Lead-Acid Battery Strap Design for Overcurrent Protection

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Solution Overview

Problem

Lead-acid batteries are prone to short circuits when a large current exceeds expected levels, causing the strap to melt and potentially rendering the battery unusable due to molten material coming into contact with internal elements.

Innovation Solution

The battery design includes straps with a tab portion positioned orthogonal to the base portion, featuring a larger second cross-sectional area than the inter cell connection portion, which reduces the likelihood of tab portion melting and subsequent short circuits by directing molten lead away from internal elements, and incorporates an inclined portion to facilitate molten lead flow during molding.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the strap has a uniform cross-sectional area, then the manufacturing is simple, but the strap may melt during high current flow causing short circuit

Engineering Contradiction:

Improveresistance to melting during high current flowVSAvoidstrap structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The strap is designed with different cross-sectional areas in different regions: the tab portion has a larger cross-sectional area than the inter-cell connection portion. This local variation in geometry provides enhanced thermal mass and current carrying capacity where needed (at the tab portion near the elements) while maintaining simpler geometry elsewhere, thereby preventing melting during high current flow without excessive overall complexity

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The cross-sectional area parameter of the strap is changed along its length, with the tab portion having a larger area than the inter-cell connection portion. This parameter variation allows the strap to withstand high current loads at critical locations while maintaining manufacturing feasibility and appropriate electrical connection at other locations

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the strap melts during high current flow, then the current can be redirected, but molten strap may drip onto elements causing short circuit

Engineering Contradiction:

Improveprotection against short circuitVSAvoidmolten strap dripping onto elements

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The strap design intentionally allows the tab portion to melt during extreme overcurrent conditions, but the larger cross-sectional area and positioning of the tab portion ensures that molten material is contained and redirected away from the elements. The harm of melting is converted into a protective mechanism that sacrifices the strap rather than allowing element damage

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The tab portion acts as an intermediary sacrificial element between the external circuit and the internal battery elements. During overcurrent events, the tab portion melts first due to its larger thermal mass, serving as a buffer that prevents direct contact between molten strap material and the elements, thereby protecting the battery from short circuits

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of manufacture

If the tab portion is positioned in the second direction, then the connection is simplified, but the molten lead flow direction cannot be controlled

Engineering Contradiction:

Improvestrap connection simplicityVSAvoidmolten lead flow control

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The strap is designed with asymmetric geometry where the tab portion extends in the third direction (orthogonal to both the first direction of plate layering and the second direction of lug connection). This asymmetric positioning, combined with the larger cross-sectional area of the tab portion, creates a preferred path for molten lead flow that directs it away from the elements while maintaining simple connection geometry

Inventive Principle:

Principle #4Asymmetry

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 configuration minimizes the risk of short circuits during high current flows, maintaining battery functionality and improving productivity by preventing release failures during manufacturing.

Implementation Method 1

when a large current overwhelming the expected level flows in the lead-acid battery, a part of the strap may melt due to heat

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

incorporates an inclined portion to facilitate molten lead flow during molding

Methodology Applied

Scientific EffectGravity: Gravitation

Data Source

PatentEP3869582B1Lead storage battery

Publication Date: 2022.12.14 GS YUASA INT LTD

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AI summary

A lead-acid battery (100) includes a strap (20) including a base portion (21) including a connection region (22a), a tab portion (30), and an inter cell connection portion (40). A second cross-sectional area is larger than a first cross-sectional area, where the first cross-sectional area is a minimum cross-sectional area of the inter cell connection portion (40) in a plane orthogonal to a first direction (D1), and the second cross sectional area is a minimum cross-sectional area of the strap (20) in a plane (P) dividing the strap (20) into one side corresponding to the connection region (22a) and another side corresponding to the inter cell connection portion (40).