Tuesday, December 22, 2015

Range Anxiety never goes away completely

The longer you drive your electric car the more you grow accustomed to how much energy it will consume along the routes you regularly drive.  The occasional new route is usually no sweat because you already know your safe driving radius from your home.  I know I can generally count on driving 4 miles per tick (out of 16) on the charge-level gauge, with each tick representing about 1KWh of charge.  So, I can safely drive about 60 miles without much worry and still have a margin of about 4 miles remaining.  My drive to work regularly uses up nine ticks, leaving me with six or so to run errands near home after work.  Most places I’ll visit are within 5 miles of home, so this works out well.  The problem comes when I start traveling unknown routes that extend to the range of my safe-driving radius, especially when a significant elevation change is involved.

The case-in-point happened last Mother’s Day (actually, the day before – to avoid the crowds).  My siblings decided to treat mom to a picnic at one of the nearby wineries in the Saratoga foothills.  Ordinarily, the trip from my house to the winery is about 16 miles, with the final 3 miles involving a significant climb in elevation.  32 miles round-trip is easy to do.  But, it was my turn to bring along mom, so I had to drive first to her place (14 freeway miles) and then to the winery (10 miles), for a total distance of 48 miles round-trip.  But, that morning I had to run an errand and used up 9 miles of charge already, making the total trip for one charge about 57 miles.  Factoring in the uphill climb was starting to make me nervous about completing the trip.  Fortunately, I had surface streets as backup options for the return trip home.

The trip went better than I had expected, thanks in part to two factors.  First, my morning errand was done entirely on city streets, which uses about 20% less charge to drive the same distance.  The second factor was more significant.  I keep thinking like I did in my gasoline powered car …  If I started my trip with 14 ticks on the gauge,  I would need 7 remaining by the time I reach my destination or I might not make it home.  As I was about a mile from the winery, the seventh tick cleared and I knew I would only narrowly make it home if I didn’t plan my driving carefully.  But, I wouldn’t have to worry about that until after the picnic at the winery.  Then, on the way home, the second factor kicked in.  Driving three miles downhill give me back one tick on the charge gauge, meaning that I had an extra four miles I could drive, and I used nothing for those three miles – for a total of seven miles.  (I’m telling you, it’s a mind game driving the hills in an electric car.)  The end result is that I had two ticks remaining on the charge gauge when I pulled into my driveway, and I was even able to run to the local store and back for dinner supplies.

Friday, December 4, 2015

A busy day ahead

It all started off easy enough…  I was invited to a party at my younger sister’s place on the east side of town.  Then, my mom called and told me that my older sister would be arriving the same afternoon and asked if I could give her a ride to mom’s place on the west side of town.  Then my older sister called and wanted to join me at our sister’s party before heading to mom’s.  With a reliable 60+ mile range, I was starting to worry about whether I could drive that far.  I tried estimating energy use in my head by counting the charge-level ticks it usually takes me to drive each stretch and came up with too many unknowns (and not enough ticks leftover for comfort).  So, I let the real engineer inside me solve the problem.  That, and a little help from Google Maps.

So, I needed to bring supplies (ie: wine) to the party on the east-side, wait for a phone call for a trip to the airport (and back), then a trip from my sister’s party to my mom’s house, and finally home.  I broke the trip into segments and measured each using the Google Maps directions feature:  (1) my house to my sister’s party: 4.7 miles city/5.6 miles freeway; (2) my sister’s place to the airport: 8 miles mixed/10 miles freeway (each-way); (3) my sister’s place to my mom’s place: 18 miles freeway; and (4) my mom’s place to my place 13 miles.  If I saved time and stayed on the freeway, I would drive just under 57 miles, which is too close to the 60+ miles that tends to limit my car on the freeway.  So, I favored city routes where it made sense, cutting the trip to just over 52 miles, and extending the range by three miles or so along the way (by driving a little slower). 

How did it turn out?  The extra city driving added about five minutes to each leg through town, which was easily managed and really did not impact my plans at all.  After driving the 52 miles, I needed to make two more errands near home, bringing the total trip to 55.7 miles according to the trip odometer.  So the car made it, but how much charge was left?  Driving home from the last errand, the gauge ticked down just a few hundred feet from home, leaving three bars (out of sixteen) on the charge gauge.  Typically, this is enough to drive another 11 miles on the freeway or up to 14 miles around town (the range gauge suggested 15 miles remaining).  So, all told, I could have safely driven 68 to 70 miles this day.  Fortunately I didn’t need to run the A/C on the car, or the results would have been different.