Care and Feeding of Rechargeable Batteries

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