18650 battery pack 12v protection board function and wiring

　　1. Lithium power battery protection board composition

　　The lithium power battery protection board is an integrated circuit board designed for the protection of lithium power batteries. The need for protection of lithium power batteries is determined by its own characteristics. Since the material of the lithium-powered battery itself determines that it cannot be overcharged, over-discharged, over-current, short-circuited, or charged and discharged at ultra-high temperatures, a protective board will be designed when designing a lithium-powered battery pack.

　　Lithium power battery protection board usually consists of control IC, switch tube, precision resistor, NTC, PTC, ID memory, etc. The control IC controls the switch tube to conduct when the 18650 battery pack 12v is normal, so that the battery core is connected to the external circuit. Communication, and when the cell voltage or circuit current or temperature exceeds the specified value, it immediately controls the switch tube to turn off (tens of milliseconds) to protect the safety of the cell.

　　NTC is the abbreviation of Negative temperature coefficient, which is a negative temperature coefficient resistor. When the ambient temperature increases, its resistance decreases. ID memory is often a single-wire interface memory. The ID memory stores information such as 18650 battery pack 12v type and production date, which can provide product traceability and service life information.

　　PTC is the abbreviation of Positive Temperature Coefficient in English. It is a positive temperature coefficient resistor. PTC in 18650 battery pack 12v products can prevent the occurrence of high temperature discharge and unsafe high current of 18650 battery pack 12v. According to the voltage and current density characteristics of 18650 battery pack 12v and The application environment has special requirements for PTC. PTC is a very important component in 18650 battery pack 12v products and plays an important role in the safety of 18650 battery pack 12vs. Its performance and quality are also an important factor in the performance and quality of 18650 battery pack 12vs.

　　2. Lithium power battery protection board function

　　The protection of lithium power batteries consists of electronic circuits, which accurately monitor the voltage of the battery core, the current of the charging and returning circuit, and the temperature of the battery core at all times in an environment of -40°C to +85°C, and instantly control the on and off of the current loop. The design of a protective plate for the protection of a single battery cell will be relatively simple, while the design of a protective plate for the protection of a lithium-powered battery pack will have different design complexity according to different needs.

　　There are many factors that need to be considered in the design of the 18650 battery pack 12v protection board, such as voltage platform issues. 18650 battery pack 12vs are often required to have a large platform voltage during use, so when designing the 18650 battery pack 12v protection board, try to make the protection board It does not affect the discharge voltage of the battery core, so the requirements for control IC, sampling resistor and other components will be very high. The current sampling resistor should meet the requirements of high precision, low temperature coefficient, and non-inductance. The circuit of the lithium battery protection board is shown in Figure 1. In Figure 1, B+ and B- are the positive and negative poles connected to the battery core respectively; P+ and P- are the positive and negative poles of the protection board output respectively; T is the temperature resistance ( NTC) port. The main functions of the lithium battery protection board are overcharge protection, over-discharge protection, over-current protection, short-circuit protection, and temperature protection.

　　(1) Overcharge protection

　　The definition of 18650 battery pack 12v overcharge protection: When the voltage of a certain string of 18650 battery pack 12v is greater than the (overvoltage) maximum value and the protection delay time is reached, the IC controls Q2 to turn off the charging circuit. Field effect transistors Q1 and Q2 can be equivalent to two switches. When the G electrode voltage of Q1 or Q2 is greater than 1V, the switch tube is turned on. The internal resistance between D and S of the turned-on switch tube is very small (tens of milliohms), which is equivalent to the switch being closed; when the G electrode voltage is less than 0.7V, the switch tube is turned off, and the internal resistance between the D and S poles of the turned-off switch tube is The resistance is very large (several megaohms), which is equivalent to the switch being turned off.

　　When charging a lithium-powered battery pack, when the lithium-powered battery pack is charged normally through a charger, as the charging time increases, the voltage at both ends of the battery cell will gradually increase. When the battery cell voltage rises to 4.4V (commonly known as When the overcharge protection voltage is exceeded), the control IC will determine that the battery core is in an overcharged state, and the control IC will cut off Q2. At this time, the B pole of the battery core and the P- terminal of the protection circuit are disconnected and maintained. That is, the charging circuit of the battery cell is cut off and charging stops.

　　When the P+ and P- terminals of the protection circuit are connected to the discharge load, although the overcharge control switch Q2 is turned off, the forward direction of the diode inside it is the same as the current direction of the discharge circuit, so the load can still be discharged. When the voltage at both ends of the battery cell is lower than 4.3V (commonly called overcharge protection recovery voltage), the control IC will exit Q2 from the overcharge protection state, that is, Q2 is turned on, that is, the B- terminal of the battery core and the P- terminal of the protection circuit After reconnecting it, the battery can charge normally again.

　　(2) Over-discharge protection

　　The definition of over-discharge protection of lithium-powered battery pack: When the voltage of a certain string of lithium-powered battery pack is less than the (undervoltage) maximum value and the protection delay is reached, IC controls Q1 to turn off the discharge circuit.

　　When the battery core is discharged through the external load, the voltage at both ends of the 18650 battery pack 12v will slowly decrease. At the same time, the control IC will monitor the voltage of the 18650 battery pack 12v in real time through resistor R1. When the single cell voltage drops to 2.3V ( (usually called over-discharge protection voltage), the control IC believes that the single cell is in an over-discharge state, and the control IC will cut off Q1. At this time, the B- and P- of the cell are in a disconnected state, that is, lithium power The discharge circuit of the battery pack is cut off and the cells will stop discharging.

　　The protection board is in an over-discharge state and remains until the voltage between P+ and P- of the protection board rises to the IC's threshold voltage (generally 3.1V, usually called over-discharge protection recovery voltage), and the control IC will turn Q1 on again. That is, B- of the 18650 battery pack 12v and P- of the protection board are reconnected, and the 18650 battery pack 12v is charged directly by the charger.

　　(3) Overcurrent protection

　　Overcurrent protection definition of 18650 battery pack 12v: When the output current of the battery pack P+ and P- exceeds the overcurrent/short-circuit current value and reaches the overcurrent delay, the control circuit controls the discharge switch to turn off the discharge circuit and stop discharging. Heat accumulation caused by excessive current requires a continuous process, so overcurrent generally has two levels of protection. The first level of protection has a smaller setting value and a longer delay time, and the second level of protection has a relatively large setting value. , the delay time is very short. When the overcurrent protection is activated, the loop current instantly becomes 0A. To restore the protection state, there are generally two conditions:

　　1) No manual intervention is required. After a period of time, the circuit is automatically opened. If it is still in the overcurrent state at this moment, the 18650 battery pack 12v will enter protection again. If the overcurrent is relieved, the 18650 battery pack 12v will enter the working state.

　　2) Manual intervention is required. After the load or charger is removed, the overcurrent protection is manually reset.

　　During the normal discharge process of the 18650 battery pack 12v to the load, when the discharge current passes through the two switch tubes in series, due to the on-resistance of the switch tubes, a voltage will be generated at both ends. The voltage value U=I×RDS× 2 (RDS is the on-resistance of a single switch tube), the control IC detects this voltage value. If the load is abnormal for some reason, the loop current increases. When the loop current is large enough to make U>0.1V (this value Determined by the control IC (different ICs have different values), the control IC turns Q1 from on to off, thereby cutting off the discharge loop and making the current in the loop zero, thus playing the role of over-current protection.

　　There is a delay time between the control IC detecting the occurrence of overcurrent and sending a shutdown signal. The length of this delay time is determined by C2, usually about 13 milliseconds, to avoid misjudgment caused by interference. In the above control process, the overcurrent detection value not only depends on the control value of the control IC, but also depends on the conduction resistance of the switch tube. The larger the conduction resistance of the switch tube, the overcurrent protection of the same control IC will The smaller the value.

　　(4) Short circuit protection

　　Short-circuit protection is actually a type of over-current protection, but when the system is short-circuited, the current will theoretically become infinite, and the heat generated will also be infinite. If you have to wait for the software to react before protecting, the 18650 battery pack 12v may have Damage, therefore, for short-circuit protection, hardware is generally used to automatically trigger, and after triggering, a signal is transmitted to the control IC.

　　When the output current of the 18650 battery pack 12v P+ and P- exceeds the short-circuit current value and reaches the short-circuit delay, the control circuit controls the discharge switch to turn off the discharge circuit and stop discharging. Short-circuit protection is an extreme form of over-current protection. Its control process and principle are the same as over-current protection. The short-circuit is equivalent to adding a small resistance (about 0Ω) between P+ and P- to make the protection plate The load current reaches the set value instantly, and the protection board triggers short-circuit protection immediately.

　　(5) Temperature protection

　　18650 battery pack 12v temperature protection definition: When the temperature of the 18650 battery pack 12v reaches the temperature threshold and reaches the protection delay, the control circuit controls to turn off the charge and discharge switch tube and stop charging and discharging. Temperature protection is relatively simple. The temperature protection value has an upper limit and a lower limit. It can even be divided into temperature protection during charging and temperature protection during discharging. It needs to be designed according to actual needs.

　　What needs to be noted when designing is that in actual tests, it was found that the temperature is a value that is relatively easy to jitter (this is related to the sensor selected, such as the use of a thermistor), so the protection value and recovery value must be determined when judging. Make a reasonable interval, otherwise the system will be unstable.

　　The T port on the protection board is the over-temperature protection terminal. A common over-temperature protection circuit is to connect an NTC resistor (see R3 in Figure 1) between the T terminal and the P- terminal. The resistor is installed close to the battery core. When a lithium-powered battery pack is in high-power operation for a long time, the temperature of the lithium-powered battery pack will rise, and the NTC resistance will gradually decrease. The control IC of the lithium-powered battery pack protection board detects the NTC resistance. When the resistance When it drops to the set threshold, the control IC immediately issues a command to turn off the charge and discharge switch tube, thereby achieving the purpose of protecting the 18650 battery pack 12v.

　　3. Lithium power battery protection board wiring

　　The lithium power battery protection plate is divided into a positive plate and a negative plate. The negative plate is divided into a negative plate with the same port and a negative plate with a separate port. Their functions are the same. It does not support modifying the settings of the positive and negative protection plates through software, so you can only Determine the protection method according to the protection board wiring diagram.

　　(1) Negative plate split wiring

　　The negative plate branch wiring is shown in Figure 2, and the negative plate branch wiring sequence is shown in Table 1.

　　(2) Connect the negative plate to the same port

　　The wiring of the same port of the negative plate is shown in Figure 3, and the wiring sequence of the separate ports of the negative plate is shown in Table 2.

　　(3) Connect the positive plate to the same port

　　The wiring of the same port of the positive plate is shown in Figure 4, and the wiring sequence of the separate ports of the positive plate is shown in Table 3.

　　(4) Wiring steps for the same port protection board

　　Because the cables of 18650 battery pack 12v protection boards from different manufacturers are not universal, you should make sure to use matching cables when wiring. The steps for wiring protection boards with the same port are as follows:

　　1) Do not insert the cable into the protective board before connecting it.

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

　　3) The first thin black wire of the cable is connected to B-, the second wire (thin red wire) is connected to the positive terminal of the first string of batteries, and then the positive terminal of each string of batteries is connected in turn until the last string B+.

　　4) After the cable is connected, measure the voltage between each two adjacent metal terminals on the back of the plug. If it is a ternary polymer battery, the voltage should be between 2.8 and 4.2V, and for lithium iron battery, it should be between 2.5 and 3.65V. , lithium titanate battery should be between 1.6~2.8V.

　　5) After detecting that the voltage is correct, insert the protection board into the protection board socket.

　　6) Measure whether the voltage of battery B+ and B- is consistent with the voltage of P+ and P-. If the two voltages are consistent, it means that the protection board is working normally (the protection board is equivalent to a switch. The switch has been opened and the current can pass safely). If not, check whether the wiring is correct according to the wiring sequence above.

　　The wiring methods of the same-port and split-port protection board cables are the same, but the difference lies in the wiring methods of the discharge and charging cables. The negative electrode of the same port for charging and discharging is connected to the P- line; for the separate port, the charging line is connected to the C- line, and the discharge line is connected to the P- line.

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