Transcript Project Testing - University of Louisville

Battery Basics
A guide to battery use in engineering projects
Thomas G. Cleaver
University of Louisville
Department of Electrical and Computer
Engineering
Jan. 28, 2013
References
This presentation was developed using the following sources:
• T.E. Bell, “Choosing the Best Battery for Portable Equipment,” IEEE
Spectrum, March, 1988, pp 30-35.
• Walt Kester, Joe Buxton, “SECTION 5, BATTERY CHARGERS,” available
at
http://www.analog.com/UploadedFiles/Associated_Docs/43241673Power_s
ect5.PDF#search=%22batteries%20%22discharge%20profiles%22%22
• Custom Power Solutions, available at
http://www.mpoweruk.com/performance.htm
• New Technology Batteries Guide (1998), available at
http://www.nlectc.org/rwscripts/rwisapi.dll/@JUSTNET.env?CQ_SESSION_
KEY=CUANXLBUKMIR&CQ_TPT_VIEW_DOC=YES&CQDOC_NUM=2
• Green Batteries, available at http://www.greenbatteries.com/libafa.html
• Steve Garland, Kyle Jamieson, “Battery Overview,” available at:
http://nms.csail.mit.edu/fun/battery.ppt#268
• Harding energy Inc, available at http://www.hardingenergy.com/
• BatteryUniversity.com, available at http://www.batteryuniversity.com/
Battery Terms 1
• Capacity: The charge a battery can hold in ampere-hours (Ah) or
milliampere-hours (mAh) or the energy the battery can hold in watthours.
• C: Charge or discharge rate. Battery capacity in Ah or mAh divided
by 1 hour. Also know as C rate.
• Charge life: The total capacity over the life of the battery (capacity x
cycles).
• Discharge rate: The maximum allowable load or discharge current.
• End voltage: The voltage below which a battery will not operate
satisfactorily. Also know as “final voltage.”
• Energy density: The energy storage capacity of a battery
compared to its mass or volume. The higher the energy density, the
better.
• Memory effect: The tendency of some rechargeable batteries to
lose capacity when not periodically totally drained – a particular
problem in NiCd batteries.
Battery Terms 2
• Primary battery: A disposable battery.
• Polarity reversal: The reversal of the polarity of an overdischarged cell of a rechargeable battery in a series
connection. If one cell in a series string discharges before the
others, the discharged cell may reverse polarity. If the current
is maintained, the reversed cell may be permanently
damaged.
• Secondary battery: A rechargeable (storage) battery.
• Self-discharge: The loss of charge over time of a battery
when it is unused.
• Service life: The length of time a battery is expected to be
usable.
• Shelf life: The length of time a battery will retain useful
charge when stored.
Primary (Disposable) Battery Types
• Zinc-carbon:
– “Ordinary” battery
– Voltage decreases steadily during discharge
• Zinc-alkaline:
– “Alkaline” battery
– Better than zinc-carbon
– Voltage decreases steadily during discharge
• Zinc-air:
– Button cell hearing aid batteries
– Voltage almost constant over useful life
• Lithium ion:
– High energy density
– Voltage almost constant over useful life
Secondary (rechargeable) Battery Types
•
Sealed Lead-Acid (SLA):
– Automobile batteries
– Low cost
– Lead is toxic; sulfuric acid is corrosive.
•
Nickel-Cadmium (NiCd):
– Inexpensive
– Memory effect
– Cadmium is toxic.
•
Nickel-metal-hydride (NiMH):
– Moderately expensive
– Voltage almost constant over useful life
•
Lithium ion (Li-ion):
–
–
–
–
Expensive
High energy density
Voltage almost constant over useful life
Dangerous if overcharged
Standard Sizes
• Button – used in hearing aids and in other
applications that require small size
• Cylindrical – like AAA, AA, C, D – all
usually 1.2 to 1.5 V
• Prismatic – like 9 V batteries
• Rechargeable Li-ion does not typically
come in standard cylindrical sizes.
Discharge and Voltage
• The voltage of some batteries doesn’t
change much as the battery is discharged,
for example, NiCD and NiMH.
• The voltage of others drops off as the
battery is discharged, for example, zinccarbon, and alkaline.
Discharge and Current
• Battery capacity, usually expressed in
mAh, is measured under specific
conditions.
• The higher the current, the less the
effective capacity.
• Example: A battery rated at 1500 mAh
may be able to deliver 150 mA for 10
hours, but it may not be able to actually
deliver 1500 mA for 1 hour.
Peukert Curve
(from http://www.batteryuniversity.com/partone-16a.htm)
C Rate Calculations
• C = Rated capacity/ 1 hour
• Example: A 2800 mAh NiMH battery has
a C of 2800 mA.
• Batteries can be tested at various
multiples of C.
• Example: For the 2800 mAh battery, C/4
would be 700 mA; 3C would be 8400 mA.
Voltage Dependence on Current
• Batteries are not ideal devices – They
have internal resistance.
• Vloss = IRinternal
Battery Type
NiCd 1.2 V AA
Typical Internal Resistance
(milliohms)
30
NiMH 1.2 V AA
150
Li-ion 3.6 V
320
Alkaline 1.5 V AA 150
Maximum and Suggested Drain
Battery Type
Max Drain
Alkaline
.5 C
Suggested
Drain
< .2 C
SLA
.2-5 C
.2 C
NiCd
2-20 C
< .5 C
NiMH
Li-ion
.5-5 C
1-2 C
.5 C
<1C
Batteries in Series
• Batteries should be identical.
• Total voltage = Voltage of each cell x
number of cells
• When using rechargeable batteries in
series, beware of deep discharge because
of polarity reversal.
Batteries in Parallel
• Batteries should be identical.
• Total current = Current of each cell x
number of cells
• Usually a bad idea
• Good batteries may discharge through bad
battery.
Illumination Economics
Incandescent, Compact Fluorescent (CFL), and LED lighting characteristics
Cost of
bulb
Lumens
Efficiency
Lifetime
$1
840
2%
1K hours
(~ 1 Month)
13 W CFL
$2
825
9%
10k hours
(~ 1 year)
10 W LED
$16
810
12 %
50k hours
(~ 5 years)
Type
60 W
Incandescent
Total Cost by Bulb Type
Cost for purchase of bulb(s) and for electrical
energy @ 10 ₵/kWh.
Type
1 month
1 year
5 years
60 W
Incandescent
$7
$70
$350
13 W CFL
$3
$15
$75
10 W LED
$17
$26
$65
But this assumes you turn the light on and never
turn it off until it blows out and you replace it.
What’s so Bad about CFLs?
•
•
•
•
•
On/off cycling shortens lifetime.
They are sensitive to physical shock and breakage.
Most CFLs are not dimmable.
Some people don’t like the quality of the light (too harsh).
Some CFLs take time (~ 30 seconds) to achieve
maximum light output.
• CFLs contain a small amount of mercury (a disposal
issue).
• Low temperature reduces CFL light output (an outdoor
use issue).
• High temperature shortens CFL light (a luminaire issue).