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| HV voltage between the Battery Terminals to Chassis |
The voltage between the HV battery positive terminal and chassis ground measures approximately half of the total HV battery voltage and this behavior is expected due to the high resistance grounding method often used in isolated high voltage systems, such as in electric vehicles (EVs) and industrial battery systems.
Typically a voltage divider circuit is used in the insulation resistance measurement to scale down the high voltage present in an electric vehicle's HV system, allowing safe measurement and assessment of insulation resistance.
HV battery system in EV vehicles are generally floating ( not directly grounded ) . so, both the positive and negative HV lines are connected to chassis ground via high-value resistors (e.g, 500kΩ to 10MΩ).These resistors are sometimes called symmetrical voltage dividers or bleeder resistors.How it Works:
The high voltage (HV) is applied to the first resistor, and the second resistor is connected to chassis ground.
A measurement point or Test point is placed at the junction between the two resistors, where a lower voltage proportional to the HV battery voltage is obtained.
This scaled down voltage is used by the insulation monitoring device to assess the insulation resistance without exposing the measurement circuitry to full HV.
To read more on Insulation measurment click below...
How Insulation Resistance in EV Vehicles measured and Why?.
Lets say, for 400V Battery EV Vehicle.
HV+ to chassis: ~ +400 V
HV− to chassis: ~ −400 V
HV+ to HV−: 800 V
This is normal and expected behavior in a floating HV battery connected to an EV Vehicle.
Conclusion :
Measuring approximately half of the HV battery voltage between either HV+ or HV− and chassis is normal behavior in electric vehicles (EVs) that use a floating high-voltage system.
Intentional and compliant with international standards such as:
ISO 6469-3:2018 - Electric shock protection
ISO 21498-1/2 - HV power supply systems
UNECE R100 - Legal compliance for EV safety in many countries
These standards explicitly allow such floating systems with high-resistance paths to chassis and require insulation monitoring (IMD) to detect loss of isolation. The presence of a measurable voltage to chassis confirms the system is working correctly as long as it's symmetric and monitored.
The above design ensures Electrical safety,Improved fault detection and Compliance with global EV regulations.
ISO 6469-3:2018 - Electric shock protection
ISO 21498-1/2 - HV power supply systems
UNECE R100 - Legal compliance for EV safety in many countries
These standards explicitly allow such floating systems with high-resistance paths to chassis and require insulation monitoring (IMD) to detect loss of isolation. The presence of a measurable voltage to chassis confirms the system is working correctly as long as it's symmetric and monitored.
The above design ensures Electrical safety,Improved fault detection and Compliance with global EV regulations.
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