Lamar Technologies Alpha C-25 - Manual (Page 21)

APPENDIX A – BATTERY OVERVIEW
ALPHA C-25 Manual V2.1.doc Page 21
NICKEL-CADMIUM BATTERIES
The nickel-cadmium battery is a rechargeable system using alkaline electrolyte (a 31%
aqueous solution potassium hydroxide). Nickel-cadmium batteries, which may be
vented or sealed, have overcharge capability, high rate charge acceptance and nearly
constant discharge voltage. The disadvantages are the high initial and maintenance
costs as well as the cost to discard the battery at the end of life. The open circuit voltage
of a fully charged cell is about 1.35 volts. The discharge voltage is about 1.2 to 1.1 volts
and varies with temperature, discharge rate, charge state, and age.
Nickel-cadmium batteries are used in auxiliary power units, aircraft engine starting,
space satellite power, missile electrical systems, and electrical propulsion
DEFINITIONS
AMPERE-HOURS. The term "ampere-hours" is a unit of measure that refers to the
electrical capacity of a battery. It is the product of the current in amperes multiplied
by the period of time in hours during which the current is delivered. For example, a
battery that discharges at 5.0 amperes for 4.0 hours has delivered 5.0 x 4.0 or 20
ampere-hours. To convert ampere-minutes to ampere-hours, simply divide by 60.
E.g. 10 amperes x 40 minutes = 400/60 ampere-hours = 6.6 ampere-hours.
END POINT VOLTAGE. The End Point Voltage is the end point of the discharge
curve, for a specified discharge rate, at which the battery or cell is considered to be
discharged for all practical purposes. Lead acid batteries can be permanently
damaged if discharged below their END POINT VOLTAGE.
CAPACITY RATE (C
1
-RATE). The capacity rating of a lead-acid or nickel-cadmium
battery is based on a one hour discharge rate with the battery initially at temperature
77.5°F (25°C) and a cutoff terminal voltage of 20.0 volts for a 24-volt battery or 10.0
volts for a 12-volt battery. For example, a 24-volt battery rated at 30.0 ampere-hours
should deliver 30.0 amperes for a minimum of 51 minutes before reaching the 20
volt EPV (end point voltage) . This is a one-hour, C
1
-rate discharge.