Most efficient charging method when traveling....

[Cottonwood]

Also keep in mind most high amp L2 stations on Sun Country Highway are 208V 70A (14.56kW) which will increase charge times by 30% compared to 240V 80A.

The spreadsheet clearly shows the need for SuperChargers on road trips. With high amp L2 it's counterproductive to drive faster than 60mph - you'll spend more time charging than you save driving. High amp L2 is great as a destination charger, but doesn't cut it for long distance road trips.

Mostly, I agree with your statement. A favorite method of travel for me is to stay at a hotel with L2 charging available, that is within easy range of Superchargers. As you say L2 charging at a destination is perfect; charging while I sleep takes no time from me.

The one exception where L2 charging is useful, is for moderate distance travel. That is, where the total trip distance for the day (or between Superchargers) is slightly more than you can do in one charge. Having a good, high-amp, L2 charger about half way can make such a trip very nice. A good example, that I often do, is driving between my two houses in Pagosa Springs and Boulder, Colorado. They are about 300 miles apart. Salida, Colorado is about half way between the two, and I have worked with P.T. Wood, the owner and chief alchemist of Wood's High Mountain Distillery, to install a 70A, 240V J1772 at Wood's in downtown Salida. It makes for a pleasant trip to stop in Salida for an hour or two charge, talk to PT, have lunch, etc and then continue on to Pagosa.

 

[Mayhemm]

Also keep in mind most high amp L2 stations on Sun Country Highway are 208V 70A (14.56kW) which will increase charge times by 30% compared to 240V 80A.

The spreadsheet clearly shows the need for SuperChargers on road trips. With high amp L2 it's counterproductive to drive faster than 60mph - you'll spend more time charging than you save driving. High amp L2 is great as a destination charger, but doesn't cut it for long distance road trips.

Good point about the real-world charge speed of EVSE's. Most, if not all promotional material assumes 240V (sometimes even 250V) in their calculations. The current trend of placing EVSE's at businesses means you'll be getting converted 3-phase power (max 208V). This combined with electrical code only allowing 80% load on a circuit can make for some very different numbers in reality.

Also agree about L2 chargers not being ideal for travel. I can't see why anyone would use them when they have access to Superchargers. For those of us without SC access, however, High-power L2 stations are a definite step up and I'm glad they're there.

Based on this curve from Tesla's website I did some calculations. It shows the energy usage vs speed.

Now that you've went to all the work of finding the ideal speed at which to travel, could you weigh in on which of the following results in the shortest overall charging time (assuming readily available 15kW+ EVSE's but no Level 3 stations)?

A) Stopping frequently and charging for a short time
B) Stopping infrequently and charging for extended periods

 

[Cottonwood]

Based on it I made a very simple spreadsheet to find out what the ideal drive speed is depending on the charger speed available. It is based on driving 100 miles. I used three different chargers: a typical 7 kW public L2 station, a 20 kw HPWC with dual chargers and a 100 kw Supercharger. I used 100 kW as it seems a reasonable average considering tapering. All times are in minutes.
View attachment 48694

You need a small correction to your table because of a common 10% efficiency error. AC chargers are usually rated at their AC power in, Superchargers are rated at their DC power out, and the car does its accounting on DC battery energy. The typical power of the Tesla charging module is about 90%. That means that in your spreadsheet, you need to multiply the AC power ratings on the L2 chargers by 0.9 before doing the calculations. For example the L2 Charger with 7 kW AC power will only put 6.3 kW DC into the battery, and the 20 kW AC charging will only put 18 kW DC into the battery. Because the Superchargers are rated at their DC output, they do not have to be corrected.

These small, 10% corrections will probably not change your results, but will tilt the table just a little.

 

[djp]

Now that you've went to all the work of finding the ideal speed at which to travel, could you weigh in on which of the following results in the shortest overall charging time (assuming readily available 15kW+ EVSE's but no Level 3 stations)?

A) Stopping frequently and charging for a short time
B) Stopping infrequently and charging for extended periods

To do the math you'd need to know the ramp-down curve as the battery approaches full charge. Intuitively (B) should have a shorter travel time since charging the battery from a lower SOC avoids the ramp-down, and you don't waste time getting on and off the highway as often.

 

[David99]

I'm totally aware it's a very simplified spreadsheet with only three scenarios. The point isn't to have a 100% accurate model, the point is to show how charge speed and drive speed correlate. It's showing that slower charge speed require slower drive speeds to be faster overall. And faster charge speeds are optimal at higher drive speeds. It shows that Superchargers give you the option to go as fast as you (safely) can and always know you are getting the optimum total travel time. Yes in the real world the conditions nudge the results a little up or down, but are almost irrelevant to the basic findings.

In any case charging is always more efficient when the state of charge is low. It makes a small difference on L2 chargers, but a big one on Superchargers.

 

[EVFest]

It's actually not a complicated mathematical problem. It's pretty straight forward.

assume you travel 100 miles (which is the average leg between Superchargers). It's just a random number, you can extend it to longer trips, but it doesn't change anything. It just repeats each driving and then charging cycle. So it's fine to just look at a single drive/charge cycle.

Going at 65 mph: drive time is 92 min, charge time is 17 min = 109 min total
Going at 75 mph: drive time is 80 min, charge time is 24 min = 104 min total
Going at 85 mph: drive time is 70 min, charge time is 30 min = 100 min total

You are using more energy to travel the same distance, hence the charge time is longer, but since the Superchargers are so fast the time lost in driving slow outweighs the extra time spent charging.

This Must be the Thinking - that got an owner in trouble - driving the (high) speed limit (120 Kph) in BC a short while ago - on the Coquihalla - a Mountain Pass if there ever was one, in Cold Weather!

The Other thought - is if the conditions and road are not well known, drive a bit/bunch slower until there is no way you could not make the Supercharger, and then speed up, watching the range adjustments, and leave a buffer - in winter - for road closures! The 9 minutes save by driving fast only work - if you don't end up to need a $200 Flat bed tow for a few short miles to the next Charger - be it supercharger or otherwise!!

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Simple math:
Driving is 60-90mph
Charging is 340mph
No matter how fast you drive, Supercharger is still faster than you
So Supercharger will offset the loss of speeding

It will - if you don't end up 3 miles short and need a $200 Flat Bed Tow to it!

 

[Chipper]

This Must be the Thinking - that got an owner in trouble - driving the (high) speed limit (120 Kph) in BC a short while ago - on the Coquihalla - a Mountain Pass if there ever was one, in Cold Weather!

The Other thought - is if the conditions and road are not well known, drive a bit/bunch slower until there is no way you could not make the Supercharger, and then speed up, watching the range adjustments, and leave a buffer - in winter - for road closures! The 9 minutes save by driving fast only work - if you don't end up to need a $200 Flat bed tow for a few short miles to the next Charger - be it supercharger or otherwise!!

- - - Updated - - -



It will - if you don't end up 3 miles short and need a $200 Flat Bed Tow to it!

I assume you do realize you are responding to a post from 9 months ago, right?

 

[Mayhemm]

I assume you do realize you are responding to a post from 9 months ago, right?

And it's not still relevant today?

 

[Chipper]

Probably not for David99!

And it's not still relevant today?