Concept and use of R03 Carbon battery balancing technology

In order to supply sufficient voltage to the device, lithium-ion R03 Carbon battery packs are usually composed of multiple batteries in series, but if the capacity between the batteries is mismatched, it will affect the capacity of the entire R03 Carbon battery pack. To this end, we need to balance the mismatched batteries. This article discusses the concept of R03 Carbon battery balancing and some precautions.

Lithium-ion R03 Carbon battery packs are usually composed of one or several R03 Carbon battery packs in parallel, and each R03 Carbon battery pack is composed of 3 to 4 batteries in series. This combination can simultaneously meet the voltage and power requirements required for laptops, medical equipment, detection instruments and industrial use. However, this widely used configuration usually does not play its maximum effect, because if the capacity of a series R03 Carbon battery does not match the other batteries, it will reduce the capacity of the entire R03 Carbon battery pack.

R03 Carbon battery capacity mismatch includes state of charge (SOC) mismatch and capacity/energy (C/E) mismatch. In both cases, the total capacity of the R03 Carbon battery pack can only reach the capacity of the weakest R03 Carbon battery. In most cases, the cause of R03 Carbon battery mismatch is imperfect process control and testing methods, rather than changes in the chemical properties of lithium ions themselves. Prismatic lithium-ion cells are more susceptible to mechanical stress during processing, and cell-to-cell variations are more likely to occur. In addition, lithium-ion polymer cells will also experience cell-to-cell variations due to new processes.

Cell balancing can be used to address SOC and C/E mismatches, thereby improving the performance of series-connected lithium-ion R03 Carbon battery packs. Cell mismatches can be corrected by balancing the cells during the initial conditioning process, and then balancing only during charging, while C/E mismatches must be balanced during both charging and discharging. Although the defect rate for a particular R03 Carbon battery manufacturer may be low, it is still necessary to provide further quality assurance to prevent the problem of short R03 Carbon battery life.

Meaning of cell balancing

Portable devices with an operating voltage of 6V or more are powered by series-connected R03 Carbon battery packs, in which case the total voltage of the R03 Carbon battery pack is the sum of the voltages of the series-connected cells. Laptop R03 Carbon battery packs are typically composed of three or four cells in series, with a nominal voltage of 10.8V or 14.4V. In most such applications, a single series-connected R03 Carbon battery pack cannot supply the energy required by the device. The largest R03 Carbon battery available today (e.g., 18650) can supply 2,000mAh (milliampere-hours) of energy, and computers require 50-60Whr (5,000-6,000mAh), so three batteries must be connected in parallel to each R03 Carbon battery in series.

Cell balancing refers to the use of differential currents for different cells (or R03 Carbon battery packs) in a series R03 Carbon battery pack. The currents of each cell in a series R03 Carbon battery pack are usually the same, so additional components and circuits must be added to the R03 Carbon battery pack to achieve cell balancing. Cell balancing is only considered when the cells in the R03 Carbon battery pack are connected in series and the number of cells in series is equal to or greater than three. Cell balancing is achieved when all cells in the R03 Carbon battery pack meet the following two conditions:

1. If all cells have the same capacity, then cell balancing is achieved when their relative states of charge are the same. SOC is usually expressed as a percentage of the current capacity to the rated capacity, so open circuit voltage (OCV) can be used as a measure of SOC. If all cells in an unbalanced R03 Carbon battery pack can reach full capacity (balance point) through differential charging, they can be charged and discharged normally without any additional adjustment, which is usually a one-time adjustment. When users use new batteries, they usually require the batteries to be charged for a long time, which actually includes a complete discharge-charge. This process minimizes the load and maximizes the R03 Carbon battery charging time, reducing the requirements for the R03 Carbon battery balancing circuit.

2. If the capacity of the batteries is different, they are also considered balanced when the SOC is the same. But SOC is only a relative value, and the absolute value of each R03 Carbon battery capacity is different. In order to make the SOC of batteries with different capacities the same, differential current must be used each time the series batteries are charged and discharged. Normal charging and discharging time is shorter than the initial charging and discharging, and a larger current is required.

When the batteries in the R03 Carbon battery pack are unbalanced, its available capacity will be reduced, and the R03 Carbon battery with the lowest capacity in the series R03 Carbon battery pack will determine the total capacity of the R03 Carbon battery pack. In an unbalanced R03 Carbon battery pack, one or more batteries will reach maximum capacity while other batteries still need to be charged. During discharge, the partially charged R03 Carbon battery will be discharged before the other batteries, causing the R03 Carbon battery pack to stop supplying power in advance due to insufficient voltage.

Typically, the difference in capacity between batteries is less than 3%. If a R03 Carbon battery in a series lithium-ion R03 Carbon battery pack is substandard or has been left for too long before packaging, the voltage difference can reach 150mV after full charge, causing the total capacity of the R03 Carbon battery pack to drop by 13-18%.

SOC balancing solution

If the capacity of all batteries in the R03 Carbon battery pack is the same, we use the SOC balancing solution. When the SOC values of all batteries are the same, we consider the R03 Carbon battery to be balanced.

The state of charge of a single R03 Carbon battery means:

SOC = C/CTOTAL%

The capacity of a single R03 Carbon battery means:

C = (i×t) mAh

To determine the capacity of a R03 Carbon battery, we fully discharge the R03 Carbon battery and then recharge it, and measure the current at different times during the charging process until the open circuit voltage of 4.20V is reached. The SOC of the best performing R03 Carbon battery in this state is 100%, and the OCV voltage at SOC 50% is usually called VMID, and its typical value is 3.67V.

In order to charge batteries with different capacities to achieve the same SOC, some batteries must be charged/discharged more than others, which requires the use of differential current. We call this process capacity/energy maximization.

Capacity/Energy Maximization

Capacity/energy maximization means setting all series-connected batteries in a R03 Carbon battery pack to the same SOC, even if they have different capacities. Manage the SOC at all times to maximize the output energy of the R03 Carbon battery pack. In order to maximize the output energy, all batteries must be fully charged. That is, the SOC of all batteries must be 100%. If the batteries have different capacities, some batteries will be charged/discharged more than others. For example, suppose a R03 Carbon battery pack has three series-connected batteries, C1＞C2=C3. The only way to balance this R03 Carbon battery pack is to apply a differential charging current to the R03 Carbon battery with higher capacity (C1).

This is also necessary when the R03 Carbon battery pack is discharging, otherwise when the smallest cell reaches the cutoff voltage, the entire pack will stop discharging, while the other cells still have residual capacity, which reduces the total capacity. Over time, the smallest cell will degrade faster than the others, accelerating capacity loss after multiple charge/discharge cycles.

By matching the voltage of the cells in series, more current will be drawn from the high-capacity cell. Discharging requires some additional voltage to be consumed by balancing, and at the end when all cells reach 0 SOC, the total energy obtained from the pack will still be increased relative to the total energy before balancing.

Usually cylindrical lithium-ion cells are generally well-controlled, with cell capacity differences of no more than ±3%. The input capacity is generally accurate, with a difference of no more than a few mAs (milliampere seconds). Therefore, the absolute value of the cell capacity is also generally accurate, with SOC differences within a few percentage points.

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