Relay Welding Detection Circuit to Block False AC Current Paths
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Solution Overview
Problem
Existing welding detection devices inaccurately detect welding in relays when using a single-phase three-wire AC power supply, as alternating current can flow from the power line to the detection element without passing through the relay, leading to erroneous detection.
Innovation Solution
A welding detection device with a first circuit connected to the power supply and load lines, powered by a DC supply, and a second circuit that detects voltage differences between these lines, cutting off the first circuit when a voltage difference is present to prevent alternating current from flowing through the relay and triggering false welding detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a welding detection device detects current flow through the detection element to identify welding in the relay, then welding detection capability is provided, but erroneous detection occurs when alternating current flows from the power line to the detection element without passing through the relay
Solution Approach 1:
A second circuit is introduced as an intermediary between the AC power supply and the first circuit. This second circuit detects voltage differences between the first line (power supply side) and second line (load side) of the relay, and based on this detection, controls a switching element to connect or disconnect the first circuit from the AC power supply. This intermediary circuit prevents erroneous detection by isolating the detection circuit from AC voltage that could cause false current flow through the detection element.
2Ease of operation
If the detection circuit remains connected to the AC power supply during relay operation, then the circuit is simple and responsive, but false current flow triggers erroneous welding detection
Solution Approach 1:
The connection state of the first circuit to the AC power supply is dynamically changed based on relay operation state. The second circuit detects whether the relay is in the on-state or off-state by measuring voltage differences, and accordingly controls the switching element to connect the first circuit during off-state (when welding detection is needed) and disconnect during on-state (when false current flow would occur). This dynamic adjustment maintains detection accuracy while preserving operational responsiveness.
Data Source
AI summary
A welding detection device includes a first circuit including a detection element, a first circuit power supply, and a second circuit. The first circuit is connected to a first line connecting a power supply and a main relay and a second line connecting a load and the main relay. The first circuit power supply supplies DC power to the first circuit. The first circuit detects welding in the main relay based on whether or not a current from the first circuit power supply has flowed to the detection element through the main relay when the main relay is controlled to be in an open state from a closed state. The second circuit cuts off the first circuit only when the voltage difference is present between the first line and the second line while the main relay is controlled to be in an open state from a closed state.