Wednesday 19 March 2014

Impact of 'slow' vs 'fast' (rapid) charging on batteries

ecomento.com: DC fast (rapid) charging your electric car won’t unnecessarily damage its battery


Recharging any battery will cause it to degrade, although given the size and cost of electric vehicle batteries people are rightly more concerned about what happens with their cars than their laptops.

Furthermore, it has long been thought that the faster an electric car battery pack is recharged, the greater the degradation it will experience. This is true, but only on a much smaller scale than previously thought, a new study has shown.

After driving four Nissan LEAFs for 40,000 miles apiece – charging two from a domestic Level 2 charger (3.3kW) and the remaining two exclusively via a DC fast (rapid) charging station (50kW) – the Idaho National Laboratory discovered that battery degradation was roughly the same. The Level 2-charged cars experience 22 percent battery degradation while the fast-charged cars registered a 25 percent loss.

The study’s method is as stringent as realistically possible, with all four cars driven by dedicated drivers on fixed public road routes. Every day a morning drive is followed by an evening drive and the cars are charged up twice. When the LEAF shows an estimated remaining range of 5 miles, it’s time to head home.

It isn’t known whether the discrepancy widens as more miles are logged. After 6,000 miles there was no difference in battery degradation, but after 30,000 miles there was a three percent difference – equal to the difference after 40,000 miles.

The study also gives an idea of what kind of battery degradation LEAF owners can expect regardless of how they charge up. After 40,000 miles of driving with the climate control set at a constant 72 degrees Fahrenheit, the Level 2-charged cars had an average range of 57.5 miles while the fast-charged LEAFs managed 53.6 miles. The 2012 Nissan LEAF models used by the study had a EPA-rated 73-mile range when they left the factory.

While the study is ongoing, it has already revealed that fear of battery degradation is no reason to abstain from using the convenient and increasingly widespread network of DC fast charging around the US.

DC fast chargers are capable of replenishing 80 percent of an electric car’s battery capacity in around 30 minutes, compared to between five and nine hours for a 240V Level 2 charger, so the benefits are plain to see.