PACK includes battery packs, copper bars, nickel sheets, protective plates, outer packaging, output (including connectors), green paper, plastic brackets and other auxiliary materials. These items form a PACK lithium battery pack through a series and parallel design. When designing a lithium battery PACK, it is always the focus of debate among engineers, should it be connected in series first and then in parallel or first in parallel and then in series. Then let ’s take a look at the advantages and disadvantages of the battery be connected in series first and then in parallel or first in parallel and then in series.
First, the battery PACK in series and parallel design characteristics analysis:
1. The battery PACK requires a high degree of consistency (capacity, internal resistance, voltage, discharge curve, life).
2. The cycle life of the battery PACK is lower than the cycle life of a single battery.
3. Use under limited conditions (including charging, discharging current, charging method, temperature, etc.)
4. After the PACK of the lithium battery pack is formed, the battery voltage and capacity have greatly increased, and it must be protected, and it must be monitored for charge balance, temperature, voltage, and overcurrent.
5. The battery PACK must meet the design voltage and capacity requirements.
Second, Analysis of the advantages and disadvantages of the battery that pack in parallel first and then in series or first in series and then in parallel:
1. Disadvantages of the battery pack in parallel first and then in series connection: due to the difference in internal resistance and uneven heat dissipation in parallel, battery cycle life after parallel connection will be affected.
2. Advantages of the battery pack in parallel first and then in series connection:
A. A single battery will automatically exit if it fails, except that the capacity will be reduced, and it will not affect the use after parallel connection. The parallel connection process is stricter.
B. When a unit battery in parallel is short-circuited, the current in the parallel circuit is very large. Usually, fuse protection technology is used to avoid it.
3. When lithium battery PACK, the advantages of batteries that be connected in series and then in parallel or first in parallel and then in series:
A. According to the battery capacity of the whole group, it is connected in series first, such as 1/3 of the capacity of the whole group, and finally connected in parallel, which reduces the failure probability of the large-capacity battery group.
B. The battery packs are connected in parallel first and then in series, which is very helpful for the consistency of the battery.
Third, the battery PACK in parallel first and then in series and first in series and then in parallel common characteristics :
1. Requires good battery consistency. Regardless of whether the battery is a flexible package or a cylindrical battery, multiple strings are required. If the consistency is poor and affects the battery capacity, the battery with the lowest capacity in a group determines the capacity of the entire battery.
2. Requires high-current discharge performance. Is the lithium battery PACK designed to be connected in series first and then in parallel or first in parallel and then in series? The starting current of the motor is three times the normal working current, and high-current discharge can improve the motor's dynamic performance.
3. Require the battery to dissipate heat well. The number of batteries is large, and the temperature rise of the battery inside the battery box is not easy to spread, resulting in uneven temperature between the batteries, different discharge characteristics, and long-term degradation of battery performance.
4. High level of production technology. The battery must be able to withstand the vibration shock of bumpy roads. The production process, especially the spot welding process, is highly demanding. After welding, test to prevent false welding and desoldering.
Fourth, the battery pack is connected in parallel and then in series, or in series first and then in parallel, the wiring harness requirements are as follows:
Generally, we have certain requirements on the wiring harness when we do battery PACK series and parallel, mainly output current or docking with customer product ports. Normal series and parallel wiring harnesses can be classified into power lines, ground wires, network lines, and signal lines according to the role of the wires Etc, while lithium battery packs like 6.4V emergency lights are used in series and parallel.
A. Power cables are connected in parallel first and then in series: power cables refer to the positive and negative power lines that provide power to each electrical load below 36V. The diameter of the power cable is based on the matching relationship between the cross-sectional area of the conductor and the ampacity. The cross-sectional area of the conductor is initially determined. When the load is 5-9A, select 1.5 mm, and so on to ensure the current carrying capacity due to aging of the wiring harness or higher temperature.
B. In determining the cross-sectional area of the wire, the voltage drop and heat of the wire should be considered, and the wire diameter should be considered in the following cases:
a) If the wire is too long, the wire diameter can be appropriately enlarged;
b) In the case where the wire is connected to the consumer after being transferred through multiple connectors, considering the large voltage drop at the terminal, the wire diameter can be appropriately enlarged.
C. Ground wire in series first and then in parallel: diameter of ground wire
a) For the ground wire of a single wire, select the wire diameter wire according to the current.
b) The ground wire requires good contact with the chassis or body frame.
c) The grounding point needs to be smooth and polished, without insulation coating.