Battery Pack Relay Testing to Prevent Inrush Current Damage
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Solution Overview
Problem
Electric working machines powered by multiple battery packs face damage from inrush current when internal relays are activated, leading to potential circuit failures.
Innovation Solution
The implementation of external relays and a controller that performs tests to ensure the locking status of these relays before connecting battery packs in parallel, using a discharge relay test process to assess contact integrity and prevent inrush current damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If internal relays of battery packs are closed when electric circuitry is in conducting state, then battery packs can be connected in parallel to supply power, but inrush current damages the internal circuits of battery packs
Solution Approach 1:
The controller performs a preliminary test process before connecting battery packs in parallel. It checks whether the internal relay contacts are in the open state by measuring voltage across the relay contacts. Only after confirming the relay is open does the controller close the external relay to connect the battery pack, preventing inrush current damage.
Solution Approach 2:
The controller continuously monitors the voltage across relay contacts to determine relay state. Based on this feedback information, the controller decides whether to proceed with connecting the battery pack or to indicate a relay lock failure, ensuring safe operation.
2Reliability
If external relays are added to control battery pack connections, then relay locking status can be tested before connection, but device complexity increases
Solution Approach 1:
The external relay serves multiple functions: it controls the connection/disconnection of battery packs to the electric circuitry, and its coil circuit also serves as the test circuit for detecting relay locking status. This multi-functionality reduces the need for separate test circuits and components.
Solution Approach 2:
The system uses its own existing components (external relay coil circuit and voltage measurement capability) to perform the relay locking status test, rather than requiring separate external test equipment or additional dedicated test circuits.
Data Source
AI summary
An electric working machine includes an electric device, battery packs, and a controller. The electric circuitry includes external relays corresponding to the respective battery packs. The controller is configured or programmed to perform an external relay test process to examine whether contacts of a corresponding external relay which corresponds to a second battery pack to be connected to second or later are locked, and, in the external relay test process, if a voltage between the positive and negative external terminals of the battery pack is equal to or more than a threshold, determine that the contacts of the external relay are locked, and, if the voltage between the positive and negative external terminals of the battery pack is less than the threshold, determine that the contacts of the external relay are normal.