AC Relay Switch-On Timing for Minimum Inrush Current
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Solution Overview
Problem
Existing methods for switching relays connected to AC-powered loads result in inrush currents, leading to switching sparks, contact damage, and ghosting or flashing of LED lamps due to galvanic isolation requirements and bypass currents, which increase space and cost needs.
Innovation Solution
A method that monitors mains voltage to determine a synchronization point and uses a magnetic field sensor to detect inrush currents over different time intervals, activating the relay at the time corresponding to the minimum inrush current to minimize inrush currents during switching, thereby avoiding ghosting and reducing installation space requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If galvanic isolation is implemented using optocouplers for each switching contact, then reliability is improved, but device complexity increases and installation space requirements increase
Solution Approach 1:
The patent combines multiple functions into a single magnetic field sensor that simultaneously detects inrush current magnitude and polarity, eliminating the need for separate optocouplers on each contact. This merging approach maintains galvanic isolation reliability while reducing device complexity and installation space requirements.
Solution Approach 2:
The magnetic field sensor serves multiple functions: it detects inrush current, determines current direction (polarity), and provides galvanic isolation. This multi-functional approach replaces what would traditionally require multiple separate components, reducing overall system complexity while maintaining isolation reliability.
2Measurement precision
If contact voltage monitoring is performed via each relay contact, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent combines voltage monitoring and current detection functions into a unified magnetic field sensing approach. By monitoring the magnetic field generated during switching, the system obtains both current magnitude and polarity information without requiring separate voltage monitoring circuits for each contact, thus reducing complexity while maintaining measurement precision.
3Object-affected harmful factors
If relay switching occurs at zero crossing points, then harmful factors are reduced, but switching inertia causes delayed response
Solution Approach 1:
The patent performs preliminary detection of the magnetic field in the time interval before the expected zero crossing point. By identifying the precise moment when inrush current reaches its minimum (at or near zero crossing) and anticipating the relay's switching inertia, the system triggers switching at the optimal moment, ensuring minimal sparks while maintaining timely response.
Solution Approach 2:
The system uses real-time magnetic field feedback to determine the actual inrush current characteristics and adjusts the switching timing accordingly. This feedback mechanism allows the relay to adapt to varying load conditions and accurately identify the optimal switching moment, minimizing harmful effects while responding promptly.
4Object-affected harmful factors
If inrush current is minimized by precise timing, then harmful factors are reduced, but device complexity increases
Solution Approach 1:
The patent replaces complex electronic current sensing and control circuits with a magnetic field sensing approach. The magnetic field sensor naturally provides galvanic isolation and delivers both magnitude and polarity information, simplifying the control electronics while effectively minimizing inrush current through precise timing based on magnetic field characteristics.
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 minimizes inrush currents, preventing contact damage and ghosting, and allows reliable switching of small signals with reduced space and cost, ensuring efficient relay operation.
Implementation Method 1
detecting the inrush current through the relay contacts with the aid of a magnetic field sensor which detects the magnetic field generated by the switch-on process
Implementation Method 2
The inrush current can be determined using a suitable magnetic field sensor, in particular a conductor loop (corresponding to an antenna), and the voltage induced in it. The intensity of the induced voltage is proportional to the inrush current.
Data Source
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AI summary
A method for switching on an AC-powered relay to cause a minimum inrush current Imin through the relay, wherein the method comprises the following steps: - monitoring the mains voltage to determine a fixed synchronization point tsync at the mains frequency, and - detecting the inrush current I through the relay contacts using a magnetic field sensor that detects the magnetic field generated by the switching process for different time intervals tDelta between the time tein of its switching control and the time of the synchronization point tsync over at least one half-cycle, - identifying the time tein2 corresponding to the minimum inrush current Imin, - controlling the relay at time tein2 such that the closing of the relay contacts causes a minimum inrush current Imin.