Some suggestions for DIY lithium battery
Recently, many people have consulted and learned DIY lithium battery packs, which are used to refit electric toys, electric vehicles and other battery packs. During the communication process, many friends were a little overly optimistic, and they were not very thorough and rigorous about lithium battery technology. A few prominent issues are sorted out here for your reference.
1. Cell selection problem
1. 3.2V lithium iron phosphate, 3.7V ternary lithium battery, this is a simple distinction.
2. The battery cells are divided into many grades, with capacity and power models distinguished. The difference involved is the discharge rate. In theory, the higher the discharge rate, the better, but power batteries also have a distinction between high, medium and low.
3. In terms of operation, it is impossible to buy good batteries in retail purchases. Good batteries are given priority to electric vehicles, and only the selected ones can flow into the market. Large merchants in the market will screen again, good ones are used for battery packs, and bad ones enter the retail market.
Note: Regardless of the brand, it will not be very good to enter the retail market, even if it is a first-line brand. Of course, the higher the premium you pay, the better you can get it.
4. The battery screening problem, how to distinguish the good from the bad after the batteries are in hand. It is necessary to use an internal resistance tester and a power test. Test how much MH is nominal and how much MH is actually. The larger the distance from the nominal parameters, the worse the quality. The lower the internal resistance of the battery, the better, usually below 50. If it is more than 50, it may be an old battery or a bad battery.
5. The problem of cycle life is a big problem.
Many friends assemble it by themselves, the capacity is not up to the standard, and the power failure is obvious after a period of time. Most of these are battery problems, and it is difficult for retail customers to bypass this pitfall. After all, there is no channel to get good products and no equipment to check the quality of batteries.
2. Cell handling problems
After we get the batteries now, it doesn't mean that we can deal with them immediately. It needs to be processed again before it can be used. (for power battery packs)
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. How to deal with it?
1. If conditions permit, use the machine to screen. If there is no machine, use the internal resistance tester to measure one by one. Put the voltage, internal resistance, and capacity together, and let it stand for a period of time (7~15 days). After standing, then If it is still consistent, it can be processed. This is also a physical method to judge the stability of the cell.
2. Many friends will also say, why is it so troublesome, can't it be assembled and used directly? Of course, it can be used directly, but in the case of mismatch, the battery pack will abide by the barrel theory, and the capacity is limited to the lowest board. The worst battery in the battery pack is the upper limit. Generally speaking, 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. Inspection and maintenance work is more cumbersome.
3. Battery spot welding problem
1. The processing and assembly of the battery pack is given priority to machine processing, and manual assembly is not recommended. (Multiple strings and other battery power packs, the requirements for single parallel are not high)
2. Why is manual spot welding not recommended? The spot welding strength of the battery is not well controlled, the battery leaks through the spot, and the nickel sheet is not strong and welded.
Soldering with a manual soldering iron. If the soldering temperature is too high, it will damage the pole piece. Low temperature soldering is recommended. (Most households use high-temperature solder)
3. The thicker the battery connecting wire, the better. The thicker the nickel sheet, the better.
3. The battery is used as a charge and discharge capacity container, and heat will be released during energy conversion. Non-standard processing may cause problems in the battery pack. The processing of the battery pack must be cautious and cautious. Many industry personnel suffered a lot. There was no battery in that year. The PACK manufacturer caught fire.
Fourth, the use of the battery pack environment.
1. The battery pack is required to be waterproof! There is a high probability of short circuit fire!
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. The power glue packaging proposed by the editor before 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.
5. Lithium battery protection board selection
1. Electric two wheels below 40A are sufficient, and three wheels above 80A. 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 ternary, iron-lithium, and the number of strings.
3. Use large capacity and low power as much as possible, stable and durable. If the battery is high-power and small, it must be calculated whether the discharge rate is supported.
4. Try to choose the protection board with low protection voltage if possible, and give the battery a certain amount of surplus. For example: 4.25V is not as well protected as 4.2V~4.1V, because the battery will not be charged to 100%, and the limit will not be posted. However, most protection board designs do not pay attention to this point, and a few manufacturers are doing it.
6. Charger selection
1. Match according to the protection voltage of the protection board, how many strings of iron lithium/ternary lithium
2. Choose a suitable A/H charger according to the total capacity. Now the 8A/H routine is recommended on the market.
3. The charger should also be protected against water and shocks. If you don’t take care of it every day, it will break down quickly.
Seven, electric vehicle brake matching
Try to choose an electric vehicle with dual disc brakes. The lithium battery has a high discharge rate and fast acceleration. Without good brakes, accidents are prone to occur.
