care and feeding of rechargeable batteries
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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
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
Care and Feeding ofRechargeable Batteries
Main Battery Chemistries
Sealed Lead-Acid (SLA) e.g. Gel cell, etcElectrolyte: sulphuric acidOriginal lead acid cells developed in 1860’sSealed Lead-Acid developed in 1970’sCharacteristic Discharge Curves shown in later slide
Care and Feeding ofRechargeable Batteries
Nickel-Cadmium (Nicad)Electrolyte: Potassium hydroxideOriginal development 1890’sSealed nicad cells developed in 1940sMemory effect – especially in older designs
Care and Feeding ofRechargeable Batteries
Nickel-Metal-Hydride (NiMH)Electrolyte: potassium hydroxideDeveloped in 1980’s
Care and Feeding ofRechargeable Batteries
Lithium-Ion (Li-Ion) Developed in 1990’sDo not confuse with conventional lithium batteries. Look for the full name and nominal 3.6 or 3.7 v/cellDifficult to purchase individual Li-Ion cells.
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
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
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
Care and Feeding ofRechargeable Batteries
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
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.
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
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
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.
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.
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 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
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)
Care and Feeding ofRechargeable Batteries
Questions?
Care and Feeding ofRechargeable Batteries
Thanks for your attention.
Enjoy your visit.
73
de
Dick Bonnycastle - VE3FUA