Solar Struggles – What Tesla?


Shortly after ordering my Model S I filled out the contact form via the Tesla Motors site for Solar City to look into getting solar for my property. I wrote about the positive initial sales process and experience and wanted to provide some updates on how things were going in an ongoing series.


In my previous post I focused on just the house and what that plan would look like, but I was actually looking to do more. I live on a horse farm in Massachusetts. We have one address, but two electric meters for accounting purposes. When I signed up for Solar City I actually signed up twice, once for each meter, and got two plans.

Initially we had two separate systems sized for the needs of each. The initial house plan was for a system to generate 24,000 kWh/year and the initial farm plan was for 21,000 kWh/year.

That’s where we left off with the sales process and the design process started. Then things started to go sideways.

What Tesla?

IMG_2576Despite the fact that I signed up through the Tesla site and mentioned several times I was getting a Model S, the additional energy use was not considered in any of the planning. I was naïve at the time and hadn’t thought about how much the Tesla would affect my energy usage and you’d think the Solar City would be well versed in this. They weren’t.

Solar City knew little about what the Tesla would consume for power.

When signing up for Solar City they collect all sorts of data from you. They collect a years worth of prior electric bills, they do site surveys, they take 360 degree pictures from your roof, they do a home energy assessment etc. For me they did all this twice for my two meters/properties. It all looks fancy but it was flawed.

The home energy assessment is generic and not very tailored to your exact situation. It provides generic advice about getting more efficient appliances and other common sense things but the breakeven analysis on those recommendations make no sense. They also missed the fact I was getting a Tesla in all of the planning. My electricity use is already high, but even so thanks to my annual mileage the Tesla would be a significant factor in my future energy use.

It turned out I needed about 30% more solar generation to cover the Tesla.

After pointing this out to them and going through a round of engineering design reworks we ended up with a plan for a 37,000 kWh/year system for the house.


Before I get into the troubles encountered, its important to understand my costs for the proposed system. While there are no costs upfront, with the 20 year fixed rate per generated kWh the above combined system would cost me $170,000 over the next 20 years. One of the sales folks said the proposed combined system would be the largest residential system in New England.

I was choosing the above combined system would cost me $170,000 over the next 20 years.

All should have tipped me off to the troubles to follow. But I figured with Solar City growing fast as a public company and installing like crazy they should know what they were doing. I expected at this level of commitment that they’d get it all right. I was wrong.

More on Solar City’s execution challenges in the next part of this series.

Tesla Accessories: Tire Repair kit and 2nd UMC


I’ve been thinking about buying a few Tesla accessories for a while and I finally broke down and bought them. I got a second Universal Mobile Connector (UMC) and a Tire Repair kit and I wanted to cover the reasons behind the purchases.


UMCI’ve mentioned previously that I work near the Tesla store in Natick. They have 2 HPWC’s and 4 NEMA 14-50’s available for free charging. As you’d expect the HPWC’s are in higher demand and are less likely to be available. While I have a lot less range anxiety than I did before ownership, it’s still a great option to be able to charge walking distance from work. I also recently had to use this option for my NJ road trip.

I’ve heard its not great for the NEMA 14-50 connector to plug/unplug it daily. I also don’t always know when I’ll need some extra range. It would also be annoying to have to unplug and roll up and store the cable daily. So I broke down and bought a second UMC.

Some people in the forums suggest getting a HPWC for home for just this reason so you can use your factory-supplied UMC for travel and use the HPWC at home. But I didn’t do this for a few reasons:

  1. This approach is about $600 cheaper.
  2. For very long road trips you can take 2 UMCs with you in case one fails on the road.
  3. I don’t need the extra speed/time provided by the HWPC so the extra cost was to no benefit.

I feel a lot better about having a UMC with me at all times and the new one has worked great.

One thing to know is that the second UMC does not come with a second j1772 adapter. It only comes with a NEMA 5-15 and NEMA 14-50 adapter.

Delivered the cost is about $700.

Tire Repair Kit

Ture Repair KitI really didn’t want to buy one of these. Tesla only wants you to use it if you can’t get Tesla service to where you are in a reasonable time period as the junk that goes into the tire can be a pain. But if you’re quite a ways away from where Tesla can reach it can come in quite handy in a pinch.

What pushed me over the edge is I have a slow leak in my right rear tire. I’m losing about 10 pounds per week and it had me a bit nervous about my (then) upcoming NJ road trip. In addition to fixing a flat it is also a normal tire inflator so I figured even if I never squirted the junk into my tire I could at least inflate my tires with it.

I did some research on other fix-a-flat type products and the higher end ones are very similar to the Tesla one and a little bit cheaper. I went with the Tesla version due to concerns about coverage for the TPMS (tire pressure monitoring system) sensors and making sure I wouldn’t get grief from Tesla after using someone else’s fix-a-flat product with them. The price difference wasn’t huge and I have peace of mind.

A couple things to note on the tire repair kit. I found it hard to wind the cables back up the way it came so its not as neatly bundled as it was originally. I also found the metal around the pressure hose that connects to the tire valve to be poorly constructed – it doesn’t look like it will last long.

For a non-Tesla accessory, I bought an Amazon Basics electronic tire gage. I like to see the actual numbers and this one lets you set the target pressure which is nice. It came with a nice case worked great for about a week then died. I wouldn’t recommend it at this time.

I had the opportunity to use the repair-kit for inflation only with the tire gage while on my NJ trip and both worked great. I’m coming due for another tire rotation and I’ll have them check out that tire then.

Delivered the cost for the tire repair kit was about $55. The delivered cost for the tire gage was about $20 but i’m going to return it.


While the second UMC and Tire Repair kit were pricey additions to my Model S they helped lower range and trip anxiety and are welcome additions to my gear. There’s no other source for the UMC so you’re stuck with that cost but you may be able to save a few bucks if you get a repair kit from another vendor – just check that your TPMS won’t be damaged by it.


Remembering 9/11


911I wanted to take a diversion today from the purely Tesla blog to take a moment to remember September 11, 2001.

I remember exactly what I was doing when it happened and the events afterwards vividly to this day.

I used to work in NYC and lived in NJ for years and we have family in PA so it was all very close to home in many ways. Many innocent people lost their lives that day and there were many acts of bravery. We should never forget that day and the innocence we all lost.

My prayers go out to the families and survivors of the 9/11 terrorist attacks.

10,000 Mile Wish List


It’s been 4 months and 10,000 miles since I took delivery of my Model S. As I went through various areas of the car I made notes on what I liked and didn’t like and came up with a wish list of things I’d like to see added to the car.

I focused on things that can be changed for my car through software updates as these are things Tesla can improve for me. I also have very few things I’d wish about the rest of the car. Many of the things I’d like to see are also in the global wish list being tracked at Tesla Motors Club but I have my own tastes and priorities.

The items in bold below I had on my 2007 Acura MDX and are sorely missed.


  • Commute AdviceWaypoints
  • Multiple route options (shortest, shortest time, etc)
  • Traffic-based re-routing (reportedly coming in 6.0)
  • Better map caching – AT&T coverage is spotty and slow.
  • Show Map zoom level
  • Ability to organize favorites (folders)
  • Sort favorites by distance or frequency of use (vs random!)
  • Ability to show points of interest (POI)
  • Ability to set current location as a favorite
  • Ability to route to prior starting locations

USB Music

  • Shuffle
  • Folders need cover art
  • Fast scroll when in USB folders
  • Favorite ability for folders, artists, etc.


  • Remember rear seat heater settings too (it does this for the fronts but not the rears) across power off/on
  • If a passenger gets out and the car starts traveling again turn off that passengers seat heater.
  • Ability to “pin” or lock a screen in a position – like NAV always on top so I can flip the bottom one but not lose NAV or have to do the press/drag thing
  • Let me set % regeneration setting – not just 2 options.
  • Let me set max creep speed – 5mph is far too fast.
  • Show lifetime total/average energy somewhere so we don’t have to “reserve” trip B for this.
  • Let me control how long my headlights are on after I exit (its so long now I never use it).
  • When opening trunk, allow me to press the button to reverse direction.
  • Headlight flash is too long, shorten it or let duration be set.
  • Don’t allow car in drive if rear trunk is open. Or require special override.
  • Graphs always default to “instantaneous” which is basically useless. Default to average or remember the setting.


  • Service reminders for tire rotations, annual service etc.
  • Show actual tire pressure settings for all 4 tires.
  • Provide full release notes on every software update.
  • Provide release notes prior to install for software updates.


  • Report on estimated time to complete charge to set level (in car and in app). Make this work right with non-linear charge rates at Superchargers etc.
  • Allow me to set desired charge end time (not start time).


  • Allow cruise control resume from stop (other vendors can do this)
  • Be smarter on regeneration when cancelling cruise control – its harsh.
  • If driver gets out of car (in park!) and passenger is still present don’t let the car go to sleep (or have a setting around this).
  • Using washer to clean windshield turns on lights. Be smarter about this.


  • Remember volume setting by audio source (book tapes from my iPhone are a different volume than music from Slacker)

Web Browser

  • Browser - TeslaratiMake it work with Google apps (cookies, sessions, mobile flavor, etc.)
  • Fix return/caps lock behavior
  • Have the ability for it to report itself as a mobile browser for faster loads/better visibility.
  • Support tabs
  • Support favorite syncing with desktop/mobile devices
  • Allow organization of favorites including some kind of sorting
  • Make window scrolling smoother/more obvious
  • Make it faster/more standard (Chrome/Firefox/Safari like)
  • Fix web browser time zone setting/function – many sites think I’m in PST based on IP address.


  • Allow display of lyrics
  • Support custom playlists
  • Fix car stop/start while a song is playing resulting in a partial song resume
  • If you cant play/find the searched song offer to do nothing.

iOS App

  • Show internal temperature (without requiring me to turn on climate control first).
  • Receive all alerts/warnings that car shows.

That’s a long wish list in 4 months and its not even Christmas yet. I love the car without any of it. But imagine what the Model S would be with all these improvements and they’re all very possible.

What I find interesting is that there are news reports that Tesla is hiring up to 30 hackers to make security improvements to the Model S. Security is important and they should definitely invest in that area. But 30 decent programmers focused on the list above could knock out most of that in 6 months or less. How many programmers do they have now and what are they doing? Did all the resources get diverted to supporting new international markets? Is Tesla still investing in the software layer for the Model S or are all investments going into the Model X etc?

I’ll be tracking this list over time to see when/if Tesla delivers.

What’s on your list?

Road Trip Refusal


A short while ago I planned and made my first road trip. I had another one I needed to take a week later to the Pittsburgh, PA area and wanted to take my Model S on the longer trip and drive some of the cool hills and country on the way there and in that area. After some research I decided that its not really feasible to make the trip in my Model S.

Normal routing

I live in central Massachusetts and my destination was about 40 miles northeast of Pittsburgh. We usually take I-84 East, to I-81 South, to I-80 West then come down through State College on I-99 South then west on route 22. Google puts this at about 8.5 hours of driving and 533 miles. The trip usually takes us closer to 10 hours with stops for meals, etc.

Normal Route to PA


Supercharged routing

None of the roads above in the normal routing have Superchargers on them. To get to Pittsburgh from MA through Superchargers you have to go back down the I-95 corridor like I did on the way to NJ, stopping first at the Darien, CT supercharger. Next would be a stop at the Hamilton, NJ supercharger, then to the Newark, DE supercharger, then on to the Hagerstown, MD supercharger, then to the Somerset, PA supercharger and then finally to the destination.

The image below is thanks to


Supercharged Route to PAVisually you can see how inefficient this Supercharged route is next to the initial route. The total mileage for this route is 630 miles and it goes through some much more populated areas with lots of traffic and congestion. Estimated drive time is 10 hours 18 minutes and 5 Supercharger stops with about 30 minutes each.

Taking the Tesla would add almost 2 hours of driving time, 100 extra miles, and 2.5 hours of stops for charging. The 8.5 hour trip turned into a 12.5 hour trip when Superchargers were required.

I couldn’t pitch this to the family. We ended up taking our ML-350 blutec (diesel). It gets 29 MPG for us and has about 700 miles of range on a full tank. The ML-350 is a nice car but I sure missed my Tesla. At least the steering wheel stalks were the same :p


Tesla claims that by the end of 2014 they will provide Supercharger coverage for 80% of the US population and parts of Canada.  But the fine print (not included) is that the routes they come up with for you to get from point A to point B may be very inconvenient.

If your goal is record setting leisurely trips across the country, or one of the few optimized routes then you’re in luck. If you have more specific destinations that don’t align well with Supercharger placement you may experience Tesla Road Trip Refusal.

Review: Aftermarket Frunk Cargo Net


Tesla Frunk NetIn the early days Tesla used to include the Front Trunk Cargo net with every Tesla Model S produced. Some bean counter at Tesla decided they could make money on this and now this small net is a $20 purchase plus pricey shipping from Tesla. While I wanted a net, I didn’t think it was worth the price Tesla was charging and the net wouldn’t be in a very visible area. I had to be able to do better.


I started by measuring the space and decided I wanted a net about 13″ x 13″ in size. Some Googling told me what I wanted was a “Bike Cargo Net”.

Amazon is usually my go-to for any online orders, but Amazon has been having some challenges recently with knock-off Chinese products. The one I wanted was a “Pyramid Bicycle Bungie Cargo Net” but when I went to order it standard shipping was 17-28 days which generally indicates a Chinese knock-off. I couldn’t find one that wasn’t a knock-off on Amazon.

I ended up at eBay and searched for the same thing. I found it for $8.95 with free shipping and paid for it with PayPal thanks to Elon! It arrived within a couple days.

Packaging and installation

Frunk net packagingSince its just a net, packaging was minimal which was fine.

The same goes for installation. I got this net specifically since it has 4 hooks and 4 positions in the Frunk to attach those. Beware that some nets have 6 hooks on them.

The net fit fine and will definitely hold items in place. Its not quite as nice as the one pictured by Tesla but it was about 70% less expensive and I got it faster. In the picture below its holding a 30′ NEMA 14-50 extension cord in place (subject of a future post!)

Frunk Net Installed



I think the frunk cargo net should be included standard with the Model S. Tesla has gone back and forth on some of these items like the rear parcel shelf which now appears to be included again. The little space in the frunk is useful but things will slide around unless held in place. For $9 this solution does the job.


Lessons from my first road trip



NJ DestinationA while ago I wrote about planning for my first road trip and i’m happy to report that we made it to our destination and back, but not without a few learning experiences and I wanted to share them.

Adjusting the plan

In planning my first road trip I calculated the distance from my home to the first supercharger and then to my destination. What I neglected to think about was that I also needed to go to work that day. Thats an 80 mile round trip that I had to add into my calculations.

While I had a good safety buffer built into my plan, I didn’t have enough for an extra 80 miles. So I came up with 3 options:

  1. Take a different car to work – that would be no fun!
  2. Add an extra supercharger stop at East Greenwich, RI – this would add extra time with the family in the car and its in a traffic area I was going to avoid otherwise.
  3. Gain some extra range somewhere during the day before my trip.

I went went option #3 and used the free HPWC at the local Tesla Store at the Natick, MA mall. I plugged in after lunch and range charged to the full 265 rated mile limit. This recovered the miles I had used during my commute to work and added some extra with a 100% charge versus the 90% charge. It took me just under 2 hours to charge back up from 185 rated miles to 265 rated miles on the HPWC but other than the walk to/from the mall it didn’t disrupt any of my plans.

Lesson: Think about all the driving you’ll do the day of your trip, not just the trip itself.

Supercharging along the way

Darien South SCBefore this trip my only Supercharger visit was to the East Greenwich, RI Supercharger shortly after I took delivery to make sure Supercharging worked and it was purely for the experience. With this trip Supercharging was required — I needed the range and it had to work.

We arrived at the Darien, CT Supercharger with 66 rated miles left after driving 188 miles from MA and after stopping at a nice Sushi place in CT. Of the 6 spots, only 1 was occupied — by an ICE car with a driver sitting in it. The spots were all premium spots right in front of the rest center. We backed in and plugged in.

Since I always charged to 90% at home, my instinct was to get back to 90% again and I was nervous about destination charging and didn’t think it would take too long.

Lesson: Charging all the way back up to 90% was painful and a mistake.

It took us 49 minutes to charge from 66 rated miles (25% charge) to 238 rated miles (90% charge). I only needed 102 rated miles to get to my destination plus a safety margin.

We all felt the pain of this wait which was made worse by the late hour, driving in the rain and crazy east coast traffic. The rest area was nice enough but it was only junk food and coffee shops. Nothing for a real sit down dinner.

Lesson: Not all SC stops have good food options.

After the charge stop, we headed on to our destination in NJ. There was a major accident on one of our highways forcing us to take a 12 mile detour. Thank goodness for extra range.

Lesson: Only charge for what you need plus buffer. Filling past 80% goes slowly.

Destination Charging

NEMA 10-30I knew destination charging was going to be a challenge. We arrived late and it was raining — I was not going to hunt for outlets in the dark so I waited until the next day. But that also meant I would lose 12 precious hours of destination charging.

Lesson: If you have poor destination charging then plug in as soon and as often as you can.

A careful inspection of the property the next day revealed a dryer connection I couldn’t use — a quite dirty NEMA 10-30 which is also far from where you can park a car. I ended up with just the dreaded standard US outlet (NEMA 5-15) for charging. Fortunately I could reach the outlet without any extension cords.

Charging there was at a rate of 4 miles/hour and it was a delicate balance of being plugged in all the time while I was there and wanting to drive my own car when we went places. We did resort to taking a mini-van for a few local visits due to range concerns and questionable parking situation at a local county fair.

I added a net of about 100 miles of rated range while I was there using the NEMA 5-15 outlet. I’ll cover my plans for faster charging at that destination in a future post.

Supercharging on the way back

Darien North SCSupercharging on the way back was much less painful — I was determined to only charge for what I needed plus a 25% safety margin to save time.

We arrived at the Darien, CT northbound supercharger with 72 rated miles left and charged up to 202 rated miles in 30 minutes. This felt much faster. We shaved 19 minutes off the charge time plus it was a reasonable time of day, etc. Both my girls commented that it was quick.

Darien North surprised me as it was my first Supercharger I had to pull into to charge. They also had an odd arrangement I hadnt expected — 4 SC stalls, 2 on the right of the building and 2 on the left. One of the left ones was ICE’d with nobody in the car, the other one was open and I used it.

While charging I walked around to find the other 2 and found them with cones in front. I learned that cones are to discourage ICE’ing, feel free to move the cones and charge if you’re in a Tesla but make sure you put the cone back in place when you’re done.

Lesson: Cones in SC spots don’t mean its out of order – move them and charge away!


SC ConesAfter charging up to 202 rated miles, we had enough to get home. But it was also going to be dinner time. We decided for a quick dinner at Panera and I remembered that the East Greenwich, RI Supercharger had a Panera nearby. If we were going to stop and eat at a Panera, why not charge while we did so?

East Greenwich SC

Lesson: Combine charging and eating for the win!

While Tesla advertises 170 miles of rated range added in as little as 30 minutes, if you’re not charging from near zero you’ll experience a slower rate. Each time I charged from about 70 miles of rated range to about 200 miles of rated range it took 30 minutes.

Lesson: Supercharger stops take about 30 minutes.

Thanks to this extra supercharger stop on the way home we arrived home with 165 miles of rated range left and plenty for the next day’s commute.


We drove 687 miles on our first Tesla road trip and while there were some lessons learnt along the way none of it was stressful or painful. In all those miles and through 5 states we only saw 2 other Teslas. One P85 at an ice cream store in NJ (when I was driving the embarrassing mini-van), and another S85 at the East Greenwich Supercharger.

While there weren’t many Tesla’s on the road we experienced ICE’ing of Supercharger spots at every Supercharger we visited. I believe a lot of this could be avoided if the spots weren’t premium spots right near the service center. I’d gladly park my car at the back of the lot and walk further if I could encounter less ICE’ing.

Lesson for Tesla: Choose less desirable spots in the lot for Supercharging!

5 Mistakes for new Model S owners to avoid


After buying the most expensive car in my life I was determined to take great care of it and wanted desperately to avoid anything to detract from its beauty. Despite my best efforts I’ve made mistakes. Here are 5 things for new owners to watch out for in the order I “experienced” them.

1. The car is long and low. Especially in the front. Be very careful pulling into parking spots.


Undercarriage ScrapeI got my car with the technology package and parking sensors knowing I wanted to be extra careful parking the Model S. I was coming from a SUV which clears curbs by a mile and knew this would be a challenge. What I didn’t know that you should is that the parking sensors are not very responsive. You can pull into parking spots faster than the sensors will warn you and thats when driving responsibly.

Drive extra slow when pulling into parking spots

In this one I got lucky. I was about 2 weeks into ownership and pulled into a parking lot at a Panera. The curb was just high enough to scrape the undercarriage of my front but not high enough to crunch anything. It was a good warning i’ve taken seriously since.

2. The car is low and the tires are thin — give turns a wide radius.

Curb RashA few weeks later pulling into parking lot I took a right turn into it a bit too tight and scraped the right rear wheel. Over the last few years I did this a couple times in my Acura SUV and always felt silly running over the curb but never did any damage. I’m not a careless driver but that turn is tight and sometimes people are coming out and you’re sort of forced to make a tight turn.

The Model S is a lot lower than the SUV and the wheels are a lot smaller. The standard 19″ wheels are very susceptible to what they call “curb rash” and I added some of my own. Since then I take that turn (and others like it) extra wide.

Take right turns wide around curbs to avoid “curb rash”

3. There’s no plastic bumper and you have to lift items cleanly into the rear hatch

Rear bumper ScrapeMany cars have a plastic bumper in the rear you don’t mind a few scrapes on. Or the hatch opens and its flat and you don’t have to lift over a lip. The Model S requires you to lift up and over the lip and the back of the car is all beautiful aluminum. My family knew full well to be extra careful with the car, but one of my kid’s friends “dragged” a heavy duty ice skating bag up and into the back of the car. This left a long shallow mark on the back bumper. There’s no yelling at other people’s kids for stuff like that but had I known I could have prepared them.

Warn people to carefully lift up and into the front and rear cargo areas (especially kids) or be “kind” and help them with their bags.

4. The rear hatch lifts high and its hard to know its open. Don’t drive with it open.

Rear ScrapeThis one pains me the most. Thanks to the need to charge i’ve had to back my Model S into my garage since day 1. All my other cars have been pulled into the garage. When you back them out you have to look back through the hatch. If the hatch is open you’d know before going anywhere. Also when the hatch is open on an ICE car and you start the engine you hear it. With a Model S its dead silent. So picture me getting home from work late as usual. I back in, pop the rear hatch to get my gym bag out and then remember an errand I have to run. I jump back in and close my drivers door and start to drive forgetting the hatch is open. Crunch.

I was in a rush, I was tired, I wasn’t thinking straight. But the normal things that would have warned me didn’t work with the Model S. I was facing the wrong way, it was super quiet. Wait, doesn’t it beep when the hatch is open when you put it in gear? Sometimes it does, but its not very loud. Also my car always beeps when I pull it into and out of the garage. The parking sensors go off with the proximity of the sides of the garage so i’ve grown used to extra beeps as I pull in or out and ignore them. The hatch open one isn’t distinctive and didn’t do its job. And despite the car being much lower than the SUV the hatch opens nice and high for ease of access. Too high in this case.

Pay extra attention to any warnings/beeps when shifting into drive or reverse.

This one was the most visible of the scrapes. It will take a body shop to fix and it won’t be cheap. Thats a post and project for another day.

5. Watch out for door dings. Pick your parking spots carefully.

Perfect spot?

Perfect spot?

Fortunately this is one i’ve avoided so far but it’s likely only a matter of time. The Model S doesn’t have a strip running horizontally along the middle of the door to catch the edges of inconsiderate people. The sides of the Model S are clean and sleek but the Model S is also pretty wide. To minimize risk of dings do the following:

  • Try to find a spot with one edge along a curb or otherwise blocked from other cars. Better yet, find 2. But beware the pitfalls above.
  • Park where nobody else wants to park — walk for your health. Admire your Model S sitting out by itself. Let it be a loner. Your Model S stands alone.


Do you have your own moments to share? I’d love to hear (and avoid) them. Drop me a line in the comments below.

How does Model S Traction Control work?


The other day I was pulling out of my work parking lot and there was sand on the road from some construction thats going on and I felt my Model S do the right thing with the tires — one spun with no grip on the sand and the other pushed me through the patch and it was all automatic and trouble free. That got me thinking. How does Model S traction control work?

Before I get into this, a caveat: I’m an electrical/software engineer and not mechanical. I can change a tire, I used to change my own oil many years ago but otherwise I let the shop (usually a dealer) do all the work and I find one I can trust. The information below is from my own research as I wondered how it all worked.

Open Differential

GearboxI had a very basic concept of how the AC induction motor drove the wheels on my Model S. I thought it was just a motor you applied positive and negative current to and that drove the shaft one way or the other (forward and reverse) which then drove the wheels. This kind of thinking comes from the hobby kits you can get at Radio Shack and other places. I hadn’t thought about how that may translate to driving two wheels, nor how it could drive them at different speeds or how any of this could handle tricky situations like sand and ice.

The answer to that is the drive shaft that comes out of the Model S motor goes into an open differential gear box that then drives the two wheels. This gearing allows the outside drive wheel to rotate faster than the inner drive wheel during turns. Without this gearing either the inside wheel will rotate too fast or the outside wheel will drag and this leads to tricky handling, damage to your tires and a lot of stress on the drivetrain. HowStuffWorks has great animated images showing how this stuff works in action.

Tesla describes the gearing well (albeit in the more-detailed Roadster area of their site):

The motor is directly coupled to a single speed gearbox, above the rear axle. The simplicity of a single gear ratio reduces weight and eliminates the need for complicated shifting and clutch work. The elegant motor does not need a complicated reverse gear – the motor simply spins in the opposite direction.

Limited Slip

Traction ControlThe downside of the open differential approach is that torque (force if you will) is evenly applied to both wheels. The traction control system limits the maximum amount of torque to the largest amount that will not make the wheels slip. It doesn’t take much torque to make a tire slip on sand, ice etc.

When the wheel with good traction is only getting the very small amount of torque that can be applied to the wheel with less traction, your Model S isn’t going to go far.

While you can turn traction control off, essentially telling the motor not to back off when one of the tires is spinning, this can often result in a lot of tire spinning and will not necessarily get you unstuck. It could also get you dug in deep. On the other hand it can be fun if you want to burn off that last bit of rubber before getting some new tires :)

Usually this problem is solved with a much more complicated system called a Limited Slip Differential which replaces the open differential and allows for different amounts of torque to be applied to the different wheels. That approach involves much more complicated gearing which involves more parts and weight and may not be as reliable, especially with the high torque the Model S motor produces. Tesla chose to go with a simpler and sturdier open differential approach. But they needed to solve the slip problem.

Tesla solves this problem by selectively applying the rear brakes to transfer torque to the the non-slipping wheel. This is tied into the electronic stability control system which also needs to brake the rear wheels independently to improve the handling of the car under various conditions.

When a wheel starts slipping, Tesla applies the brake to the slipping wheel giving the “impression” that the tire has traction and allowing torque to be applied to the other wheel without spinning the slipping wheel. This is all done super fast with computers watching how things are going and backing off on torque, applying brakes where needed, etc.

Tesla describes both traction and stability control this way:

Model S Traction Control is designed to ensure maximum contact between the road and the tires. Whether you are accelerating off the line, zooming along the winding roads of the Rockies or find yourself in a Gulf Coast rainstorm, Traction Control prevents loss of traction and maintains control. Stability Control reacts in moments of under-steer or over-steer by reducing torque and applying the brakes to individual wheels for enhanced control when cornering.


People think mostly about the Model S as a premium electric vehicle and sometimes miss the rest. Tesla is about re-thinking the entire car. If you start from scratch and question every design decision, every part, every ounce of weight, every approach and use some of the best minds on the planet what kind of car will you end up with? The Model S is Tesla’s current answer — and not their last. The 17″ display is one example of re-thinking what has been tried and re-tried many times. The unique approach to battery placement is another and there are many more.

Tesla’s traction control and emulated limited slip functionality is another case of Tesla replacing complex static hardware with lighter and simpler hardware while replacing the functionality advanced software algorithms that can take advantage of today’s computing power.

Next time you slam that “go” pedal and take off like a space ship, think about all the technology thats helping you launch into the future.

Planning for the first road trip in the Model S



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. – 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?



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