is around 1.5V! However, 18650 lithium batteries need to be charged with a constant current and constant voltage of 4.2V! You can modify a mobile phone charger for this purpose!

Sure. One is for testing. Q: Won't the system firmware think there's a problem with the battery? A: If it's from China, there won't be a problem. Just pay attention to the positive and negative poles. Foreign ones might have chip detection.