BATTERIES CHARGING ONBOARD SHIP

Battery Charging On Board Ship.

Batteries are one of the energy sources available onboard vessels which are used in case of blackout and emergency situations on board a ship. These batteries are used for low voltage dc system like bridge navigational instruments and thus need to be kept charged to be used in case of any need of temporary power.

Also, arrangement should be available on board to charge the batteries again after the use. Moreover, the arrangement should be such that the batteries are able to be fully charged as they gradually lose charge over the time.

The batteries can be charged with the help of dc power supply; however presently there are no ships working on dc supply system and thus it is required to change the ac power into dc to charge the batteries.

A simple circuit used for battery charging is shown below:-

For converting ac into dc several components are required as shown in the circuit diagram above. First of all the ac is stepped down to the required voltage and then the AC is converted to DC with the help of rectifier system which changes sinusoidal wave of ac to dc system.

The only problem in the above circuit is that there is no arrangement provided for maintaining the charge, and the usage of same circuit will lead to overcharging and reduction of the battery life. In order to avoid this, a slight modification is done in the same circuit and an arrangement is provided to maintain the charges at the terminals. Also an arrangement to connect automatically to low voltage dc system is provided in case of a power failure.

In normal circumstances the battery is charged using the full charge circuit and once the battery is fully charged, the charges on the battery are maintained by the trickle charge circuit

As it can be seen in the diagram, the batteries are in standby mode with the charging switches C closed and the load switches L open. The positions of these switches are held with the help of an electromagnetic coil against the spring tension. The electromagnetic coil gets its supply from the main power source available on the ship. As soon as there is a loss of main power, the electromagnetic coil loses its power and the batteries are connected to load switch L which gets disconnected from the charging switch C.

Once the power is available from the main system, the batteries are connected back to the charging circuit again manually. Also there is a test switch provided to test the system as a part of the routine checks.

Steps to Prevent Explosion in Battery Room of Ships

The battery room of a ship is always under explosion risk as batteries release hydrogen during charging. Hydrogen is a highly explosive gas and it is therefore important to take necessary steps or actions while working inside the battery room during maintenance. In this article we will go through the measures that need to be taken to ensure battery room safety.

Following are the two basic steps that need to be taken to prevent any kind of explosion:-

1) Providing proper ventilation inside the compartment.
2) By preventing any source of ignition.

Moreover, the ventilation is provided with the help of ventilation fans. The ventilation arrangement should be such that there is no accumulation of hydrogen in the space. The hydrogen is lighter than air and thus tends to accumulate in the top of the compartment. The fans should be of non sparking type and should not produce any static charge.

Also, the ventilation ducts should be below the battery level which would help in forcing the gases out. The motor used should be of a standardized approved type so that there is no chance of spark from the motor.

The tools used for maintenance should be rubberized coating to prevent any chance of short circuiting by mistake. The coating would also prevent any kind of spark generation when the tool falls on the floor.

The paint used in the battery room and materials for ducting should be corrosion resistant. No metal jugs should be used for filling distilled water inside the batteries. Other precautions include preventing usage of naked lamps and avoiding smoking in the battery room.

The battery should not be placed in the emergency switchboard room for there are chances of sparking due to arcing of the circuit breakers.

Maintenance carried out on battery.

1) The batteries should be maintained in fully charged condition and this is done by the charging circuit.
 
2) The state of charge can be seen with the help of hydrometer. A sample is taken in this instrument and the condition of specific gravity is checked. For a fully charged lead acid battery the specific gravity is 1.280 at 15 deg. Centigrade. Please make a note that there is no change in specific gravity in alkaline batteries during charging and discharging. This test is only for lead acid batteries.
 
3) Top up the batteries with distilled water as there is a loss of water during charging.
 
4) The battery terminals should be kept clean and should be smeared with petroleum jelly.