Multi-parallel multi-series 18650 lithium battery pack design skills1. The principle of priority and easy operation is adopted, that is, employees are easy to operate.2. Adopt the principle of giving priority to operation safety, that is, employees are not easy to short-circuit or have better preventive measures when operating.3. The principle of equipment is adopted, that is, the work done with the aid of auxiliary equipment should be done without manual labor, or at least semi-automatic.4. The packaging design should be reasonable, easy to take and put away, and the product should not be delivered to the customer for a long time.
Before designing the 18650 battery pack, we need to have a certain understanding of the customer’s needs. We need to know the basic information of electrical equipment (current, voltage, working time, etc.), battery pack (cell, size, weight, nominal voltage, nominal capacity), connector (plug model and direction, wire length, wire number ), charger (charging mode, charging voltage, charging current, time), power management (power display, temperature control, communication protocol), structural part (structural part, color requirements, protection requirements), others. Of course, the content of these battery parameters is very large, which will be a hassle for unfamiliar customers. You can fill in as much as you can, the latter click the parameter link here and fill in.
Because this page is about battery packs, it needs to be implemented in a multi-series multi-parallel method. The parallel connection of lithium batteries can increase the total current, and the series connection can increase the total voltage. Using lithium batteries in parallel and in series sounds simple, but only when used correctly and with some precautions can you avoid unnecessary problems. Below I describe the entire battery pack manufacturing process, we explain some basic concepts and precautions, I hope to help you.
First, start to select the 18650 lithium battery cells, that is, to select the voltage, internal resistance, and capacity of the 18650 cells, also called the capacity grading and group. In terms of capacity, it can be that the matching has been completed when the material is received. Before assembling the battery pack, it is only necessary to screen the voltage and internal resistance of the battery cells. The general selection standard is that the voltage difference is within 5mV, and the internal resistance The difference is within 3mΩ. Only cells within the range of this voltage difference and internal resistance difference can be assembled into a set of lithium battery packs, so that the consistency of the assembled battery packs will be better, and the performance of the battery packs will be better. The equipment used is a cell sorting and assembling instrument.
Do not mix lithium batteries of different brands, different capacities or old and new lithium batteries, and choose batteries with the same performance. When the battery power is low, replace all batteries. When lithium batteries are used in series, the same type of batteries should be used.
The best way to assemble a battery pack is to put a bracket for the battery cells, so that after assembling the battery pack, there can be brackets between the cells for isolation. There is isolation on the top, the battery pack is safer, and the vibration does not affect the safety of the lithium battery pack.
When two groups of lithium batteries with a large difference in internal resistance are connected in parallel, it is unfavorable for batteries with a small internal resistance. It is recommended to discharge them separately and not directly parallel. When two sets of lithium batteries are connected in parallel, attention should also be paid to the internal resistance. In short, if the internal resistance of the two groups of batteries in parallel is not much different, they can be directly connected in parallel, but the internal resistance is very different, so it is advisable to discharge them separately. Or first use a group of batteries with small internal resistance, and then connect them in parallel for a period of time, at this time the difference between the two groups of batteries is not significant.
Share the basic knowledge of multi-series and multi-parallel lithium battery packs here. The parallel connection of lithium batteries can increase the total current, and the series connection can increase the total voltage.
The material used in spot welding is nickel strip, which is divided into pure nickel-nickel strip and nickel-plated steel strip. The price of pure nickel will be much more expensive. Comparatively speaking, the price of nickel-plated steel strip is much cheaper, and the disadvantage is of course that the internal resistance is larger, the overcurrent capability is lower, and it is more likely to rust.
For the thickness of the nickel strip, the current requirements of conventional products, the thickness of the nickel strip is generally 0.15mm, so the power of the spot welding machine is more suitable. If the current is relatively small, a 0.1mm thick nickel strip can be used, and if the current is particularly large, a 0.2mm nickel strip can be used. Nickel strips that are too thin or too thick are not recommended.
When spot welding, it is necessary to pay attention to check the effect of spot welding. The power of the spot welding machine should not be too small, which will lead to virtual welding of the cell, or the power of the spot welding machine should not be too large, which will lead to the frying or spot welding of the cell. Put on. After spot welding, the 7KG tensile test can be passed.
The protection board used is a ternary lithium 16-series 48V lithium battery protection board. The welding of the protection board needs to be based on the specification of the protection board. The wiring definition diagram shows the welding, from B-, B0, B1, to the last section, B13 , all need to be welded according to the specification of the protection board. After soldering the wires of the protection board, it is necessary to use heat shrinkable sleeves to insulate the solder joints to prevent the solder joints from short-circuiting and malfunctioning.
The following is an example of a 2000mAh 18650 lithium battery. It is known that the battery pack is 30Ah and divided by 2Ah (ie 2000mAh) to get 15 cells. Because the voltage of the lithium battery is 4.2V when fully charged, three 15-parallel units are required to be connected in series. 15 parallel* 3 = 45 pieces.
Since the lithium battery is strictly prohibited from overcharging and overdischarging, a protection board should be added. This determines that the battery pack must be connected in a parallel-to-serial mode. That is, connect 15 cells in parallel and then in series. This connection method has high requirements on the consistency of the cells, so it is necessary to do some classification and pairing work. That is, the internal resistances should be connected in parallel with the same or close resistance as possible.
The connection between lithium batteries is best welded with nickel strips and spot welders. As shown in the schematic diagram above, the wiring method of the nickel tape is clear and predictable.
In addition, clean the two poles of the battery, then buy some zinc chloride melt water as flux, use a 70-100W soldering iron to tin the two poles for backup, carefully clean up the residual flux after completion, and finally change to rosin flux, use copper The wires connect the battery. Note that the welding time is not too long to prevent the battery from overheating.
This step is to carry out insulation packaging and shaping of the battery pack, fix the wires of the battery pack, and pack them. In order to better insulate the assembly process of the lithium battery pack, the battery pack is blown with PVC film and glued on both ends behind the PVC film. To prevent water and dust, better protect the lithium battery pack.
This step is to carry out insulation packaging and shaping of the battery pack, fix the wires of the baThis step needs to connect the exposed wires of the battery pack to the shell material connectors of the casing, including charging and discharging terminals, fuses, switches, etc. Generally, the current of the charging port is relatively small, so the wire diameter of the wire used is relatively small; while the current of the discharge port is relatively large, the wire diameter of the wire used is relatively thick, so that the overcurrent will be more ideal. Soldering the wires needs to be done according to the schematic diagram of the connection between the battery pack and the case.ttery pack, and pack them. In order to better insulate the assembly process of the lithium battery pack, the battery pack is blown with PVC film and glued on both ends behind the PVC film. To prevent water and dust, better protect the lithium battery pack.
The final test includes charge-discharge cycle test, capacity test, internal resistance test, open-circuit voltage test, overcurrent test, overcharge test, overdischarge test, short circuit test, etc. of the lithium battery pack. In order to verify the performance of the battery pack, the test steps need to be carried out item by item according to the performance requirements of the battery pack. The equipment used includes lithium battery pack charging and discharging aging cabinet, whole product tester, charger and so on.
Below is a picture of the equipment tested and assembled by our 18650 lithium battery pack.
In addition, our company has long-term cooperation with LG, Samsung, Rova, BAK and other battery cell factories to customize 18650 battery packs, such as 11.1V, 22.2V, 25.9V, 36V, 48V and other 18650 battery packs. If you have similar battery pack requirements, please fill in the basic battery requirements information as shown below, and we will provide you with the optimal battery solution.
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