3.5 - DC Sources of Electricity - 4q Flashcards
Each battery consists of cells connected ….
in series
What is a primary cell?
Electrolyte in paste form
Discharge from one plate
-electrolyte becomes weaker and eventually plate destroyed
CANNOT BE RECHARGED
What is a Secondary Cell?
CAN BE RECHARGED
by passing current in opposite direction to how it was discharged
What does the terminal voltage of a cell depend on?
The terminal voltage of a cell depends on the material of the plates and the electrolyte used
What is the voltage of the following single cell:
Carbon/Zinc cell (dry cell)
1.5 V
What is the voltage of the following single cell:
lead/acid
2 V
What is the voltage of the following single cell:
Nickel/Cadmium
1.2 V
What does cell capacity depend on?
The area of the plates
The larger the area of the plate, the greater the amount of active material and therefore the higher the capacity, that is the amount of current the call is capable of supplying
When the cell is supplying current, the terminal voltage will reduce if there is :
1.
2.
An increase in load current
An increase in cell internal resistance
The cell internal resistance is affected by:
1.
2.
Temperature
State of charge
What is the effect of increasing temperature in a battery cell?
An increase of temperature will increase the resistance of the metal, but will reduce the resistance of the electrolyte. The overall effect of an increase of temperature is to reduce the internal resistance
What is the formula associated with the internal resistance of a cell?
What are thermocouples used to measure on aircraft and corresponding material?
Thermocouples are used on aircraft to measure:
exhaust gas temperature - Chromel and Alumel
Cylinder head temperature - Constantan and Copper
What forms on the plates as the cell discharges>
Lead Sulphate forms on both plates as the cell discharges and acts as an insulator. This reduces the effective area of the plate.
What is a Sediment well used for?
Plates shed when in used in the cell. These plates must be raised high enough to clear the bottom of the container or else the material may short the plates.
Carbon/Zinc battery
Lead Acid Battery:
The cell contains two ____ _____ and an _____
A cell stores _____ _____ and converts it to ____ ______
dissimilar elements
Electrolyte
Chemical energy
Electrical energy
Lead Acid Battery:
A primary cell _____ be charged
A secondary cell _____ be charged
cannot
can
Lead Acid Battery:
Cell voltage depends on _____ ____ and ______
____ ______ is the amount of current a cell is capable of supplying size of plates
electrode material
electrolyte
Cell capacity
Lead Acid Battery:
Cells in series _____ the _____
Cells in parallel _____ the _____
increase
voltage
increase
capacity
What are the three basic types of alkaline cells?
Nickel Cadmium (NiCad)
Nickel Iron (Ni/Fe)
Silver/Zinc (Ag/Zn)
How many cells are required for 24V of NiCad vs Lead Acid
NiCad single cell 1.2 = 20 cells
Lead Acid 2V (varying) = 12 cells
What is the electrolyte of Nickel Cadmium?
Electrolyte is a solution of:
Potassium Hydroxide and Distilled or De-ionised water
What are the 3 primary functions of the cell cap or vent cap of a cell?
- To prevent foreign objects entering the cell
- To allow inspection or adjustment of the level of the electrolyte
- To permit gassing (hydrogen and oxygen)
What 4 things would happen if large quantities of oxygen do reach the negative plate because of a damaged gas barried?
- Loose voltage
- increase temperature
- decrease internal resistance
- Increase charge current (Thermal Runaway)
When making a solution of Nickel Cadmium electrolyte, how should this be done?
AAA - Always Add acid or Alkali
Slowly add Potassium Hydroxide to the water
NOT VISE VERSA
How do you determine if a Ni/Cd battery is fully charged?
There is only one precise method to determine if a Ni/Cd cell is fully charged and that is to fully discharge it as a measured rate against time.
