Battery Isolation Checking by Voltage Change Threshold

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Solution Overview

Problem

Existing insulation testing methods for high-voltage batteries in electric vehicles are time-consuming, typically taking up to 30 seconds or more, compromising user safety and vehicle readiness due to the need for voltage saturation, which is undesirable for rapid vehicle use.

Innovation Solution

A method involving measuring voltage change over a predetermined time to determine a time-based threshold for insulation state, allowing quick detection of serious faults by evaluating dU/dt at a specific time threshold, reducing the test time to approximately 0.3 to 2 seconds.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If a battery system is designed for high voltage and high capacity, then energy storage capability is improved, but the risk of internal faults and isolation issues increases

Engineering Contradiction:

Improveenergy storage capabilityVSAvoidisolation safety

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The isolation checking device performs proactive detection of isolation faults before they develop into serious safety issues. By continuously monitoring insulation resistance between battery cells, modules, and the housing, the system identifies potential problems early and can take preventive measures, thus resolving the contradiction between high energy storage and safety reliability.

Inventive Principle:

Principle #10Preliminary action

2Device complexity

If traditional multimeter-based isolation checking is used, then device complexity is reduced, but measurement precision and reliability are insufficient

Engineering Contradiction:

Improvechecking device simplicityVSAvoidisolation resistance measurement accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent replaces traditional mechanical multimeter-based measurement systems with an electronic isolation checking device that uses microcontrollers, ADC converters, and dedicated isolation measurement circuits. This substitution enables automated, high-precision measurement of isolation resistance with better stability and reliability, while reducing manual operation complexity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If comprehensive isolation checking is performed across all battery modules, then measurement precision and safety are improved, but checking time and operational complexity increase

Engineering Contradiction:

Improveisolation checking accuracyVSAvoidchecking time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The battery system is divided into multiple independent modules, each with its own isolation checking capability. The system can perform measurements on individual modules or groups of modules independently, allowing for parallel checking operations. This segmentation enables comprehensive safety coverage while reducing total checking time compared to sequential whole-system measurement.

Inventive Principle:

Principle #1Segmentation

4Ease of operation

If isolation checking device is integrated into battery housing, then ease of operation is improved, but device complexity and manufacturing difficulty increase

Engineering Contradiction:

Improveintegrated checking convenienceVSAvoidintegration manufacturing complexity

Core Design Contradiction:

Ease of operationVSEase of manufacture

Solution Approach 1:

The isolation checking device is designed with multi-functionality, serving both as a monitoring system and as an integrated part of the battery housing structure. The device can check isolation for multiple modules simultaneously and provides both alarm and data recording functions, justifying the increased manufacturing complexity through enhanced operational value and safety benefits.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

Ensures rapid and accurate insulation checks, minimizing user wait times while maintaining safety by identifying serious faults within seconds, preventing potential short circuits and ensuring battery system readiness.

Implementation Method 1

an isolation checking device is used to check the isolation between the battery cells, the battery modules and the battery housing

Methodology Applied

Scientific EffectElectrical Resistance: Electrical Resistance

Data Source

PatentEP4308946B1Method for checking the state of isolation of a battery or of a battery system

Publication Date: 2026.05.06 WEBASTO AG

Figure 1A~1B
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Figure 3A~3B

AI summary

The present invention relates to a method for checking the state of isolation of a battery (10) or of a battery system (1) comprising at least two batteries (10), preferably a high-voltage battery or a high-voltage battery system for use as a traction battery of an electric vehicle or for use in stationary storage applications, said method comprising the following steps: - measuring an electrical voltage (U) between a terminal element (12) of the battery (10) and a ground (18) over a predetermined time (t); - evaluating the measured voltage (U) and determining whether a change (24) in the measured voltage (U) occurs at a time which corresponds to a predetermined time threshold value (22); and - emitting a safety signal characterising the state of isolation according to the result of the determination.