Electrical System of Battery

The electrical design of the battery pack is associated with fundamental electrical elements. These elements are Busbars, Contactors, Fuses, pre-charge resistors, current sensors, HV (High Voltage) and LV (Low Voltage) Connectors, and wiring harnesses.

Busbars are electrically conductive materials that maintain current flow from the cells to the external electrical loads. Aluminum and copper are preferred materials for busbars to be used in battery systems. Busbars are used instead of cables in battery packs since they are rigid.

Contactors are electromechanical switches that ensure electrical connection or isolation of battery cells.
Fuses are electrical safety devices that prevent short circuit currents. A fuse has a melting element that disconnects the circuit in case of an undesired current.

A pre-charge resistor is used specifically in battery systems connected to capacitive loads. An EV electrical system has multiple power electronic converters which have DC link capacitors. These capacitors need to be pre-charged to avoid inrush currents. Pre-charge resistors are used with pre-charge contractors to equalize capacitor voltage to the battery system voltage.

Current sensors are devices for measuring current flow from and to the battery cells. The current measurement information is used by BMS (Battery Management Systems) to estimate battery cell states as well as contactor control.

HV and LV connectors are used as interfaces between electrical components within and outside of the battery. HV connectors for carrying high currents are assembled with busbars and HV cables. There are also HV connectors that are used as interfaces to HV voltage measurement nodes. Such connectors are assembled with HV signal cables. On the other hand, LV connectors are interfaces to low voltage signals between electrical components that are mostly used for communication and control purposes.

The electrical system of an EV battery is designed based on vehicle driving profile and environmental conditions. While the driving profile defines required voltage and current levels, environmental conditions create boundaries such as mechanical, thermal, and chemical loads. A small battery like a 12V starter battery can have PCB (Printed Circuit Board) size components. In this case, the electrical components occupy approximately 10% volume in the battery system. However, an EV (Electric Vehicle) battery has a hazardous voltage potential which is greater than 60V. Therefore, it has larger electrical components due to safety concerns.

A typical electrical circuit of an EV battery is shown below:

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