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Life With Tesla Model S: Pushing the Range Limits In 60-kWh Car


2013 Tesla Model S electric sport sedan [photo by owner David Noland]

2013 Tesla Model S electric sport sedan [photo by owner David Noland]

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In the eight months I've owned my 60-kWh Tesla Model S, I've never had occasion to drive it more than 120 miles, comfortably within the car's  EPA-rated 208-mile range. The phrase "range anxiety" was not in my lexicon.

But last week, I got an invitation from Don Sherman, Technical Director of Car & Driver magazine, to meet him in Danville, Pennsylvania. It's 168 miles from my home in New York's Hudson Valley.

Sherman was making a dry run for an upcoming article about a 700-mile cross-country race in a Model S--and Danville, just off Interstate-80, was going to be a charging stop.  We'd e-mailed back and forth about Model S driving and charging strategies, and this would be a chance to meet and compare notes.

The journey seemed short enough to be eminently doable--yet long enough to engender, if not range anxiety, then at least acute range awareness.

Fast and hilly

Although I supposedly had a 40-mile cushion in the 208-mile EPA range, I knew very well that my mileage may vary. 

2013 Tesla Model S [photo: David Noland]

2013 Tesla Model S [photo: David Noland]

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I was planning to drive fast, from 70 to 75 mph along the Interstates that made up most of the route. The terrain was hilly. There would be a prevailing headwind. And the advancing fall season promised cooler temperatures.

All of these factors would eat into range.

100-percent charge

In preparation for the trip,  I set the battery charge level at 100 percent, the first time I'd done so.

Previously, I'd always used the  "standard" setting, 90 percent of capacity. To get a full 100 percent, you set the charger to "range" mode, which Tesla recommends only when maximum range is necessary.

(The reason:  Lithium-ion batteries degrade more quickly when charged to 100 percent of capacity.)

A couple of months ago, a software update from Tesla allowed the charge limit to be set at any level. Tesla recommends 50 to 90 percent for everyday driving. I had settled on 75 percent, which was plenty for my normal driving routine.

But for this trip, I set the charger to 90 percent the night before, then topped off the battery to 100 percent before departure the next day. The topping-off process took longer than I anticipated; charge rate dropped from the usual 10 kW to about 3 kW for the last few kilowatt-hours. 

As I rolled out of my driveway, on an unseasonably warm Indian Summer day, the range meter read 199 miles.

David and Adam Metcalf beat 400 miles on a charge in a 2012 Tesla Model S (Image: David Metcalf)

David and Adam Metcalf beat 400 miles on a charge in a 2012 Tesla Model S (Image: David Metcalf)

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Vanishing regen

The first thing I noticed was that the regenerative braking virtually disappeared with the 100-percent charge.  Charge rates in max regen can approach 40 kW,  way too much for a nearly full battery.

Going down a long, steep hill near my house, I actually had to use the brakes. Damn! Wasting precious energy already!

Fortunately, full regeneration came back quickly, within 10 miles.

Efficiency readouts

I don't have a lot of faith in the Model S range meter. Its number is a projection based on rule-of-thumb efficiency assumptions, battery temperature, and a safety fudge factor.  (New York Times reporter Jonathan Broder famously fell victim to wildly fluctuating range numbers.) I call it the guess-o-meter.

Instead, I monitor the  dashboard readout of trip efficiency, measured in Watt-hours per mile. During my earlier shorter stints of highway driving, in warm weather, I'd averaged  290 to 300 Wh/mi.

I figured if I could maintain that level of efficiency, I'd make it to Danville with about 30 miles to spare. The Wh/mi reading thus became my prime focus for the trip.

Initial anxiety

For the open stretches of Interstate, I set the cruise control on 74 mph. (I figured no self-respecting cop would stop me for breaking the speed limit by single digits.

Forty miles out, along I-84, the e-meter settled in at around 310 Wh/mi. With the usual minor ups and downs for hills, the number crept steadily upward as I crossed into Pennsylvania.  By the time I reached Wilkes-Barre--about halfway--it was reading 330.

Not good.


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