Saturday, February 13, 2016

Gone with the wind

Walking into the wind takes a little extra effort than walking in still air.  Walking into a strong wind takes a lot of extra effort.  Bicycling into a strong headwind really slows you down, and that’s only at a speed of about 15 to 20 miles-per-hour.  So, you can imagine my surprise at how quickly the power depletes from my car’s battery while driving down the freeway into a strong headwind.  At first I thought that maybe the tires were a little low and in need of a good pumping up.  Then I looked at the tree tops.  (The palms are a dead giveaway.)  The top branches were swaying in the wind, suggesting a strong wind was working against me. 

How big is the difference in energy consumption driving into the wind?  Normally, my drive from home to the exit I would usually take for work (and to visit mom, and to drive up to the winery) uses about three ticks of energy on the gauge.  Driving into a strong wind, I noticed that the energy used at any moment to maintain speed was slightly higher, but shortly after taking my exit, I noticed the forth tick drop off.  I cover a distance of about 13 miles, suggesting that the extra wind load uses about 20% more energy.  Considering that the battery performs a little worse in colder weather (such as typically happens with a strong wind), I would attribute about 10% to 15% of the extra 20% power drain to the wind itself.

The impact of this extra power drain is more significant than it seems, especially for freeway trips.  Under better conditions, my now four-year-old battery can travel about 58 to 62 miles on a charge, mostly on the freeway.  If I am driving into a strong headwind, that range drops to 49 to 56 miles.  Even when I was working in Palo Alto, the 49 miles was enough to get me to work and back, and a quick trip for tacos nearby for dinner.  But, if I had planned to visit the wine store (an “errand”) in Redwood City during lunch, then that would add another 12 miles to my trip, meaning that I would be at risk of not making it home from work on a windy day.  When the battery was newer, the range was closer to 70 miles, and even a 15% drop in efficiency would still get me to the wine shop and home.

Monday, February 1, 2016

Charging atop a mountain

After losing my job due to a company layoff, and while searching for work (a full-time dedication for an older engineer), I found myself missing the moral support of coworkers (and a paycheck).  So, I decided to apply for work at a winery that was only open to the public on weekends.  This would mean that I would have the option to keep the job even after I resume my career, allowing me to build my experience working in the wine-hospitality industry.  The winery is atop the mountains in Cupertino at an elevation of 2,200 feet.  (Home is a mere 100 feet above sea level.)  The winery also has a level-2 EV charger available to employees.  Having driven to the winery twice before, I knew that the EV charger would be a comfort more than a necessity for getting up and back on one charge.

My prior experience driving up the mountain suggested I would use one-half of the total charge to drive up the mountain.  I would also regenerate about 10% coasting back down the hill, allowing me more than enough power to make it home (and to the store).  So, on my third trip up the mountain for work, I learned about charging atop the mountain.  I had only driven about eight miles the day before and decided not to recharge before driving to work.  When I got to work, the power level was lower than I am usually comfortable with, so I plugged in the car (just towards the end of my shift).  By the time I had disconnected, there was just one bar remaining (out of 16) to be filled, and I knew that the remaining energy would be generated while braking on the trip down the mountain.

Apparently, the engineers at Mitsubishi had anticipated my very situation and had to prioritize the survival of the charging system.  Once the car’s battery is nearly full, most EV chargers will send less current to the car (as observed using the ChargePoint web site dashboard).  It would seem that this is at the request of the car, not the charging station.  While driving downhill, this time I noticed that the amount of regeneration happening was a fraction of its usual potential.  It dawned on me then that the same battery-protection logic had kicked in and the battery was accepting less charge from the brakes.  That meant that I had to work harder using the friction brakes to slow down the vehicle.  As the charge level approached full-charge, the regeneration brakes were almost completely ineffective and I was relying almost entirely on the friction brakes.  While this is only a minor problem, the biggest concern is having to take the turns more slowly because the friction brakes act on all four wheels, while the regeneration affects only the rear wheels, allowing the front wheels to dedicate all friction to traction in turns.  (Only the Tesla and BMW share this rear-wheel drive configuration with my Mitsubishi – all others are front-wheel drive.)   

So, what have I learned from this experience?  I have to time my charging carefully when atop the mountain.  I estimate the time needed to attain a full charge (say about four hours), then I deduct an hour from the charge time and start a timer on my phone.  When the timer’s alarm goes off, I dash out quickly to unplug the car.  This leaves me with just enough empty battery capacity to run the regenerative brakes nearly all the way down the mountain.  (In the winter months, I soon learned that I could drive down the mountain in toasty comfort by channeling excess power generated by the brakes into the cabin heater.)

Monday, January 18, 2016

The new charging stations arrive too late

Actually, the new charging stations at work could not have arrived soon enough.  The demand for (free) charging at my company quickly outstripped the availability of charging stations.  Even with a four-hour limit, there still was not the right combination of etiquette and charging points available to meet everyone’s demands (as opposed to their needs).  Of course, had there been a cost for the electricity delivered for car charging, the situation would have changed.  Adding a nominal charge (say eight to ten cents per kilowatt hours) likely would have driven away the folks trying to get their EV charge for free while still allowing those needing a recharge to make the return trip home a chance to charge economically.  I know this because what happened next supports my theory.

The next week, I needed to make a shopping run at lunch time that would add another 12 miles to my 39-mile commute.  While the extra distance could be covered safely by the full charge I had started with when leaving home, it would have been more comfortable knowing I had some extra range instead (just in case I needed to rush somewhere).  So, upon returning from my errands, I found that the existing chargers were oddly vacant, so I pulled into a parking spot happy to have found the charger available.  Regrettably, the company had made the decision to stop subsidizing the cost of electricity for car charging and had begun charging $1.00 per hour connected.  Since my car draws electricity at a rate of just three kilowatts per hour, this amounts to about 33 cents per kwh.  At home I pay about 11 cents, so I decided to just rely on the remaining charge in the car battery and forgo any evening driving.  It would seem that with the installation of the new charging stations, the company had decided to switch to market-rate pricing at the same time.  Had they simply made the switch earlier, they would not have needed the new charging stations, as there were plenty of open spaces without the new stations.

Alas, all of this no longer matters to me.  I just received notice that my talents will no longer be needed and I was given a standard severance package.  This time, I am hoping to find work a little closer to home where I don’t have to worry about forgetting to charge the car one night.  There are a number of possibilities ahead for me, many of which offer EV charging on-site.  I’m both hopeful and a little scared at this point – this is my first time to be on the lay-off list since I began my career so many years ago.

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.

Friday, June 19, 2015

Good things come of people behaving badly

Somebody must have noticed the situation at work with the level-2 electric vehicle chargers.  Lately, the EV mailing list has been fired off with regular announcements of people leaving their car in the charging spaces after they have finished charging while others practically beg for a couple of hours of connection time.  (It doesn’t help that nearly all the convenient parking is now in use too, leaving disconnecting folks limited parking options.)  People are struggling to learn the new etiquette surrounding public infrastructure sharing.  We all struggle to find an opportunity to charge, but we seldom think about our impact when we fail to disconnect and vacate the charging space in a timely manner.  Sharing is a trait acquired in one’s youth when growing up with siblings, although this can also lead to hoarding.  Fortunately, the company decided to take the next step toward being a good advocate of electric vehicle adoption.

About two weeks ago, I noticed that a number of parking spaces near the employee entrance to the building had been roped off, and digging/trenching was underway.  I followed the route (visually) of the trenching and saw that it connected to the building and up to the roof (where the solar panels are).  I asked one of the construction crew members what the project was and they said they were working on installing four new charging stations with two plugs each, producing eight new charging spaces.  Added to the existing fourteen plugs and that amounts to more than 50% more charging points for us electric vehicle drivers.  Now, as I walk past the site each evening as I leave, I admire the new stations as they await final connection in the coming days.  Soon, we won’t have to depend quite so much on everybody’s etiquette and consideration.  I can hardly wait.

Saturday, June 6, 2015

To charge, or not to charge

Anybody over the age of 30 remembers the first NiCad rechargeable batteries from the 1990’s.  These batteries needed to be depleted completely before recharging or they would “remember” how much you used and only recharge that amount in the future.  NiMH batteries got rid of the “memory” issue, but did little to improve charge capacity or battery life.  My first hand-held device had a Li-Ion battery and came with instructions to let the battery drain to 25% to 75% before recharging.  I followed that advice to a large degree and managed to get three years of useful charge from the battery before it started to dwindle.  I did not follow that advice for my laptops and those batteries all failed to hold the originally promised charge beyond two years.  With my first two cell phones, I was diligent about appropriate battery charging and managed to get more than four years of nearly full charge capability from each before the batteries started to degrade.
Five ticks remaining on the I-MiEV charge gauge (5/16)

So, before I even bought my electric car back in 2012, I knew how to better care for the battery.  Wait for the charge to drop below 75% full before recharging and avoid complete discharges when possible.  My commute usually draws the battery down to about 45% remaining, so this represents an ideal point at which to recharge the car.  But, when I know I will be working from home the next day, should I wait to charge the car or charge it right away?  The ideal choice for extended battery life (according to articles I have read) is to complete charging within an hour or two of when you expect to drive again.  The thinking here is that maintaining a full charge for an extended period strains the battery, ultimately weakening it.  But, the practical choice is to have the car ready to drive in case of an unexpected need the next day (which seldom happens for me).  So, I choose to charge at night and have the car sit fully charged the next day.

The real trouble arises when I use the car the next day to run a short errand and I use less than 25% of the battery capacity.  (Typically 85% to 90%of the charge will remain.)  Then I have to drive to work on the following day.  I admit that I like my comfort zone when it comes to the car’s range.  I don’t enjoy learning just how far I can push the car without running out.  While I can get to work and back and still have at least 25% of the charge remaining, it reigns-in my after work activities, limiting me to a short trip to a local store.  On the other hand, recharging with only 10% to 15% drawn off the battery will accelerate its decay.  When I know I need to do some extra driving I will recharge before driving to work.  When I have no plans, I drive on the reduced charge and hope for the best.  Sometimes, I have the option to charge once I get to work, which allows me to run those after-work errands.  To date, my efforts have paid off as I have lost less than 5% of the original driving range after 41 months of ownership.  (Mitsubishi warrants that 80% of the charge capacity will remain useful for ten years.)