Contact Wetting Circuit Using RC Charging for Low Power Switches
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Solution Overview
Problem
Existing circuits for supplying wetting current to dry contacts in electronic devices are costly and consume significant power, making them unsuitable for low-powered and self-powered devices where power consumption needs to be minimized to avoid measurement errors.
Innovation Solution
A contact wetting circuit utilizing a Resistor-Capacitor (RC) circuit and a controller that charges a capacitor with a limited current, allowing the capacitor to supply a wetting current to the switch, thereby reducing power consumption and eliminating the need for active devices like current sources and multiplexors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional current sources and multiplexors are used to supply wetting current, then the wetting current can be supplied reliably, but the power consumption becomes significant and the cost increases
Solution Approach 1:
The patent implements periodic wetting current pulses instead of continuous current supply. The controller activates the wetting current only during brief intervals (e.g., 10-100 milliseconds) at scheduled times, rather than maintaining constant current flow. This periodic activation maintains contact cleanliness while dramatically reducing average power consumption from tenths of a watt to microwatt levels.
Solution Approach 2:
The patent pre-charges capacitors during low-power intervals before wetting current is needed. The capacitors are charged through resistors from the available power supply, storing energy in advance. When wetting current activation is required, the pre-charged capacitors discharge to provide the necessary current surge, eliminating the need for high-power continuous supply circuits.
2Reliability
If wetting current is supplied directly from the power supply, then the contacts are properly wetted, but the average current consumption exceeds the wetting current parameter and causes measurement errors
Solution Approach 1:
The patent uses periodic pulsed wetting current activation rather than continuous current. By confining wetting current to brief intervals (10-100ms periods) with low duty cycle, the average current consumption is reduced to levels that do not interfere with measurement signal accuracy, while still maintaining effective contact wetting during the active pulses.
Solution Approach 2:
The patent changes the temporal parameters of current supply by using variable pulse widths and duty cycles. The controller adjusts the duration and frequency of wetting current pulses based on operational conditions, allowing optimization of both wetting effectiveness and power consumption to stay within measurement accuracy thresholds.
3Use of energy by moving object
If the electronic device is designed to consume minimal power, then it can operate as low-powered or self-powered, but it cannot supply sufficient wetting current to clean surface oxidation on dry contacts
Solution Approach 1:
The patent pre-charges energy storage capacitors during low-power intervals using minimal current from the power supply. These capacitors accumulate energy gradually through resistor charging circuits, storing sufficient charge to deliver high-current wetting pulses when needed, thus enabling low-powered devices to achieve high-current capability on demand.
Solution Approach 2:
The patent introduces capacitors as intermediary energy storage elements between the low-power supply and the high-current wetting requirement. The capacitors act as a buffer, accepting charge slowly from the weak power supply and delivering charge rapidly during wetting events, decoupling the power consumption level from the peak current capability.
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
The solution effectively supplies a wetting current to dry contacts while minimizing power consumption, reducing measurement errors, and is applicable to low-powered and self-powered electronic devices, such as motor starters and circuit breakers, without increasing complexity or cost.
Implementation Method 1
A Resistor-Capacitor (RC) circuit and a controller are provided. The controller is configured to supply a first voltage to the RC circuit to produce a charging current to charge the capacitor of the RC circuit
Data Source
AI summary
A contact wetting circuit 100 is disclosed for supplying wetting current to sense the state of dry contacts of a switch SW1 setting for an electronic device 10. The contact wetting circuit includes an RC circuit 110 having a resistor R1 and a capacitor C1, and a controller 120 connected to a power supply 130 of the device. The controller supplies a first voltage to the RC circuit to produce a charging current having an average current and/or a peak current below the wetting current parameter of the dry contacts. The charging current is used to charge the capacitor C1 during the first time period. The controller stops the supply of the first voltage to the RC circuit after sufficient charging to allow the charged capacitor C1 to supply a second voltage, across the switch SW1, to produce a wetting current. Thereafter, the controller polls and senses the state of the switch SW1, and performs certain operations accordingly.