batteries and current sources Flashcards
electric cells
chemical energy is converted into electrical energy.in the case of primary cells , the actin is not reversable
secondary cells can be recharged
passing current through the the opposite direction to the current floe w during discharge.
essential materials of any cells
two electrodes of dieffernt type of material and electrolyte.
primary cells the elcttrolyte
is combined with with an absorbant material form of a paste
in an open circuit a leclanche cell
1,5 volts
most generally used primmary cel is the
leclanche cell
uses of miniature cells
wrist watches , hearing aidds guideed missiles. cells such aas mucury oxide , silver oxide were deveeloped
nickel caadnium cells
alkaline electrolyte, are rechargeble , minature , computers, video camaras for slightly larger uses, slab shaped. much larger ones are used for aircrafts
lead acid cells
mostly used in motors and is a secondary cell
emf of lead acid cell
depdends on the materials used to manufacture the cell
reletive density
ratio of the mass of a unit voolume of the electrolyte to the mass of the same vollume of water is know as the relative density. it is specified by the manufacturer.it ussually between 1,230 to 1,280
what happens to relative density during discharge?
decreases
capacity of a lead acid cell
20 hour ampere hour rating. refers to the constant current through which the batterycan deliver for 20 hours before the terminal pd drops below 1,85 volts per cell
the capacity of a lead acid cell depends on
number and the size of plates
rate of discharge
temp
age and the condition of the cell.
fully charged lead acid cells state
positive plates haave a choclate brown colour and negative light grey
relative deensity of electrolyte increases.
discharged lead acid cell state
terminal voltage drops below 1,85
specific gravity of the cell drops.
postive and negative terminals have matt grey colour
5 ways to care for lead acid cell
cells should not be discharged below 80% of their capacity
vent holes in the filter plugs must be kept open
they should not be left in discharged state and musst be recherged as soon as possible.
acid may not be addes to the battery…
diffferern types of lead acid cells available today
conventional, kow mainatainance , maintainance free , hybrifd long life types
leisure batteries
boats caravans can withstand fequent deeep discharge an dcharge cycles
6 factors that should be considered when purchasing a cell
voltage required by the load internal resistance of the cell operting tempertures physical size of the cell and mass life expectancy of the cell cost of the cell rechargeble or not storage life of a cell
5 methods of producing elecrtricity
chemical reaction electromagnetic induction solar energy conversions heat friction
