Let’s talk about the BMS sampling board connection method of blade battery

May Day is coming next week, and it feels like it’s not long since the New Year. I have planned a lot of things for May Day, and I don’t know how much I can do in the end. I guess I’ll just lie down at home.

Blade cells are a product that has been widely used in automotive battery packs in recent years. As a new product application, it also brings some new usage scenarios to the BMS sampling board. (Pictures come from the Internet)

A typical feature of blade batteries is that they have a relatively long body, with the positive and negative poles at both ends of the long side of the battery. Therefore, the series connection form when grouped is different from the previous prismatic batteries.

Let’s draw a detailed picture. Taking 8 strings of blade cells as an example, the positive and negative poles of each cell are distributed at the upper and lower ends, as shown in the figure below: The directions of the cells are alternately placed, and copper bars or copper bars are used at both ends of the cells. The aluminum bars connect the 8 strings of cells in series, and everything is OK so far.

Then we arranged a sampling board at one end of the blade cell, and needed to connect the sampling wire harness to the sampling board. At this time, a problem occurred, as shown below: We found that only 5 sampling lines can be connected to the collection board, and the remote The four sampling lines cannot be pulled over, or it will cost a lot to pull them over .

Let’s actually look at what the blade batteries look like after being put into a group. As shown in the picture below, the left and right ends are distributed as the positive and negative poles of the blade batteries. At such a long distance, the batteries are closely together with each other. It is not easy to lead the sampling line to the other side.

Then the engineers came up with a way to use the metal aluminum shell of the blade battery core as a conductor to connect the sampling point of the battery core away from the sampling plate to the shell of the corresponding battery core, so that the battery core can be connected to the sampling plate end. The casing to obtain the sampling point , draw a diagram to illustrate: In the picture below, the odd-numbered cells No. 1, 3, 5, and 7 are short-circuited together with the positive electrode and the casing at the upper end , and then at the sampling plate at the lower end, you can start from 1 , 3, 5, and 7 battery cells, take sampling points on the casing , so that 9 sampling lines are collected to collect 8 strings of battery cells.

The specific implementation method of this solution is as follows: through the combination of FPC and nickel sheets, two nickel sheets are welded to the corresponding battery core, one is welded to the battery core electrode, the other is welded to the shell, and then these two nickel sheets Then they are shorted together through FPC to complete the connection between the shell and the battery core electrode.

Then the sampling board at the other end is also welded to the battery core in the form of PCB + nickel sheet. I have studied BYD Han's sampling board before, and this form is introduced in it, as shown in the picture below.

Then the collection board is welded to the blade battery as shown below, with nickel sheets arranged above and below the PCBA.

At this point, the problem of the blade battery sampling line has been clearly explained, and then it leads to another thing. On the collection board of some blade battery modules, it is found that the number of nickel flakes is far more than the required number of sampling points , as follows As shown in the picture, the nickel flakes on the upper side of the collection board are next to each other, and they are all welded to the casing of the battery core . The total number of nickel flakes far exceeds the required quantity. Why is this?

So I looked for this board, as shown in the picture below: I found that the extra nickel flakes were all even-numbered positive poles, that is, there were two nickel flakes on the PCBA at the same time for the even-numbered positive poles.

At this point, things are relatively clear. We connect the casing of the odd-numbered cells to the positive pole through FPC, and the board above connects the positive pole of the even-numbered cells to the casing through PCB, so that the casings of all cells are connected to their positive poles. They are connected together. The purpose of this is to avoid corrosion of the aluminum shell. I consulted a battery expert. The electrochemical principle of corrosion is relatively complicated and I can't understand it. Briefly speaking, when the potential of the aluminum shell is higher than the negative electrode by a certain value When, the problem of aluminum shell corrosion can be reduced.

Finally, through the continuous improvement of battery cell technology, many battery cells no longer need to short the casing to the positive electrode to solve the problem of casing corrosion, so the current sampling plate does not require so many nickel flakes.

Summarize:

Through the above understanding, you can also find that the blade battery collection board is indeed difficult to maintain. It is neither easy to remove nor install, haha; all the above are for reference only.