05_li-ion battery capacity detection

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Li-ion Battery CapacityDetection

Author: Arul Prabahar A.

ASCNT 2012



• Project Titled “ Design and Development of

low cost real-time monitoring system forharmful gas detection” funded by Department

of Information and Technology (DIT).

ASCNT 2012

Introduction



• Rechargeable batteries

• Fuel gauge IC

•

BQ27510• Focus on steps involved in capacity detection using TI’s

Impedance Track Algorithm

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Li ion Battery



Presentation Flow

• Basic aspects of capacity detection

• Steps involved in single cell capacity detection

• Multi cell capacity detection

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Capacity detection• Capacity: The battery capacity represents the maximum

amount of energy that can be extracted from the battery(Ah, Wh)

•

Importance of determining Remaining Capacity• Rechargeable batteries

• Strong Correlation between the battery open circuitvoltage and residual capacity- Temperature dependence

• More reliable when load current is low

• Discharge curve for known load current- low accuracy

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Capacity detection contd.

• Discharge curve is affected by battery chemistry,ageing, anode used ,temperature and loadcurrent

• Fuel Gauge chips-Capture parameters, Algorithms

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Battery Under Test

• Li ion battery with capacity approximately

1500mAh – Discharge curve method• Use of Fuel gauge

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Steps Involved

• Step 1 Chemistry Cycle

•

Step 2 Learning CycleTools Used

• BQEasy TI Tool for data capture

• Math Cad - mapping



• Battery Chemistry

• TI Data Base

•

ADCs Calibration• “rel-dis-rel” cycle – o/p log file from BQEasy

• Mathcad Tool – Matches with TI database

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Step 1-Chemistry cycle



• load current

• battery voltage

•

time elapsed• time stamp

• temperature

• different flag status

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Chemistry cycle



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Voltage vs Time plot of logged data



Step 2: Battery learning cycle• The Chemistry information as input

• Learn the battery capacity and impedance of the

battery at different stages• Generate Image using BQEasy tool

• This image can be used to program any BQ27510chipset to determine the capacity of a given Li-Ion

battery model

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• I2C interface

• O/P Remaining time, Current drawn, Battery

voltage , SOC etc.

• Battery Capacity – 1439mAh @ 2.9V cutoff

Results



Multi cell in series Application

• Assumption - all the multi-cells are made of

identical cells with same characteristics• Multi-cell treated as single cell

• High precision voltage divider

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Battery Under Test

• Li ion battery with capacity approximately

11.1V , 6600mAh (3 cell series 3 cell parallel)• Voltage divider (1:3 ratio) compensate for 3

cell series

•

3 cell parallel handled in learning curve



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Voltage vs Time plot



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• Battery Capacity – 6461mAh @ 9V cutoff

Results



Hardware Implementation

• Battery good flag to enable power regulators

• Kelvin connection for the current sense

•

LDO (3V) to supply power to fuel gauge

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Conclusion

• Developed a technique to use TI’s BQ27510

Single cell System side Fuel gauge IC for multi

cell applications.

• Future work – Temperature compensation to

increase the accuracy

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Thank You

ASCNT 2012

05_li-ion battery capacity detection

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