Motor Start Circuit Reducing Switch Wear via Delayed Capacitor Charging
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Solution Overview
Problem
Circuits for starting up electric motors in hand-held devices face high electrical switching loads when the device is switched on after a long period of non-use, leading to rapid wear of mechanical operating switches due to high charging currents and contact chatter.
Innovation Solution
An electronic switch is placed in series with a capacitor in the parallel branch, with its operation delayed via a control circuit after the main switch is closed, allowing a gradual application of supply voltage to reduce the abrupt current load on the operating switch, and disconnecting the capacitor when battery voltage falls below a critical limit to prevent leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a capacitor is arranged in parallel to the electric motor or battery pack to cover temporarily increased power requirements, then the power supply capability is improved, but the electrical switching load on the operating switch increases due to high charging current
Solution Approach 1:
The capacitor is pre-charged through the electronic switch before the operating switch needs to handle full load. The control circuit charges the capacitor in advance when the motor is stationary or under light load, so that when high power is needed, the capacitor can immediately discharge to supplement the battery, reducing the peak current through the operating switch.
Solution Approach 2:
The electronic switch acts as an intermediary between the capacitor and the main circuit. It controls the charging and discharging of the capacitor, allowing the capacitor to provide power support during high-demand periods without subjecting the mechanical operating switch to excessive current stress and contact bounce.
2Power
If the capacitor is charged immediately when the operating switch is closed, then the power requirement is met, but contact chatter and wear increase due to high charging current
Solution Approach 1:
The capacitor is charged in advance during periods when the motor is running at normal speed or stationary, before the high-power demand occurs. This preliminary charging action ensures that when the operating switch is activated, the capacitor is already ready to provide current, avoiding the need for immediate high-current charging that causes contact bounce.
Solution Approach 2:
The control circuit periodically monitors the capacitor charge state and the motor operating conditions, charging the capacitor in periodic cycles during normal operation rather than attempting to charge it continuously or only at switch-on moments. This periodic charging approach maintains optimal capacitor charge levels without creating harmful current spikes.
3Ease of operation
If a mechanical operating switch is used to control the electric motor, then the device is simple to operate, but the switch wears out quickly due to electrical switching load and contact chatter
Solution Approach 1:
The electronic switch serves as an intermediary device between the user's simple mechanical switch operation and the complex electrical circuitry. It transparently manages the capacitor charging/discharging operations without requiring additional user input, thus maintaining ease of operation while extending switch lifespan by eliminating harmful current spikes.
Solution Approach 2:
The patent replaces the function of directly controlling high current through the mechanical switch with an electronic switching system. The mechanical switch continues to provide simple user input, but the actual high-power switching is performed by electronic components that are not subject to contact wear, effectively substituting the mechanical switching function for electronic switching.
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 design significantly reduces the electrical switching load on the operating switch, enabling over 50,000 switching operations without damage and preventing contact bouncing, while allowing the use of inexpensive capacitors with high leakage currents.
Implementation Method 1
a capacitor (14) which provides a portion of the motor current in special operating cases
Implementation Method 2
The electronic switch (15) has a control terminal (17) via which the electronic switch can be switched between a blocked position and a fully conductive position
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The circuit (7) has a ring main system (11) provided with an electromotor (2), and parallel branches comprising an electronic switch (15) lying in series to a capacitor (14) i.e. electrolytic capacitor. A series circuit (16) is provided with the capacitor, and the electronic switch comprises two ends (16a, 16b). The ends form a single electrical power connection of the capacitor to the main system. The electronic switch applies power supply voltage provided by a rechargeable battery pack (3) to the capacitor after closing an operation switch (4) and expiration of time period. The operation switch is designed as a mechanical on- or off switch (10). The electronic switch is designed as a power transistor i.e. MOSFET (19).