How does a lithium-ion battery in an e-bike work?

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Hello friends!

Today, the lithium-ion battery is the most common type of battery used in electric vehicles, and in particular on e-bicycles.

And since this is a rather expensive component, it is advisable when buying it to understand what you should pay attention to in order not to make a mistake with the choice, and for this it would be nice to know in general terms its structure and principle of operation.

A lithium-ion battery, in the form in which it is used on e-bikes, is a set of series-connected blocks, each of which has the same number of parallel-connected cells, they are also called cells (for example, size 18650).

From each unit there is a separate wire to the control board (BMS, battery management system), but about it a little later.

The number of blocks connected in series is denoted by the letter «S», and the number of parallel-connected elements within each block is denoted by the letter «P». The nominal battery voltage is defined as the nominal voltage of one lithium-ion cell (3.7V) multiplied by the number of blocks (S).

For example, the 13S4P battery assembly diagram means that the nominal voltage of the battery is 48 volts (13 x 3.7 V), and that if it is assembled from cells with a capacity of 3 Ah each, then its capacity is 12 Ah (3 Ah x 4).

As a rule, the cells are either glued together using superglue (cyanoacrylate) or a glue gun, or they are assembled into special holders that ensure their fixation.

The second option is more preferable, since in this case the cells do not touch each other, that is, they are better isolated from each other.

For normal operation of the battery, it is necessary that all its elements have the same voltage — in this case, it will give out the full capacity.

Compliance with this condition is monitored by the control board, or BMS, which I already mentioned — at the end of the charging process, it connects resistors to those cells that were charged before the others so that the voltage across them decreases, and gradually the voltages on all cells are equalized.

In addition, BMS performs the function of protecting cells from overcharging (no more than 4.2 V per cell), over-discharge (no less than 3 V per cell) and short-circuit protection, that is, closing the output contacts to each other.

At the same time, the so-called

Some BMS have

Also BMS boards are equipped with

The use of a thermal contact provides additional protection for the battery and increases safety — BMS will disconnect the load if the battery is too hot.

Before the purchase

In addition, before buying, you should search the net

You can read more about battery operation in

Soon, the channel will publish a detailed article about assembling a lithium-ion battery with your own hands. If you are interested, do not forget to subscribe.

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