GMDSS Battery capacity test

Regulation for Radio battery capacity test

6.   Where a reserve source of energy consists of a rechargeable accumulator battery or batteries: 

.1   a means of automatically charging such batteries shall be provided which shall be capable of recharging them to minimum capacity requirements within 10 h; and 

.2   the capacity of the battery or batteries shall be checked, using an appropriate method, at intervals not exceeding 12 months, when the ship is not at sea.

 (SOLAS 1974, as amended, regulation IV/13)

7.4.6   The capacity of the radio batteries should be checked at intervals not exceeding 12 months when the ship is not at sea. One method of checking the capacity is to fully discharge and recharge the batteries using normal operation current over a period of 10 hours. Assessment of the charge condition can be made at any time, but it should be done without significant discharge of the battery when the ship is at sea. Another method could be to check the capacity by means of a battery tester, e.g., in connection with a radio survey. (SOLAS 1974, as amended, regulation IV/13, IMO resolution A.702(17) and COMSAR/Circ. 16)

Note: - When determining the battery capacity, the following should also be taken into consideration:

- the battery is normally not fully charged.
- reduction of capacity due to ageing.
- reduction of capacity due to high or low temperatures; and
- reduction of capacity due to rapid discharge.

                                                                                                                                (COMSAR/Circ.32, ANNEX, Page 33)

Radio battery capacity requirement

7.4.4   If the capacity requirement of radio batteries is to be maintained over their normal life cycle, an extra 40% capacity should be added to the minimum calculated capacity.

                                                                       (COMSAR/Circ.32, Annex, page 32)

2.2   For guidance, the nominal battery capacity to comply with the minimum capacity requirements at all times is 1.4 times the load determined in paragraph 2.4 multiplied by the intended period of operation (1 hour or 6 hours in accordance with SOLAS IV/13.2).

                                                         (COMSAR/Circ.16, Annex, page 4)

Key terminologies to understand:

minimum capacity requirement = load determined for the radio system x 1hr or 6hr

Most of the ships are required to have only 1hr intended period of operation.

hence, minimum capacity requirement = load determined for the radio system.

nominal battery capacity = 1.4 x minimum required capacity 

The installed battery capacity will be equal to or greater than the nominal battery capacity, whichever is available in the market.

The minimum required capacity can be safely taken as 72% of the installed battery capacity.

The radio battery capacity should not be less than the minimum required capacity at any time. The annual battery capacity test is being carried out to ascertain whether the present battery capacity is higher than the minimum required capacity or not. During charging cycle after the capacity test, the battery should be charged to minimum required capacity in 10hrs. However, the battery requires more hours of charging to get it fully charged.

The capacity of a lead acid battery is normally quoted at 20 hours of discharge at an operational temperature of 20°C. But in general, most of the lead acid batteries having capacity of 100Ah or more can deliver the battery capacity in 10 hours of discharge. Battery capacity will decrease over the period of time due to various factors. Hence the battery capacity needs to be checked.

Consider if a radio battery of 200Ah, 12V, 02nos are in use:

for 10 hours discharge, we need 20A constant discharge (200 / 10 = 20A).

But the current will be decreasing rather being constant due to decreasing battery voltage and increasing internal resistance. The rate of current decrement is related the health of the battery.

For a 20A current discharge we need a 24V lamp load of 480W (20A x 24V) which can be made with 8nos 60W,24V lamps.

So, we can prepare a lamp load bank of 24V, 60W, 8nos for capacity test with each lamps having its own switch.

Disconnect the battery from the system and the charger.

Connect the load bank to the battery through a switch or breaker.

Connect a multimeter across the battery terminal to measure the battery voltage.

Connect a DC clamp meter to the load bank.

Switch on all 8nos individual lamp switches and then switch on the main breaker of load bank.

Immediately note down the voltage and current. 

Continue to note down the voltage and current every minute for next five minute. In this five minute, the battery voltage will dip and rise which will indicate the general health of the battery. A good battery will have a shallow dip and will rise soon.

Continue to note down the voltage and current every half an hour until the battery voltage drops to 21.12V, 88% (1.76V x 12cells). The safe discharge voltage of a cell according to most of the makers is 1.75V (end cell voltage). SOLAS chapter IV does not say anything about how much should be the maximum voltage drop while discharging. However, following can be considered for any battery; as per SOLAS Reg II-1/13-4, a battery "which shall operate without recharging while maintaining the voltage of the battery throughout the discharge period within 12% above or below its nominal voltage". The 12% drop of a cell voltage resulted to be 1.76V and it will be 21.12V (88%) for the battery. 

Calculate the Ah discharged (current x time) for every half an hour and add all to get the total discharged Ah.

Calculate the battery % capacity with respect to nominal battery capacity.

Disconnect the load bank and connect the battery to the charger.

Connect the multimeter and DC clamp meter accordingly.

Switch on the charger and note down the voltage and current.

Continue to note down the voltage and current every hour for next 10hrs.

Connect the battery to the system and keep charger on. The battery will continue charging. The automatic battery chargers will not charge the battery to its nominal value in 10hrs. The charger will control the charging current throughout to avoid any battery damage. However, the charger can easily charge the battery more than the minimum required capacity in 10hrs which is required by SOLAS if the battery is good.

Calculate the Ah charged which should be more than the minimum required capacity.

Plot the discharging and charging parameters on graph for record keeping.

If the battery capacity is less than 80% or the Ah charged in 10hrs is less than minimum required capacity, then initiate the battery replacement procedure.

Capacity test can be carried out at PORT or at anchorage inside port limit while awaiting berth & not proceeding/waiting for sea passage as per Singapore flag state. The 10hr charging has to be completed before ship leaves the port.