SECTION 7 |
General Information on Lead
Acid Batteries
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7.1 GENERAL
Lead-acid batteries can be categorized by the type of application:
1. Automotive service - Starting / Lighting / Ignition (SLI, a.k.a. cranking), and
2. Deep cycle service.
Deep Cycle Lead Acid Batteries of appropriate capacity are recommended for
powering of inverters.
7.2 DEEP CYCLE LEAD ACID BATTERIES
Deep cycle 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. Use Deep
Cycle batteries for powering these inverters.
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-Rate”: 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. 10.7V for 12V battery, 21.4V for 24V battery and
42V for a 48V 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.
