OCV, CCV and Internal Resistance

OCV = Open Circiut Voltage
CCV = Closed Circuit Voltage

There are 2 ways of measuring battery voltage. There are OCV and CCV.
Voltage measured when no load connected to battery is called OCV and voltage measured when load is connected to battery is CCV.
CCV is always lower than OCV because battery can maintain higher pressure (voltage) when no current flow from it.
The OCV of a 12v Lead-Acid battery is about 13.2V (for Battery rated 12V). When even a small load apply to the battery, the CCV will measure near 12v.
The CCV of a batteryis the function of the load applied and the state of charge of the battery. If the battery is connected to heavy load, the CCV will lower than if the battery connected to the light load.
If the battery is totally near its discharge state, the CCV is at its lowest. OCV typically not affected until the battery is near complete discharge state.

INTERNAL RESISTANCE(IR)

The opposition or restriction of direct current flow within the cell or battery. Its value may vary with the current, state of charge, temperature and age.
With an heavy load applied such as engine starting, the battery voltage may drop to a certain value because of the internal resistance in the cells. The cell that has near discharge has higher internal resistance than fully charged cell. So, nearly discharge cell/battery will have higher voltage drop.
The IR is determine by the load applied and state of charge of the battery. A battery IR is equal to difference between OCV and CCV, divide by applied load.

IR = (OCV - CCV)/I load

Principles of Secondary cells

Secondary cells can be recharged.

The chemical action inside the cell can be reversed by applying a higher voltage to the battery terminal. This is done by connecting the +ve terminal of the charger to the +ve terminal of the cell and -ve terminal of charger to -ve terminal of the battery.

This will return the original composition of the cell elements.

At this time the cell is said to be charged. Secondary cell can be charged and discharged many times until it is deteriorate.

Commonly used aircraft battery is LEAD-ACID and NICKEL-CADMIUM.

Principle of primary cells

Principle of primary cells

Batt is two or more electrochemical cell.
Batt is a device to convert chemical energy into electrical energy.
Batt characteristic may vary due to many factors like internal chemistry, temperature and current drain.
There are 2 types of batt: primary and secondary. Primary batt is design to used once only and cannot be rechargeable. Secondary batt are rechargeable becoz their chemical reaction can be reversed.

Primary Cells

Ex:of primary cell is carbon-zinc battery.

primary cell : carbon-zinc












Zn plate form -ve electrode and Carbon Rod form +ve electrode.
+ve electrode is also called anode and -ve electrode is called cathode.
Solution of Ammonium chloride form the electrolyte.
As soon as the Zn plate immersed in the electrolyte, Zn atom which carries +ve ions go into the solution. This make the Zn plate becomes more -ve.
Ammonium chloride in electrolyte separate into +ve Hydrogen ions and a combination of Ammonium and chlorine which -vely charged.
When the electrodes are connected by external connection, the electrons flow from Zn plate to Carbon Rod.
These electrons will react with H+ ions and become neutral.
-vely charged ammonium and chlorine combine with the ions Zn++.

The effect of the chemical action is to remove electrons from carbon rod and to liberate free electrons at Zn plate.This will results in continuous supply of electrons available at Zn plate(-).
As there are more H atoms at the carbon rod, POLARIZATION will occur.

POLARIZATION occurs when hydrogen bubbles accumulate at the carbon rod thus insulate it from the solution. This will prevent the current to flow.
Practically, a method of DEPOLIRAZATION is employed. This is done by adding a compound called manganese dioxide.