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How to make a lithium or lifepo4 battery pack ?
Date: 2022-11-23 14:35:04Downloads: 1895
Pack Description
lithium battery pack and lifepo4 battery are widely used in Home Energy Back-up System, industrial equipment, solar energy storage. Solar/wind energy storage,Back-up power for UPS
Different products require different voltages and capacities, so lithium ion batteries are connected in series and parallel.
PACK can be a single battery with PCB, such as 18650 battery, 26650 battery ,32700 battery, 21700 battery single cell with PCB
It also can be a series and parallel combination Battery, such as golf cart Battery, medical device battery, Home Energy Storage Lithium Battery, electric vehicle battery, Mounted Solar System Lithium ion Battery, UPS battery,
Stackable Home Energy Backup etc.
1. Composition of BATTERY PACK:
Battery pack consists of a Cell Pack, BMS (with different function like RS485/CAN communication/ Bluetooth), Switch, fuse,outer packaging or Case, output (including connectors), display, indicator, EVA, barley paper, cell holder ,nickel ,connector, and other auxiliary materials . PACK's external features are determined by the application. There are many differen kinds of battery packs
Prismatic cell pack
Cylindrical cell Pack
2. Features of PACK
★ Maintenance free
★ Battery PACK requires the cell have same consistency (capacity, internal resistance, voltage, discharge curve, life).
★ Use under limited conditions (including charging, discharging current, charging mode, temperature, humidity conditions, vibration, stress degree, etc.)
★ The lithium battery PACK BMS must have the charge balancing function.
★ High-voltage and high-current battery packs (such as electric vehicle batteries and energy storage systems) are required to be equipped with communication ,battery management system ( BMS),With CAN, RS485, etc.
★ The battery PACK has high requirements on the charger, and some requirements can communicate with the BMS. The purpose is to make each battery work normally, and ensure the safe and reliable use.
3. Design of PACK
★ Fully understand the application requirements, such as working environment (temperature, humidity, vibration, salt spray, etc,decide if need to use waterproof/Cooling battery case), service time, Max charge /discharge current and electrical parameters, output mode(charge /discharge same port or difference port), life requirements(use lifepo4 or NCM cell?), etc.
★ Reliable packaging, meet the requirements.
★ Simple production process
★ Select qualified Cell and BMS according to use requirements. Meet the requirements of size and weight.
(Ensure the long cycle life and good performance of lifepo4 battery pack, We suggest match the capacity/resistance/voltage before you assemble lifepo4 battery pack, ensure one battery pack with same grade cell ,similar capacity/voltage/resistance)
Cylindrical cell grading machine( For 18650 Battery /26650 Battery/32700Battery/21700 Battery/34135 Battery......)
Automatic sort machine:
(sort and select the voltage and resistance of cell,ensure the same grade)
Prismatic cell grading machine
(For Prismatic 52Ah/80Ah/100Ah/120Ah/200Ah/280Ah/300Ah lifepo4 cell and lithium battery.........)
Ii. Introduction of important components
1. Battery pack
★ configuration: Parallel connection increase capacity, the voltage is unchanged.
series connection increase the voltage, thecapacity is unchanged.
Such as : If we have 3.2V IFR32700 6000mAh lifepo4 cell,And we want to make 48V 100Ah battery pack, There will be 15 series connection and 17 parallel connection.
Total you will need: 15*17=255PCS 32700 LIFEPO4 CELL.
★ configuration requirements: Parallel and series batteries require the same model, the difference of capacity, internal resistance and voltage should not more than 1-2%. The reason is we require the consistency of the battery charge and discharge curve (dynamic consistency).
But it is difficult to find such same cell,(This is the reason why we need BMS). under normal circumstances, after the ce;; through parallel series combination, the capacity loss of 2%~5%, the more the number of batteries, the more capacity loss.
★ configuration realization: the combination of the battery through two ways to achieve, one is through nickel spot welding or laser welding or ultrasonic welding, this is commonly used means, the advantage is good reliability, but not easy to replace. The second is through the elastic metal sheet contact, the advantage is that there is no need to weld, the battery replacement is relatively easy, the disadvantage is that it may lead to poor contact.
★ Requirements: The battery pack should meet the requirements of the user's working time, environment, vibration, charging, service life, etc. Do not use the battery pack without BMS. Overcharging, overdischarging, or overcurrent may damage the battery .
2. BMS
BMS tester:
★ Composition: protection IC, MOSFET, transistor, resistor and capacitor and PCB and heat dissipation device……
★ Function: Protect the battery working in normal condition. Prevent the battery due to overcharge, overdischarge, short circuit and other causes of battery failure and smoke, fire, explosion caused by the risk.
★ Specific functions:
A. Overcharge protection. The overcharge protection voltage of batteries of different systems is different. In general, the overcharge protection voltage of lithium iron phosphate is 3.65V~3.85V, and the overcharge protection voltage of lithium cobalt oxide, lithium manganese oxide and terpolymer lithium batteries is 4.2V~4.35V.
B, overdischarge protection, the overdischarge protection voltage of lithium iron phosphate is 2~2.5V, the other three kinds of lithium batteries are 2.3V~2.9V.
C. Short circuit protection. It is determined by the IC and MOSFET parameters. Different IC and MOSFET have different short circuit protection values.
D, overcharge protection voltage recovery. IC has this function, the general recovery voltage is lower than the protection voltage 0.1-0.2V.
E. Recovery voltage of overdischarge protection. Some ics do not have this function. After overdischarge, it needs to be restored by charging.
F. Short circuit protection delay time. Generally ten milliseconds.
G. Balancing function. Some applications require balancing functions. Because the battery discharge current is high, the balance is not easy to achieve, most of the current charge balance, the purpose of balance is to ensure that each battery can be fully charged, extend the service life, maximize the role of the battery.
★ How to connect BMS with Battery?
A The lithium battery cannot be used alone without the BMS.
B Pay attention to the isolation between the bms and the battery.
C When installing multiple protection boards and batteries, connect them in the sequence of low level first and high level later. That is, connect B- first, then B1, B2...... B9, and then B plus. See the picture below.
When removing the protective plate, the installation sequence is reversed.
The Battery should pass aging test after assemble
Aging machine: