Before taking delivery of my Model S I had some range anxiety, but since taking delivery it has rarely come up. I charge daily to 90% in my 85 kWh Model S and drive about 100 miles a day commuting, running errands, etc. I return home with about 140 miles of range left every day which is enough to do it all again without charging. There have been a few longer round trips where I did about 180 miles round trip, and one intentional (but not required) visit to a Supercharger, but none of my trips have required charging en-route or destination charging.
As the end of the summer approaches I have two road trips coming up. One to NJ, about an hour west of NYC, and another to PA about an hour northeast from Pittsburgh. The NJ one is this week and is the subject of this post. The PA one is the subject of a future post.
The first thing I did was look at the distance. There are a few routes that I could take but the travel distance is about 244 miles. If I range charge i’d have 265 miles of range but those are rated miles which are not the same as actual miles. Your actual mileage may differ from rated mileage due to terrain, traffic, air conditioning, pit stops/detours etc. These numbers were close enough that I was already convinced i’d need to charge along the way and that wasn’t a big surprise to me. I also needed a safety margin.
Recommendations for a safety margin vary. Here are 3 popular options and what I would be able to use if I started at a 90% charge of 240 rated miles:
- A fixed amount: 50 miles – Can only use 190 rated miles
- Only plan on using a fraction of rated range: 2/3 – Can only use 160 rated miles
- Maintain a safety margin percentage: 25% – Can only use 180 rated miles
So somewhere between 160-190 rated miles i’m going to need to charge. I could stretch that a bit with an initial range charge if needed.
Note that all these safety margins are pretty conservative and experienced owners cut these margins way down and/or vary their margins based on the time of year/weather.
Next I looked at Supercharger locations along my route. There are a many ways of doing this, i’ll just mention two:
- Google maps – Enter your start and end addresses and then type “Supercharger” and have Google find Superchargers on the map along your route. Pick a good one (or more if needed) as waypoints.
- EVTripPlanner.com – This is a cool site put together by an enterprising 16 year old. With this site you enter your start and end addresses and some car information and click the “Route through Superchargers” button and it gets you to your destination through superchargers. Its not perfect and it can add more stops than needed so check the work and adjust as needed. One great benefit from the site is it predicts how many rated miles you will use and reports both actual and rated miles used.
I used EVTripPlanner and found that while it wanted me to hit the Milford, CT Supercharger and the Darien, CT Supercharger, I would have plenty of range to skip the Milford, CT Supercharger. From my home to the Darien Supercharger its 147 miles and the tool estimates 161 rated miles needed. That’s well within the most conservative of the safety margins above starting with a 90% charge.
From there it was only 93 miles to my destination or 102 rated miles estimated and no more charging would be needed to get there.
But the planning doesn’t stop there.
How much to charge
With an ICE car, when you fill it up it fills quickly, doesnt really slow down as you fill and generally you fill it all the way. EV’s are different. EV charge rates taper off quickly as they approach the 100% mark which can add significant time to your charge. Also EV’s charge faster from near empty than they do from half full.
When you look at charge times and rates on Tesla’s site, those are generally ideal conditions with a perfect Supercharger to current specs, nobody sharing a portion with you and charging your car from empty. You will likely need more time to charge than those estimates.
So from the section above, I start with 240 rated miles on a 90% charge. I drive to the Darien Supercharger and use 161 rated miles. I have 79 miles of rated range left. Not enough to get me to my destination and the reason for my stop. The planner estimates 93 miles needed with no safety factor. Safety factors are generally added to standard (not rated) mileage. I need to add some safety factor so lets take the 2/3 approach. 93 x 3/2 = 140 miles of rated range needed to arrive at my destination. So I need to add 61 miles of rated range at the Supercharger to get to my destination and have a good safety margin.
Sometimes you may need to charge more than you think – plan for the return.
Tesla claims 170 miles of rated range added in 30 minutes, but as we’ve mentioned they’re overly optimistic with this. Even so, planning for a stop of about 30 minutes is very reasonable and thats after driving for a couple hours.
So i’ve got myself there with a safety margin with a short Supercharger stop along the way, but i’m still not done.
Unlike our homes as EV owners, our destinations will rarely have a decent charging setup. Unless you’ve “gifted” charger setups to the people you’re visiting (several have done this), you’re likely to find some pretty poor charging infrastructure at the destination.
In my case as far as I know the best i’ll see at my destination will be a standard 110V 15A plug that provides about 3 miles of rated range per hour. I’ll definitely poke around when I get there to see if I can find a better outlet that I can reach, but I need to plan for the worst.
If I charge the minimum at the Supercharger to get to 140 miles of rated range, drive and use the estimated 102 miles of rated range i’ll arrive at my destination with 38 miles of rated range left. On the way home I need to go back the same route and I need that 140 miles of rated range for the distance plus safety. Oops — I can’t get home.
Destination charging is important.
So I need to add 102 miles of rated range while i’m there. More if I plan on doing things with my car while I’m there like showing it off with test drives, going to dinner, etc. Lets say I need 50 miles to use while i’m there, plus the 140 to get back to the Supercharger. I need to add 152 miles of rated range. At 3 miles/hour thats 51 hours of charging. For a 3 day weekend it almost means I can’t use the car while there as it needs to be juicing up the entire time.
So now I had to look at options:
- Find a Supercharger near my destination – NJ only has one and its more than an hour away. No good.
- Find a faster charger nearby – A local college has a J1772 reported at 30A/240V which would give 18miles rated/hour added. But i’d have to leave my car there or sit there for the charge. Better, but not great.
- Charge more at my Supercharger stop on the way down and arrive with more left.
The best option seemed to be stopping a bit longer at the Supercharger on the way down and charging up more. I’ll charge back up to 90% (240 rated miles), use 102 rated miles to get to my NJ destination and have 138 rated miles left. If I don’t go anywhere while there that’s plenty to get back with a safety margin. If I want to drive around while i’m there I only need to charge enough for that. I figured about 50 miles, so thats only 16 hours of charging or 2 decent nights. That’s doable.
If I did my planning well the return trip will be uneventful. That’s because I thought about the return before I started the trip. If I had only planned for the trip down it could have gotten trickier.
Another angle to consider is detours along the way. On our way down to NJ we have a favorite Sushi place we like to visit in CT. Thats a bit off the route and will add a couple miles. Being the planner, I also looked at the case where the Darien, CT supercharger was offline/broken when I arrived. What would I do? Fortunately there’s another one on the Northbound side of I-95 and then more only a few miles away on the Merritt parkway in a pinch. Unlike MA and NJ, CT is pretty blessed with Superchargers!
This will be my first real EV road trip. Next to the the epic 12,000 mile trip taken by the Recargo folks and many other road trips that are happening daily this is a tiny and simple trip. For me, as a new owner and still struggling with range anxiety, its been eye opening thinking about the options and things I have to consider that I never once thought about in an ICE car. With an ICE car I drove until I needed gas and then it was easy to find and fast to get. With an EV a little more planning is needed, but thanks to the growing Supercharger network “filling up” my EV along the way is a minor inconvenience.
Oh, and did I mention that the Supercharger use is free?
First of all, when starting on a long trip like this, there’s no reason not to range charge to 100%. You get 25 more miles starting out, which ripples down to all following charging stops (i.e. less time to get to your desired state of charge). There are zero detrimental effects of range charging, as long as you *use* the car shorting after range charging. Don’t let it sit fully charged at 100% for more than a day, since that could degrade your battery a little bit. I’ve taken many LONG trips, and before I go to bed the night before, I’ll set the car to charge to 100%, so by the time I leave in the morning, it’s at 100% and ready to go, and it hasn’t stayed there for more than a few hours at that 100% rate.
Second, this summer I logged over 4,000 miles on my two half-cross country trips (NY to Chicago — all via SC), and the buffer I use is 25%. So if I have to drive 100 miles to the next SC, I make sure I have at least 125 rated miles of charge. And in every single case, I never came close to using up the full 125 miles, and that was with weather, 70mph speed limits (driving 80mph), using A/C to 70 degrees, loaded car with two people and luggage, hills and valleys, etc. If you really want to be safe, go with 30%. But as it turned out anyway, when we’d stop to charge to get an additional, say 100 miles, we got lunch or window shopped, and we’d always end up with a lot more charge then we really needed, which meant that I essentially never had to worry about range anxiety. Not once on either two long trips. At the SC, if I charged an extra 10 or 15 minutes, it was a huge bump in rated miles.
For my first trip, I was just like you, I had a detailed spreadsheet with each stop, miles, rated miles, elevation (using evtripplanner), energy required, stop time, charge time, added miles, miles to next SC, etc – everything was planned out with all the numbers.. I printed it out and took it with me to make sure I stayed on the plan. After a couple of SC stops, it really didn’t matter any more. And for the second trip, I just made sure I drove from SC to SC, charged up to 125% or 130% of miles to the next SC, and went on my way. Essentially no planning at all! It was much easier and less stressful that way. I’m sure you’ll find the same thing, too.
Finally, the key factor that you didn’t mention is watching your Wh/Mile guage. That’s the most important. I found that as long as I kept it around 330 wh/mile, I had no problems with range.. and it’s very easy to keep the car at 330 wh/mile or less on long trips. Just reset one of the trip odometers at each SC stop and watch the guage. It will start out very high (like 500 or 600 wh/mile), but after 10 or 20 miles, you’ll see it settle down to lower 300’s. Of course, if you drive the car very hard, or very fast, that will go up and use more range. On my trips, there were long some stretches where the speed limit was 70mph, and I was easily doing 80-85 most of the way, and I *still* came in at around 320 wh/mile using cruise control. (By the way, the Tesla “Rated Range” is based on 300 wh/mile, so driving at 330 wh/mile needs just a 10% buffer.) If you happen to be a slower driver in the right conditions and drive at less than 300 wh/mile, you’ll get MORE miles out of the car than the indicated rated miles.
So the bottom line is, you can try to plan out longer trips like this, or just follow a few simple rules of thumb and you’ll come out just the same with less work, less planning, less stress, and more fun.
Thanks for all the feedback. I did have some things I hadn’t thought about, so I did end up range charging before leaving MA. But a range charge wasnt really necessary except perhaps to save a few minutes on the Supercharger. Not home yet but so far the most stress has been around destination charging to get back to the supercharger grid but should be no problem with one more night’s charge in.
Michael McCauley said:
Great stuff! We got our S85 eight months ago. Our first trip was nearly disaster, ran the battery down to 17 miles range left. Sheesh. But we learned, and now I usually plot my trip in EVTRIPPLANNER and take a few notes. I live in Colorado and driving in the mountains (going up) sucks lots of energy and used to make me nervous, but I am cool as a cucumber now. I love reading your blog, it makes me happy that others are having the same experiences with the car as me!
Great to hear it. Thanks for the comment.
Also, BTW, you probably mean your NJ destination is an hour “west” of NYC and there is a new Edison, NJ supercharger coming online any day now (if not already): http://www.teslamotorsclub.com/showthread.php/26730-Supercharger-Edison-NJ
Thanks, good catch. An hour east would be quite wet. Edison and Hamilton are both far from my NJ destination (parents). They’ve basically near the last exit on 78W before PA. I’ve got a plan for better charging for next visit involving a dryer outlet and a converter.
Brian H said:
There’s the 3 thirds method, too. Charge enough to give you about your minimum comfortable buffer to begin. For the first third of the trip, drive slowly enough to gradually increase the buffer. For the middle third, speed up to keep it constant. For the last third, burn it down as close to nil as you want/dare!!.
I considered that method but one of the nice things about the Model S is you don’t have to really think about how you drive. I think this method may work for the long cross country hops Supercharger to Supercharger but not necessarily when you’re fighting east coast traffic etc.