PTC and Bi-Stable Relay Thermal Protection Circuit
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Solution Overview
Problem
Transportation vehicles face thermal hazards due to overheating from excessive current loads, which can lead to vehicle fires, as the existing thermal breakers' 'time over current' operation masks the deleterious effects of added electrical accessories, often resulting in wiring or component overheating before the main breaker trips.
Innovation Solution
A thermal hazard protection circuit comprising an interruptible power circuit with a Positive Temperature Coefficient (PTC) component and a bi-stable relay, connected in series, and a failsafe circuit with a relay that permanently interrupts current flow under overcurrent conditions, using a PTC component to limit current and a bi-stable relay to open the circuit, ensuring safe operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thermal breaker with time over current operation is used, then the breaker allows temporary current exceedance without tripping, but this masks the deleterious effects of added loads and allows wiring overheating before tripping
Solution Approach 1:
A PTC (Positive Temperature Coefficient) component is introduced as an intermediary element between the power source and the load. This PTC component monitors current flow and automatically increases its resistance when excessive current causes temperature rise, thereby limiting current before the thermal breaker trips and preventing wiring overheating.
Solution Approach 2:
The PTC component performs preliminary protection by responding to overcurrent conditions before the thermal breaker's time-delayed tripping mechanism activates. The PTC's rapid resistance increase at elevated temperatures provides immediate current limitation, preventing the harmful overheating that would otherwise occur during the breaker's delay period.
2Adaptability or versatility
If accessories are added to transportation vehicles, then functionality is improved, but the electrical bus may overheat due to exceeded current draw
Solution Approach 1:
The PTC component provides automatic feedback control by continuously monitoring its own temperature and the current flow through it. When temperature rises due to excessive current from added accessories, the PTC's resistance increases, automatically reducing current flow and preventing electrical bus overheating without requiring manual intervention or complex control systems.
3Duration of action of stationary object
If the main breaker is designed to never trip at the design point, then normal operation is maintained, but it will trip based on time over current which allows overheating to occur
Solution Approach 1:
The patent replaces the purely mechanical/time-delayed thermal breaker response with a thermally-sensitive electrical component (PTC). Instead of relying on the mechanical tripping mechanism that operates on a time-overcurrent curve, the PTC component uses the electrical property of positive temperature coefficient to automatically limit current based on real-time temperature conditions, providing more immediate and precise thermal hazard protection.
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 prevents thermal overload and potential fires by immediately interrupting current flow when excessive heat is generated, providing permanent isolation of the load and visual indicators for safe or hazardous conditions, thus protecting the vehicle's electrical system.
Implementation Method 1
The interruptible power circuit comprises a Positive Temperature Coefficient (PTC) component in series with bi-stable relay configured as a SPST switch
Implementation Method 2
a bi-stable relay connected in series with the first PTC component and operative to selectively open or close the interruptible power circuit
Implementation Method 3
The failsafe circuit comprises a failsafe relay energized by current in the interruptible power circuit
Data Source
AI summary
A thermal hazard protection circuit for a transportation vehicle comprises an interruptible power circuit connected between a power source and load, and a failsafe circuit operative to permanently interrupt current flow under an overcurrent condition. The interruptible power circuit comprises a Positive Temperature Coefficient (PTC) component in series with bi-stable relay configured as a SPST switch. The failsafe circuit comprises a failsafe relay energized by current in the interruptible power circuit. An input of the failsafe relay is connected to the power source, and a normally closed (NC) output (not connected to the input so long as the failsafe relay is energized) is connected to a control input of the bi-stable relay that opens the SPST switch. In an overcurrent condition, the PTC component limits current flow, switching the failsafe relay input to its NC outputs, providing a control signal to open the SPST switch, rendering the interruptible power circuit non-conductive and isolating the load.