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EV Battery Range: answers to common questions

Discussion in 'Model S: Battery & Charging' started by Daniel R. Lucas, May 19, 2017.

  1. Daniel R. Lucas

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    A friend asked, "What is the range [of your Tesla Model S]? Do you have the smaller battery or bigger one? Have you taken it on road trips where there is mountains and how does that affect the batteries?"

    Range is a very common question among electric vehicle potential buyers, and the short answer is "it depends". I have the 90kwh battery with a rated range of 265 miles, which is one of the larger sizes available. The largest battery size available is currently 100kwh, and the minimum from a new vehicle is 75kwh. Keep in mind that I have the P (Performance) model, which tends to be less efficient than the non-P.

    I get ~265 miles (especially with highway driving) during most of spring/summer/fall and a small portion of winter when it's around 50+ degrees; in fact, I've gotten over 300 miles range out of my car--not that I actually drive it to 0 miles remaining. What I mean is my efficiency was good enough to get that much range. For example: I just took a road trip to St. Mary's County (75 miles each way) and averaged under 250 Wh/mile. Given that my car has a 90kwh battery, if I charged it to 100%, then here is the math to determine my actual range at 250 Wh/mile:

    250Wh/mile * 4 = 1kwh. My car has 90kwh, so multiply 4*90 = 360 miles of range. Since I believe my actual efficiency was 239 Wh/mile, I could do 360 miles with a little to spare. The best I've seen was on a road trip to Shenandoah Valley (I did the 100 mile Skyline Drive) where I saw 190Wh/mile and routinely in the 200's for almost the entirety of the drive.

    As far as impact on range due to mountains/hills, what one needs to consider is Net Elevation Gain. As long as you go back down a mountain, you'll regain most of the energy spent to get up it. I've heard online that the regenerative braking system is better than 80% efficient; in other words, if the car speeds up to 40mph then allows the regenerative brakes to take it to a complete stop, it will regain ~80% of the energy spent. I'm sure that some of that ~20% energy is lost to friction from tire rolling resistance, electric heat, running the vehicle electronics, etc.

    The smaller the wheel and less heavy it is, the less rotational weight the car must overcome. You'll see an improvement in range when running 19" wheels on the Model S vs 21" wheels on the Model S. My car started with 21" wheels, which I swapped out for 19" wheels. I saw an improvement from efficiency around 400-450Wh/mile on average to into the 300's.

    In addition to the wheels, the tire tread compound has a large impact on range due to rolling resistance. A less grippy tire will be more efficient but suffer worse cornering capability. I'm pretty happy with my 19" wheels with all-season Michelin Sport tires as a compromise somewhere in the middle of grip/rolling resistance. It's also a pain to swap out wheels + tires twice a year, so even though the 21" wheels are beautiful, I plan on selling mine soon and keeping the 19" wheels all year.

    The Model S gets the best efficiency on the highway; in the city, I'll see ~350-400 Wh/mile, which is a little worse than the rated 265 miles ideal range. How do I know that? Read below...

    So, what efficiency must be driven to get 265 rated miles out of a 90kwh battery? Another math equation:

    90kWh/265 miles = .339 kwh/mile. Convert to Wh/mile as follows: .339kwh/mile * 1000 = 339Wh/mile. So, as long as you drive at 339Wh/mile or better efficiency for the entirety of a drive, you will see at least 265 miles rated range.

    During the winter is when you'll notice a very significant drop in range due primarily to the following factors:
    1. The heater uses up to 6kw of energy. Run that for an hour at full blast, and that's 6kwh of a 90kwh battery used up just to heat the cabin.
    2. The battery's energy density decreases when it is cold, like during the winter--especially in sub-50 degree weather.

    How to compensate for these factors? Pre-heat the cabin using the phone app before driving. This will not only make the car comfy from the start, but it will save your range AND preheat the battery to a certain extent. Instead of using the cabin heater, use the seat heaters (standard on all models) and steering wheel heater (winter package). It also helps to dress warm with gloves and hat!

    Keep in mind that for long distance driving, you only need enough range to get to the next supercharger. The superchargers tend to be spread out at a max of ~125 miles between chargers. Since you're unlikely to pull into a supercharger with 0 miles remaining, let's say you need to charge enough to get 150 miles to easily reach the next supercharger. The superchargers currently charge at up to 135kw/hour, but the speed at a supercharger depends on a few factors:
    1. Usually a supercharger stall has up to the max charge rate, but that charge rate is shared between two outlets from the given stall.
    2. The car significantly limits the charge rate from the supercharger once the battery has reached ~80% capacity. If I'm getting 135kwh/hour from the supercharger, then it's possible to charge from 0-72kwh (80%) of my car's 90kwh battery in 72kwh/135kwh = 0.533 hours, or a little over 30 minutes. So generally speaking, ~20-30 minutes at a supercharger is enough time to get to the next one with some range to spare.
     
  2. azred

    azred Member

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    Personally, I'd modify the math using wk057's data. For my S75 I would take 72600 (not 75000) and divide it by Wh/mile. I find 300 is my Wh/mile average, which means my average max range in my typical flat, warm Arizona driving should be about 72600/300 = 242 -- and that in fact seems very close to my actual max range (vs the 249 Tesla-rated max range).


    I am a little puzzled by your calculations and why they seem to work for you. I think wk057 rates your car at 81.8 kWh usable -- not 90 and that's a nearly ten percent difference.
     
  3. Daniel R. Lucas

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    Could you please link to wk057's data, azred?

    That's right about battery size; if you want to get really technical, then you have to take into account that the battery size in the various Model S vehicles may not be exactly as advertised. I believe the 100kwh battery is larger than 100kwh, for example.

    I wouldn't recommend that anyone drive their Model S down to 0 miles; this post is meant to help people gain a better understanding of real world EV range in the Model S/X.
     
  4. azred

    azred Member

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    #4 azred, May 19, 2017
    Last edited: May 19, 2017
    You can find the 12/13/16 article that he originally posted here at his website skie.net. Obviously your results and mine are heavily dependent on the constantly changing Wh/mi actual data but I think any mathematical calculation based on kWh hours probably should use his data. To my knowledge no one has found errors in his data. Of course, Tesla has ignored him.

    For my car 72.6 usable vs 75 advertised is only a 3% difference, but he found the 90's usable was 9% less than advertised. When he posted he was particularly upset with the 85s and 90s. At least the 75s were really 75s total capacity albeit with 72.6 usable, whereas ignoring the usable number, the 85s total capacity were more like 80s and the 90s total capacity more like 85s. There was a lot of debate when he posted the data and he eventually got irritated and I think stopped posting. Honestly, I don't really share his passion for the matter but do use his data when doing range calculations. For example if my car is showing 250 Wh/mi average since last charge, I would divide that into 72600 not 75000. Most people probabaly wouldn't bother and of course the calculation is only relevant for full charges, something I very rarely do.
     
  5. gregd

    gregd Active Member

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    Even in your specific case where you know the person, I would go light on the math and physics. Their mind is open, but concerned. Acknowledge the range reduction factors and those which apply to ICEs too, but perhaps focus more on the tools the car provides to help you plan the trip and keep you informed and safe. They're going to be using the tools, not engineering them.

    In general, if someone stops me in the parking lot and asks how far I can go on a charge, I tell them "a bit over 200 miles". They're not asking for a degree in EV Physics, and if you try to give them one, you're going to turn them off. We need to keep their minds open.

    If they probe further, I go into more detail, usually starting with the original rating of 248 miles (it's a 2010 Roadster), and how well the battery has held up. Then engage them in a balance of EV advantages and why (stuff like how inefficient ICEs are) if they're still interested, but focus on how easy EV ownership is. For example, I ask how wonderful would it be if their gas car came with (as standard equipment) "magic elves who fill up their gas tank every night"? Keep it light. Range anxiety will come (and go) in due time; we don't need to plant any unnecessary seeds.
     
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  6. Daniel R. Lucas

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    Thanks for the feedback. I agree with the more simplistic approach and use it for the most part. My friend happens to be an engineer (I am a Software Engineer), so I tailored the response to be a bit more precise.
     
  7. TexLaw

    TexLaw Member

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    While I admire your work and understand your particular audience, I very rarely go into that sort of detail. Typically, I answer with my rated range at 100% (or often say "about 300 miles") and let them know that range varies in the same way an ICE's mileage varies with conditions and driving practices.

    Frankly, I don't want anyone thinking that there's really anything different between an ICE and an electric motor beyond the torque delivery and the "fuel." Sure, if you have a truly interested party (such as your friend), it might be worth going into all that detail. However, most folks don't understand it, and it leads them to believe that driving an EV is a great deal more complex than it actually is.
     
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  8. Drekar

    Drekar Member

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    Here is a link to the Electrek article that uses Jason Hughes (aka wk057) work.

    Tesla’s hacked Battery Management System exposes the real usable capacity of its battery packs

    • Original 60 – ~61 kWh total capacity, ~58.5 kWh usable.
    • 85/P85/85D/P85D – ~81.5 kWh total capacity, ~77.5 kWh usable
    • 90D/P90D – ~85.8 kWh total capacity, 81.8 kWh usable
    • Original 70 – ~71.2 kWh total capacity, 68.8 kWh usable
    • 75/75D – 75 kWh total capacity, 72.6 kWh usable
    • Software limited 60/60D – 62.4 kWh usable
    • Software limited 70/70D – 65.9 kWh usable
     
  9. SteveG3

    SteveG3 Active Member

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    Thanks for posting this thread, it looks encouraging for my plans to buy a Model 3 (longer range), but was wondering if you can fill in some pieces for me, particularly your typical average speed on the highway trips where you have been able to achieve about 265 miles of range.

    For some context- I drive about 550 miles quite a few times a year, almost all highway driving up and down I95 (NC-NY). Over several years of being close to taking the full EV plunge, I've played with the range calculator on Tesla's site, and it's given me the impression that if I drive at 75 mph I'd need to deduct about 50-60 miles of range vs. there base calculation at 65 mph. What's more, I've wondered if I might need to be ready for trips where I might average 5 mph headwinds, perhaps even 10 mph. I'm leaving out the outside temperature part of this... I tend not to do this drive in the winter months.

    So, your post has me wondering if Tesla's range calculator is actually quite conservative... or maybe you average about 65 on the highway, and/or I may be overestimating headwind issues. Maybe you've found autopilot lets you mix in some drafting behind larger vehicles... or maybe I'm missing something on all this, lols.
     
  10. Rocky_H

    Rocky_H Active Member

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    Best place to look to start figuring out more of this is probably to play with www.evtripplanner.com. Set up a trip there, and then you can see the real distance and the amount of rated miles it will use up. Then, start adjusting the speed multiplier. 1.0 represents the average speed of traffic on that road, not the speed limit. So then try some adjustments to that up to 1.05, 1.1, 1.2, etc. and see how that affects the amount of rated miles it uses. You can check the data tabs to see what actual speed the calculator is using for that condition. They don't have a thing to enter headwinds specifically, but since most of the speed difference is because of wind resistance, a headwind acts almost the same as the equivalent increase in speed.
     
  11. smilepak

    smilepak Active Member

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    So original 70 is more efficient than software limited 70?
     

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