VS - Electrical Systems From Stop-Start to Hybridization

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Cranking capability vs. Depth of Discharge The scheme below illustrates the link between the battery Depth of discharge and the cranking power @ 25°C ●● A brand new battery can support a higher Depth of discharge providing the required power for cranking. ●● Progressively as the battery drops in performance, it can no more withstand a large Depth of Discharge to support the required cranking demand.

The cranking capability in Stop-Start systems is highly dependent on the Depth of Discharge; it relies on battery type and sizing, ambient temperature, charging system, overall electrical demands and cranking energy demand. Cranking capability is assured if a sufficient power level can be supplied whatever it is a reinforced starter or a belt driven reversible machine as i-StARS. The cranking phase can be completed as long as the state of charge is sufficient, in other words as long as the usual battery Depth of Discharge does not go over a certain level. The usual depth of discharge relates to a certain range where the battery state of charge varies according to the bordnet needs and generator charging ability (engine rpm).

As long as the maximum depth of discharge allowed to crank is higher than the usual Depth of Discharge range, the cranking ability is guaranteed.

Evolution of cranking capability at 25°C

Battery power

Usual DoD

NEW battery USED battery

The maximum Depth of Discharge to re-crank securely at 25°C after aging of the battery must be HIGHER than the usual Depth of Discharge (DoD) zone in green.

25°C

Aging

Depth of Discharge

Max. Depth of Discharge to re-crank securely at 25°C with a new battery

Max. Depth of Discharge to re-crank securely at 25°C after aging of the battery

The maximum Depth of Discharge to re-crank securely at 25°C after aging of the battery must be HIGHER than the usual Depth of Discharge (DoD) zone in green.

The temperature level affects dramatically the cranking power and the battery capacity; this must be considered during the battery choice.

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