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Fractal Battery Charging by Dynamic Change of Battery Voltage Target

IP.com Disclosure Number: IPCOM000012292D
Original Publication Date: 2003-Apr-25
Included in the Prior Art Database: 2003-Apr-25
Document File: 4 page(s) / 73K

Publishing Venue

Motorola

Related People

Daryoush Rahmanzadeh: AUTHOR

Abstract

This method optimizes the overall lithium battery performance by optimizing the charging algorithm. The main target is to extend the lifecycle of lithium batteries in mobile subscriber terminals.

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Fractal Battery Charging by Dynamic Change of Battery Voltage Target

by Daryoush Rahmanzadeh

Abstract

This method optimizes the overall lithium battery performance by optimizing the charging algorithm. The main target is to extend the lifecycle of lithium batteries in mobile subscriber terminals.

Introduction

This paper describes improvements in lithium battery charging. Lithium batteries have become standard in many new products. Meanwhile, the quality of the performance of the various types of lithium batteries is not satisfactory.

Problem(s) To Be Solved

The common lithium battery charging method is charging with a constant voltage. When the battery becomes fully charged, maintenance charging (Trickle or Float) takes over. Low voltage charging is used at high temperatures. The critical point is when the charging voltage exceeds Vmax and the internal resistance of the battery increases (battery cell temperature increases too) causing the battery characteristics to deteriorate. Long exposure to charging at Vmax and/or charging at high temperature may cause the battery to leak or corrode. Normally, lithium battery is charged at constant voltage and current until battery becomes full. Charging will terminate when the timeout timer expires or maximum temperature limit is passed. The problem is that the battery heats up, because after short charging time battery voltage stays at the maximum battery voltage. This high battery temperature damages the battery cells.

Proposed Solution to the Problem(s)

This method gives the battery a longer cycle life and reduces the heat generation under charging. The novel feature of the method is that the charging process is comprised of a series of charging events, allowing the battery to gradually reach maximum charging voltage, Vmax. In the intervening relax periods (low current periods) the chemical processes taking place internally in the battery are allowed to reach equilibrium thereby avoiding increase in the internal battery resistance. The charging procedure is described in the following.

Figures

Icharger:                 � � � � � � � � � � � � � Charger current.

Vbatt :                � � � � � � � � � � � � � � � Battery voltage.

Vmax :                � � � � � � � � � � � � � � Maximum voltage for charging the battery as recommended by the supplier.

Vlow :                � � � � � � � � � � � � � � � Minimum battery voltage limit as defined by battery supplier.

Vmax low :        � � � � � � � � � � Safe maximum battery voltage. This value is determined experimentally, and depends on battery capacity (e.g. 600 mAh, 1200 mAh) and supplier (e.g. Sony, Sanyo). It must be below Vmax and if the battery is constantly charged at this voltage the battery temperature must not increase.

Vx :                � � � � � � � � � � � � � � � � � Difference between Vmax and V max low.

Rindicator :        � � � � � � � � � � Resistance which indicates the battery capacity. Normally placed inside the battery pack.

Tbat :                � � � � � � � � � � � � � � � � Present temperature of the battery.

Tmin :                � � � � � � �...