DIY Lithium Battery Precautions
2023-10-09
Many friends want to learn DIY lithium battery packs for refitting electric toys, electric vehicles and other battery packs. But some friends don't know much about lithium battery technology. Therefore, I have summarized some DIY precautions for you.
- Cell selection problem：
1. It is necessary to distinguish between 3.2V lithium iron phosphate and 3.7V ternary lithium battery.
2. There are multiple grades of battery cells, which are distinguished by capacity and power models. Generally speaking, the difference between them is the discharge rate. In theory, the higher the discharge rate, the better, but it should be noted that the power battery also has a distinction between high, medium and low.
3. The screening of batteries should also be paid attention to. After the batteries are in hand, it is necessary to distinguish whether the batteries are good or bad.
It is necessary to use an internal resistance tester and a power test. Test the nominal capacity and the actual capacity. The larger the distance from the nominal parameters, the worse the quality. It may even be a fake product, so pay attention to screening.
It is necessary to use an internal resistance tester and a power test. Test the nominal capacity and the actual capacity. The larger the distance from the nominal parameters, the worse the quality. It may even be a fake product, so pay attention to screening.
4. The issue of cycle life should also be paid attention to. The capacity assembled by many friends is not up to the standard, and the power failure will be obvious after a period of use. Most of these are battery problems, and retail customers have no channels to get good products and no equipment to check the quality of batteries.
- Cell handling problems：
After we get the battery, it needs to be processed again before it can be used. (For the power battery pack) The battery pack must be assembled with a matching protective plate! Batteries require matching consistency, the more consistent the better and more stable.
If the matching is inconsistent, the capacity will be insufficient, which will seriously cause the detection failure of the battery protection board and the battery pack will not work.
If the matching is inconsistent, the capacity will be insufficient, which will seriously cause the detection failure of the battery protection board and the battery pack will not work.
1. If you have a machine at home, you can use the machine to screen. If you don’t have a machine, you can only use the internal resistance tester to test each one. Put the voltage, internal resistance, and capacity together, and let it stand for a period of time (7~15 days). After setting, measure again, if it is still consistent, it can be processed. This is also a physical method to judge the stability of the cell.
2. A friend asked if the battery cannot be assembled and used directly?
It can be used directly, but if the battery capacity is inconsistent, the capacity will be limited to the worst battery in the battery pack. To put it simply, the capacity of the battery pack will drop by 10-40%. Seriously, if there is one bad battery in the battery pack, the whole pack will not work. Later maintenance is more troublesome.
- Battery spot welding problem：
1. The processing and assembly of the battery pack is recommended to be machine-based. If manual spot welding is used, the control of the spot welding force of the battery is not good, the battery will leak through the spot, and the nickel sheet will not be strong. Soldering with a manual soldering iron. If the soldering temperature is too high, it will damage the pole piece. Low temperature soldering is recommended. Machining can avoid most of the problems.
2. The thicker the battery connecting wire, the better. The thicker the nickel sheet, the better.
3. As a container for charging and discharging, the battery will release heat during energy conversion. Non-standard processing may cause problems in the battery pack. Be careful when processing the battery pack.
- The use of the battery pack environment.
1. The battery pack is required to be waterproof!
2. The battery pack requires shockproof! When electric vehicles are in use, they cannot be used as off-road vehicles! It is also not possible to use the outer skin of the battery pack to achieve buffer collision, deformation will cause a short circuit! Try to use the grid bracket + cushion + outer box. Without the grid support, the battery pack will cause the nickel sheets to fall off under the pressure of years of activity!
3. The battery pack has the conditions to provide a heat conduction channel. During energy conversion, timely heat conduction can realize the optimization of the battery. Steel outer box + fan auxiliary are both conventional solutions. Previously, it was proposed that power supply glue packaging is also a solution, but it is troublesome for later maintenance.
4. Anti-corrosion problem, the battery has been rusted for a long time, and anti-corrosion measures should be taken as much as possible if possible.
- Lithium battery protection board selection:
1. It is recommended to be below 40A for two electric wheels, and above 80A for three electric wheels. The specific choice should be judged according to the power of your own motor.
2. The voltage must match, 60V is mostly conventional, and it is necessary to distinguish between lithium iron phosphate and ternary lithium batteries.
3. Use large capacity and low power as much as possible, stable and durable. If the power is high and the battery is small, be sure to pay attention to calculating whether the discharge rate of the battery is sufficient.
4. Try to choose the protection board with low protection voltage, and give the battery a certain amount of surplus.
- Charger selection:
1. Match according to the protection voltage of the protection board, how many strings of batteries.
2. Choose a suitable A/H charger according to the total capacity.
Brake matching for electric vehicles Try to choose an electric vehicle with double disc brakes. The lithium battery has a high discharge rate and fast acceleration. Without good brakes, accidents are prone to occur.
In summary, self-assembled battery packs are supported for learning and personal use, but for commercial use, a series of after-sales issues must be considered. Traditional manual spot welding is not supported for electric vehicle battery packs.
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