Tom Saxton: December 2009 Archives

Cathy and I are both puzzle nuts. We have two daily puzzle calendars to jump start our brains during breakfast. Cathy has a diverse taste in puzzles and is frequently working her way through a book of Japanese puzzles while I'm reading the newspaper at night. I'm not talking about Sudoku, she chews through puzzles like Kakuro and Hanji.

In addition to solving puzzles, she also likes to create puzzles, which is much harder and far more time-consuming than solving them. Quite often, I get a sequence of puzzles on my birthday each of which has an embedded clue to the next puzzle, eventually leading to my birthday gift.

This year we were extremely busy for the two weeks leading up to my birthday. We spent a week in Hawaii prepping our condo for a new rental agency, then spent the next week being EV groupies attending all of the Nissan Leaf events in Seattle, then on Saturday Cathy was the head judge at the Washington State FIRST LEGO League Championship. Anyway, we were busy and I was sure Cathy didn't have time to create any puzzles.

So, I was quite to surprised to find a puzzle sitting on the bar at breakfast. I like doing Marilyn vos Savant's Numbrix puzzles that accompany her column in Parade magazine, so Cathy created a jumbo size version. This is probably the only puzzle format for which I am more practiced at solving than Cathy, but she still managed to create a puzzle in that format, larger than normal, challenging for the type, and yet still solvable.

It was a good puzzle and I enjoyed solving it. If you want to try, download this PDF version. When I was done, I was amazed she had created such a nice puzzle and couldn't imagine when she had time. I wondered if it was the first clue of a treasure hunt, but I didn't want to assume it was and have her think I was disappointed to have just a single puzzle. I also couldn't imagine how solving a Numbrix could yield a clue to another puzzle. While all of this was running through my brain, she was giving me the look that says, "you're not done yet." Stop reading now if you want to try to find the clue to the next puzzle without a hint.

While I was solving the puzzle, I realized that sometimes when I work these puzzles, instead of writing in the numbers, I just draw the path through the sequence connecting the centers of the boxes in order. It actually occurred to me that might be interesting, but I couldn't imagine how that could yield a message. Cathy realized that by drawing lines in the manner I described, there are 7 letters that can be easily formed: CEHISUY plus maybe a couple of others like T and L that might work but leave odd shaped areas to be filled to complete rectangular blocks. If you solve the puzzle then draw the sequence line you'll see a word that told me where to look for the next puzzle.

If you'd like to try working this one on paper, download the PDF version. Four of the clues require a bit of inside knowledge, but it's probably doable anyway. Stop reading now if you want to try it without any hints, if you perhaps know the cars we drive, enjoy shows at the Village Theatre and were an applications programmer at Microsoft in the 1990s.

1 Down is a reference to the Hungarian naming convention used by some programmers at Microsoft where "max" means "one more than is allowed." This photo of one of our cars  will give you the answer to 4 and 6 Down. 25 Down is a reference to a line in Chasing Nicolette, but you can probably get it from the other clues without knowing the show.

For the month of November, I drove the Roadster 762.2 miles. That's mostly with just me in the car driving a variety of city and highway miles. I tend to drive enthusiastically most of the time, but the month also included a roundtrip drive to Longview, WA on cruise control at 55 mph.

During the month, I put about 247.8 kWh into the car from the wall (213.3 kWh metered from my garage plus approximately 34.5 kWh from an unmetered NEMA 14-50 outlet in Longview). That's 325.1 Wh/mi and includes charging losses, battery pack self discharge, heater, headlights, etc. That's my wall-to-wheel number and is based completely on things I can measure.

From July 25th to August 27th, I drove the Roadster 696 miles and pulled 234 kilowatt hours (kWh) from the grid, giving us 336 Wh/mi. That included some hot weather and four 1/4 mile runs at Pacific Raceways.

On individual charges, I see efficiency vary from 240 Wh/mi to over 400 Wh/mi, and obviously much higher for things like drag racing.

I charge consistently at 240V and 40A at home. In Longview it was 230V and 40A. Because of charging overhead, I assume I would get slightly better charging efficiency if I charged at home at 70A. So, my numbers are just that, my numbers. Another driver would get different numbers depending on driving, weather, road conditions, and charging habits.

The EPA estimates documented in the paperwork for our car say 260 Wh/mi city and 290 Wh/mi highway. I've seen information from early 2008 Roadsters that had the EPA numbers and 340 and 360 Wh/mi.

You may have heard Roadster owners talk about numbers well below my 330 Wh/mi numbers. These are most often the number reported by the car's info screen which are not wall-to-wheel numbers, and in fact are (as far as I know) not at all documented as to what that number means. I have figured out some things about the numbers reported by the car, which I'll now explain.

For the month of November, the Roadster's trip meter says that I used 207.9 kWh, and thus 272.8 Wh/mi. But what does that mean? Did I push 207.9 kWh into the motor, or is that net of energy pushed back into the pack from regenerative braking (regen)? Does it include energy used to run the accessories and/or running the coolant pump and fans during charging?

On the "Energy History" screen, the Roadster tells me my "net energy used" for the month was 233 kWh and that I got 26 kWh from regen. What does "net" mean? I would assume that "net" means "net of regen," i.e., power from battery pack minus power into battery pack from regen. Except, if I compare those numbers to what the trip meter says, I notice that 233 - 26 = 207, which is suspiciously close to the energy use number reported on the trip meter.

From that, I infer that the trip meter's number is net energy use from the battery pack (power drawn minus regen put back in), and thus the so-called "net energy" from the energy use screen is really the gross energy pulled from the battery pack including energy that went into the pack from both wall charging and regen charging.

Do these numbers include the energy spent on accessories? Is the difference between what I put in through charging (247.8 kWh) and the car's reported net energy use (207.9 kWh) just charging losses or does that also include accessory use? I have no idea.

The only number I can stand behind, and the only number I can compare with other electric vehicles, is the wall-to-wheel number. The efficiency number reported on various of the Roadster's info screens is useful for understanding how driving style and conditions affect efficiency and for predicting/optimizing range, but is seemingly useless in any other context.

I believe the same is true of any efficiency number for the Leaf given out by Nissan, or any other EV manufacturer or driver, unless that number is as clearly defined and directly measured as the wall-to-wheel number.

It used to be that the Tesla screen reported an energy number after each charge that was much lower that what was actually drawn from the wall. I suspect that was the energy that actually made it into the battery pack, but I never saw it defined by Tesla. More recent firmware versions are reporting a number that is close to the number I read from the wall meter (and averaging multiple consecutive readings together agrees to within 1% of the wall reading). This is a big step forward for drivers who want to monitor their actual wall-to-wheel energy use and efficiency, but don't want to go to the expense of installing a dedicated meter. It would be a real benefit to the Tesla community if Tesla would (a) define the number they currently report and (b) make the energy drawn from the wall across multiple charges easily available.

Regarding range on a single charge, my personal record is 192 miles driven with a passenger in 100+ degree weather starting with a bit less than a full charge and ending with 10 miles of range left. On the trip back from Longview in cool weather, I drove 136.9 miles using cruise control at 55 mph using 55% of the battery. To the extent that you can extrapolate that to the full battery, that figures out to about 249 miles of range. On the trip down to Longview earlier the same day, also using cruise control at 55 mph, it was raining and colder, so I had the wipers, headlights and heater on and used 65% of the battery pack, for an extrapolated range of 208 miles.

My car is a 2008 Tesla Roadster with firmware version "3.4.15 15" (upgraded from "3.4.13 15" on 11/15/2009).

Edited at 10:23 pm on 12/13 to correct typo in second paragraph.

Today, Cathy and I both got to drive the Nissan Leaf test vehicle, apparently a Nissan Versa outfitted with the Leaf's drivetrain. Coincidentally, last week we rented a Versa on vacation, so we were treated to a virtual side-by-side test of gas versus electric. They had a course laid out with cones in a parking lot, which I treated as a small autocross course. The test vehicle handled well and had good pick-up, better than the gas-burning Versa.



Most interesting was how quiet it was. The Roadster has a loud gearbox whine when accelerating, plus road and wind noise. The whine is much quieter than a gas engine doing similar acceleration, but it's not silent. The RAV4-EV has a comparable road noise level, maybe a few dB below the Roadster and minus the loud drivetrain whine. Both the Roadster and RAV4-EV are about 7 to 8 dB noisier than Cathy's parents' Honda Accord doing 60 mph on the same section of average freeway surface. (We measured all three vehicles with a Radio Shack sound level meter.) The Nissan test vehicle was very quiet from the inside, I think quieter than the Accord, but we didn't do any measurements. From the outside, you hear the same tire sound you hear from any decent modern sedan.

Before buying, I'd want to take it for a real test drive, get it up to speed on the freeway, etc. That said, based on our test drive today, I'd highly recommend it to anyone who is an early adopter, very interested in driving an all-electric family sedan, and whose driving habits could be met by the Leaf's range.

That assumes that Nissan doesn't bungle the whole thing by forcing buyers into some ludicrous over-priced battery lease.