How to increase the capacity of a lithium-ion battery?

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Hello friends.

After riding an e-bike for a while, you may find for yourself that the available battery is no longer enough for you, and you want to travel much longer distances on a single charge.

This is possible in two cases: if the capacity of the battery was initially insufficient, and if the battery has lost part of its capacity during operation. In this article, we will consider both options and ways out of this situation. Before further reading, we recommend that you familiarize yourself with

If the electric bike was very cheap in relation to its analogues, it is logical to assume that it is assembled from rather low quality components. And among them, most likely, a low-capacity battery with a high internal resistance.

In this case, most often the most reasonable solution would be

Although, if there is enough free space in the battery case, you can

Another thing,

First, you need to make sure that the voltage on all blocks and new cells is the same, and before starting work, do not forget to disconnect the balancing connector from the BMS.

In the diagram, the green dashed line indicates the cells of the original battery, in this case, according to the 13S4P scheme, and the lilac dotted line — additional cells with which the battery will have the 13S6P scheme.

That is, if the capacity of one cell is 3 Ah, the capacity of the entire battery will increase from 12 Ah to 18 Ah, that is, one and a half times.

However, this solution is far from always suitable, due to the limited space in the battery case. An easier way to extend the range may be to purchase a second battery.

Quite often, owners of electric bicycles have the idea to buy a second battery, and in this case, the question of their correct connection will certainly arise. The first thing that usually comes to mind is to connect the batteries

If in one of the batteries some cells start to fail (go into a closed state), the voltage from the working battery will be divided between the remaining cells of the first battery, and they will be recharged (the maximum voltage threshold of 4.2 V will be exceeded), which is quite dangerous. Then, at best, you can be left with two faulty batteries, or even cause a fire altogether.

A more reasonable option would be

Now let’s consider the case when the battery has lost its capacity during operation. This usually happens for two main reasons.

The first

Then this cell will be charged first and the BMS will stop the charging process, although the rest of the cells are not fully charged, that is, the battery will not be able to charge up to its maximum voltage and give out full capacity on discharge. In this case, balancing will be required, but more on that below.

The second reason for the loss of capacity

If the cells are before battery assembly, or are already in the battery,

If the battery

The higher the internal resistance of the battery, the worse it gives out current, and the greater the voltage drop when the load is connected. This means that the BMS will interrupt the charging and discharging process earlier, that is, the battery capacity will decrease.

In both cases (with an increased internal resistance), unfortunately, it will not work to restore the battery. Not if it’s an imbalance, there’s a chance.

Balancing a battery is equalizing the voltages across all its cells. It can be done in two ways. The first is using a lithium-ion battery charger, the second is using a special charger that plugs directly into each battery cell block.

Before proceeding to a detailed consideration of balancing methods, it is worth noting that if the voltage on one or several cells differs significantly from the voltages on the others, then this

Most modern BMS have a balancing function, which is implemented as follows. When the process of charging the battery is nearing completion, a balancing resistor is connected in parallel with the most charged cell, which discharges this cell a little.

At the same time, the voltage on the remaining cells continues to grow, and the voltage difference between the battery cells decreases, and after a while the voltage on all cells becomes the same. Thus, balancing is performed every time the battery is charged.

After winter storage, the voltage across the cells may «run away» so much that one charge will not be enough. In this case, you need to leave the battery connected to the charger for a longer time, for example, for several days or even a week.

In some cases, balancing the battery with a battery charger may not be enough, as the process will take too long.

Then a specialized charger is used, such as iMax or its analogues.

When using it, the battery case is opened, the balancing connector is disconnected from the BMS and connected to the charger. Specialized chargers allow balancing with higher currents than the BMS itself, as well as charge or discharge a specific cell to the desired voltage.

Hope the article was interesting or even helpful.

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