Circuit/System Description

The A28 Hybrid/Electric Vehicle Battery Disconnect Relay assembly contains all ten high voltage contactors, and two single-use High Voltage cut-off actuators. The high voltage contactors allow the high voltage DC batteries to be connected to the vehicle or contain the high voltage DC within the A4 Hybrid/Electric Vehicle Battery assembly during normal operation. Additionally, they allow for series configuring the two battery layers for 800V DC charging.

The high voltage contactors connect and disconnect the high voltage batteries from the high voltage components located throughout the vehicle. These high voltage components may contain capacitors that store high voltage even when disconnected from the high voltage batteries. Whenever the contactors are commanded open it is important that this stored capacitance is also discharged.

Two different methods are available to discharge the stored capacitance. Under normal operation, after the contactors are commanded open, the drive motor control module will connect the stator coil of it's 3 phase motor to the high voltage DC bus, essentially causing a resistive short that will discharge any stored capacitance remaining in the high voltage system external of the high voltage battery. If conditions do not allow for the drive motor control module to perform the 3 phase short, the high voltage E54V Hybrid/Electric Vehicle Coolant Heater and the high voltage G1HV Air Conditioning With Motor Compressor will be commanded on and they will discharge the stored capacitance.