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

Care and Feeding of Rechargeable 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

Care and Feeding of Rechargeable 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

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

Care and Feeding of Rechargeable Batteries Nickel-Metal-Hydride (NiMH) Electrolyte: potassium hydroxide Developed in 1980’s

Care and Feeding of Rechargeable 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.

Care and Feeding of Rechargeable Batteries Characteristics (all at room temperature) CharacteristicSLANiCdNiMHLi-Ion Vmax/cell Vnom/cell Vmin/cell Cycles: 100% DOD Watt-hours/C$ Life WH/C$ Watt-hours/oz Watt-hours/cu in Self dischg %/mo550255

Care and Feeding of Rechargeable 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

Care and Feeding of Rechargeable 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

Care and Feeding of Rechargeable 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

Care and Feeding of Rechargeable 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.

Care and Feeding of Rechargeable 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

Care and Feeding of Rechargeable 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

Care and Feeding of Rechargeable 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.

Care and Feeding of Rechargeable 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.

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.

Care and Feeding of Rechargeable 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

Care and Feeding of Rechargeable 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)

Care and Feeding of Rechargeable Batteries Questions?

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