Electronic Overload Relay Thermal Memory Using Capacitor Discharge
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Solution Overview
Problem
Existing motor overload relays face challenges in maintaining accurate thermal memory during motor stops due to limited power budget and additional circuitry requirements, failing to adequately account for motor heat dissipation and cooling.
Innovation Solution
An electronic overload relay system utilizing a microcontroller with volatile memory and a power supply capacitor to maintain and adjust the motor thermal model based on capacitor voltage changes, eliminating the need for nonvolatile memory and additional circuitry by estimating motor stop duration through voltage changes and discharge rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If nonvolatile memory is used to maintain thermal model during motor stop, then thermal memory duration is improved, but device complexity and cost increase
Solution Approach 1:
The patent creates a copy of the thermal model data in volatile memory that can be maintained during unpowered states by storing the thermal state information and using capacitor discharge characteristics to preserve this information without requiring nonvolatile memory components
Solution Approach 2:
The patent uses volatile memory with capacitor-based power storage instead of expensive nonvolatile memory, accepting that the memory is temporary but sufficient for the application's thermal memory requirements, thereby reducing device complexity and cost
2Reliability
If additional circuitry is added to maintain thermal model during unpowered state, then thermal memory reliability is improved, but device complexity increases
Solution Approach 1:
The patent makes the existing capacitor serve multiple functions: its primary power storage function plus an additional function of maintaining thermal model data during unpowered states, eliminating the need for separate dedicated circuitry and reducing overall device complexity
Solution Approach 2:
The system uses its own existing components (capacitor and volatile memory) to maintain thermal memory functionality during unpowered states, rather than requiring external or additional specialized components, thereby maintaining reliability without increasing complexity
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 solution provides a low-cost, efficient implementation of nonvolatile thermal memory that accurately accounts for motor heat dissipation and cooling, reducing component costs and complexity while maintaining reliable overload protection.
Implementation Method 1
a power supply having a bulk storage capacitor. In response to a trip or stop condition of a protected motor, the thermal model is maintained in the RAM by energy stored in the bulk storage capacitor
Implementation Method 2
When the motor restarts, the microcontroller uses an algorithm to calculate a change in capacitor voltage to estimate the motor stop duration
Data Source
AI summary
An electronic overload relay includes a microcontroller having an internal random-access memory (RAM) in which a motor thermal model is stored. The microcontroller is coupled to a power supply having a bulk storage capacitor. In response to a trip or stop condition of a protected motor, the thermal model is maintained in the RAM with no timing or decrementing. When the motor restarts, the microcontroller calculates a change in capacitor voltage to estimate the motor stop duration. The thermal model is decremented based on the estimated duration.