Pacific Automotive Network lithium iron phosphate batteries can be deeply discharged. Lithium batteries consume energy inside the battery during normal use, and this process is called discharging. Lithium batteries also have self-discharge. If the battery voltage remains below 3.6V for a long time, the battery will discharge excessively and damage the internal structure of the battery, thereby reducing its service life. Deep charging and discharging can extend the life of lithium batteries.
Precautions for lithium battery discharge Lithium battery discharge, for batteries, normal use is the discharge process. There are only a few things to pay attention to when discharging lithium batteries:
1. The discharge current should not be too large. Excessive current will causen internal heating of the lithium battery, which could cause internal heating of the lithium battery. permanent damage. On mobile phones this is no problem and can be ignored. The higher the discharge current of a lithium battery, the lower the discharge capacity and the faster the voltage drops.
2. Never overload. The internal storage of electrical energy in lithium batteries is achieved by a reversible chemical change in electrochemistry. Hence, lithium batteries. are the best Fear of excessive discharge. Once the discharge voltage is below 2.7V, the battery can be discarded. Lithium batteries in cell phones have a protection circuit installed inside. When the voltage is not low enough to damage the battery, the protection circuit comes into effect and stops discharging.
3. Do not discharge high-power lithium batteries. Li+ is deintercalated from the negative electrode and integrated into the positive electrode through the electrolyte. the battery will be discharged during normal use, and the opposite happens during charging. The voltage decay of lithium batteries declines more quickly as the discharge rate increases, and the sooner it reaches the termination voltage, but the decay rate slows down at the end. Therefore, the characteristics of low-rate discharge are better than those of high-rate discharge. rate and high power discharges are avoided as much as possible.
In general: the higher the discharge current of a lithium battery, the lower the discharge capacity and the faster the voltage drop. Therefore, under normal circumstances, once the battery is subjected to a large load, the voltage will increase as the load is increased.educed, what is called the “recharge” phenomenon.
Knowledge of deep discharge of lithium batteries Deep discharge refers to the extent to which the battery power is discharged as much as possible without damaging the battery structure. Generally, discharge to 0.7-1.0 V can be. considered a deep discharge. The depth of discharge of a lithium battery refers to the ratio of the energy discharged from the lithium battery to the total energy stored (rated capacity). The smaller the number, the weaker the discharge. For example, a depth of discharge of 80% means that the battery is discharged to the remaining 20% of capacity.
The impact of depth of discharge on the battery is: the deeper the depth of discharge, the easier it is to shorten the life of the lithium battery; another aspect is the performance on the discharge curve. The deeper the discharge. goes, the less voltage and current there is. Depth of discharge is closely related to voltage and current. We can say that it is expressed in voltage and acts on current. Under the same discharge regime, the lower the voltage value, the deeper the depth of discharge.
The more the lithium battery is discharged, the greater the battery loss will be; The more fully charged the lithium battery is, the greater the battery loss will be. It is best for lithium batteries to be in an intermediate state of charge, where they have the longest life.
(Photo/Text/Photo: Pacific Automotive Network Q&A)
Why does gas appear when a lithium battery is overcharged or discharged?
No. Causes lithium batteries to overdischarge and affect their lifespan.
The lithium battery protection board is ae charge and discharge protection for lithium batteries connected in series. When fully charged, it can ensure that the voltage difference between each cell is less than the set value (usually ±20mV), thereby achieving uniform charging of each cell in the battery, effectively improving the effect of charging in series charging. At the same time, it detects the overvoltage, undervoltage, overcurrent, short circuit and overheating status of each battery cell to protect and extend battery life. Undervoltage protection prevents each battery from being damaged due to over-discharge when used for discharge.
Summary
The finished lithium battery mainly consists of two parts, the lithium battery core and the protection plate. The lithium battery core is mainly composed of a positive plate.e, a separator, a negative plate and. electrolyte; positive electrode Plates, separators and negative plates are rolled or rolled, packaged and filled with electrolyte. After packaging, the cells are manufactured. Many people don't know the role of lithium battery protection plates. , as the name suggests, are used to protect lithium batteries. Lithium The function of the battery protection board is to protect the battery from discharge, overcharge and overcurrent, as well as output short circuit protection:
Technical parameters
Balance current: 80 mA (when VCELL = 4.20 V)
Balance starting point: 4.18 ± 0.03 V
Schematic schematic of lithium battery protection board< /p>
Overcharge threshold: 4.25 ± 0.05 V (4.30 ± 0.05 V optional)
Threshold overdischarge: 2.90 ± 0.08 V (2.40 ± 0.05 V optional)
Discharge delaye over-discharge: 5 mS
Over-discharge trip: Disconnect the load and the voltage of each battery is higher than the over-discharge threshold;
Over-current trip: Disconnect the load and release
Overheating protection: There is an interface that can be restored after installation. Temperature protection switch;
Operating current: 15A (according to customer selection).
Static power consumption: <0.5mA
Short circuit protection function: able to protect, cut off. It can automatically recover when charging is turned on.
Main functions: overcharge protection function, overdischarge protection function, short circuit protection function, overcurrent protection function, overheating protection function, equalization protection.
Challengeinterface: the charging port and the discharge port of the board are independent of each other and share the positive electrode B- is the negative electrode connected to the battery, C- is the negative electrode. of the charging port; P- is the negative electrode of the discharge port; pads B, P and C are all through-hole type, and the pad hole diameter is 3mm for each battery charge detection interface; was released as a DC pin holder.
Parameter description: Configuration of maximum operating current and overcurrent protection current value, unit: A (5/8, 8/15, 10/20, 12/25, 15 /30, 20/40, 25 /35, 30/50, 35/60,50/80, 80/100), special overcurrent values can be customized according to customer requirements.
Test lithium battery performance
1. , MCU, etc. ) Data writing part:
1. Writing and verifying I2C data,such as O2, DS, TI and various MCU solutions, etc.
2. Write production date (today's date) and serial number --- Write serial number and manufacturing date
Notes: SMBUS, I2C, HDQ communication port, etc. . ;
A.Current /Voltage offset correction
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B. Voltage gain correction and reading comparisonVoltage calibration
C.Temperature correction and reading comparisonTemperature calibration
D. Gain correction and reading comparison -- Current calibration
2. Substrate characteristics:
3. Open circuit voltage test: After measuring the charging voltage, whether the MOS tube can open normally;
4. Load voltage test: measure the load capacitance of the protection board to reflect the DC impedance of the protection.
5. VCC voltage measurement (if the chip operating voltage is high). normal)
6. Frequency measurementchip operating frequency (chip operating crystal oscillator frequency)
7. Resistance measurement (MOS tube and FUSE resistance measurement);
8. Identification resistance: IDR measurement;< /p>
9. Thermistor ---THR;
10. Static power consumption in normal state and static power consumption in standby (standby)
11. Off Static power consumption current in the off state (Shout Down);
Three: Testing the protection characteristics part:
12. Single battery overcharge protection (VOC) test. ),
A. Lower limit of protection: test whether the protection board is protected in advance, which affects the battery capacity value;
B. Upper limit of protection: test whether the protection board is protected, which affects the safety of the battery;
< p>C. Upper and lower limits of protection delay time: if the timeprotection delay is within design range;D . Recovery Test: Whether the battery can be restored after protection depends on whether the battery can be reused.
13. Single cell battery over discharge (CUV) protection test;
A. Upper and lower limits of protection values: The first is whether the battery can be placed at the lowest level; value and if the capacity is fully released, it should be protected, otherwise it will affect the battery life;
B. Protection delay time: Is the protection delay time within the design range?
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C.Reset value and recovery time: the ability to restore it after the Protection depends on the possibility of reusing the battery.
14. Battery overvoltage protection (POV) test protection value, protection delay time, recovery valueration, recovery time (if COV is measured, POV does not need to be measured. Generally, it is not recommended to do so. only measure POV, because the total Even if the group's POV is protected, it does not mean that every section can be protected. If a section is not protected, it will be very dangerous)
15. PACK battery low voltage protection (PUV) test; protection value, protection delay time, recovery value, recovery time; the principle is the same as CUV, CUV should measure CUV, but PUV cannot be measured, the reason is the same as POV;
16. Over-current charging protection (OCCHG);
A. Upper and lower limits of protection value: If the current is too low, it affects the charging time; if the current is too large, it will affect the battery life;
B. Protection Delay Time: This affectste heating the battery to the point where the protection board is burned;
C. Recovery value, recovery time: battery reuse;
17. Over-current discharge protection (OCDSG);
A. Protection Value Upper and Lower Limits: It is important to be excellent. The lower limit cannot be protected in advance, otherwise it will affect the power, the car will not run fast, the power tool cannot rotate, etc. The upper limit must be protected. Failure to protect will cause problems such as motor. combustion and heating of the battery;
< p>B. Upper and lower limits of protection delay time: This is also important if the lower limit is not protected, if it is protected in advance, the power tool will not be tightened. ; if the upper limit is not protected, it may cause problems such as engine combustionand heating the battery;C. Recovery value, recovery time: affect battery reuse;
18. Stall current test; protection value, protection delay time, recovery value, recovery time (power tools must be very large)
19. The short circuit protection test --- (short circuit protection) is generally difficult. to test and will damage the protective device
20. Load overheat protection test and recovery test;
21. Discharge Overheat Protection Recovery Test;
< p>22. Load Overheat Protection Recovery Test;23. Discharge overheat protection recovery test;
Four: Balance function test:
Test whether the balance function of the protection board can be turned on and detect the value of the cobalance current of each section;
Five: Preload check:
Preload test --- UDPPC. ;
Over-discharge protection: When the battery is about to run out and the voltage reaches a minimum required value, the protection board will also do so. When closed, it can no longer discharge, so the product automatically turns off, forming a kind of protection against excessive discharge.
Overcharge protection: When charging the product, when the voltage reaches the maximum battery voltage (4.2V), the protection board will automatically turn off and turn off, indicating that it is fully charged and will not work. keep charging. A form of overcharge protection.
Short circuit protection: When the battery is accidentally short circuited, the protection board will automatically close within a few millisecondses and will not be on at that time, everything will be fine even if the positive and current. the negative poles touch each other, forming a sort of protection against short circuits. Will not cause an explosion.
Overcurrent protection: When the battery is discharged, the protection board will have a maximum current limit. Different products are different. When the discharge exceeds this current, the protection board will automatically turn off.
Does anyone know the dangers of overcharging and overdischarging lithium batteries?
Ordinary lithium ion batteries will produce a small amount of gas when inside the battery during the charging process, which is usually absorbed during discharge.
If the charging current is too large and overcharging is frequent, it will aggravate gas generation, increase the internal pressure of the battery and cause swelling. A slight renBattery drain is allowed. Avoiding overloading is the key to reducing the bulge.
In addition, the chemical properties of lithium are very active and easy to burn. As the battery is charged and discharged, the temperature inside the battery continues to rise. The gas generated during the activation process expands and. the internal pressure of the battery increases until it reaches a certain level. It will rupture, causing a leak, fire or even explosion, so it is absolutely important to ensure its safety performance.
If the lithium battery is overcharged, continuing to charge when the battery is full will cause the structure of the positive electrode material to change, resulting in loss of capacity. , and its decomposition releases oxygen and the electrolyte will undergo violent chemical reactions, and the worst result is naturally an explosion.
After the lithium battery discharges the internally stored energy and the voltage reaches a certain value, continued discharge will lead to over-discharge. The discharge cut-off voltage is generally determined based on the discharge current.
Working principle of lithium batteriesLithium metal batteries: lithium metal batteries generally use manganese dioxide as the positive electrode material, lithium metal or its metal alloy as the negative electrode material and use a non-aqueous electrolyte solution. Discharge reaction: Li+MnO2=LiMnO2.
Lithium ion battery: Lithium ion battery generally uses lithium alloy metal oxide as the positive electrode material, graphite as the negative electrode material, and non-aqueous electrolyte.