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RECHARGE TIME is a major shortcoming of battery electric vehicles. As an all but impossible target, a conventional car’s fillup at the corner gasoline station takes perhaps five minutes.
By comparison, a typical BEV’s Level-1 recharge, using a dedicated 110-volt/20-amp AC outlet, can be 10 hours or more. A Level-2 recharge, with its own 220-volt/40-amp AC source, cuts the time approximately in half.
Level-3 Quick Charge involves specialized hardware for its 440-volt high-amp DC source as well as on the car. It’s still no contest with a conventional refill, though, taking perhaps 30 minutes to refresh 80 percent of a battery pack’s capacity.
Any recharging involves chemical activity within the battery which causes inevitable battery degradation. There’s no counterpart with a conventional car: It would be like its gasoline tank shrinking slightly with each refill.
What’s more, Level 3 achieves its Quick Charge through accelerating the chemical activity—and this comes with increased degradation.
This was one of the topics addressed by Matt Shirk of the Idaho National Laboratory at the SAE 2014 Hybrid & Electric Vehicle Symposium.
Shirk’s presentation, “DC Fast, Wireless, and Conductive Charging Evaluation Projects,” described on-going activities at INL, one of 21 national labs. (Other labs doing automotive research include Argonne, Oak Ridge, Sandia and the National Renewable Energy Lab).
Summarized here are INL results to date, specifically on DC Quick Charge and its effects on battery capacity and BEV performance.
Four Nissan Leaf BEVs are being evaluated, two charged exclusively with Level-2 AC, the other two exclusively with Level-3 DC Quick Charge. The cars are driven in pairs, one Level-2, one Level-3, charged twice each day with switched pairing.
Leaf climate controls are set to an automatic 72 degrees Fahrenheit. When any one car gets down to an estimated five miles of estimated range, they return to base.
Recharging of either type demonstrated degradation of battery capacity. At 10,000 miles, for instance, both pairs exhibited an average six-percent degradation in capacity.
At 30,000 miles, the Level-2 pair degraded an average 14 percent; the Quick Charge pair, 17 percent. By 40,000 miles, the average degradations were 22 percent and 25 percent, respectively, for the Level-2 and Quick Charge pairs.
That is, INL data suggest that the amount of degradation depends more on the miles traveled than on the nature of recharging.
The slight differences in degradation based on charge type resulted in relatively small differences in average range. Over 10,000 miles of their Phoenix road route, the Level-2 Leafs averaged 72.5 miles per charge; the Quick Charge pair, 71.0 miles. In the interval of 40,000 to 48,000 miles, the average ranges were 57.5 miles and 53.6 miles, respectively, for the Level-2 Leafs and Quick Charge pair.
The study is continuing into this month, March 2014. The final paper will include track performance testing, road data and laboratory analysis. Details can be accessed at http://avt.inl.gov.
To summarize the results, both miles traveled and recharge type degrade EV battery capacity and range, something that has no counterpart with conventionally fueled cars. Also, the type of recharging appears less crucial than the miles traveled. ds
© Dennis Simanaitis, SimanaitisSays.com, 2014