Friends who like hands-on, will consult some knowledge about assembling lithium battery packs, which can be used to modify battery packs such as electric toys and electric cars. I have sorted out several outstanding issues here for your reference.
#1-How to Choose the Battery Cell to Assemble the Lithium Battery Packs?
① The voltage of lithium iron phosphate battery is 3.2V, The ternary lithium battery’s voltage is 3.7V, this is a simple distinction.
② Lithium Batteries are divided into many levels, for example: capacity type and power type. The difference involved is the discharge rate. In theory, the higher the discharge rate, the bettery, but the power battery also has a distinction between high, medium and low.
③ According to the lithium battery supply chain, generally good batteries are given priority to electric vehicles, and only those that are screened can flow into the market. Large merchants in the market will re-screen, the good ones will be used for battery packs, and the poor ones will enter the retail market.
④ The problem of battery screening, how to distinguish between good and bad after the battery is in hand. Must use internal resistance tester and power test. Test how much is the the nominal capacity, and the actual capacity. The greater the gap from the nominal parameters, the worse the quality. The lower the internal resistance of the battery, the better. Conventionally, it is below 50. More than 50 may be old or poor batteries.
⑤ The cycle life is a big problem. A good battery cycles more than 7000 times, the medium is about 3500 times, and the low-end battery is generally about 2000 times.
#2-How to Test and Select Batteries Before Assembling Lithium Battery Packs?
①If you have the conditions, use the machine to screen. If there is no machine, use the internal resistance tester to test one by one. Put the voltage, internal resistance, and capacity together, and let it stand for a period of time (7-15 days). If it is still consistent, it can be processed. It is a way to judge the battery cell from physical method.
②Many friends will also say, why is it so troublesome, can’t it be directly assembled and used? Of course, it can be used directly, but in the case of mismatch, the battery pack will follow the barrel theory, and the capacity is limited to the lowest board. The worst battery in the battery pack is the upper limit. More serious, if there is a bad battery in the battery pack, the whole pack will not work. Inspection and maintenance work is more cumbersome.
#3-How to Weld Lithium Battery Packs?
①The processing and assembly of the battery pack is given priority to machine processing, and manual assembly is not recommended. (Multi-string battery power pack, single-parallel battery power pack is not high)
②Why is manual spot welding not recommended? The battery spot welding strength is not well controlled, the battery spot is leaking, and the nickel spot is not solid and welded.Manual soldering iron soldering.If the soldering temperature is too high, it will damage the pole piece.Low temperature soldering is recommended.(Most households use high temperature solder)
③The thicker the battery connection wire, the better. The thicker the nickel flakes, the better.
④As a container for charging and discharging, the battery will also release heat during energy conversion. Therefore, during the welding process, prevent the battery from short-circuiting.
#4-The Use of Lithium Battery Packs Environmental Issues.
① The battery pack is required to be waterproof! High probability of short-circuit fire!
② The battery pack is required to be shockproof! Electric vehicles cannot be used as off-road vehicles in use! The outer skin of the battery pack can’t be used to buffer the collision. Deformation will cause a short circuit! Try to use the grille bracket + cushion + outer box. The nickel sheet on the lithium battery packs will fall off under the squeeze of many years of activities without bracket.
③ The battery pack has conditions to provide a heat conduction channel. During energy conversion, timely heat conduction can optimize the battery. Steel outer box + fan assist, both are conventional solutions. The power supply glue package proposed by the editor before is also a solution, which is troublesome in post-maintenance.
④ Anti-corrosion problem. The battery will rust after being left for a long time. If possible, take anti-corrosion measures as much as possible.
#5-How to Choose the Lithium Battery Packs ‘Protection Board?
① Two electric wheels below 40A are sufficient, and three wheels above 80A are sufficient.
②The voltage must be matched. 60V is mostly conventional. It is necessary to distinguish ternary, iron-lithium, and the number of strings.Try to use large capacity and low power, stable and durable. If you need the battery high-power but small size, please calculate whether the discharge rate is supported.
③If possible, choose the protection board with low protection voltage as far as possible to give the battery a certain amount of surplus. For example: 4.25V protection is not as good as 4.2V~4.1V, because it will not put the battery to 100% power and not stick to the limit. However, most protection board designs do not pay attention to this point, and a few manufacturers are doing it.
#6- How to choose the charger for lithium battery packs?
①According to the protection voltage of the protection board, choose suitable electrical appliances suitable for lithium iron phosphate and ternary lithium batteries.
②The suitable charger depends on the total capacity, The 8A/H routine is now recommended on the market.
③The charger should also be protected against water and shock, and it will break quickly if you don’t care about it every day.
#7-How to Choose the Brake to Support the Lithium Battery Packs ‘Electric Vehicle?
Try to choose an electric vehicle with dual disc brakes. The lithium battery has a high discharge rate and a fast acceleration speed. Without a good brake, it is prone to accidents.
#8-Summary About the Lithium Battery Packs.
Self-assembled battery packs are supported for personal use for learning and interest, but for commercial use, a series of issues such as after-sales must be considered. Traditional manual spot welding is not supported for electric vehicle battery packs. At the same time, the battery cycle life is also a point that everyone has overlooked. Many battery packs made by themselves have a capacity that does not meet the standard and quickly loses power after a period of time. These are common problems encountered in self assembly.
