Thermal Protector Terminal Member Dynamics for PTC Hot Spot Elimination
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Solution Overview
Problem
Conventional thermal protectors using polymer PTC elements can experience hot spots due to restricted volume expansion during thermal expansion, leading to ineffective current disruption and self-holding functionality.
Innovation Solution
The design incorporates a polymer PTC element with terminal members that allow fluctuation with thermal expansion, preventing hot spots by maintaining the degree of freedom of volume expansion and ensuring efficient heat conduction to a bimetallic element for self-holding functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polymer PTC element is used as an embedded resistive element, then current disruption function is improved, but hot spots occur due to restricted volume expansion
Solution Approach 1:
The terminal member is designed to be movable relative to the PTC element, allowing the connection position to dynamically adjust as the PTC element expands thermally. This dynamic adjustment prevents restriction of volume expansion and eliminates hot spots while maintaining current disruption functionality.
Solution Approach 2:
The terminal member acts as an intermediary between the PTC element and the external circuit. It provides a flexible connection that accommodates thermal expansion of the PTC element while maintaining electrical connectivity, thereby preventing hot spots without compromising the current disruption function.
2Stability of the object's composition
If terminal members are fixed rigidly to PTC element, then connection stability is improved, but volume expansion is hindered causing hot spots
Solution Approach 1:
The terminal member transitions from a static fixed connection to a dynamic movable connection. It can shift its position along the PTC element surface, providing both stability during normal operation and flexibility during thermal expansion to prevent hot spots.
Solution Approach 2:
The connection parameters between terminal member and PTC element are designed to change with temperature. The terminal member maintains stable electrical contact at operating temperatures but allows positional adjustment during thermal expansion, resolving the contradiction between connection stability and expansion freedom.
3Reliability
If polymer PTC element is used instead of ceramic PTC element, then resistance is reduced for low voltage circuits, but volume expansion restriction causes hot spots
Solution Approach 1:
The movable terminal member design specifically addresses the greater thermal expansion characteristics of polymer PTC elements compared to ceramic PTC elements. This dynamic connection allows the polymer material to expand freely during thermal events while maintaining reliable electrical connection for low voltage circuit applications.
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
This configuration stabilizes current disruption and self-holding functions even with polymer PTC elements, preventing hot spots and ensuring effective thermal protection.
Implementation Method 1
a conductive path via conductive particles dispersed in a polymer is disconnected by a volume expansion caused by a thermal expansion in the vicinity of the melting point of the polymer due to an increase in a temperature
Implementation Method 2
a conductive path via conductive particles dispersed in a polymer is disconnected by a volume expansion caused by a thermal expansion in the vicinity of the melting point of the polymer
Implementation Method 3
a bimetallic element which inversely warps at a predetermined temperature
Implementation Method 4
performing self-holding with heat produced by an embedded resistive element
Data Source
AI summary
A self-hold type thermal protector according to the present invention includes a movable contact of a movable plate rises and separates from a fixed contact when a bimetal of the thermal protector inversely warps at a predetermined temperature, an electric current between the contacts, namely, an electric current between a movable contact side terminal and a fixed contact side terminal is disrupted, and the disrupted current flows into the polymer PTC element, which is then made to produce heat and is thermally expanded to increase a resistance value. A second terminal member on a side opposite to a first terminal member where the polymer PTC element is positioned and fixed forms a bowing part, and a gap h is formed between an upper inner wall of a housing and the upper surface of the second terminal member.