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Care and Feeding of Rechargeable Batteries

Care and Feeding of Rechargeable Batteries. Introduction Rechargeable (or secondary) Can be charged and discharged many times, versus one time use of "primary" batteries. Charging is done electrically. Voltage varies significantly in both charge and discharge phases.

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Care and Feeding of Rechargeable Batteries

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  1. Care and Feeding ofRechargeable Batteries Introduction • Rechargeable (or secondary) • Can be charged and discharged many times, versus one time use of "primary" batteries. Charging is done electrically. • Voltage varies significantly in both charge and discharge phases

  2. Care and Feeding ofRechargeable Batteries • "C" rating is the number of ampere-hours of charge the battery can hold, usually based on a current of C/20 amps, i.e. a 20 hour rate. • Most current specifications are normalized to multiples or fractions of C. • These batteries are all available in sealed configurations, which are recommended for safety and ease of handling

  3. Care and Feeding ofRechargeable Batteries Main Battery Chemistries • Sealed Lead-Acid (SLA) e.g. Gel cell, etc Electrolyte: sulphuric acid Original lead acid cells developed in 1860’s Sealed Lead-Acid developed in 1970’s Characteristic Discharge Curves shown in later slide

  4. Care and Feeding ofRechargeable Batteries • Nickel-Cadmium (Nicad) Electrolyte: Potassium hydroxide Original development 1890’s Sealed nicad cells developed in 1940s Memory effect – especially in older designs

  5. Care and Feeding ofRechargeable Batteries • Nickel-Metal-Hydride (NiMH) Electrolyte: potassium hydroxide Developed in 1980’s

  6. Care and Feeding ofRechargeable Batteries • Lithium-Ion (Li-Ion) Developed in 1990’s Do not confuse with conventional lithium batteries. Look for the full name and nominal 3.6 or 3.7 v/cell Difficult to purchase individual Li-Ion cells.

  7. Care and Feeding ofRechargeable Batteries Characteristics (all at room temperature) Characteristic SLA NiCd NiMH Li-Ion Vmax/cell 2.3 1.45 1.45 4.2 Vnom/cell 2.1 1.2 1.2 3.6 Vmin/cell 1.75 1.0 1.0 3.0 Cycles: 100% DOD 300 1000 300 500 Watt-hours/C$ 0.96 0.26 0.34 0.12 Life WH/C$ 288 260 102 60 Watt-hours/oz 0.96 0.98 2.37 5.2 Watt-hours/cu in 1.24 1.51 4.77 7.4 Self dischg %/mo 5 50 25 5

  8. Care and Feeding ofRechargeable Batteries Discharging • Should not be discharged below "Vmin" (lithium-ion can be damaged) • Use of a fuse between battery and load is strongly recommended. A short circuit can damage the battery and cause a fire. • Available amp-hours depend on discharge rate and temperature 

  9. Care and Feeding ofRechargeable Batteries • Load should be able to work over full range of battery voltage. Load should be automatically switched off at "Vmin" to protect battery • “Memory effect" in Nicads can be prevented by: - avoiding repeated, small discharges, followed by recharge - periodic full discharge and recharge

  10. Care and Feeding ofRechargeable Batteries

  11. Care and Feeding ofRechargeable Batteries Charging • See manufacturer's recommendations for charging • The charging technique is different for each battery chemistry • Options: 1) Buy a charger designed for that particular battery’s - chemistry - number of cells in series, i.e. voltage - amp-hour rating

  12. Care and Feeding ofRechargeable Batteries 2) Design your own, using information from battery manufacturer or charge control integrated circuit supplier. - Ensure that battery cannot discharge into charger if power source goes off. - Charging current should be limited, with a fuse backup.

  13. Care and Feeding ofRechargeable Batteries • Do not: - Use a power supply as a charger unless the charging is monitored continuously - Use a charger designed for a different type of battery - Exceed the maximum allowable battery voltage - Overcharge battery

  14. Care and Feeding ofRechargeable Batteries Storage for more than one month • Follow manufacturer's instructions for storage • Fully charge battery before storage, except lithium-ion should be 50% charged • Store at room temperature or below • Provide trickle charging or periodic recharge if there is significant self discharge (keep battery well charged) • Perform one full discharge/charge cycle before use

  15. Care and Feeding ofRechargeable Batteries Safety • Fuses should be used in the charging and discharging paths • Battery is sealed, but has pressure relief valve which will open if internal pressure exceeds safe value (for example, due to a short circuit or overcharging). Do not operate in a sealed container.

  16. Care and Feeding ofRechargeable Batteries • Battery may vent gas and electrolyte if abused. The electrolyte is corrosive. If this material gets into the eyes, flush with water and get immediate medical attention.  • Use caution when working on a battery and its wiring. Do not wear rings, especially when working on high current batteries.

  17. Main Battery Chemistries Battery Failures • Sulphation is the primary cause of failure in lead-acid and SLA cells • Self-destruction results in Li-Ion cells from v/cell greater than 3.0 volts • Surplus batteries, with unknown storage history, may be failure prone.

  18. Care and Feeding ofRechargeable Batteries Manufacturers and Dealers • Batteries and Chargers - Electronic parts suppliers (Digi-Key, Electrosonic, Newark, Active, etc.) - Battery suppliers (incl local) and manufacturers  Panasonic produces a full line of batteries  • Charging circuit components - Unitrode and Benchmarq (both part of Texas Instruments) plus others for charging control ICs

  19. Care and Feeding ofRechargeable Batteries References • Application notes and spec sheets from battery manufacturers • Application notes and spec sheets from charger and control circuit manufacturers • Book "Batteries in a Portable World" Second edition, by Isidor Buchmann, Cadex Electronics, Inc., Richmond, BC ($52.96 Canadian) (The "bible" for serious battery users)

  20. Care and Feeding ofRechargeable Batteries Questions?

  21. Care and Feeding ofRechargeable Batteries Thanks for your attention. Enjoy your visit. 73 de Dick Bonnycastle - VE3FUA

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