Battery balancing

The term Balancer to German, ( cell state of charge ) balancer ' or Adjustment Control designates an electrical device, which ensures the uniform voltage of all cells in a battery pack or a battery of accumulators.

Problem

Batteries are made to increase the nominal voltage in the control of a plurality of series connected individual cells or cell blocks. For production reasons, there are variations in capacity and internal resistance of these cells. In practical use of multi-cell, series-connected batteries this circumstance means that the cells are different unloaded and loaded and can take critical loading conditions. The differences in voltage of the individual cells perform within a serial network in the discharge to the risk of deep discharge of individual cells. In series -connected cells do not reach the same final charge voltage, which can cause overloads of individual cells in the common store. Particularly relevant are the various types of lithium battery balancer technologies but also for lead - acid batteries in trucks devices are available.

The state of charge of a battery is usually determined by the voltage at the ends of the series circuit ( overall voltage). Whether in between are stronger or weaker cells can not be determined in this way. Upon reaching the discharge voltage is weak cells may already be in Tiefenentladebereich, while the stronger cell still contain energy. When charging achieve lower capacitance cells and cells that were not fully discharged before the final charge voltage and be overloaded. The remaining cells are, however, not fully charged. This circumstance also can not be seen from the total voltage. The divergence of the charge states in a battery pack is called the drift cell. Cells that are deeply discharged over - or age faster and lose their capacity, bringing the total battery damage and cell drift exacerbated. For non- loaded cells, the entire sum of the capacities of the individual cells can not take advantage because the weakest cell determines the total capacity.

With traditional battery types (Pb, NiCd, NiMh batteries ) the complete loading of all cells is achieved by selective overloading of the entire pack. The cell resistance increases when reaching the charging circuit. The excess energy of the already full cells is then converted into heat or degraded by gassing in lead-acid batteries. Within certain limits, these batteries take it no harm. The situation is different in modern batteries based on Lithium. This leads overcharging immediately to cell damage due to decomposition of the electrolyte, some of them even to strong heating to fire. Balancerschaltungen have the task of bringing all the cells in a battery pack on the same charge voltage and thus to achieve a full charge of all cells. In this way, can be permanently used the full capacity of the battery pack and counteracted the cell drift.

Especially in multi-cell battery systems may continue based on the total voltage is not possible to determine whether individual cells are defective. Individual Balancer from the same small fluctuations of the charge state of the cells. However, you can only limit the cell voltage when the load current does not exceed its capacity to limit the current or power dissipation. You therefore do not fulfill the function of a protective circuit of the individual cells against overvoltage and undervoltage. Many Balancer signal to which cells they are active, and so allow the purposeful control of suspicious cells or are part of a larger battery management system.

Ways of working

Balancer work in the area of the charging circuit, so if the cells are almost fully charged. There are two main methods have been established to compensate for the different cell voltages. The most common variant destroys the charging energy of the cells, which have a higher voltage level by being converted by a parallel with the cell resistance to heat. Alternatively, cells can be selectively loaded with a higher current with lower charge, until they also reach the final charge. In this case, less energy is lost, but it is a much more complex loading control necessary that usually can not be justified on the achievable energy savings.

The balancing of cells in the area of ​​Entladeschlusses is also possible, but can then be conditionally achieved by variations between the cells no common final charge. There is a danger of overcharging of individual cells during charging. In practice, this option is therefore not significant. Balancing in the partially charged state is practically no importance. The state of charge can be determined precisely by the cell voltage only in the area of the fully charged or almost empty state. Also, cells with the same open-circuit voltage may have in partially charged state greatly different charge states. Only devices that compensate with low circulating currents the 12V block voltages in lead-acid batteries ( PowerCheq ), for example, have in CityEl attained a certain distribution.

The charging of battery cells used together, such as flashlights or toys into chargers with individually controlled charging slots also provides a form of balancing issues dar. In this way the battery cells are fully charged independently until the switch-off. Chargers, where several batteries must be inserted at the same time, do not take into account different charge states and contribute to regular use for faster battery wear at.

Practical implementation

Balancers can be used wherever multiple lithium battery cells are connected to a battery pack. Typical examples are battery packs for notebook computers, camcorders, cordless power tools and electric vehicles. In most applications in the consumer sector balancer and battery cells are combined in a common module that often contains other functions of a battery management system. At larger battery cells Balancermodule can be placed directly on the cells. They work independently of each other and limit the charge voltage of each cell by discharging it above the charge voltage specifically about heating resistors.

For complex systems, such as traction batteries in electric cars, including the balancer for battery management system. The modules used there can sometimes also return information to the charging control over the cell state ( eg overvoltage; Balancer active, etc. ) give. With an active balancer, the charging current can then be reduced so as not to overload the Balancermodule, or it can worn or defective cells are identified.

In contrast, RC model battery and balancer be used separately, or the balancer is integrated into the external charger. During the discharge process in the model, the balancer are not required. They can be used already for the next charging. The connection between battery and balancer is carried out with partially standardized connector systems with which each cell can be monitored individually. In addition, it is mainly during commissioning newly compiled battery packs, especially those of large capacity, possible manually balance the cells. This is usually done by selectively discharging the cells with the highest voltage level or by charging all the cells in parallel to the charging circuit before they are connected in series. During regular operation, then usually assumes an automatic Blancingsystem minor corrections.

Since the manufacturers have not agreed on a common standard for their balancer connectors, there are now a variety of connector systems. The most common is a single-row female header, which includes the outside overall plus and minus total. In between, the taps are located between each of the cells for individual measurement of each cell voltage and equalization charge / discharge.

• Robbe
• Graupner
• Simprop
• TanicPacks ( new)
• Hyperion
• Emcotec
• Carson
• Kokam
• Wellpower
• Polyquest ( new)
• Fullriver
• Xcell
• Model -Expert
• Robitronic
• LRP
• SLS

• Dualsky
• Hyperion
• Walkera
• Align
• E-Flite
• FlightMax
• Rhino
• Lite Storm
• Polyquest ( old)
• Most imports from China

• Flightpower
• Thunder Power
• Multiplex

• Hyperion

• Emcotec

• Schulze Elektronik