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Fastest driving speed if only AC charging is available

Discussion in 'Model 3: Battery & Charging' started by Candleflame, Aug 25, 2018.

  1. Candleflame

    Candleflame Member

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    I wonder what the most efficient speed is during a road trip when you only have AC charging available. No point going superfast if you just have to then charge for longer.
    I guess for the Model 3 with a 40ah charger this means a maximum charge rate of 9.6kw.

    Driving at 110kmh/70mph we are using about 18kw/hour in a Model 3 so clearly this is way too fast.

    at 90kmh/55mph this seems to be around 12kw/hour judging from one of bjorns video so somewhere between 80 and 85kmh is probably optimal?
     
  2. SSedan

    SSedan Member

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    Thought with a wall connector you could get 48amps?

    I also think this overly academic since speed doesn't matter near as much as LOCATION. Who cares if you can go 320miles at 50mph vs 290 at 65mph( numbers pulled from my ear not legitimate) but the charger is at 270miles.
    AC charging for travel will be mostly looking for hotels in which case battery size and location are bigger factors than speed. During a meal you might get another hour worth of travel if you find a restaurant with a 48amp destination charger.
    Maximum travel time efficiency will be Superchargers during the day and attractions and hotels with destination chargers.
    Public AC Tesla charging is called destination charging because it only makes sense if it is your destination.
     
  3. sduck

    sduck Member

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    These are unrelated things. Driving efficiency doesn't affect charging efficiency, and vice versa.
     
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  4. Xenoilphobe

    Xenoilphobe Active Member

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    Sounds like a problem for a Porsche Taycan owner...or a Jaguar iPace owner... we will know soon enough, because we will hear them bitching about no charging locations... which is why I am sticking with Tesla.
     
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  5. OBX John

    OBX John Autonomous Driving Enthusiast

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    Slower is generally better down to about 45mph if you want to "hypermile". So it all depends on how pissed off you want to make the people behind you ;-)

    But rather than going slow, try to find a truck or other large vehicle and stay within a couple car lengths - drafting will significantly reduce your energy use.
     
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  6. ewoodrick

    ewoodrick Active Member

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    30-40 mph is the optimal speed for the 3.
    Anything above or below uses more energy
     
  7. RDoc

    RDoc S85D

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    It depends a lot on how far you are going. If you can get to your destination and charge overnight with a comfortable margin, go for it. If you really need to charge along the way and AC is the only system available, you're going to have a long trip.

    Optimal speed is about 40 mph, but if the difference in range between 40 and 65 is enough to get you there or not, it's pretty fraught. A good headwind, altitude gain, stop and go traffic, heavy rain, cold weather, etc. makes a huge difference in power usage.
     
  8. ulrichw

    ulrichw Member

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  9. MikeATL

    MikeATL Member

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    Understanding where the optimal speed vs energy tipping point is at is interesting to know, but I’ll be driving 80mph on the highway and supercharging whenever I need to, thank you very much!
     
  10. Candleflame

    Candleflame Member

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    pretty much everyone here is missing the point or just does not understand charging speed vs vehicle speed vs traveling speed.

    Of course living in America you have a sick supercharging network and you cant reach the optimum speed (which is I think about 160kmh provided you can make it to the next charger on a 5-80% battery charge. This is of much bigger interest in europe) but not everyone lives in America and not the entire world is covered with superchargers.

    This is about using 3phase/destination chargers on trip where you are going to continue as soon as possible to reach your destination as fast as possible. A full charge on a 3 phase for a Model 3 takes about 8 or 9 hours. At such slow charging speed aerodynamics really come into play because a very slow speed of i.e. 70kmh might actually be much faster than 120kmh due to slow charging. Of course I could calculate the optimum speed but I hoped someone else would have done that already.

    Yeah unfortunately the Model 3 only has a 40 amp charger. This makes sense as Tesla is covering USA/Europe/China with superchargers so the internal charger isnt as important now as it used to be back in the S which could have a dual charger and get 20kw from a 3 phase...

    going 320 miles at 50mph vs 65mph is in so far very different as you use much more watt/mile. Given the slow charging speed this does make a big difference.
     
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  11. DannyHamilton

    DannyHamilton Member

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    As you pointed out "At such slow charging speed aerodynamics really come into play".
    This includes not only your driving speed, but also altitude and the wind speed and wind direction.

    Unfortunately, there are other factors that will also have a significant effect such as:
    • Changes in elevation
    • Temperature
    • Humidity
    • Rain
    • Snow
    • Type and condition of the tires
    • Road conditions
    Trying to come up with a single "driving speed" that will maximize your overall trip speed isn't going to work. If you stick with a specific calcualted speed, then sometimes you'll be going too fast. Other times you'll be going slower than necessary.

    To accurately figure out your optimum speed on any give trip, you'll want to keep track of your watt hours per mile (or kilometer) as well as your average speed. Then you can multiply those two numbers and know if you are burning through electricity faster than you'll be able to restore it and can adjust your speed up or down accordingly.

    Based on nearly 10,000 miles (approximately 16,0000 kilometers) of experience driving the Model 3, I'm getting a long term average of 199 watt hours per mile (123 watt hours per km). I've seen it as low as 166 watt hours per mile (103.1 watt hours per km) at speeds of 55 mph (88.5 km per hour) in perfect conditions with a tail-wind. I've also seen it as high as 300 watt hours per mile (186 watt hours per km) at the exact same speed (in a rainstorm with a headwind on a trip that had a slightly higher elevation 50 feet (15.25 meters) at the end than the beginning.

    On top of all of this, you may want to also consider that (depending on the length of your trip) there may be times when the time spent charging isn't effecting your overall trip speed at all (because you were going to be stopped for that length of time regardless of whether you were charging or not). Examples include:
    • Rest breaks
    • Time spent at a restaurant eating
    • Time spent at a hotel along the way
    • Time spent charging AT your final destination
     
  12. dhanson865

    dhanson865 Active Member

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    #12 dhanson865, Aug 27, 2018
    Last edited: Aug 27, 2018
    Maximum range on a Leaf is done at 12 mph no matter the temperature so long as you don't use climate control. The battery pack has no cooling so the math is simple. Also on the oldest leafs the charger was 3.x KW and good for about 5 mph. The newer ones had a 6.x KW charger good for about 11 mph. Literally in a charging desert the Leaf would get you there faster the slower you drive.

    Maximum range on a Tesla will vary widely with too cold or too hot changing the optimal speed to achieve that. Superior pack with more aggressive cooling and heating mean even if you don't use cabin climate control the car is keeping the battery pack heated and cooled. Figure your minimum charging speed in mph (KW / mile / kWh) and round up to the next higher 5 and you'll be close to optimal speed. If you plan to use climate control you should drive 5 mph faster. If your planned charging is very slow speed you should keep the fan speed on the lowest setting to reduce energy use by the climate control.

    The OP says 9.6kw is his expectation for charging. That is about 35 mph if you do 275 wh/mile or 40 mph if you do 240 wh/mile. So on an extended trip he should be looking at driving about 35 to 40 mph if he wants minimum trip time with AC charging mid trip. Adjust as needed if you are using more or less wh /mile.

    Do the math while charging, set your next trip leg speed ever so slightly conservative, and speed up near the end of the trip if you have range left over.
     
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  13. Candleflame

    Candleflame Member

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    #13 Candleflame, Aug 27, 2018
    Last edited: Aug 27, 2018
    Your wh/mile seems somewhat excessive. are they based on the figures you have been getting with your 3? 275 wh/mile is something id expect at around 70-75mph. Bjorn Noland hit 230wh/mile driving 55mph. (which is still around 12.6kw so too fast for minimum travel time). That was without AC though.

    How many kwh does the aircon use in the 3 on low settings?
     
  14. dhanson865

    dhanson865 Active Member

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    you quoted it, but didn't consider it?

    I'll repeat

     
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  15. Rocky_H

    Rocky_H Active Member

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    I'm just getting to this thread, but I absolutely do get what you're talking about, since I've had my Model S since 2014 and had to do some traveling early on on routes that don't have Superchargers, so involved 2 or 3 stops of AC charging, limited to the 240V 40A that my car could take. So early on I was realizing that recharging could only be as fast as 29 miles per hour, while driving would be about double that, at 60 mph. So it was basically working out to for each hour of driving would require about two hours of recharging. So yes, driving speed and aerodynamics and conserving energy makes a big difference to not add some unnecessary hours to your charging stops.

    I don't think there's one speed that is your answer though, because it almost does get to "slower is better", down to maybe 20 mph or so, which just isn't very reasonable for a public road. I'd say this is accurate:
    I have actually done this on a trip that had no Supercharger coverage. It was going to be a long drive that went late into the night, and I didn't want to have to stop at 1:00AM or whatever to try to use slow charging, so I just set my cruise control at 45 to 47 mph the whole way to really extend the range and cover 238 miles straight with no stops. (Model S 85 RWD) So yes, with charging speed almost always being half of your driving speed, as slow as you think other drivers will tolerate is about the most efficient overall trip speed you can do.
     

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