Outdoor Unit Relay Circuit for DC Motor Overheat Cutoff
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Solution Overview
Problem
Conventional temperature protection systems for DC motors fail to prevent current flow when a motor driving element is short-circuited, even after shutting down the power supply, due to potential voltage application that can still allow current to flow to the motor.
Innovation Solution
An air conditioner design incorporating a first relay with a PTC thermistor and a temperature protector on the relay-driving power supply, which switches the AC current path and disconnects the power supply when a temperature abnormality is detected, 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 the power supply of the motor driving element is shut down to stop the motor, then the motor is protected from overheating, but current can still flow to the motor if the motor driving element is short-circuited and a power supply voltage is applied
Solution Approach 1:
The power supply system is segmented into two independent parts: the motor driving element power supply and the relay-driving power supply. The temperature protector is placed on the relay-driving power supply line to control the first relay, which in turn controls the motor driving element power supply. This segmentation ensures that even if the motor driving element is short-circuited, the relay-driving power supply can independently cut off power through the temperature protector, preventing harmful current flow to the motor.
Solution Approach 2:
The first relay acts as an intermediary between the relay-driving power supply and the motor driving element power supply. The temperature protector controls the relay coil, which through its contact part either connects or disconnects the power supply to the motor driving element. This intermediary mechanism ensures that the temperature protector can indirectly control the motor power supply without being directly connected to it, providing reliable protection even in case of short-circuits in the motor driving element.
2Reliability
If a temperature protector is attached to the DC motor to shut down power supply when temperature reaches predetermined level, then the motor is protected from temperature abnormalities, but the system complexity increases with additional components
Solution Approach 1:
The first relay serves as an intermediary that amplifies the protection function. The temperature protector only needs to control the low-power relay coil, rather than directly switching the high-power motor supply. This intermediary approach simplifies the temperature protector's requirements and integrates smoothly into the existing relay-controlled motor driving system, minimizing additional complexity while maintaining reliable temperature protection.
3Ease of operation
If the first contact part is placed in electrically-disconnected state when no current flows through the first coil part, then the relay provides normal switching function, but a current path can still be formed if the contact part is short-circuited
Solution Approach 1:
The power supply control is segmented into two independent circuits: the relay-driving power supply circuit (controlled by temperature protector) and the motor driving element circuit (controlled by relay contact). By placing the temperature protector on the relay-driving power supply line, the invention ensures that even if the relay contact part is short-circuited, the temperature protector can cut off the relay-driving power supply, preventing current from flowing through the short-circuited path to the motor.
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, ensuring safe operation and preventing potential damage from short-circuits, while allowing for efficient operation and downsizing of temperature protection components.
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 that is a power supply of the first relay and provided to the motor, 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 provided on a supply line of an alternating current power supply, 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
AI summary
An air conditioner includes an indoor unit and an outdoor unit. The outdoor unit includes: a DC motor; an inrush-current prevention relay having a coil and a contact provided on a supply line of an AC power supply as a power supply of the outdoor unit, in which the contact is in an electrically-disconnected state when any current does not flow through the coil and is in an electrically-connected state when a current flows through the coil; a PTC connected in parallel to the contact; and a temperature protector provided on a supply line of a relay-driving power supply as a power supply of the inrush-current prevention relay, which is in an electrically-connected state when a temperature of the DC motor is lower than a predetermined temperature, but is in an electrically-disconnected state when the temperature of the DC motor reaches a predetermined temperature or higher.