Ni-Cad Flashcards
Ampere Hours
A unit of electrical measurement used to describe the capacity of a cell or battery.
The product of discharge current (in amperes) x the time of discharge (in hours). It is also used to describe the amount of electrical energy put back into a battery during the charging process. Abbreviated as Ah or Amp. hrs.
Capacity
A measurement of the stored electrical energy that is available from a charged battery.
Generally expressed in Ampere hours, or as a % of the nominal (nameplate) capacity. Capacity is measured quantitatively in ampere-hours delivered at a specified discharge rate to a specified cutoff voltage at room temperature. The cut-off voltage is a 1.0 voltage per cell time the number of cells in a battery.
Battery available capacity depends upon several factors including such items as:
Cell design (cell geometry,plate thickness, hardware and terminal design governor performance under specific usage conditions of temp, discharge rate etc)
Discharge rate (high current rates yield less capacity than low rates)
Temperature (capacity and voltage levels decrease as battery temperature moves away from the 60⁰F (16⁰C) to 90⁰F(32⁰C) range toward the bought and low extremes)
Charge rate (higher charge rates generally yield greater capacity)
Constant current charging
A method used to charge a battery in which a predetermined, FIXED current is passed through it.
Constant potential charging (constant voltage)
Refers to the method in which a fixed voltage source is applied across the battery terminals. The charge current is variable and depends primarily upon the difference in voltage between the voltage source and that of the battery. The initial charge current is high and decreases as the battery accepts the charge and its voltage increases
Trickle charge
A continuous constant current, low-rate charge (slightly more than self-discharge rate) suitable to maintain a battery in fully charged condition.
Rated or Nominal Capacity
The Nominal nameplate Capacity rating of a nickel cadmium battery generally refers to the number of ampere-hours that the battery can deliver when discharged at the 1-hour rate to 1.0 volt per cell
C Rate
That discharge rate, in Nominal or nameplate amperes, at which a battery or cell will yield its capacity to a 1.0 volt per cell endpoint in one hour. Fractions or multiples of the C rates are also used.
C/5 refers to the rate at which a battery will discharge is capacity in 5 hours
2C is twice the C rate or the rate at which a battery will discharge is capacity in about 1/2 hour.
Ex: a 25 ampere hour battery will have a C rate of 25 amperes, a C/5 rate of 5 amperes and a 2C rate of 50 amperes.
State of Charge
The amount of stored energy (capacity) available in a rechargeable battery. Usually expressed as a percentage of its full capacity.
Electrolyte
The conductive medium that provides for the movement of ions (current flow) between the positive and negative plates of a cell; an alkaline solution of potassium hydroxide in nickel cadmium aircraft cells
End-of-charge Voltage
The voltage of a battery at the conclusion of a charge measured while the battery is still on charge
Fading
The loss of capacity that occurs when a battery is cycled with minimal overcharge. A correctable condition through reconditioning
Separator
A material that is used to prevent the metallic contact between the positive and negative plates
Gas barrier
A membrane on the separator system that prohibits the recombination of oxygen (produced at the positive plate) on negative plate
Nominal Voltage (Nameplate)
The voltage of a fully charged cell or battery while delivering current. The nominal voltage of a nickel cadmium battery cell is 1.2 volts; therefore a 20-cell battery would have a nominal voltage of 24 volts, and 19 cell is 22.8 volts. (Older batteries use a different convention for nominal voltage)
