Chewing up time savings at the Supercharger

[WSE51]

I am not going to win any popularity contests for this, but now that EVPlanner is back online, I queried it for the tough St. George UT to Beaver UT leg, which is 104.6 miles and 3283 foot elevation increase, at 15 degrees outside temperature and 68 degrees in the car. S85 car with 19 inch wheels. Assumed 175 Rated Miles per Hr charging, which some will argue is too low but is my average experience.
I don't know what algorithm they use for speed vs. RM consumed but it does not appear linear; and that makes sense, since wind resistance is not linear. These results differ from all the rules of thumb people have stated in their replies in this thread, they imply there is no net time savings for going faster once you pass the typical highway speeds for that region.

If you re-run this at an average charging speed of 225 RM/hr, the conclusion changes. But under either assumption, the majority of time savings from speeding up are lost to increased charging times. Perhaps someone else can analyze other routes and see if the conclusion changes. See attached PDF of the results along with the Excel file used to generate it. The Rated Miles Consumed and Gross speed in mph come from EVPlanner website.

View attachment speed.pdf
View attachment speed vs charging time.xlsx

 

[Cottonwood]

I am not going to win any popularity contests for this, but not that EVPlanner is back online, I queried it for the tough St. George UT to Beaver UT leg, which is 104.6 miles and 3283 foot elevation increase, at 15 degrees outside temperature and 68 degrees in the car. S85 car with 19 inch wheels. Assumed 175 Rated Miles per Hr charging, which some will argue is too low but is my average experience.
I don't know what algorithm they use for speed vs. RM consumed but it does not appear linear; and that makes sense, since wind resistance is not linear. These results differ from all the rules of thumb people have stated in their replies in this thread, they imply there is no net time savings for going faster once you pass the typical highway speeds for that region.

If you re-run this at an average charging speed of 225 RM/hr, the conclusion changes. But under either assumption, the majority of time savings from speeding up are lost to increased charging times. Perhaps someone else can analyze other routes and see if the conclusion changes. See attached PDF of the results along with the Excel file used to generate it. The Rated Miles Consumed and Gross speed in mph come from EVPlanner website.

Good analysis, but I have not checked your details. Assuming a constant charge rate for Superchargers simplifies the charging rate on a Supercharger too much. Because of the taper, the charge times for the slower speed, lower rated mile cases will be even less, and for the higher speed cases even more. That will further push the fastest overall time away from the high speed case.

Doing the runs at a low temperature ups the rated mile needs and also pushes the best time to a slower speed. What if you do this at 68˚/68˚?

 

[WSE51]

Update to calculations

As suggested by Cottonwood, I used non-winter temperatures and also took account for the "taper" at a Supercharger when the State of Charge gets higher. I used the Tejon Ranch to Harris Ranch route on EVPlanner, this is a relatively flat 126.5 mile segment. The results are similar to the Utah run .. at speeds over 61 mph ("speed factor 1.0" at EVPlanner), the majority of any speed gain is offset by extra time at the Supercharger. At speeds above 70 mph, essentially all of the time gained in going faster is lost at the Supercharger. This is so different than what everyone has been saying that it begs to be tested in real life to see if the EVPlanner model is accurate.

I've attached my spreadsheet below and invite comparisons and other routes to be analyzed. I used this website to compute the charging time: Charge-off 90kW vs. 120kW | Tesla Owner and attempted to eyeball the curve as best I could. I used the 90 kWh curve because I have an "A" battery pack, but directionally the same result should be there for newer battery packs.

View attachment speed vs charging time 2.xlsx

 

[Nigel16494]

Yesterday I did something dumb, I had a long trip and forgot about terrain and managed to limp to the supercharger at Fremont. I was the only one there at 10pm and it the car claimed +377 mi/hr , 300A , 371V. I had 32 miles range when i arrived. It seems that empty batteries charge a lot quicker. I have never managed that charge rate before but also being on my own and every stall empty helped. I agree with the previous post, I never seem to have a constant charge rate at a supercharger.

 

[ckessel]

At speeds above 70 mph, essentially all of the time gained in going faster is lost at the Supercharger.

Uh, in short, no.

Unless you're doing a 100% charge each time. I'm typically charging from 10%->70% to make the 120 miles between SCs. Going 80 instead of 70 saves me 15-20 minutes between super chargers. That extra 10mph absolutely, positively, in no possible way uses up 15-20 minutes of SC time. It only takes me 20 minutes total to use the SC at all for most stops.

I have an A pack.

 

[WSE51]

ckessel, I should not have said "essentially all" .... the model that EVPlanner uses and the taper results in about 75% of the time gain being lost in extra charging time.

120 miles at 80 mph is 90 minutes. 120 miles at 70 mph is 102.9 minutes, so you save 12.9 minutes of driving. The faster speed uses up about 29.5 extra Rated Miles according to the EVPlanner.com model that I used on the Tejon Ranch to Harris Ranch run. (hopefully someone can verify that with real world driving). That's an extra 10% SOC on the battery, and it means charging to 70% instead of 60% in your example. In this graph, it looks to me that will take about 9 - 10 minutes more to charge: Charge-off 90kW vs. 120kW | Tesla Owner. Net gain is maybe 3 minutes?

 

[ckessel]

One of us is misinterpreting the graphs. You said your interpretation was 9-10 minutes for 60->70%. Looking that first graph, as best as I can eyeball it, with 60%(160)->70%(185) looks to me like around 5-6 minutes (37->43 minutes to charge that 10%).

There's also difference in whether you're getting the minimal charge possible or charging to a set point. I'm always charging to 70% for cushion, so I'm always burning that 60-70% mark in time anyway.

Or, stated another way. I can go 70mph and charge for 20-70% or I can go 80mph and charge 10->70%. Consequently, the extra charging time in my typical usage pattern is spent in that extra fast 10->20% phase.

If you're trying completely optimizing SC time, as Tesla did in their cross country trip, that's uses a significantly different charging strategy where you'd be trying to arrive at 0 SOC charge and leave with the minimum possible miles.

 

[David99]

In theory getting the minimum charge and stopping in SJC was best, but there are real world variable that come into play.

...

Sometimes spending a known 30 minutes is better than possibly saving 10 minutes or loosing a additional 30 at the next stop.

Very true. Some Superchargers are so close to freeways that it only takes a few minutes to go off and on. Other locations are far off. St George for example is about 13 min away from the freeway. It adds 26 min to your trip. Unfortunately it's hard to skip this one.

 

[WSE51]

One of us is misinterpreting the graphs. You said your interpretation was 9-10 minutes for 60->70%. Looking that first graph, as best as I can eyeball it, with 60%(160)->70%(185) looks to me like around 5-6 minutes (37->43 minutes to charge that 10%).

There's also difference in whether you're getting the minimal charge possible or charging to a set point. I'm always charging to 70% for cushion, so I'm always burning that 60-70% mark in time anyway.

Or, stated another way. I can go 70mph and charge for 20-70% or I can go 80mph and charge 10->70%. Consequently, the extra charging time in my typical usage pattern is spent in that extra fast 10->20% phase.

If you're trying completely optimizing SC time, as Tesla did in their cross country trip, that's uses a significantly different charging strategy where you'd be trying to arrive at 0 SOC charge and leave with the minimum possible miles.

ckessel, I've attached a screenshot of the graph on that website and attempted to draw in the lines necessary to carefully look at the charging minutes. I've also asked the author, who has the raw data, for help and we may hear from him later. The 60% SOC mark is at 160 miles (60% of 266.7) and that is at 34 minutes on the graph best I could draw. To compensate for the 29.5 Rated Miles lost by driving 80 mph instead of 70 mph is actually 11% SOC (29.5/266.7) and so we should look at 71% of 266.7 which is 190 Rated Miles. My line is a little too far to the right, I think it should be placed at about 45 minutes on the graph. So it would take 11 minutes of extra charging vs. 13 minutes of time saved driving faster.... Net of 2 minutes saved.

View attachment Supercharging rates.pdf

However, I also agree with your point that for experienced Tesla drivers, this is not how most people would drive. They would drive at 80 mph, knowing that by doing so they probably only have a 20-25 Rated Mile cushion, and as they progress they would carefully watch their RM vs. miles left, and if need be they would slow down as required to not eat too deeply into their reserve.... thus arriving at the SC with a low SOC. On the other hand, another driver could use the same technique at 70 mph with a target 10% SOC cushion, knowing he could slow down to 60 mph if his estimate was off.... so ultimately both of them should be considered to be doing the incremental charge at the tapered end of the curve.

A strict apples-to-apples comparison would be arrive at SC with 10%, charge to 71% and drive 80 mph vs. arrive at the SC with 10%, charge to 60% and drive 70 mph ... and in this case, as I have said in earlier posts, the great majority (11 of the 13 minutes) of time saved driving is lost supercharging.

 

[Owner]

I'll get to it but I've been sick for a week - nasty GI issue.
Although I can read the forums don't quite yet have the energy to go into spreadsheet land. Stay tuned.

ckessel, I've attached a screenshot of the graph on that website and attempted to draw in the lines necessary to carefully look at the charging minutes. I've also asked the author, who has the raw data, for help and we may hear from him later.

 

[mspohr]

Empty batteries charge faster. Best to arrive at the SC with an empty battery. You can do this by speeding up as you get closer to the SC. You may want to drain the battery by driving the last section at 100+ mph! This speeds up your travel time and your recharge time! Win win!!!

 

[Doug_G]

My rule of thumb for Level II charging is, "don't drive faster than you can charge". If the charge station you will be visiting can only charge at 80 km per hour, it doesn't make much sense to drive at 120 kph to get there. You'll just use more power driving and end up waiting longer while charging.

When using Superchargers, the converse is true... it makes sense to stop charging and leave when the rate of charging is slower than your expected driving speed. Unless of course you need a totally full charge to make it to your destination.

 

[felixtb]

My rule of thumb for Level II charging is, "don't drive faster than you can charge". If the charge station you will be visiting can only charge at 80 km per hour, it doesn't make much sense to drive at 120 kph to get there. You'll just use more power driving and end up waiting longer while charging.

When using Superchargers, the converse is true... it makes sense to stop charging and leave when the rate of charging is slower than your expected driving speed. Unless of course you need a totally full charge to make it to your destination.

Thanks Doug!

that's a good rule of thumb.

 

[liuping]

My rule of thumb for Level II charging is, "don't drive faster than you can charge". If the charge station you will be visiting can only charge at 80 km per hour, it doesn't make much sense to drive at 120 kph to get there. You'll just use more power driving and end up waiting longer while charging.

When using Superchargers, the converse is true... it makes sense to stop charging and leave when the rate of charging is slower than your expected driving speed. Unless of course you need a totally full charge to make it to your destination.

I think it's important to add the out-of-the-way time penalty to this rule of thumb. It you are going to charge for 30 minute at a supercharger, but it takes 5 minute to get there and 5 minutes to get back to the freeway, you need to reduce the "effective" charge rate by 30%.

Maybe Tesla should add the "estimated time from freeway" to the info on each supercharger?

 

[ckessel]

As of yet, super chargers I've used haven't been much farther off the freeway than gas stations, but that's for I5 on the west coast. And I do have to stop about 2x as often for SC as I would for gas.

Maybe going 80mph didn't save me much in time, but it certainly didn't hurt Plus, at each stop, whether it's for 20 minutes or 30, I'm getting out regardless and stretching my legs and probably getting a coffee nearby, which typically meant I get back to my car and it's good to go. So, it's not like I've actually waited extra time. Two of those stops were full sit down and have a meal (even if it was sit down at a Subway), so the car got a lot more charge than was necessary on those stops.

I've done Sonoma, CA -> Portland, OR in 12 hours (last summer). Google says 9:43 for that trip, which presumably doesn't involve stops for gas or food, so my total extra "EV time" for the trip was ~1 hour time.

FWIW, stopping for a 45 minute lunch makes a big difference in perceived total wait time for the trip. You leave that lunch with nearly a fully charge an can ZOOOM to the next SC and still arrive with ~100 rates miles, meaning you barely need 15 minutes to get enough miles for the next leg. That's about enough time to walk to a nearby restroom and back and check your phone for email.

I guess if my there's at moral to my story is that, in practice, optimizing Supercharger charge times ended up a non-factor.

 

[Zapped]

My rule of thumb for Level II charging is, "don't drive faster than you can charge". If the charge station you will be visiting can only charge at 80 km per hour, it doesn't make much sense to drive at 120 kph to get there. You'll just use more power driving and end up waiting longer while charging. ......

I suppose there's a trade off. A) spend more time in the car or B) have more time stopped for a coffee, bite to eat or shopping.
Even though the overall time for B) would be more, I think my wife would preferr it.

 

[Cottonwood]

When using Superchargers, the converse is true... it makes sense to stop charging and leave when the rate of charging is slower than your expected driving speed. Unless of course you need a totally full charge to make it to your destination.

But that will often have you putting more charge into your MS than you need to get to the next Supercharger with enough margin. For example, you may have enough charge to make it to the next Supercharger when the charge rate is 45 kW or 150 mph charging. At that point, it is time to leave to get to the next Supercharger and be able to charge quickly there.

My rule of thumb, when conditions are well predicted by EVTripPlanner (little wind, snow, or rain), is a 15% cushion on EVTripPlanner or 25 miles whichever is greater. I used to use 25% and 40 miles until I became more comfortable with the accuracy of EVTripPlanner.

With Superchargers closer than 133 miles, I don't think that I have ever charged until the charge rate dropped to the speed limit. For greater distances, pushing well into the taper, you can often reduce the total time by driving slower and leaving before the charge rate goes to glacial speed. I don't claim to find the optimum, but I will twiddle with EVTripPlanner with slower speeds to reduce charge times. I bet this is close to your rule of thumb.

A final case that I often do, is the Silverthorne Supercharger to my home in Pagosa. I can hypermile it on a 100% charge (forever at the Supercharger), but it is a little faster and a lot more fun, to leave Silverthorne when the charge rate is down to 50 mph (about 35 Amps) and head for the HAL2, 70 Amp charger in Salida which charges at 50 mph (~35 Amps). Staying longer at the Supercharger and charging at less than 50 mph takes longer than charging at Salida at 50 mph, and I get to drive a little faster. Besides, Wood's High Mountain Distillery, location of the HAL2, is a nice break in the drive.

 

[invisik]

As of yet, super chargers I've used haven't been much farther off the freeway than gas stations, but that's for I5 on the west coast. And I do have to stop about 2x as often for SC as I would for gas.

I'm in the Midwest and I'd say most are fairly close to the freeway (5 minutes or less). Some are pretty far, like Normal, IL, I think it was like 15-20 minutes to get there through a zillion traffic lights and then it's inside a parking ramp on the 3rd floor. Almost need to map the route and then count the segments after exiting the freeway to see what your extra time is going to be.

But 5-7 minutes is probably a wise average for general calculations....

-m

 

[Cottonwood]

See supercharge data from cross-country road trip for a great set of real world data for charge time. In particular, see the last page of the spreadsheet, "Timer".

 

[Owner]

I'm feeling better and started the number crunching last night. The data is more interesting than I expected.... reporting coming soon.