Multi-Battery Pack Controller for Power Tools
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Solution Overview
Problem
Parallel-connected battery packs in power tools face issues such as cross-charging, permanent damage due to uneven state of charge or capacity, and overheating, which can lead to hazardous conditions and reduced tool performance.
Innovation Solution
A power tool system with a controller that manages multiple battery packs by using pulse-width modulation (PWM) signals to selectively connect and disconnect battery packs based on their state of charge, preventing cross-charging and ensuring balanced discharge, and incorporating a soft start mechanism to reduce startup stress on the motor and battery packs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple battery packs are connected in parallel to increase capacity, then the battery system capacity (ampere-hours) increases, but cross-charging occurs when battery voltages are not approximately equal
Solution Approach 1:
A controller is introduced as an intermediary device between the parallel-connected battery packs. The controller monitors the voltage of each battery pack and uses switching elements (MOSFETs or relays) to selectively connect or disconnect individual battery packs based on their state of charge, preventing cross-charging while maintaining the ability to operate with multiple packs in parallel when conditions are appropriate.
Solution Approach 2:
The system dynamically adjusts the connection state of each battery pack based on real-time voltage monitoring. The controller continuously evaluates the voltage of each pack and modifies the circuit configuration accordingly, transitioning between parallel connection modes and isolated connection modes to optimize both capacity utilization and safety.
2Quantity of substance
If multiple battery packs are connected in parallel, then the battery system capacity increases, but one battery pack may become fully discharged before others causing permanent damage
Solution Approach 1:
The controller implements feedback control by continuously monitoring the voltage of each battery pack and using this information to control the switching elements. When a battery pack approaches full discharge (voltage threshold), the controller automatically disconnects that pack from the parallel configuration, preventing over-discharge damage while allowing other packs to continue supplying power.
3Quantity of substance
If multiple battery packs are connected in parallel, then the battery system capacity increases, but overheating may occur causing permanent damage
Solution Approach 1:
The controller acts as an intermediary that monitors temperature conditions and adjusts the operational status of each battery pack accordingly. When overheating is detected in any pack, the controller disconnects that specific pack from the parallel configuration, preventing thermal damage while maintaining system operation with the remaining packs.
4Adaptability or versatility
If battery packs with unequal capacity sizes are connected in parallel, then the battery system can accommodate different pack sizes, but cross-charging occurs
Solution Approach 1:
The controller provides intelligent mediation between battery packs of different capacities. By monitoring individual pack voltages and using switching elements to selectively connect or disconnect packs, the controller prevents cross-charging between packs of unequal capacity while still allowing the system to accept various pack configurations.
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
The system effectively prevents cross-charging and ensures balanced discharge of battery packs, extending their lifespan and maintaining consistent tool performance by managing battery state and reducing mechanical and electrical stress during startup.
Implementation Method 1
The controller includes a first pulse-width modulation (PWM) output coupled to the first switching element and a first PWM signal to selectively close the first switching element. The controller further includes a second PWM output coupled to the second switching element and a second PWM signal to selectively close the second switching element.
Data Source
AI summary
A power tool including a motor, a first battery pack, a second battery pack, a first switching element coupled between the first battery pack and the motor, a second switching element coupled between the second battery pack and the motor, and controller coupled to the first switching element and the second switching element. The controller includes a first pulse-width modulation (PWM) output coupled to the first switching element and a first PWM signal to selectively close the first switching element. The controller further includes a second PWM output coupled to the second switching element and a second PWM signal to selectively close the second switching element.