Transcript Care and Feeding of Rechargeable Batteries

Care and Feeding of
Rechargeable Batteries
Introduction
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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
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"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
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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
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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
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Nickel-Metal-Hydride (NiMH)
Electrolyte: potassium hydroxide
Developed in 1980’s
Care and Feeding of
Rechargeable Batteries
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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)
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 of
Rechargeable Batteries
Discharging
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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
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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
Care and Feeding of
Rechargeable Batteries
Charging
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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
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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
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Follow manufacturer's instructions for storage
Fully charge battery before storage, except lithiumion 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
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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
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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
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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
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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
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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