Hybrid Electric Vehicle Training Educator

Hybrid Battery Junction Block Assembly

  • information
  • technical details

Internal components:

  • Relays
  • Battery smart unit
  • Current sensor
  • Precharge resistor

All four components listed above are electrical devices responsible for transferring energy contained within the high-voltage battery to the rest of the system. Relays are high-current electrical switches that can stop currents from flowing through high-voltage cables, isolating the electricity to the high-voltage battery. The battery smart unit is an electronic control unit (ECU) that monitors information, temperature, and voltage of internal battery cells. The battery smart unit ECU processes information and then sends it on to the hybrid vehicle ECU (HV ECU). The current sensor monitors the amount of current flowing through a circuit (amps) and reports the data to the battery smart unit. The precharge resistor protects system components from power surges that could cause damage.

The battery current sensor, which is located in the high-voltage battery junction block on the positive side of the high-voltage battery, detects the amperage that flows to and from the high-voltage battery. The battery smart unit receives a voltage between 0 and 5 volts, which is in proportion to the amperage flowing in the cable. A battery current sensor output voltage below 2.5 indicates the high-voltage battery is being discharged, and a voltage above 2.5 indicates the high-voltage battery is being charged. The HV ECU uses these signals and others to determine the battery state-of-charge (SOC).

See figure below.

Battery Smart Unit and Battery Current Sensor Diagram

Battery Smart Unit and Battery Current Sensor Diagram

The system main relays illustrated below are high-current electric devices controlled by a 12-volt, low-current source controlling the (low-amperage side) relay. The received signal enters the low-amperage side to energize the relay. Once energized, the high current is permitted to flow through the high-voltage cables. The HV ECU supplies a (feed-side) control signal to the relay. The ground for the all three relays is connected and will be present only if the interlock system is not disabled. For example, an inverter cover that is removed would open the ground circuit to the relays. Each of the three relays must receive individual control signals from the HV ECU and have a good ground to energize.

System Main Relays (SMR) Diagram

System Main Relays (SMR) Diagram

© 2012 National Alternative Fuels Training Consortium.

Hybrid Battery Junction Block Assembly

Hybrid Battery Junction Block Assembly

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