Life With 2013 Tesla Model S: 'Vampire' Thirst For Electricity At Night?


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

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

Enlarge Photo

A couple of weeks ago, shortly after I took delivery of my 2013 Tesla Model S, I noticed that my home electric meter seemed to be running a bit faster than normal.

I keep a close eye on my meter, but that seemed odd.

After all, the long-awaited new luxury sport sedan delivered to my house in February by Tesla Motors [NSDQ:TSLA] was simply replacing electric miles I had been driving in my Chevrolet Volt.

The two cars have about the same efficiency in winter. So it shouldn't have taken notably more power to run the Model S than the Volt, right?

I decided to try an experiment. Unplugging my 60-kilowatt-hour Model S for the night at 9 p.m., I made a note of the Rated Range display, which read 169 miles.

Next morning, the range had dropped to 153 miles.

I left the car unplugged again the next night. (Temperature was in the 20s, a bit colder than the previous night.) Range dropped  from 89 miles to 66, a loss of 23 miles. 

What was going on here? Many days, I don't drive even 23 miles.

Was the Model S actually a "vampire" that used more electrical power just sitting overnight in my driveway than it might use during a typical day's driving for me?

Two more unplugged tests confirmed the pattern: 10 miles range lost in 9 hours, then 23 miles lost over 22 hours. On average, I'd been losing roughly a mile of range for every hour the car sat unplugged.

This was different: It wasn't just a design quirk, like the good and the bad points of the Model S that I wrote about recently.

This was taking money out of my pocket and putting carbon into the atmosphere.

No State-of-Charge Readout

Unfortunately, the Tesla Model S has no direct readout of the battery state of charge (SoC). There's just an undelineated bar graph that gives you a rough idea of remaining charge.

With no direct SoC readout (either as a percentage or in actual kWh), the only way to estimate vampire losses is to extrapolate from the lost range. 

In normal driving, the Model S uses about one-third of a kilowatt-hour per mile.  My apparent 24-mile-per-day loss thus translated into about 8 kWh of electricity.  That's about a third of my total daily home electrical consumption, not counting the two electric cars.

If those mileage-loss numbers were correct, my Model S's apparent vampire losses would amount to almost 9,000 miles of driving a year. 

Delusional Owner's Manual?

My numbers were wildly contradicted by the Model S owner's manual.

"When you're not driving Model S," it purrs reassuringly, "the Battery discharges very slowly to power the onboard electronics. On average the battery discharges at a rate of 1 percent per day."

One percent? Based on my unplugged mileage-loss numbers, my battery appeared to be discharging at about 12 percent per day.

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

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

Enlarge Photo

Hotline to the rescue

Tesla has recently established a hotline phone number for Model S owners with problems or questions, so I decided to give it a call.

The guy on the phone quickly confirmed the vampire problem.  It seems that the "sleep mode" in the original Model S software--the basis for the owner's manual statements--had caused so many glitches in other car functions that it had been disabled.

With sleep mode missing from the current v4.2 software, he said, I could expect to lose about 8-10 miles of range per day when unplugged.

Using the rough three-to-one conversion ratio, that worked out to about 3 kWh per day.

He assured me Tesla was working  to come up with new sleep-mode software as soon as possible, but he offered no estimate of how long it might take.

Last week, Elon Musk addressed the vampire/sleep-mode issue in a meeting with Norwegian Model S buyers in Oslo. Musk promised that the new sleep mode would reduce vampire losses to a mere 0.2 percent--a miniscule 170 watt-hours--per day.

And, he said, the new sleep-mode software would be installed by the time the Model S was introduced in Norway--currently set, he said, for July.

Faulty mileage readings

But my apparent vampire losses were more than double what the hotline rep said they should be. Did I have a special problem?


 
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