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Selection of starting accumulator batteries

Power of starter [kW] in range from 0 to 20 kW Battery capacity [Ah]

Selection of cross-section of the cable supplying starter:
due to heating
S1= [mm2],
due to permissible voltage drop
cable length l= , S2=[mm2]


standarised cable: [mm2]


Rated voltage: Type of accumulator battery:
24 V Lead-acid with latticed structure plates
12 V Alkaline cadmium-nickelic

Temperature of electrolyte:
25 °C, batteries placed on board of ships sailing in the tropical zone,
15 °C, batteries fitted on board of ships sailing in unrestricted zone,
5 °C, batteries fitted on board of ships sailing in unrestricted zone or operated in moderate zone and installed in the engine room or compartments to heated by adjacent rooms,
-15 °C, batteries fitted on board of ships sailing in unrestricted zone or operated in moderate zone and installed in non-heated rooms,
-25 °C, batteries fitted on open decks on ships other than sailing only in the tropical zone.
Temperature coefficient a= , assumed:

Battery capacity is rated at start of one combustion enegine for 6 starts-up taking 5 seconds each. In case when one battery is a source for more than one starter, the total capacity should be calculated as a sum of the required capacity of the greatest starter and a half of the required capacity for each of the remaining starters.

Calculations were carried out based on the Polish standard PN-W-89509:1997 Merchant ships, batteries, selection, in accordance with the following equations:

wzór, where

Qr - required of capacity of the starting battery,

C - capacity related to the starter power (curves are available in the standard),

a - temperature coefficient (curves are available in the standard) taking into account reduction of the capacity due to electrolyte temperature,

0,75 - undercharge coefficient,

wzór, gdzie

S1 - minimum cross-section of the feeding cable due to heating [mm2]

Izw - short circuit current in the starter during start-up (curves available in the standard),

j - permissible current density shall not exceed 20 [A/mm2]

wzór, where

S2 - minimal cross-section of the cable due to voltage drop related to short-circuit current Izw, [mm2]

l - lenght of the cable, [m],

Un - rated voltage of starter, [V].