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Types of Battery

Ships rely on batteries as an emergency power source and to supply certain equipment with low-voltage DC power. To fulfil these needs, it’s important to use the appropriate battery size and type, and to have them regularly maintained.

 

Two main types of batteries are used on board ships: lead-acid and alkaline, along with various circuits and control gear.

Nickel Cadmium battery [alkaline battery]

The alkaline battery is made up of a positive nickel hydroxide plate and a negative cadmium and iron plate that are submerged in potassium hydroxide solution. This creates a cell voltage of around 1.4V, and typically, five of these cells are grouped together to produce approximately seven volts. Each cell is housed within a steel casing, and an interleaved construction is used.

 

The battery is made up of multiple cells that are mounted in hardwood crates with space between them. These cells are connected in series to produce the desired battery voltage.

 

When the battery is charged, the nickel hydroxide plate is positive, and the negative plate is cadmium. Common properties of alkaline battery:

  • + ve plate is Nickel hydroxide + graphite
  • –  ve plate is Cadmium + Iron
  • The electrolyte here is Potassium hydroxide alkaline solution
  • During discharge, the oxygen is transferred between the plates without affecting the potassium hydroxide solution’s specific gravity,
  • The specific gravity of the electrolyte gradually decreases, and the electrolyte should be renewed when the specific gravity becomes [1.160]
  • It is a sealed battery, thus no gassing occurs during charging
  • It requires 67% more cells than a Lead Acid battery [1.2 V per cell and when fully charged 1.7 V per cell]
  • Not harmful when overcharged
  • Left for a long period, either fully charged or fully discharged, without deterioration
  • It provides better mechanical strength and durability than a lead acid battery
  • High initial cost but a longer life

Lead Acid Battery

The lead-acid battery is composed of several cells, each containing a lead peroxide positive plate, a lead negative plate, and a dilute sulfuric acid solution known as the electrolyte.

 

When a wire connects the two plates, a voltage is produced, resulting in the flow of current. Initially, the voltage is around 2.2V, but it stabilizes to approximately 2V. A 12V battery can be obtained by connecting six separate cells in series.

 

The term ‘accumulator’ is sometimes used interchangeably with the term ‘battery’.

Common properties of Lead Acid Batteries –

  • + ve plate is Lead Peroxide
  • – ve plate is Spongy Lead
  • The electrolyte H2SO4 has a specific gravity of 1.8 when fully charged. It is to be renewed when the specific gravity is 1.110.
  • When undercharge, + ve plates are pale brown or yellowish, instead of deep chocolate and very difficult to convert back to normal form
  • Efficiency (watt hour efficiency) is higher than Alkaline Cells

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