Battery Definitions
Batteries come in all shapes and sizes and there could be as many types
as there are species of dog. Rather than giving batteries unique names
as we do with pets, we distinguish batteries by chemistry, voltage,
size, specific energy (capacity), specific power, (delivery of power)
and more. A battery can operate as a single cell to power a cellular
phone, or be connected in series to deliver several hundred volts to
serve a UPS (uninterruptible power supply system) and the electric
powertrain of a vehicle. Some batteries have high capacity but cannot
deliver much power, while a starter battery has a relatively low
capacity but can crank the engine with 300A.
The largest battery systems are used for grid storage to store and
delivery energy derived from renewable power sources such as wind
turbines and solar systems. A 30-megawatt (MW) wind farm uses a storage
battery of about 15MW. This is the equivalent of 20,000 starter
batteries and costs about $10 million. One mega-watt feeds 50 houses or a
super Walmart store. Let’s now examine each of the battery
characteristics further.
Chemistry
The most common chemistries are lead, nickel and lithium. Each system
requires its own charging algorithm. Unless provisions are made to
change the charge setting, different battery chemistries cannot be
interchanged in the same charger. Also observe the chemistry when
shipping and disposing of batteries; each type has a different
regulatory requirement.
Voltage
Voltage describes the nominal open circuit voltage (OCV), which varies
with chemistry and number of cells connected in series. Always observe
the correct voltage when connecting to a load or a charger. Do not
proceed if the voltage does not agree.
Capacity
Capacity represents the specific energy in ampere-hours (Ah).
Manufacturers often overrate a battery by giving a higher Ah rating than
it can provide. You can use a battery with different Ah (but correct
voltage), provided the rating is high enough. Chargers have some
tolerance to batteries with different Ah ratings. A larger battery will
take longer to charge than a small one.
Cold cranking amps (CCA)
CCA specifies the ability to draw high load current at –18°C (0°F) on
starter batteries. Different norms specify dissimilar load durations and
end voltages.
Specific energy and energy density
Specific energy or gravimetric energy density defines the battery capacity in weight (Wh/kg); energy density or volumetric energy density
is given in size (Wh/l). A battery can have a high specific energy but
poor specific power (load capability), as is the case in an alkaline
battery. Alternatively, a battery may have a low specific energy but can
deliver high specific power, as is possible with the supercapacitor.
Specific energy is synonymous with battery capacity and runtime.
Specific power
Specific power or gravimetric power density indicates the
loading capability, or the amount of current the battery can provide.
Batteries for power tools exhibit high specific power but have reduced
specific energy (capacity). Specific power is synonymous with low
internal resistance and the delivery of power.
C-rates
C-rates specify charge and discharge currents. At 1C, the battery
charges and discharges at a current that is par with the marked Ah
rating; at 0.5C the current is half, and at 0.1C it is one tenth. On
charge, 1C charges a good battery in about one hour; 0.5C takes 2 hours
and 0.1C 10 to 14 hours. Read more about What is the C-rate?
Load
Also known as electromotive force (EMF), the load draws energy from the
battery. Internal battery resistance and depleting state-of-charge
cause the voltage to drop.
Watts and Volt-amps (VA)
Power drawn from a battery is expressed in watts (W) or volt-amps (VA). Watt is the real power that is being metered; VA is the apparent power
that determines the wiring sizing and the circuit breakers. On a purely
resistive load, watt and VA readings are alike; a reactive load such as
an inductive motor or florescent light causes a drop in the power
factor (pf) from the ideal one (1) to 0.7 or lower. For example, a pf of
0.7 has a power efficiency of 70.
For more information click here
All information has been referenced from http://batteryuniversity.com/
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