22 | SAMLEX AMERICA INC.
SECTION 7 |
General Information - Battery Related
fully charged to 2.105 V will measure a standing voltage of 12.63 V at Standard Room
Temperature of 77º F / 25º C. Also, in a healthy battery, all the individual cells will have
the same voltage and same specific gravity. If there is a substantial difference in the
voltages (0.2 V or higher) and specific gravities of the individual cells (0.015 or more), the
cells will have to be “equalized".
7.2.3
SLI (Starting, Lighting, and Ignition) Batteries:
Everybody is familiar with the
SLI batteries that are used for automotive starting, lighting, ignition and powering
vehicular accessories. SLI batteries are designed to produce high current in short bursts
for cranking. This current is also called also called “Cranking Amps”. SLI batteries use
lots of thin plates to maximize the surface area of the plates for providing very large
Cranking Amps. This allows very high starting current but causes the plates to warp
when the battery is cycled. Vehicle starting typically discharges 1%-3% of a healthy
SLI battery’s capacity. The automotive SLI battery is not designed for repeated deep
discharge where up to 80 % of the battery capacity is discharged and then recharged.
If an SLI battery is used for this type of deep discharge application, its useful service life
will be drastically reduced. This type of battery is not recommended for the storage of
energy for inverter backup applications.
7.2.4
Deep Cycle Lead Acid Batteries
:
These batteries are designed with thick-plate
electrodes to serve as primary power sources, to have a constant discharge rate, to have
the capability to be deeply discharged up to 80 % capacity and to repeatedly accept
recharging. They are marketed for use in recreation vehicles (RV), boats and electric golf
carts – so they may be referred to as RV batteries, marine batteries or golf cart batteries.
7.3 RATED CAPACITY SPECIFIED IN AMPERE-HOUR (Ah)
Battery capacity “C” is specified in Ampere-hours (Ah). An Ampere is the unit of
measurement for electrical current and is defined as a Coulomb of charge passing
through an electrical conductor in one second. The Capacity “C” in Ah relates to
the ability of the battery to provide a constant specified value of discharge current
(also called “C-r
ate” - see Section 7.6)
over a specified time in hours before the battery
reaches a specified discharged terminal voltage (Also called “End Point Voltage”) at
a specified temperature of the electrolyte. As a benchmark, the automotive battery
industry rates batteries at a discharge current or C-rate of C/20 Amperes corresponding
to 20 Hour discharge period. The rated capacity “C” in Ah in this case will be the
number of Amperes of current the battery can deliver for 20 Hours at 80ºF (26.7ºC) till
the voltage drops to 1.75V / Cell. i.e. 10.5V for 12V battery or 21V for 24V battery. For
example, a 100 Ah battery will deliver 5A for 20 Hours.
7.4 RATED CAPACITY SPECIFIED IN RESERVE CAPACITY (RC)
Battery capacity may also be expressed as Reserve Capacity (RC) in minutes typically for
automotive SLI (Starting, Lighting and Ignition) batteries. It is the time in minutes a vehicle
can be driven after the charging system fails. This is roughly equivalent to the conditions
after the alternator fails while the vehicle is being driven at night with the headlights
on. The battery alone must supply current to the headlights and the computer/ignition
system. The assumed battery load is a constant discharge current of 25A.
Reserve capacity is the time in minutes for which the battery can deliver 25 Amperes at
