Battery Voltage Control for Cordless Power Tools
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Solution Overview
Problem
Battery-driven electric tools experience frequent interruptions due to undervoltage lockout, especially in low temperatures, leading to inefficient use and potential battery damage, as the battery voltage drops below the monitoring limit during load peaks and temperature changes, causing erratic shut-offs and deep discharge risks.
Innovation Solution
A mains-independently operated electric tool with a monitoring device and adjustable resistor component using pulse width modulation (PWM) to set operation-values, ensuring the battery voltage remains above the monitoring limit by selecting a lower PWM duty cycle if it rises above, and adjusting the operation-value limit based on temperature to prevent rapid drops and maintain tool functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If undervoltage lockout is implemented to protect battery and control electronics, then battery damage and system malfunction are prevented, but tool usage is frequently interrupted especially at low temperatures
Solution Approach 1:
The patent implements dynamic adjustment of the monitoring operation-value limit based on temperature conditions. At low temperatures, the limit is raised above the battery's operation-value limit to account for increased internal resistance and voltage drop under load, preventing false undervoltage lockouts while maintaining protection at normal temperatures
Solution Approach 2:
The monitoring operation-value limit parameter is changed based on temperature conditions. The system transitions from a fixed voltage threshold to a dynamic threshold that adapts to environmental conditions, specifically raising the limit at low temperatures to prevent premature shut-off while maintaining battery protection
2Reliability
If monitoring operation-value limit is set above battery operation-value limit to prevent deep discharge, then battery protection is improved, but tool shuts off prematurely during temporary load peaks
Solution Approach 1:
The system dynamically adjusts the monitoring limit based on temperature rather than using a fixed threshold. This dynamic approach allows the system to distinguish between temporary voltage drops during load peaks and actual undervoltage conditions, maintaining tool availability while protecting the battery
Solution Approach 2:
The system performs preliminary temperature-based adjustment of the monitoring limit before undervoltage lockout is triggered. By pre-adjusting the threshold based on temperature conditions, the system prevents false shut-offs during temporary load peaks while maintaining protection against actual undervoltage conditions
3Power
If PWM duty cycle is increased to meet load demand, then power output is improved, but battery voltage drops below monitoring limit causing shut-off
Solution Approach 1:
The system changes the monitoring operation-value limit parameter based on temperature conditions. At low temperatures, the raised limit accounts for the voltage drop that occurs during high power demand, allowing the PWM duty cycle to be increased to meet load requirements without triggering false undervoltage shut-offs
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
Prevents unnecessary shut-offs and allows continuous use of the electric tool by maintaining battery voltage above the monitoring limit, reducing the risk of deep discharge and damage, while optimizing performance across varying temperatures.
Implementation Method 1
an operation-value controller for setting at least one of the operation-values present at the electrical motor by means of pulse width modulation (PWM)
Data Source
AI summary
An electric tool is disclosed. The tool includes an electric motor, a battery, a monitoring device for monitoring a monitoring operation-value limit, where the monitoring operation-value limit lies above an operation-value limit of the battery, an adjustable resistor component, and an operation-value controller for setting at least one operation-value of the electric motor by a pulse width modulation (PWM) duty cycle. The PWM duty cycle is a first value that is derivable from a current setting of the adjustable resistor component or a second value that corresponds to a PWM duty cycle last used for setting the at least one operation-value plus an offset value. A lower of the first value or the second value is selected for the PWM duty cycle, if an operation-value of the battery lies above the monitoring operation-value limit.