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Engine Starting |
Home -> Applications -> Engine Starting |
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Diesel engine cranking requires a battery capable of very high output current for a very brief period of time. When the battery is located in a cold ambient temperature and/or the battery is required to supply control loads in addition to the cranking current, the selection of the best battery will depend on all of these parameters.
The formula for calculating the capacity of the battery is:
C = Cc(hours) + Cs
where
C = Capacity in ampere-hours of the battery required
Cc = Continuous control load in amperes x time in hours the battery must supply the load
Cs = Capacity in ampere-hours of the battery required to crank the engine
The current required to crank a diesel engine is a function of the following parameters:
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Displacement of the engine (either in cubic inches or cubic centimeters) |
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System voltage (either 12 VDC or 24 VDC nominal) |
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Viscosity of engine oil |
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Temperature of engine oil |
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Lowest temperature of the battery |
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Efficiency of the starting motor(s) |
The lowest acceptable system voltage during the cranking cycle will further influence the required capacity of the starting battery. This will normally be 8.50 volts for a 12 VDC system and 17 .0 volts for a 24 VDC system as specified in EGSA-100b Standard  . Where the engine control/monitoring system requires a higher voltage or where a best battery selector is used with dual batteries, a higher capacity battery will be required to maintain the battery at a higher voltage.
In addition the capacity of the battery will be influenced by the number of cranking cycles and the duration of each cranking cycle. These are typically determined by regulatory requirements or by a specifying engineer.
Choosing the particular cell to achieve the lowest cost or other parameter (e.g. smallest physical size) is best done iteratively, using our Optisize computer program. Please complete deliver the completed sizing worksheet to our sales representative and we will be happy to size the battery for you.
Engine start battery sizing worksheet
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