how many cycles can i expect from my battery?
TRANSCRIPT
DELIVERING QUALITY SINCE 1952.
Why Is It So Difficult To Answer This Simple Question:
“How Many Cycles Can I Expect From My Battery?”
10.14.15Special thanks to our strategic partner Texas Instruments for the
charts and graphs contained in the in this presentation.
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Expected Number of Cycles
There are many factors involved in predicting cycle life of a battery pack.– Chemistry selected/used– Amount of time the battery is exposed to temperature extremes.– Average charge state the battery is in.
• Charge voltage
– High discharge and charge rates (localized internal heating)
– Pack design and construction • High current path routes / cells exposed to same load• Inner cells and thermal management
– Number of series cells and parallel cells• Cell balancing
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Expected Number of Cycles
Chemistry Selected/Used– The core chemistry plays a large role in the cycle life of the battery. There
are always tradeoffs, however.• 20 to 50 cycles, Li-Sulfur• 300 to 500 cycles, Li-Ion • 1000 to 3000 cycles, LiFePO4• 20000 cycles Li-Titanate, Li4Ti5O12
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Expected Number of Cycles
Amount of time the battery is exposed to temperature extremes.
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Expected Number of Cycles
Charge Voltage Affects Battery Service Life– The higher the voltage, the higher the initial capacity– Overcharging shortens battery cycle life
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Expected Number of Cycles
Charge Current versus Battery Degradation– Charge Current:
• Limited to 1C rate to prevent overheating that can accelerate degradation
– Some new cells can handle higher-rate
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Expected Number of Cycles
Pack Design and Construction– High current path routes / cells exposed to same load– Internal Cells and thermal gradients
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Expected Number of Cycles
Series Cells, Full Pack Limited by Cell ImbalanceCell misbalance can cause significant degradation to battery pack performance and cycle life
– When the first cell becomes full, charge must stop– When first cell becomes empty, discharge must stop– Weak cells will age faster than strong cells– Weakest cell ultimately limits pack usable energy (weakest link)– Systematic temperature gradients in the pack weaken cells running at
higher average temperature– Without balancing, at every cycle the voltage difference between the
weakest and strongest cell increases– Eventually one cell will always be near the
maximum voltage and another cell nearthe minimum voltage => can notcharge or discharge pack
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Expected Number of Cycles
Capacitive current redistribution – more complex implementation, no energy loss. Low balancing rate. Moderate size requirements.
Inductive current redistribution – most complex implementation, no energy loss. High balancing rate can be supported. Highest size requirements
Current bypass (Passive) – simplest method, but some energy loss. Both high and low rates can be implemented. Easy to integrate, small size and cost.
Cell Balancing
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In Summary the primary factors that affect cycle life are:– Chemistry selected/used– Amount of time the battery is exposed to
temperature extremes.– Average charge state the battery is in.
• Charge voltage
– High discharge and charge rates (localized internal heating)
– Pack design and construction • High current path routes / cells exposed to
same load• Inner cells and thermal management
– Number of series cells and parallel cells• Cell balancing
Summary
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Our Products
Battery Packs Flex & Rigid-Flex PCB’s User Interfaces
Fans & Motors Cable Assemblies Printed Circuit Boards
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Design Centers & Technical Support
Battery Pack & Power Management – Denver, CO User Interfaces – Largo, FL Fans & Motors – Wales, UK PCB’s – New Bedford, MA & Shenzhen, China Flex & Rigid Flex – Toronto, Canada Cable Assemblies – New Bedford, MA
Our Engineering and Design teams are ready to help our customers create world class and cost effective product solutions.
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Q&A
Questions?– Enter any questions you may have
in the Control Panel
– If we don’t have time to get to it, wewill reply via email
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Thank YouCheck out our previous webinars at www.epectec.com.
For more information email [email protected].
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