How to assemble a 60V battery pack for 18650 lithium batteries?

by:CTECHi     2021-08-23

How to assemble a 60V battery pack for 18650 lithium batteries? Lithium battery does not actually have a voltage stabilizing function. It can only be understood as a reservoir. The voltage represents the water level. The water level has a certain range of variation and is not a fixed value. The nominal voltage of the 18650 cell is 3.7 volts. If it exceeds 4.2 volts, the minimum cannot be lower than 2.5 volts. In fact, the minimum discharge is generally controlled at about 3 volts.

To boost the voltage, it must be connected in series

We know that the essence of a calculator is a binary code like 01. Each unit can be refined to a single flip-flop, billions of flip-flops can form very complex and very fast arithmetic logic. It is many times more powerful than human computing power.

18650 is just a small lithium battery cell, its nominal voltage is 3.7 volts, if you want to form 60 volts, according to the principle of circuit voltage, if you want to boost, Need to use concatenation. 60÷3.7u003d16.21, the integer is 17. Therefore, as long as 17 18650 cells are connected in series, a battery pack of about 60 volts can be realized, 17*3.7u003d62.9 volts.

Of course, this voltage range is not really fixed at 60 volts, but an approximate value. The lowest discharge voltage is 2.75*17u003d46.75 volts, and the highest charging voltage is 4.2 *17u003d71.4 volts.

The protection board must be added

Although the simple series connection can increase the voltage like a stacked Arhat, but the lithium The battery is too delicate and dangerous. It cannot be over-discharged or over-charged, that is, the charging voltage cannot be too high, otherwise it may explode, and it cannot be discharged at any cost, otherwise the battery will be damaged, so something is needed. To protect overcharge or overdischarge, this is the lithium battery protection board.

The essence of the lithium battery protection board is to detect the temperature, voltage and current of the lithium battery pack, so that these parameters are controlled within a certain range, so as to avoid the trend of the lithium battery 'Extreme' damage may even cause safety problems. For example, if the voltage is high, the charging circuit needs to be cut off; if the voltage is low, it is necessary to prohibit the circuit from discharging; if the current is too large, input or output must be prohibited.

There are mature off-the-shelf protection boards on the market, just buy them and use them directly, connect them according to their drawings and use them according to the requirements of the instructions, don’t connect them wrongly The line is just fine.

Because the cost of the protection board is not cheap, there are few people who use a protection board for each 18650 cell, often multiple lithium battery cells are connected in parallel Later, as a unit to protect, in fact, it can only protect the unit after parallel connection, and can not really protect each monomer. The function of the parallel connection is to increase the capacity of the battery pack. The single capacity of the 18650 lithium battery currently on the market is about 3000maH, if the two are connected in parallel, it will be 600maH, and so on.

Avoid excessive internal resistance and heat generation

Generally, the internal resistance of 18650 single-cell lithium batteries is about 70 milliohms. If there is too much series connection, the internal resistance will of course increase with the series connection, while parallel connection is just the opposite. The larger the internal resistance, the greater the heat generation, the lower the efficiency, and the higher the temperature. If the temperature is higher than a certain value, the lithium battery will be damaged. .

Lithium battery connection is also a problem, because the battery shell is steel, and ordinary electric soldering iron is not good for welding. It is often necessary to use a special spot welder. If it is not good, it will increase the internal resistance of the battery pack, which will easily cause heat during frequent charging and discharging, which may cause unexpected safety accidents.

The copper wire copper strips between the batteries are also very important. It is necessary to calculate the selection based on the current. Of course, the thicker the better, it can also reduce the difference between the battery packs. Internal resistance.

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