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Care and Feeding of Your New Lithium Ion Battery

Rich Carroll Past President, Fox Valley Electric Auto Assoc. Copies of this presentation in .odp, .ppt, and .pdf format can be found at: http://rc.to/NSB. Care and Feeding of Your New Lithium Ion Battery. Lithium Battery Primer. As an overview:

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Care and Feeding of Your New Lithium Ion Battery

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  1. Rich Carroll Past President, Fox Valley Electric Auto Assoc. Copies of this presentation in .odp, .ppt, and .pdf format can be found at: http://rc.to/NSB Care and Feeding of Your New Lithium Ion Battery

  2. Lithium Battery Primer As an overview: • Lithium Batteries are about 4 or 4.2 Volts per cell • In most applications, cells are packaged together into a 'battery' • When cells are wired in series, voltage is additive, so 3 cells of 4 volts in series gives 12 volts • When cells are wired in parallel, amperage is additive, so 3 cells rated at 1500 mAh in parallel would be rated at 4500 mAh Several different Lithium substrates are used: • Lithium ion • Lithium Iron Phosphate • Lithium Iron Yttrium Phosphate • Lithium Iron Cobalt Phosphate • Other “proprietary combinations”

  3. Cycle life as a function ofdepth of discharge A partial discharge reduces stress and prolongs battery life. Elevated temperature and high currents also affect cycle life.1

  4. Cycle life as a function ofdepth of discharge A partial discharge reduces stress and prolongs battery life. Elevated temperature and high currents also affect cycle life.

  5. Estimated recoverable capacity when storing Li-ion for one year at various temperatures Elevated temperature hastens capacity loss. The capacity cannot be restored. Not all Li-ion systems behave the same. 1

  6. Estimated recoverable capacity when storing Li-ion for one year at various temperatures Elevated temperature hastens capacity loss. The capacity cannot be restored. Not all Li-ion systems behave the same.

  7. Discharge cycles and capacityas a function of charge Every 0.1V drop below 4.20V/cell doubles the cycle; the retained capacity drops accordingly. Raising the voltage above 4.20V/cell stresses the battery and compromises safety. Summary: battery life can be extended by not charging to full charge.

  8. Here are some things they won't teach you: Amperage related to acceleration Power (Watts = Amps x Volts) is related to overcoming friction Students won't have a choice of amps or volts, they are pre-selected Torque of an electric motor is high at virtually all speeds, from motor speeds of 2 RPM to over 2000 RPM Speed of a DC motor is directly related to voltage Plan to have the electric motor at top (peak) RPM at or near the end of the track Lithium Batteries in Vehicles

  9. Lithium Ion delivers the most power from a full charge (at maximum possible voltage) Lithium Ion tends to deliver the most power about 30-35º C (about 86 – 95º F) These cells can be left on the charger at 100% SOC, as long as theyare not in an enclosed area and they are kept below 40º C (104º F) 2 Occasionally (once every 30 cycles) cycle from 100% SOC to 10-20% SOC. Otherwise, short cycles are suggested, with recharge each time to 100% SOC 2 Lithium Battery Secrets

  10. Lithium Ion energy delivery slows down at lower temps and with use. This means the battery may be able to deliver full power at first, but have slightly reduced power after a couple of seconds. (Due to the chemistry of the battery cell not fully reacting immediately.) This is shown by a voltage 'sag' Voltage will go down significantly, but come back over time Lithium Battery Secrets

  11. Vcell = 4.20 at the starting line Vcell = 4.17 as the vehicle starts Vcell = 3.60 at the finish line Vcell = 4.06 fifteen minutes later without charging Vcell = 4.09 thirty minutes later without charging Lithium Battery Sag Secret

  12. Lithium Batteries Voltage vs. SOC • Between 100% SOC and 90%, there is considerable variation in battery voltage • Between 90% SOC and 10%, there is very little variation in battery voltage • Between 10% SOC and 0%, there is consierable variation in battery voltage

  13. Voltage vs. State of Charge

  14. Vcell = 4.20 when fully charged Vcell = drops to 3.6 at about 90% SOC Vcell = drops about 0.003V to 0.005 V for each % change in SOC down to about 10% SOC Vcell = after 10% SOC, voltage plummets to 2.50 Don't let cell get lower than 3.4 V. Voltage vs. State of Charge

  15. DC voltages less than 50 are considered non-lethal Your cell will be around 4 volts Cells too hot to hold in your closed hand are unsafe. Temperature ~ 50º C (122º F) Any rapid charge or discharge will warm battery If the battery is not constrained, it may bulge or warp Warped batteries means internal plates can touch which can be a 'short' Lithium Ion cells can have 'thermal runaway' Safety

  16. 1 http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries 2 http://batterycare.net/en/guide.html 3 http://johndayautomotivelectronics.com/?p=517 Copies of this presentation in .odp, .ppt, and .pdf format can be found at: http://rc.to/ANL Footnotes

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