MEO Orals on Marine Electro Technology Function 5- Part 3

Inspection and Maintenance of Battery Room

1. Battery installation and its charging rectifier checked.
2. Battery room environment must be dry and well ventilated.
3. Battery tops shall be clean and dry, and terminal nuts must be tight and a smear of petroleum jelly applied to prevent corrosion.
4. Electrolyte at proper level, and shall have correct value of specific gravity by checking with a hydrometer.
5. Rubber gloves and goggles used when handling electrolyte.
6. Charging equipment checked for dirt, overheating, loose connection and correct functioning of indicators.
7. Ventilation arrangement for battery locker checked. Battery installation of both lead acid and alkaline needs good ventilation.
8. Since both type generates hydrogen gas during charging, no smoking and naked light allowed.
9. Steel works and decks adjacent to lead acid battery, should be painted with acid proof paint. [For Cad-Ni cell, alkaline resistance paints].

Battery Room Safety Arrangement

Safety is provided by 

1. Proper ventilation
2. Prevention of heat source for ignition

Ventilation

• Independent exhaust fan provided
• Inlet duct should be below battery level, and outlet at top of the compartment

Prevention of heat source for ignition

• No naked light and no smoking
• Uses of externally fitted light or flameproof light
• Cables of adequate size and they are well connected
• Never place Emergency Switchboard in this room
• Use insulated spanner and plastic jug for distilled water, to prevent short circuit
• Room temperature, maintained at 15 ~ 25 °C

Nickel Cadmium battery [alkaline battery]

• + ve plate is Nickel hydroxide + graphite
• –  ve plate is Cadmium + Iron
• Electrolyte is Potasssium hydroxide solution (strong alkaline)
• Normal specific gravity [1.21] does not change with charging or recharging
• But specific gravity of electrolyte gradually decrease, and electrolyte should be renewed when specific gravity becomes [1.160]
• It is a sealed battery, thus no gassing during charging
• Very low open circuit losses, but requires 67% more cells than Lead Acid battery [1.2 V per cell and when fully charged 1.7 V per cell]
• Not harmful when overcharged
• Left for long period, either fully charged or fully discharged, without deterioration
• Better mechanical strength and durability than lead acid battery
• High initial cost but longer life

Lead Acid Battery

• + ve plate is Lead Peroxide [chocolate brown]
• – ve plate is Spongy Lead [slate gray colour]
• Electrolyte is H2SO4 , specific gravity 1.8 when fully charged, renew when specific gravity is 1.110.
• 1.8 V per cell when fully charged 2 V per cell
• 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

How do you know when the battery is full charge ?

• It can be known by measuring the electrolyte specific gravity by using hydrometer.
• If fully charge it has a specific gravity of about (1.27 – 1.285), hydrometer scale 1270 to 1285
• If fully discharge which fall to a specific gravity of 1.1 (1100)

How can you know battery is over charge ?  Effect of overcharge ?

• When battery is overcharged bubbles will form at the surface, the current flowing into the cell causes breakdown or electrolysis of water in the electrolyte.
• Both hydrogen and oxygen are evolved and released through cell vent caps into the battery compartment.
• There is an explosion risk if hydrogen is allowed to accumulate. (4% of H2 in air).

What happens when lead acid battery is overcharged ?

• Overheating cause buckling of plates
• Internal short circuit
• Sludge formed at the bottom of cells (lead peroxide)
• Battery may be ruined
• Lower the capacity

What happens when lead acid battery is undercharged ?

• Over discharging
• + ve plates are pale brown or yellowish, instead of deep chocolate
• –  ve plates, almost white colour
• Falling of voltage 1.8 V / cell, and specific gravity of H2SO4  1.15

Depolarisation

• Liberation of hydrogen ions at – ve electrode (cathode) and that will decrease the current flow.

Reference:

Oral Guide by – MIN ZAR TAR

MEO Orals on Marine Electro Technology Function 5- Part 3