HVCH Insulation Resistance: Pre-Commissioning Checks

Before energising a high-voltage coolant heater in an electric bus or lorry, the original equipment manufacturer (OEM) should verify the insulation, earthing, connectors, coolant condition and control status in accordance with the vehicle’s established operating procedures. The parameters in the component data sheet are provided for reference only; a comprehensive inspection of the installed high-voltage system must be carried out.

This document is intended to provide a commissioning framework, rather than an operational guide for live-line work. High-voltage-related work must be carried out by trained personnel, in strict compliance with the vehicle manufacturer’s regulations regarding ‘Lockout/Tagout’, measurements and personal protective equipment.

Define and Establish Test Boundaries

It must be clarified whether the measurement applies solely to the heater itself, to the heater and its wiring harness, or to the entire connected high-voltage circuit. Disconnecting or connecting other equipment will affect the measurement results. The condition of the vehicle, the condition of the connectors, the condition of the coolant and the specific measurement points should be recorded.

In accordance with the EVLINK general specifications, when testing by applying a 1,000 V direct current (DC) voltage to the high-voltage section, the insulation resistance should be at least 100 MΩ. Specific project specifications may vary; therefore, it is essential to refer to the drawings and acceptance documents published for the relevant heater model.

Checks prior to energising the high-voltage system

• Confirm the part number, voltage rating and the connector’s keying mechanism.
• Check the housing, terminals, seals and wiring harnesses for damage or contamination.
• Verify the protective connections (equipotential bonding) or earthing measures required by the vehicle design.
• Confirm that the coolant has been filled, that the system has been fully bled, and that it complies with the permitted flow conditions.
• Check the low-voltage power supply, CAN bus wiring and interlock status against the published schematic diagrams.

It is strictly prohibited to bypass a disconnected interlock or a failed safety condition by software means. Installation issues must be rectified, or the deviation must be reported and addressed in accordance with established engineering procedures.

Interpreting insulation test results in context

If abnormal test results occur, the cause may lie with the heater itself, the wiring harness, contaminated connectors, coolant ingress, other connected high-voltage components, or the test setup itself. Follow the vehicle operating procedures to systematically isolate the test boundaries during troubleshooting; under no circumstances should repeated attempts be made to energise the system.

The insulation monitoring device fitted to the vehicle monitors the high-voltage network whilst the vehicle is in operation. HELLA defines this function as: continuous monitoring of the insulation resistance between the high-voltage system and the chassis. This system-level monitoring cannot replace component acceptance testing; similarly, component test results obtained on a test bench cannot replace monitoring whilst the vehicle is in operation.

Confirm Coolant Readiness Before Heating

The heater must not be deemed ready for operation solely on the basis of a passed electrical inspection. It is essential to verify that the coolant mix ratio is correct, that air has been fully bled from the system, and that the necessary circulation circuits are unobstructed. Please refer to the rated flow rate and pressure drop data for the selected model.

During initial controlled operation, closely monitor inlet and outlet temperatures, flow conditions, commanded power, fault reports and connector temperatures in accordance with the Original Equipment Manufacturer’s (OEM) acceptance specifications. Should any anomalies be detected, operation must be stopped immediately and a fault investigation carried out; under no circumstances should operation be prolonged in the hope that the anomaly will resolve itself.

Verify control and protection functions

Confirm that CAN communication, operating mode commands, power limiting, temperature setpoints and diagnostic reporting functions are operating correctly. The EVLINK General Specification covers PID control, diagnostic functions, and protection mechanisms against overvoltage, undervoltage, overcurrent, short circuits and overheating; specific implementation methods and threshold settings shall be subject to the project technical documentation.

Record the types of faults triggered (manually simulated faults), the expected response outcomes and the actual observed responses. Destructive or unsafe fault injection tests are strictly prohibited on production vehicles.

Maintain traceable debugging records

Debugging records should include the following information: heater model, vehicle details, software/calibration version, test boundaries, instruments used, test conditions, various readings, fault inspection results, deviation records, and the personnel responsible for approval. In this way, the first power-up process can be transformed into reproducible evidence, rather than merely an informal observation.

Apply for a High-Voltage Coolant Heater (HVCH) integration review, specifying the vehicle model, voltage platform, cooling circuit, control interface and the required acceptance evidence. Subsequently, EVLINK will assist in confirming the applicable product technical documentation and project test requirements.