DC Motor Relay Cutoff for Air Conditioner Overheat Protection
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Solution Overview
Problem
Conventional temperature protection systems for DC motors do not effectively prevent current flow to the motor when a motor driving element is short-circuited, even after shutting down the power supply, due to potential residual current paths.
Innovation Solution
An air conditioner design incorporating a first relay with a PTC thermistor and a temperature protector on the relay-driving power supply line, which disconnects the power supply when the motor temperature exceeds a predetermined level, ensuring no current flows to the motor even if the motor driving element is short-circuited.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a temperature protector shuts down the power supply of a motor driving element when motor temperature reaches a predetermined level, then the motor is protected from overheating, but current can still flow to the motor if the motor driving element is short-circuited
Solution Approach 1:
The patent extracts the harmful residual current path by introducing a temperature protector that physically disconnects the power supply line from the motor driving element. When the motor temperature reaches the predetermined level, the temperature protector opens its contact, effectively removing the power supply connection and eliminating the possibility of current flowing to the motor even if the motor driving element is short-circuited.
Solution Approach 2:
The temperature protector is positioned upstream in the power supply circuit, before the motor driving element. It performs preliminary protection by disconnecting the power supply at the source level before any current can reach the motor driving element. This preliminary disconnection prevents the harmful effect of residual current flow before it can occur.
2Temperature
If the power supply of a motor driving element is shut down to stop motor operation, then motor overheating is prevented, but other functions remain operable and current paths may still exist
Solution Approach 1:
The patent segments the power supply system into two independent parts: the main power supply to the motor driving element (controlled by the temperature protector) and the relay-driving power supply (remains operational). This segmentation allows the motor protection function to operate independently without affecting other system functions, maintaining operational flexibility while ensuring motor temperature control.
3Reliability
If a temperature protector is added to the relay-driving power supply line, then current flow to the motor is completely prevented during temperature abnormalities, but device complexity increases
Solution Approach 1:
The temperature protector acts as an intermediary device between the relay-driving power supply and the motor driving element. It mediates the power flow by automatically opening its contact when the motor temperature reaches the predetermined level, thereby preventing current from reaching the motor driving element. This intermediary mechanism provides simple yet effective protection without requiring complex control circuits or additional sensing components.
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 current flow to the motor during temperature abnormalities caused by abnormal heat generation, ensuring safe operation and preventing potential damage from short-circuits.
Implementation Method 1
a PTC (Positive Temperature Coefficient) connected in parallel to the first contact part
Implementation Method 2
a temperature protector provided on a supply line of a relay-driving power supply... which is in an electrically-connected state when a temperature of the motor is lower than a predetermined temperature, and is placed in an electrically-disconnected state when the temperature of the motor reaches a predetermined temperature or higher
Implementation Method 3
a first relay including a first coil part and a first contact part... in which the first contact part is placed in an electrically-disconnected state when any current does not flow through the first coil part and the first contact part is placed in an electrically-connected state when a current flows through the first coil part
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An air conditioner (110) includes an indoor unit (2) and an outdoor unit (1). The outdoor unit (1) includes: a DC motor (3); an inrush-current prevention relay (18) having a coil part (20a) and a contact part (20b) provided on a supply line (A) of an AC power supply (7) that is a power supply of the outdoor unit (1), in which the contact part (20b) is placed in an electrically-disconnected state when any current does not flow through the coil part (20a) and is placed in an electrically-connected state when a current flows through the coil part (20a); a PTC (19) connected in parallel to the contact part (20b); and a temperature protector (5) provided on a supply line (B) of a relay-driving power supply (21) that is a power supply of the inrush-current prevention relay (18) and provided to the DC motor (3), which is in an electrically-connected state when a temperature of the DC motor (3) is lower than a predetermined temperature, but is in an electrically-disconnected state when the temperature of the DC motor (3) reaches a predetermined temperature or higher.