Battery pack

Battery pack as an interconnected package of multiple battery cells will be referred to, which are held together for practical use by an envelope or a housing and is often also protected against external influences. Battery packs are removable and interchangeable design, and include detachable electrical contacts, often through connector.

The cells used here should all belong to the same type of manufacturer, that have an identical voltage as possible, capacity and resilience. In a battery pack and a plurality of blocks of cells may be connected in parallel, and a plurality of such cell blocks connected in series in turn.

Voltage of a battery pack

The nominal voltage of the battery pack is derived from the sum of the rated voltages of the series connected cells or cell blocks. It is based on the standard specifications of the manufacturers and determines the interpretation of the charger to.

The actual voltage of a battery pack varies according to the state of charge. The highest value is determined by the charge voltage of the charging method used. The lowest voltage is the discharge voltage specified by the manufacturer, in which a harmful discharge individual cells must be prevented.

Capacity of a battery pack

The nominal capacity is expressed in ampere-hours (Ah). The rated capacity of the battery pack corresponds to a simple series circuit of a single cell. Cell blocks are connected in parallel with cells present, it is derived from the sum of the rated capacity of the parallel-connected individual cells.

The usable capacity is, however, determined in series circuits the weakest link in the chain. Thus, it corresponds to the cell or the cell block with the lowest capacity.

Energy content of the battery pack

Although all cells are to be a battery pack of the same type and if possible the same production batch, the actual values ​​of the cells always differ in practice. Causes manufacturing tolerances and / or different aging of the individual cells. The nominal energy value is the sum of the individual energy levels of the individual cells or cell blocks.

The useful energy content of a battery pack obtained from the cell or the cell block of cells in parallel with the lowest capacity is multiplied by the number of series connected cells or cell blocks. It is expressed in watt-hours (Wh ) or kilowatt-hours ( kWh). It can be higher in the new state as the nominal energy content ( over-capacity of the cells) but decreases by the use, by aging and degradation.

Designation system for cell configuration

For the assembly of battery packs is a cut-off system has been established. It tells you how many cells are in parallel and reihenverschaltet within a pack.

A 3S2P battery pack for example, contains a total of 6 cells. Of these, each with 2 cells in parallel (2P ) are installed. Three of these pairs of cells in series, (3S ) so connected in series. With simple series circuits sometimes only a number and a letter will be used. 4S refers to a battery pack with 4 cells connected in series. This form of the name is often found also to balance connectors.

Use of battery packs

Especially frequently encountered are battery packs in industrial products such as network-independent credit card readers and cordless landline phones, as well. Than traction batteries for the propulsion of smaller vehicles or in model for the functionality of the models Today's packs are generally made ​​of NiMH cells or lithium batteries. NiCd cells are no longer installed in current devices due to their environmental impact of disposal.

Battery assembly

In a battery assembly individual cells are assembled into one package. The packages comprise a plurality of cells, depending on the desired voltage and the energy content. The cells can be mechanically constructed in any order: In a row, in column form, or even circular. In industrial mass production, this usually happens automatically. There are numerous variants of the battery pack, for example by a PTC resistor ( a temperature-dependent resistor reduces the charging current as the cells become too hot ), balance connectors for cell maintenance or integrated Balancerschaltungen. For the cladding is often used heat shrink tubing, half shells on the cell connectors or fixed housing. In the cell connectors and surge arresters there are various designs with simple stripes or stamped points ( so -called H- connector ). The latter are expensive, but can be welded better. Also battery packs from cells with screw terminals are manufactured. For them, an exchange of individual cells is possible.

In the model, the cells are usually first glued with super glue to the desired package, which must be paid to the polarity of the construction of the battery pack. Then the cells are connected with connectors made ​​of nickel or copper by means of soldering. Subsequently, an arrester is welded and still soldered a cable as required to the arrester at plus and minus ends yet. The packages are now provided with a shrink tube, tested and provided with a nameplate.

NiCd battery pack 6s1p with shrink tubing

Battery cell with screw and spacers for self- assembly

Lithium battery pack 2s1p with balance connectors and shell casing

Battery pack with charge status display in the solid casing for a pedelec