Understanding the Function of High Voltage PDUs in EVs
In electric vehicles, the High Voltage Power Distribution Unit (PDU) plays a central role in distributing energy from the battery to high-power components such as the drive motor, air conditioning compressor, and PTC heater. The system also incorporates protection mechanisms to prevent faults such as short circuits or overloads. A well-designed PDU integrates components like dc contactors for electric vehicles, high-voltage fuses, interlock devices, and the main battery management system (BMS), ensuring safe and efficient energy flow throughout the high-voltage system.
How PTC Heaters and Interlocks Work Together
PTC heaters leverage thermistors that increase resistance with temperature, producing heat when powered. They serve both comfort and performance roles—warming the cabin and preheating the battery pack in cold conditions.
Modern EVs also rely on multiple interlock systems to ensure safety. Structural interlocks trigger disconnection alerts through connector monitoring, prompting the VCU or ECU to isolate the high-voltage bus. Functional interlocks prevent the vehicle from operating while connected to a charging station. In both cases, a reliable dc contactor for electric vehicles is used to quickly disconnect or isolate high-voltage paths.
Core Components Featuring DC Contactors for Electric Vehicles
Key PDU Components:
- Charging positive relay – BSBC8V-300C dc contactor for electric vehicles
- Charging negative relay – BSBC8V-300C
- Water-cooled positive contactor – BSBC8V-100
- Heater-side contactors (input/output) – BSBC8V-100
- Heater fuse – RS308-HB-4G80A
- Current sensor – LEM HAH1BVW S/05
- Main negative contactor – BSBC10-600
- Pre-charge relay – BSBC9-20 pre-charge dc contactor
- Pre-charge resistor – 100W/50Ω (EVR-C51504A)
- MSD – BSB
- High-voltage connectors – Huizhou Lingyue and Shunke brands
- Main BMS – Kolei M79C1 Series
These components are commonly used in EV platforms requiring robust automotive grade dc contactors.
DC Contactor Selection in Electric Vehicle Systems
When selecting a dc contactor for electric vehicles, the rated current must exceed the system’s operational current. Leading brands like Panasonic, TE, HF, and BSB offer automotive-specific contactors designed for harsh electrical environments. Ceramic sealed designs are especially popular due to superior arc suppression and long lifespan.
Fuse and Circuit Protection Design
Fuses used in conjunction with dc contactors for EVs typically range from 200A to 400A and are rated for 500VDC or 700VDC. The fuse rating should be 2–2.5 times the nominal working current and must align with the time-delay characteristics of the system to ensure proper coordination with the contactor.
Selection of Key Electrical Components
1. DC Contactor Selection
The rated current of the selected DC contactor should be greater than the actual required current. Common high-voltage DC contactor brands include Hongfa, Panasonic, TE (Tyco), and BSB.
2. Fuse for Battery Protection
Fuses used for battery protection are mainly rated at 500VDC and 700VDC, with current ratings typically ranging from 200A to 400A.
- The rated current of the fuse should be 2 to 2.5 times the working current of the high-voltage box, but must not exceed the peak current of the high-voltage box.
- The fuse’s melting time should be verified against the high-voltage box’s peak current duration using the fuse’s time-current characteristic curve.
3. Pre-Charge Circuit
3.1 Used to limit the inrush current to the bus capacitors, relays, and rectifier components during initial charging, thereby protecting the bus capacitors and other components.
3.2 Typically, the pre-charge process is required to complete within 300ms to 500ms. When the voltage across the bus capacitor reaches 90% of the battery voltage, the pre-charge is considered complete.
3.3 Calculation of Pre-Charge Resistor Value
