18650 Lithium Battery Assembly 48V Electric vehicle Battery!
How to assemble 48V battery pack with 18650 lithium battery? In fact, the lithium battery has no voltage stabilizing function. It can only be understood as a water reservoir. The voltage represents the water level. The water level has a certain range of changes, not a fixed value. The nominal voltage of 18650 is 3.7 V, the maximum voltage cannot exceed 4.2 V, the minimum voltage cannot be lower than 2.5 V, and the actual minimum discharge is generally controlled at about 3 V.
To boost the pressure, it needs to be connected in series
We know that the essence of calculator is binary code such as 01. Each unit can be subdivided into a single trigger, a few billion level trigger, which can form a very complex and fast operation logic, which is much more powerful than human's computing power.
18650 is just a small single lithium battery, its nominal voltage is 3.7 v. if you want to form 48 V, according to the circuit voltage principle, to boost, you need to use the method of series connection. 48 ÷ 3.7=12.97, take the whole number as 13. Therefore, as long as the 13 18650 monomers are connected in series, the battery pack of about 48 volts can be realized, 13*3.7=48.1 volts.
Of course, this voltage range is not really fixed at 48V, but approximate value. The minimum discharge voltage is 2.75 * 13 = 35.75v, and the maximum charging voltage is 4.2 * 13 = 54.6V.
Importance of the protection plate
Although a simple series connection can make the voltage rise like the superimposed arhat, but the lithium battery is too delicate and dangerous, it cannot be over discharged or overcharged, that is to say, the charging voltage cannot be too high, otherwise it may explode, and it cannot be discharged regardless of the cost, otherwise the battery will be damaged, so it needs something to protect the overcharge or over discharge, which is the lithium battery protection Plate.
The essence of the lithium battery protection board is to detect the temperature, voltage and current of the lithium battery pack, so as to control these parameters within a certain range, so as to avoid the "extreme" damage of the lithium battery and even cause safety problems, such as high voltage, which needs to cut off the charging circuit; low voltage, which needs to prohibit the circuit from discharging; excessive current, which also needs to prohibit the input or output.
There are mature ready-made protection boards in the market. It's good to buy them back and use them directly. Wire them according to their drawings and use them according to the requirements of the instructions. It's good not to connect the wrong wires.
Because the cost of the protection plate is not cheap, few people will let each single 18650 use a protection plate correspondingly. It is often used as a unit after multiple lithium battery cells are connected in parallel. In fact, it can only protect the unit after parallel connection, and it can not really protect each single unit. The function of parallel connection is to improve the capacity of battery pack. The single capacity of 18650 lithium battery sold on the market at present is about 2500mah. If there are two parallel connection, they are 5000mAh, and so on.
Advantages of series parallel connection
Generally, the internal resistance of 18650 single lithium battery is about 70 milliohm. If there are too many batteries in series, the internal resistance will also increase with the series connection. On the contrary, the larger the internal resistance is, the stronger the heat is, the lower the efficiency is, and the higher the temperature is. If the temperature is higher than a certain value, the lithium battery will be damaged.
The connection of lithium battery is also a problem, because the battery shell is made of steel, and it is not well welded with ordinary electric iron. Special spot welder is often needed. If the welding is not good, the internal resistance of battery pack will be increased, which is easy to cause heat in frequent charging and discharging, and may cause unexpected safety accidents.
It is also very important to connect copper wires and copper bars between batteries. It needs to be calculated and selected according to the current. Of course, the coarser the better, it can also reduce the internal resistance between batteries..
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