Secondary Battery Over-Current Protection Relay Circuit
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Solution Overview
Problem
Secondary batteries, particularly lithium-based ones used in electric vehicles, face instability due to over-current conditions, which existing protection methods fail to adequately address, especially when dealing with high currents ranging from 100A to 300A.
Innovation Solution
An over-current protection device utilizing a main relay, an auxiliary relay, a current limiting resistor, and a controller to detect and manage over-current by turning on the auxiliary relay and turning off the main relay, allowing limited current flow through the resistor, thereby preventing damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single relay is used for over-current protection, then the device complexity is low, but the reliability of current protection is insufficient for high-capability batteries
Solution Approach 1:
The patent divides the single relay function into two separate relays: a main relay for normal current control and an auxiliary relay for over-current protection. This segmentation allows each relay to be optimized for its specific function, with the main relay handling normal operation and the auxiliary relay providing dedicated over-current protection, thereby improving overall protection reliability without excessive complexity
Solution Approach 2:
The patent implements a protection mechanism where the auxiliary relay is pre-configured to activate before the battery suffers damage from over-current. The controller monitors current levels and activates the auxiliary relay to provide a safety buffer, cushioning the battery from harmful current levels before damage can occur
2Reliability
If the main relay is turned off during over-current, then the battery is protected from damage, but the charging operation is completely interrupted
Solution Approach 1:
The auxiliary relay acts as an intermediary protection mechanism that can be activated during over-current events without completely interrupting the charging operation. The main relay remains active to maintain charging continuity, while the auxiliary relay provides the necessary protection by creating a parallel protection path that limits damage while allowing operation to continue
Solution Approach 2:
Instead of completely shutting down the charging system by turning off the main relay, the patent applies partial action by activating only the auxiliary relay for protection. This excessive protection measure is localized to the auxiliary path, allowing the main charging operation to continue uninterrupted while still providing adequate protection
3Reliability
If a current limiting resistor is added in series with the auxiliary relay, then the current magnitude is reduced during over-current, but the device complexity increases
Solution Approach 1:
The patent combines the current limiting function with the auxiliary relay by placing a current limiting resistor in series with the auxiliary relay. This merging of protection functions into a single auxiliary circuit path reduces overall complexity compared to having separate protection mechanisms, while still achieving effective current limitation during over-current events
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
Effectively reduces current magnitude during over-current conditions, preventing complete shutdown and protecting the battery from damage, ensuring continuous operation without full disconnection.
Implementation Method 1
a current limiting resistor connected in series with the auxiliary relay
Data Source
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AI summary
An over-current protection device of a secondary battery includes a main relay, an auxiliary relay connected in parallel with the main relay, a current limiting resistor connected in series with the auxiliary relay and a controller for detecting an over-current and protect the battery module. The controller turns on the main relay and turns off the auxiliary relay in a normal state where the battery module is recharged by the generator. When the over-current is detected, the controller turns on the auxiliary relay and turn off the main relay so that a limited current flows through the current limiting resistor.