The Rules of Model S Road Tripping
by, 2013-04-22 at 07:55 PM (201405 Views)
On the Road!
Driving a Tesla is a bit different from driving a gas car, or even most electric cars. On a daily basis, there is no concern about “range anxiety”. Owners expect their car to have a full “tank” every morning, and have enough range to do whatever they want. After a while they never look at the gauge. What the new Tesla owner soon realizes is that they are far more convenient than a gas car.
Road trips, though, are perhaps a bit less convenient. Unless you are lucky enough to have Superchargers on your route, charging is suddenly a lot slower than filling a gas tank. Also charging stations may be few and far between. It’s not difficult to drive long distances, but it will usually take a bit longer than a gas car, and you have to plan ahead. On the other hand, driving electric is far less expensive than using gasoline.
I’ve compiled a list of “rules” that will help you make your Model S road trips as fun and anxiety-free as possible.
Rule #1 – Use 100% Charge
Never, ever hesitate to use 100% Charge. Ever.
Some people get paranoid thinking 100% charge will ruin their battery's range. You don't want to leave your car at 100% for months at a time, because that will slightly increase the rate of degradation of the battery pack. We’re talking months here, not hours!
A few hours at 100% charge has NO measurable impact on battery pack lifetime, and may actually improve battery pack balance.
On the other hand, running your pack down to 0% is really not good for it. Drawing power at very low voltage means much higher current draw. This is more stressful on the cells. Sitting at a very low charge is not good for battery lifetime.
Suppose you didn't fully charge, and now you’re falling short. The battery pack is approaching zero range. It’s not good for the battery. You could get stranded on the side of the road. Suddenly you’re feeling pretty foolish for not fully charging!
So remember: 100% is nowhere near as bad for the battery as 0%. If you’re paranoid then top up the charge just before you leave, to minimize the time spent at 100%. This isn’t actually necessary, but it may make you feel better.
Never, ever hesitate to use 100% Charge. Ever.
Rule #2 – Be Conservative
Don’t assume you’re going to get the full “Ideal Range” or even “Rated Range” of the vehicle. No one gets EPA ratings in their gas cars. You actually can get EPA Rated Range in a Model S, but this depends on speed and temperature. Plan your trip conservatively. Learn how your vehicle works in different conditions.
Always plan for a range buffer – a safety margin to make sure you don’t run out of juice. You might want to start with 50 miles / 80 km or more at first. The bare minimum safety margin is probably 20 miles / 30 km. You just don’t know when you’re going to run into a detour, GPS glitch, dead or blocked charger, unexpectedly bad weather, or some other random problem (I’ve encountered all of these). A little extra range in your pocket comes in really handy when something goes wrong!
At first, it is probably a good idea to assume you can only get 2/3 of the promised range. As you gain experience with your driving your vehicle long distance (and remember winter is different!) you can prudently push beyond this. But start out with conservative assumptions and you will not get into trouble!
Rule #3 – Take it Easy
The most important factor is how fast you are driving. Increasing your speed from 55 to 65 mph will decrease your range by 15%. In freezing temperatures the effect is even higher. Similarly, dropping your speed to 45 mph will increase your range by over 15%.
Driving slower can actually speed up your trip quite dramatically, if you need to stop to charge. My rule of thumb is, “don’t drive faster than you can charge”. If the charging station you need to use can only charge at 30 miles per hour, there’s not much point driving there at 80 mph. You’ll use a lot more energy getting there, and have to charge for far longer. This means your total trip time will be much longer. In this case, driving slower is actually faster. Of course if you have access to a Supercharger, then it doesn’t matter how fast you drive – as long as you actually make it there!
Rule #4 – Slow Down Early
If there’s any question at all, don’t start by blasting along high speed. If you start out at 80 mph you’ll be burning energy a lot faster. Then you’ll realize you’re getting into trouble and slow down, but by then it is too late. If you had instead started out at 55 mph, and then realized you could increase to 65 mph, you’ll not only arrive a lot faster, you’ll actually arrive!
Start slow. See how it goes. If you have extra range, you can start speeding up. Don’t burn off all your power early, then desperately try to squeak it in. That is the road to failure.
Rule #5 – Watch the Weather
Your range also depends on the temperature. At lower temperatures there is more wind resistance, the rolling resistance of your tires goes up, and the efficiency of the battery pack goes down. In extreme temperatures the battery pack will require heating, which will also reduce range due to the extra power draw. You may also see less range in extremely hot temperatures, although this will not be nearly as bad as cold.
The biggest impact is in freezing temperatures. Your range could be 20% lower than Rated Range in highway driving. If the car has not been preheated, and the battery pack and cabin start out extremely cold, then you could see substantial additional power draw when you first start driving.
Also be warned that heavy rain or snow can also increase your power consumption, sometimes dramatically (i.e. double!). Same cure as always - slow down a little!
Rule #6 – Try Drafting
Drafting trucks really does work. Just do it safely. Pick a nice big truck that is driving at a constant speed, and pull in behind it. You don’t need to be right up close – don’t do something dangerous. If you are comfortable driving one second behind a large truck, you can get as much as a 15% improvement in range, or equivalently drive 10 mph faster for the same energy. Even driving a more conservative two seconds behind will help your range. Be aware that a strong crosswind may reduce the effectiveness of drafting.
If the truck driver is getting edgy – e.g. you can see him looking in his mirror, suddenly changing lanes for no reason, etc., then he’s not comfortable with you back there. You may be a safe distance back but he probably can’t tell. Just go find another truck.
Tip: Inter-city buses often drive faster than trucks, and are just as effective.
Rule #7 – Saving Power: What Works, What Doesn’t
Many people think they can save power by shutting off the radio, seat heaters, headlights, not charging their phone, etc. Don’t bother; none of this matters!
It takes over 15,000 watts to move the car at highway speeds. Turning off any of these devices might save you a dozen watts. You might save hundreds of feet of range this way. In short, simply slowing down 1 mph will do far more than turning off every device you can find.
There are only two things that matter: your speed, and cabin heat. Of these two, speed is by far the more important factor.
The cabin heating and cooling (HVAC) does have the potential to consume significant power. Fortunately the Model S has a selectable “Range Mode”. WHen you turn this on, it limits the power to the HVAC. I have found that the difference between running with HVAC off and using Range mode is relatively small. The only exception to this would be when you first start the car in extreme cold conditions. In that situation, you can preserve significant range by preheating the car.
The upshot here is “you don’t need to freeze!” If you are stretching things, slow down 5 mph instead. This will get you farther than turning the heat off, and you’ll be a LOT more comfortable! Always use your seat heaters. They take a miniscule amount of power. With the seat heater running you can reduce the cabin temperature a little and still stay nice and toasty. That will save some energy.
Rule #8 – Preheating in Winter
Even in extreme cold, the Model S is amazingly efficient at keeping the cabin warm. This is because it uses a heat pump. But when the car first starts up, it needs to use a resistive heater to warm the cabin, because the system is too cold to use the heat pump. This takes a lot of power. Worse, it will also need to heat up the battery pack. The combination of full cabin heat and full pack heat can consume 12 kW. That’s equivalent driving at 50 mph, and you’re not even going anywhere yet. Obviously if you need to drive a long distance, you want to avoid this.
The trick here is to preheat the car while it is plugged in. If you use the Remote App on your phone to engage the cabin heat, it will also engage the pack heater, AND it will draw power from the AC charger. Even better, try to arrange it so the battery pack is still charging, and that will help make it nice and toasty.
Tip: if your car has stopped charging because you had set the charge limit below 100%, you can start it up again by dialing it up to 100%.
Rule #9 – Don’t Expect All Charging Stations to Work!
Don’t just assume because you can find a station on PlugShare that you’re safe. Surprisingly often stations in these databases don’t even exist! “We’re planning to install one next year.” The station might be only available to employees at that location, or only available 9 to 5, or only to vehicles purchased at that car dealership. It might be broken. It might require a special card to access. It might be busy when you get there, or blocked by an ICE car (ICE’d).
Always call ahead if you can. Ask if they can reserve the spot for you (an orange cone in the spot really works!) See if the database has a picture and details on charging. More importantly, always have backup plans.
Some campgrounds, especially KOAs, have 50A outlets and are willing to permit EVs to charge, possibly for a fee. Again, call ahead. Ask for “50 Amp” – the owners don’t know what 240V is, and they don’t know what a NEMA 14-50 is.
More power is always better – some J1772 stations only provide 24A, and often their power source is 208V instead of 240V. Sometimes it’s just better to go to a campground. Or see if another Tesla owner from the forums will lend you a plug!
Rule #10 – The Freeway Isn’t Always Best
Given that the Model S can go much further at lower speeds, you might want to consider slowing down and smelling the roses. Sometimes the obvious route isn’t best. There’s a county road I often take that bypasses a much higher speed limit freeway. The thing is, it’s a beautiful drive, it’s never busy, and it’s much shorter. It not only takes 30% less power, it takes the exact same amount of time as the freeway!
Rule #11 – Keep An Eye On Range
Turn on your Energy App and set the display to Average. It always resets back to Instantaneous for some reason, which is pretty useless. Average will give you a good idea of your power consumption, and it will show you how far you can drive at that consumption level. That is your “Projected Range”. Tip: If you want to drive the “Rated Range” distance, be sure to keep the average below the “Rated” line.
Now enter your destination into the GPS. The GPS will show you your distance-to-go. Make sure that your Projected Range is larger than the remaining distance, by at least your safety buffer. If this is your first road trip aim for 50 miles / 80 km safety buffer. The minimum buffer you should ever aim for is 20 miles / 30 km.
If you find yourself coming in below your buffer, just slow down! Also check that you’ve turned on Range Mode to reduce HVAC power. Don’t bother trying to conserve power in any other way; the power draw of everything else in the car is insignificant in comparision. You’ll just reduce your comfort for no benefit.
Keep an eye on that difference between Projected and distance-to-go. Make sure it isn’t creeping down on you. If it is creeping down, back off the speed just a little.
If you’re coming up short, find a place to charge. Do it right away – there are many more options when you still have range. Don’t wait until you’re in trouble.
Rule #12 – Anything Else I Can Do?
There are some little things you can do…
Check your tire pressures. The 21" tires are supposed to be at 42 psi, and 19" tires (including winter tires) at 45 psi. Raising the pressure a little more will improve range a little. Don’t overdo it or you’ll wear out your tires and reduce your traction. Never exceed the maximum pressure printed on the sidewall. Note that these pressures are supposed to be set when the tires are cold, not after driving. You should check your tire pressures once a month as the cold pressure will change with the seasons.
If you need to stop, then as much as possible use your regen braking instead of the brake pedal. This will put energy back into the pack instead of wasting it heating up your conventional brakes. Try to avoid stopping at all, because even regen braking isn’t 100% efficient.
Use your cruise control. If you get going faster than you intend, you will use a lot more power than intended. If you are constantly speeding up and then slowing down you will use significantly more power without actually getting there any faster. Some have pointed out that regen braking downhill may not be 100% efficient, but if you get going too fast wind resistance will be much higher and that can be worse. So it’s probably best just to put on the cruise control in most circumstances.
Be aware of elevation changes. If there are large elevation changes along your route, then be aware that going uphill takes energy. The effect is approximately 10 miles range per 1000 feet altitude (50 km per 1000 m). You do regain a lot of that energy when you go downhill. In theory you could get pretty much all of it back if the slopes are gradual and you are never using regen braking downhill. At worst expect to get 85% of your energy back.
One other thing to keep in mind – it will take a little more energy to drive into the wind. In most areas of the USA and Canada we have westerly prevailing winds. I’ve often noticed that I get more range going Eastbound than Westbound. Strong crosswinds will also reduce your range.
Made it Home!
This All Sounds Complicated… Is an EV Right For Me?
Buying an EV does have some compromises, but it also has many benefits. EVs are better than gas cars in many ways, including cost of operation, energy efficiency, smooth and quick acceleration, instantaneous torque, quiet operation, you always have full range every morning, no standing out in the cold pumping smelly gas, and much more.
There’s one road trip I do each year where I don’t take my Tesla. It requires traveling through an area that is something of a charging station wasteland. I just rent a car for the trip. Sure, I could keep an ICE car in my garage, and pay for insurance, maintenance, depreciation, etc., but I’d only ever use it a couple of days a year. Yes, I really miss my Tesla when I have to drive an ICE, but it’s nice to be reminded once in a while just how much better the electric driving experience really is! (Update - thanks to new charging stations I can now do the trip on electricity!)
The Model S is a very capable vehicle. I have driven at -20C (-4F) in a nasty blizzard, and gone 304 km (190 miles) on one charge – with plenty of reserve. The Model S really can do long distances in rather adverse conditions, if you understand its limitations. The laws of physics take no prisoners!
With the Model S I can zoom away from a red light faster than almost anyone, but I’ve also learned a new appreciation for the slower road trip. Maybe that’s not such a bad thing.
Appendix - Charge Rates
Some have asked about how much time is required to charge. This depends mainly on how much current the charging station can deliver, but it also depends on the voltage, temperature, and whether you are doing a 100% charge. As you approach 100% full the charge rate slows down significantly. Generally speaking, because they take a long time 100% charges are usually only done overnight. If your next charging station isn't pushing your range, then you should probably stop charging when the power starts ramping down (except at a Supercharger).
You will find voltage varies pretty widely. Large commercial sites (buildings 10,000 square feet and up) typically have 3-phase power, and their source voltage is only 208V. Residential locations can have source voltage as high as 240V. Note that the voltage can drop under high load, particularly if the charging station is far from the electrical panel. I've seen differences of over 20% charging at two nominally identical stations.
You will find charging is slower in extreme cold, due to the need to heat the battery pack. If the car is cold soaked it will have to preheat the battery pack before it starts charging. In fact, below -10C (14F), 110V charging doesn't increase your range at all, as all the energy is spent heating the pack.
Remember: these numbers are rough guidelines. Mileage will vary!
Power Available Time Required Approx. Rate (mi)
Approx. Rate (km)
110V 12A (Level I) > 60 hours < 4 miles per hour < 7 kilometers per hour 220V 12A 27-37 hours 8 miles per hour 13 kilometers per hour 220V 24A 13-19 hours 17 miles per hour 26 kilometers per hour 220V 30A 11-15 hours 21 miles per hour 33 kilometers per hour 220V 40A 8-11 hours 28 miles per hour 44 kilometers per hour 220V 60A (Dual Chargers) 5-7 hours 42 miles per hour 67 kilometers per hour 220V 80A (Dual Chargers) 4-6 hours 56 miles per hour 89 kilometers per hour
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