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.


EVTripPlannerThe 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:

  1. A fixed amount: 50 miles – Can only use 190 rated miles
  2. Only plan on using a fraction of rated range: 2/3 – Can only use 160 rated miles
  3. 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:

  1. 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.
  2. 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

IMG_2598With 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.

Destination charging

ChargepointUnlike 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.

Planning Complete

Supercharger Map 082014If 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?