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The affects of stop and go traffic on range

Discussion in 'Model S: Driving Dynamics' started by SCW-Greg, Jul 13, 2012.

  1. SCW-Greg

    SCW-Greg Active Member

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    So driving from Portland to Seattle today, which without traffic would take 2:50 for 180 mile trip. Today though, it's Friday (the 13th), and it will take a little more than 4 hours. Wife is driving, while I work from the jump seat.

    We've spent about an hour in stop and go driving along I5. Mostly stopping for never more than 1o seconds, and never driving more than 15mph in speed, before the next stop and repeat process.

    Car computer says we're averaging 44 mph, getting 27mpg. Normally we could expect about 30mpg. It's 80 degrees outside, so we have some mild HVAC going.

    It would be interesting to know how much of an impact this might have on battery range. Particularly the stop and go part. I doubt the 60kWh battery would make this range, even though we're driving slower in general. It surely would tap the 85kWh battery.

    Anyone have experience in the Roadster or pseudo science to suggest how this might play out on the Model S?
     
  2. Andrew Wolfe

    Andrew Wolfe Roadster 472 - S 440

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    On the Leaf, that kind of driving has a trivial impact. 1-2%. If you jack-rabbit start and slam on brakes it would be worse, but for a calm driver, you lose very little range and may even gain as compared to 65MPH.
     
  3. steve841

    steve841 Active Member

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    I think consensus on that is .... stop and go is great for the Model S range. Long, highway speeds are not.

    Constant regen and low speeds are a good combo ..... whereas high speed is a consistent drain on the battery with little to no regen.
     
  4. dsm363

    dsm363 Roadster + Sig Model S

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    You'll see from the Roadster speed vs. range graph posted before the optimal speed is around 25 mph non-stop. Of course that's impossible in stop and go traffic but you're much better off going slower than 80 mph in terms of getting maximum range.
     
  5. cinergi

    cinergi Active Member

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    Stop & go is only a problem if you're heavily running the HVAC. Otherwise you're using virtually zero energy while stopped, and you're at least as efficient as going a steady 65MPH (in the conditions you described). The more you can smooth out the stop/go the better of course. You might get really close with the 60kWh pack depending on HVAC usage (and assume you were fully range-mode charged when you started). Personally, if I'm going to go more than 180 miles in the Roadster (about same range as the 60kWh pack), I include plans to stop and charge. E.g. my trip for the NY event next weekend is 207 miles and I'll definitely stop because a) I want to plan for the unexpected and b) and I don't want to drive like a granny :smile:
     
  6. ChadS

    ChadS Petroleum is for sissies

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    You have two competing effects. Stop & go (continuously accelerating the mass of the vehicle) is not as efficient as constantly going the same average speed. But, generally stop&go means much lower average speeds, and lower speeds mean better range, so the overall result is not clear. Regen helps reduce the losses from accelerating. So it depends on how often and how aggressively you stop & go, and what constant speed you compare it to. But for most people driving an EV (especially if they are driving carefully for good range), they find that stop&go means a bit more range--the lower speeds are generally the larger factor.

    The big caveat was noted by Cinergi--how much HVAC are you using while going slower? THIS chart of range vs speed + HVAC gives you an idea of how much HVAC can affect range in a Roadster.
     
  7. MikeK

    MikeK R#129, TSLA shareholder

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    In my RAV4-EV, stop and go like that definitely extends the range compared to driving freeway speed the same distance. Where I might normally get 8 miles of range per "tick" on my SOC gauge, I've seen 11 in these conditions. It helps to accelerate slowly so that the space in front of you stretches out a bit, so that you can coast and maybe not have to stop. Keep in mind that the RAV does not normally regen when simply lifting from the accelerator, so it's truly coasting. I'm not sure how Tesla-style regen will affect things, but my guess is not a whole lot either way in this scenario.
     
  8. SCW-Greg

    SCW-Greg Active Member

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    Yeah recouping starts with the regen makes sense, I was just concerned about starts with torque load consuming more than regen compensates for. It's encouraging that everone's input here suggests not much of a major impact.

    I remember 5 to 7 years ago a major snow storm hit Seattle, and hundreds of cars were stranded along the highways, many running out of gas sitting there idling for hours, waiting for traffic to improve. So in that scenario HVAC draw would be the only concern.

    Encouraging feedback for this drive today.
     
  9. Jason S

    Jason S Model S Sig Perf (P85)

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    +1 -- tho the temptation to jack-rabbit might be stronger in the Model S. :wink:
     
  10. stopcrazypp

    stopcrazypp Well-Known Member

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    For stop and go, I think it's safe to say if you can make the trip on highway speeds, it will be no problem in stop and go. The only caveat is HVAC draw, which varies depending on time. For example, the typical cabin HVAC load for a Leaf is 2kW (see link below). In 4 hours, you draw 8kWh. That's 13% of the 60kWh Model S pack or about 25 miles of EPA range lost just to HVAC.

    It's a much bigger deal for smaller batteries, esp. ones that rely on higher efficiency for its range. 8kWh is 38% of the 21kWh usable in the Leaf and about 28 miles of EPA range.

    The document below is actually an evaluation using a simulation of the Leaf as a taxi. This fits the stop and go traffic pattern you are asking about.

    http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2012/veh_sys_sim/vss073_jones_2012_o.pdf
     
  11. NigelM

    NigelM Recovering Member

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    Providing you use the regen to do your braking for you, stop-go scenarios are much better for range than highway driving. Most of my driving is around town, flat and many junctions/lights, and I consistently have Est miles higher than Ideal miles. As stated by others, try to go easy on the HVAC though.
     
  12. Brian H

    Brian H Banned

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    Both the driving and the recovery % from regen improve at low speeds. If you started the trip with nominal 180 miles range, you'd have a comfortable margin left when you finished, almost certainly. Even with HVAC.

    BTW, it's "Effects". There is no such noun as "Affects", unless you're using academic psychological terminology to describe emotive responses and displays. Very specialized vocabulary.
     
  13. Frankc

    Frankc Member

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    Nigel's real world observation seems reasonable. There is another issue with 'stop and go' traffic that may not be as obvious. An electric motor is under the most stress during acceleration. One way this manifests itself is heat. This is usually not a problem, since the system is designed to cool itself during steady state load. However regenerative breaking puts the motor in a very similar condition (think negative acceleration) and the motor heats up again. A constant series of stop and go can therefore be hard on motor systems. Tesla knows this and has tested for it in terms of reliability, but heat is always the enemy of high efficiency. From a practical perspective, stop and go (especially in Seattle traffic) is more stop stop stop go stop stop stop.
     
  14. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    1. It's basically the area under the curve. If the curve looks like a rectangle, you're using a lot of energy. If it has a gradual slope on both sides you're minimizing the energy used--the shallower the angle is, the less energy is used (obviously, the lower the height, the less energy used as well--Y = speed, X = time).

    2. Regen is better than throwing all the kinetic energy away by converting it to heat the way that friction-brakes-only cars do but it still throws some energy away as heat--In the Prius this is 50% to 66% of the kinetic energy. Don't know the numbers for the Model S. Some have said that it's 20% for the Roadster. (To be clear, the percentages are the energy thrown away, not the energy captured)
     

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