Earlier this week, Daimler launched the online configurator for the 2015 Mercedes-Benz B-Class Electric Drive. Priced just at just $100 more than the BMW i3 EV — its closest competitor — the B-Class Electric Drive offers seating for five, as well as a larger cargo space and more conventional dashboard when compared to the i3.
Like the BMW i3, the Mercedes-Benz B-Class Electric Drive can be built-to-order with a range-extending option.
While the range-extending optional extra does add extra features — like improved thermal insulation to minimise heater use and a more aerodynamic grille — the heart of the range-extending capabilities of the B-Class Electric Drive lies in a special mode that can be engaged when required.
Unlike the i3 however, the range-extender isn’t an occasional-use gasoline-powered engine hidden under the load bay floor. Instead, the B-Class Electric Drive’s range extender is 100 per cent zero emissions and doesn’t require a drop of gasoline to be used.
But how does it work? And how can you get range-extending capabilities without an external power source?
Physical vs Useable Capacity
The key to the Mercedes-Benz’s range-extending capabilities lies in the differentiation between the physical capacity of an electric car’s battery pack and the capacity used by the car on a day-to-day basis.
While battery packs can theoretically be drained from a 100 per cent state of charge all the way to empty, doing so dramatically reduces the shelf life of the battery in question. As a consequence it’s considered good practice to design battery management systems which prevent a battery pack from being drained or charged beyond certain limits. This applies to everything from laptop computers to electric cars.
As a consequence, there’s usually a discrepancy between the physical capacity of a battery pack — the total possible energy it can store — versus the useable capacity of the battery pack — the amount of energy which can be stored between minimum and maximum levels set by the battery management system.
Like the Toyota RAV4 EV and Smart ForTwo ED, the Mercedes-Benz B-Class Electric Drive uses a Tesla-engineered battery pack and drivetrain.
That means it has the same battery management system, powertrain and basic pack design as Tesla’s famous Model S sedan. Like the Model S, that means the B-Class Electric Drive defaults to using less of its battery pack under normal conditions than many electric cars on the market today in the interests of battery longevity.
Like Tesla’s Range Mode
Essentially then, the Temporary Range Extender mode of the B-Class — which adds around 17 miles of range to the next charging session — is a little like the ‘Range Mode’ offered on Tesla’s own vehicles.
Range Mode operates by charging the Model S’ battery pack to a higher physical state of charge than the default charge mode, allowing the car to travel slightly further as a consequence. The B-Class Electric Drive’s optional range-extender does the same thing.
Like the Model S however, using this feature all the time will eventually reduce the lifespan of the B-Class Electric Drive’s battery pack, meaning that it should be used only when absolutely necessary. Unlike the BMW i3 REx and other range-extended electric cars with gasoline engines, it’s worth noting too that you need to pre-emptively plan to use the B-Class range-extending mode.
In other words, you have to manually choose to add extra charge before a long trip, rather than expect the range extender to help you out when the battery pack has already reached a low state of charge.
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