Attempt to break Coast to Coast EV record this April - Anyone wanna join?

[David99]

You can't do a straight line approximation of charging speed since it tapers. IIRC, folks who've looked at the calculation based on real charging rates based on SOC found an ideal driving speed somewhere in the mid 80s.

I used 100 kW as a real world average which is based on my road trips using Superchargers. It's not a theoretical number, it is not an ideal number, it is real world experience. I've done a 4000 mile road trip (among many more) where I was able to test and verify it. The question was if driving faster and thus charging longer at a Supercharger is faster overall than going slower and charging shorter. It's actually pretty straight forward to do some very basic math to see it is indeed overall faster to drive faster because you always make up more time driving faster than you lose charging at a Supercharger. The Supercharger refills the battery faster than you can drive. Of course we all understand that the charge rate drops the higher the state of charge is. In this attempt of breaking the record, we would very carefully make sure we arrive at each Supercharger at a low state of charge.

The theoretical long distance travel speed is definitely not 55 mph.

 

[GSP]

Given the current state of BEV development, is driving at any sort of hyper-legal speed even desired? Since charging time is so significant, it may be better to slow down and, as much as possible, skip every other supercharger.

BEVs have developed more than you think. With Superchargers, as long as you keep your road speed below about 300 mph, you will arrive sooner if you exceed speed limits. I wouldn't drive more than 5-10 mph over for safety and law enforcement reasons.

GSP

 

[Brass Guy]

A lot of banter about driving vs supercharger speed. At some point, it will reach the top of a curve. Driving over 100 mph for 120 miles for example, you will find that the excessive Wh/m will mean charging over the 80% mark. It definitely matters how far apart the superchargers are. If a leg is going to be 220 miles, driving 55 will be faster than charging to 100%. If the spacing is shorter, I don't know maybe 75 miles or less, Model S current top speed would be the limiting factor.

 

[Bighorn]

I used 100 kW as a real world average which is based on my road trips using Superchargers. It's not a theoretical number, it is not an ideal number, it is real world experience. I've done a 4000 mile road trip (among many more) where I was able to test and verify it. The question was if driving faster and thus charging longer at a Supercharger is faster overall than going slower and charging shorter. It's actually pretty straight forward to do some very basic math to see it is indeed overall faster to drive faster because you always make up more time driving faster than you lose charging at a Supercharger. The Supercharger refills the battery faster than you can drive. Of course we all understand that the charge rate drops the higher the state of charge is. In this attempt of breaking the record, we would very carefully make sure we arrive at each Supercharger at a low state of charge.

The theoretical long distance travel speed is definitely not 55 mph.

This was my intuitive understanding at one point as well and I used to argue the same logic, but I've since been convinced otherwise both by the data of others and my own experience of multiple cross country trips. Just for fun, since you continue with a wholesale disagreement without any real data, I'd love to hear your prediction of how fast a Tesla can average over long distances. I've done 1500 mile stretches without break other than charging, so I know what I can accomplish even in areas where speeds can often approach triple digits. Better yet, calculate the length of the route and how long you think it will take. I think you'll find that the current record is probably close to a 55 MPH average speed. (I just looked it up--it was 49.5). My 24 hour record is just under 1200 miles, so 50 MPH is a more realistic real world goal, I'd say. Please prove me wrong--it'll be fun

 

[wycolo]

> the current record is probably close to a 55 MPH average speed. [Bighorn]

Ok, but what does that work out to for a driving speed between SpCs? Something for us to set CC to and knock off 1200 miles in the shortest time.
--

 

[BerTX]

Trust me, it will be a real attempt

I "trust" that your intentions are good. Have fun and good luck!

 

[Bighorn]

> the current record is probably close to a 55 MPH average speed. [Bighorn]

Ok, but what does that work out to for a driving speed between SpCs? Something for us to set CC to and knock off 1200 miles in the shortest time.
--

It is a complicated calculation based on how far apart superchargers are. Short interval, splash and dash would tend to favor maximal speeds, but if you're taxing your battery's limits, the optimal speed will be much lower. Of course frequent pit stops introduce the extra time associated with making your way to the supercharger and the charging ramp up time. I think what I remember from the most definitive blog analysis I read was that ideal traveling speed was ~86MPH, or was it 83?

Anyone remember the plane taking off from a treadmill riddle--I think I'm having a little deja vu

 

[William13]

Although driving faster and arriving with a lower state of charge is "faster" theoretically, this does not always work out better. The superchargers are not located at rest stops on the roadside. The Mishawaka Superchargers are 10 minutes each way off the toll road. The Angola Superchargers are almost 6 minutes each way off the toll road. These two Superchargers are only 70 miles apart. Careful calculations are appropriate with these issues in mind as well as practical considerations of bathroom and eating breaks. The time of arrival will influence these last two. Mishawaka for example has enough facilities (a mall, gas stations, hotels) as to be mildly time neutral. Angola has a hotel and restaurant. The restaurant has short hours.

Research and planning.

 

[Bighorn]

Okay--I found that blog post about optimal speeds. I've had a lot of back and forth banter with the author off-line, but his blog post will hopefully save me some breath going forward.

I'll also post the thread where I had my epiphany that my intuition was wrong and much debate about the issue transpired.


Driving Charging Time | TESLA OWNER


[url]http://my.teslamotors.com/forum/forums/no-need-drive-over-75-mph-when-using-superchargers




[/URL]

 

[stevezzzz]

Thanks for pointing that out that blog, Bighorn; it's really useful. I've been under the apparently mistaken impression that the optimum driving speed between Superchargers would be higher than his data show, probably because I underestimated the effect the charge ramp curve has on total time: for a given SOC on arrival at the SpC, the faster you drive the farther you fall down the charge ramp when replacing the Rated miles used.

One very useful insight the second chart reveals is this: the more conservative you are regarding the Rated miles buffer you like to maintain, the slower you should drive to optimize overall speed-made-good. It's a corollary to the general rule of thumb I've lived by since back in the days when cross-country trips were made using 10kW charging at RV parks: try not to consume energy from the battery at a rate faster than the next charging stop can replenish it. In the case of RV parks it means driving agonizingly slowly; but it's interesting that even with fast Supercharging and real-world speed limits, it's still a useful rule.

 

[Bighorn]

Mishawaka > Maumee is only 150 miles. Thus stopping at Angola makes no sense to me even if it were right at an exit (which its not).
--

Mishawaka is such a PITA to get to--I'd be looking for ways to bypass that one, if possible.

- - - Updated - - -

Thanks for pointing that out that blog, Bighorn; it's really useful. I've been under the apparently mistaken impression that the optimum driving speed between Superchargers would be higher than his data show, probably because I underestimated the effect the charge ramp curve has on total time: for a given SOC on arrival at the SpC, the faster you drive the farther you fall down the charge ramp when replacing the Rated miles used.

Steve-
Is what you're saying that the supercharger ramps up to max kWs slower if you come in hotter, from driving faster? Makes sense, but I'm just making sure I follow your second sentence.

 

[stevezzzz]

Steve-
Is what you're saying that the supercharger ramps up to max kWs slower if you come in hotter, from driving faster? Makes sense, but I'm just making sure I follow your second sentence.

No, I'm talking about the decline in charge rate at higher SOC. The effect on the average charging rate (over an entire charging session) is so great at higher SOC that it significantly affects the optimum driving speed for those owners who don't like to arrive at the next SpC near empty.

The discussion becomes more complicated when you start trying to plan a route where the average distance between Superchargers is short enough that 85s can choose whether to skip over one SpC and stop at the next, potentially improving speed-made-good even if it means driving slower than the speed limit in order to stretch to the farther SpC. You lose so much time accessing some Superchargers that it makes little sense to stop unless actually reaching the next one is in doubt. I'm thinking particularly of Glenwood Springs, which in good weather can be skipped when you're driving I-70 across Colorado, particularly westbound (downhill along the Colorado River). It's a good long way from either of the Glenwood exits to the SpC and traffic concerns can make reaching it a ten-minute ordeal. Similarly, St George, Utah's SpC is hard to access and the downhill run from Beaver to Las Vegas is eminently doable in an 85, with a modicum of care.

 

[David99]

The time needed from the freeway to the SC and then back on your way is an added time. It has nothing to do with the speed vs charging speed ratio. It matters and only makes sense to skip a SC when there is another one reachable withing a reasonable driving speed. That's a little more complicated because you can't just add/subtract the time it takes to get to and from the SC, you also have to factor in the extra charging time at the SC you are departing from to have the energy you need for the longer trip. And you might have to slow down to make it which adds time.

I just tried that with an example of Green River, Richfield and Beaver Superchargers.
Green River to Beaver can be done (in an 85) without too much worry. It takes about 2:37 to drive all the way and you need about 67 kWh or 230 rated miles. That would take about an hour to charge at your departure. So the total time is 3:37

Let's add the stop at Richfield. It takes 1:45 to get there, and 46 kWh or 150 rated miles. So you only need to charge for 27 min at your departure. For the next leg (from Richfield to Beaver) you need about 75 rated miles (23 kWh). To charge that you need 12 min. Then the last leg takes 56 min. Total time: 3:20.

In this example I used the correct Supercharger tapering curve. But I did assume arriving at pretty much zero and 120 kW as starting power when empty and plugging in. In this example the Richfield Supercharger is very close to the freeway and doesn't add much time going out of your way. You don't need to slow down to skip this SC, you can go normal speed, still you saved time just based on faster charging times.

Let's have a look at an example where the SC is far off like St George. From Beaver to Vegas you need about 74 kWh when driving 75 mph. So you probably have to slow down a bit to be able to make it safely. Going 70 mph you need 70 kWh which is realistic. Total drive time is 3:19. You definitely need a full charge before departure which takes 90 min on a Super Charger. Total time: 4:49.

Now let's add St George as a stop. Since we have the charging stop I can go normal speed. Let's assume 75 mph. To get to St George at that speed it takes 1:32 and I need 33 kWh or 110 rated miles. It takes 19 min to charge at departure to have enough energy. Stopping in St George I need to 'fill up' 43 kWh (144 rated miles) to reach Las Vegas. It takes 26 min to charge that. Then from St George to Vegas takes 1:49. Total time: 4:06. Despite the fact that stopping at St George adds time to your trip, overall we are still faster. We were able to go faster and charge less time.

Again, all of that assumes to arrive at almost zero charge. I don't think it's good for the battery to keep running it down that way. But at the same time, it;s just as bad to charge to 100% and then run it down to almost zero when you try to skip Superchargers. So in many ways, using every Supercharger on the way is a good idea.

 

[stevezzzz]

I understand your point, David99. But did you factor in the slower speeds for the part of the route that's off-highway, or just assume 75mph for the whole distance from SpC to SpC? Specifically, for the St George stop? I estimate stopping at St George SpC adds 12-15 minutes in travel time and 4.1 road miles to the direct Beaver-Las Vegas run.

If either Beaver or Las Vegas is an overnight destination (or a long meal stop), the decision swings more in favor of skipping St George. Which illustrates a general truth: if for whatever reason you're leaving a Supercharger with a full battery or planning an extended stop at the second one down the string, and if you can skip the intermediate SpC to arrive an the destination with a low SOC, it pays to do so.

 

[Bighorn]

No, I'm talking about the decline in charge rate at higher SOC. The effect on the average charging rate (over an entire charging session) is so great at higher SOC that it significantly affects the optimum driving speed for those owners who don't like to arrive at the next SpC near empty.

Thanks for the clarification. I'm not an engineer, and in my world ramps go up and tapers come down I agree that the peace of mind afforded by a nice buffer is rather time-costly. I have grown more conservative in my buffer planning. Early on, around the time of Tesla's cross country run, I was arriving at superchargers with 5 mile buffers routinely just out of a competitive spirit. But running up against an emptying battery with miles to go is no fun, especially if you've found a friendly convoy to travel with; suddenly you're confronted with having to drop your speed precipitously just to make it on fumes. If having an adequate buffer is forcing charges above 90%SOCs, I've found the splash and dash to be more efficient than skipping chargers, if the SCs are conveniently placed.

 

[David99]

I understand your point, David99. But did you factor in the slower speeds for the part of the route that's off-highway, ....

Of course. I used EV Trip Planner which calculates speed and usage on each part of the road as close to real world as it gets. I know how these numbers are so opposite to what we think it would be. I didn't believe it myself hence I took the time do play around with all these different scenarios and see what adds up in the end.

Of course, the more variables you add, the more complicated it gets. Yes when you stay over night all bets are off. But this discussion is all about breaking the record. There are, per definition, no over night stays.

 

[NoMoGas]

Of course. I used EV Trip Planner which calculates speed and usage on each part of the road as close to real world as it gets. I know how these numbers are so opposite to what we think it would be. I didn't believe it myself hence I took the time do play around with all these different scenarios and see what adds up in the end.

Of course, the more variables you add, the more complicated it gets. Yes when you stay over night all bets are off. But this discussion is all about breaking the record. There are, per definition, no over night stays.

Not necessarily. The record to be broken is "Total time spent charging". Truth is we can take our sweet time lol

 

[chickensevil]

If you are going for least time spent charging then it would also benefit you to stop at every stop feasible since it will be quicker adding miles on the low SOC taper. 5 minutes at 0 miles is much better time spent than 5 minutes at 99% SOC. So in that sense skipping wouldn't make sense.

If you were going for shortest overall time from point A to B then based on the information above it seems like it would be better to stop more often as well... Assuming of course the chargers are not far away from the highway.

 

[David99]

Okay--I found that blog post about optimal speeds.

I remember seeing that a while ago. It's definitely interesting, but as you said, it changes with the distance between the Superchargers. The shorter the distance between them, the more you can stay on the lower end of the battery charge level, thus getting a faster charge rate, thus being able to drive faster overall. But then it gets beyond the 90 mph range which is definitely illegal here. Sometimes I miss my years in Germany where it was perfectly fine and legal to drive 110 mph.

 

[wycolo]

Glenwood Springs CO SpC - Here is an example of the non-intuitive approach route being far superior. Use the *West* Glenwood exit on I-70 regardless of which direction you are traveling. You won't get lost and the service roads to the mall are empty so you can hustle. This suggestion is for folks who do not know the town intimately.

With Country Club Hills being now online one can go: Rockford > C.C.Hills > Angola and avoid the (inaccessible) Mishawaka. So Angola would indeed be pivotal to the cross country race. Apologies to William who had it right! [my bad].
--