Switching Element Cooling in Cordless Power Tool Battery Packs
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lithium battery cells in cordless power tools are prone to degradation due to overheating caused by high current flows, leading to motor locking and potential electrical short circuits, which reduces their service life and increases the weight of the power tool.
Innovation Solution
A cordless power tool design featuring a battery pack with a switching element positioned at an air flow passage, utilizing a fan for heat dissipation and a protection circuit to control the switching element's operation, preventing excessive discharging and current flow, thus avoiding overheating and degradation of lithium battery cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a switching element (FET) is disposed at the current path to protect against excessive discharging and current flow, then battery protection is improved, but heat generation in the switching element occurs due to high current levels
Solution Approach 1:
The switching element is extracted from the battery pack and disposed outside it, separating the protection function from the battery assembly. This allows the switching element to be positioned in a location with better heat dissipation conditions while maintaining its protection function
Solution Approach 2:
A heat dissipation structure is introduced as an intermediary between the switching element and the environment, facilitating heat transfer from the switching element to the surrounding air or cooling medium, thereby reducing the switching element's operating temperature
2Weight of moving object
If lithium battery cells are used to reduce the number of cells and compact the tool, then size and weight are reduced, but degradation occurs due to excessive charging/discharging and current flow
Solution Approach 1:
The protection circuit performs preliminary detection of charging/discharging conditions and current levels before excessive conditions occur, and preemptively activates the switching element to prevent degradation of the lithium battery cells
Solution Approach 2:
The protection circuit continuously monitors battery status and provides feedback control to the switching element, adjusting its operation based on real-time conditions to prevent excessive charging/discharging and current flow that would degrade the battery cells
3Reliability
If the switching element is positioned inside the battery pack for protection, then battery protection is achieved, but heat dissipation becomes difficult due to limited air flow
Solution Approach 1:
The switching element is extracted from the battery pack and disposed in the power tool's housing space, utilizing the existing air flow paths and heat dissipation structures of the power tool to cool the switching element without adding complex dedicated cooling systems to the battery pack
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 solution effectively prevents overheating of the switching element and reduces the risk of lithium battery cell degradation, enhancing the handling ability and compactness of the power tool by maintaining the battery cells' performance and prolonging their cyclic life.
Implementation Method 1
An air flow is produced in the air passage upon rotation of the fan. The switching element is connected between the at least one rechargeable battery cell and the DC motor and is positioned at the air passage.
Data Source
AI summary
A compact battery pack with high handling ability and restraining degradation of battery cells. The battery pack includes an insertion portion to be inserted into a handle portion of a cordless power tool and an accommodation portion in which all battery cells are accommodatable. A protection board with a protection circuit that protects batteries against overcharge and over-discharge is installed in the insertion portion. A switching element is connected between the battery cells and a drive motor of the power tool. An air passage in communication with the battery pack is formed within the handle and a main housing of the cordless power tool. The switching element is positioned at the air passage.