Road trip math - how fast to drive, how long to charge

[gilscales]

The close to optimal way is to get to the next must-visit SC with about 10% charge remaining

Thats what I do unless there are say 2 options, 1. ill have over 20% and if I keep going I can make it to the next with say 5% then I go for it and if it's getting to close and the car is telling me ill be at 2 or 3 % then I just slow down till I get my 5% back, most times its either in the 10 to 20% range vs. can't make it to the next one seems to be the common options for me when traveling.

 

[Daniel in SD]

It does not really produce what I want. I want to figure how to travel a certain distance in the shortest possible driving/charging time.

Let's say I have route with SC perfectly 200 miles apart.

If I drive 55mph it will take 3hr38min between chargers
If I drive 60mph it will take 3hr20min
If I drive 65mph it will take 3hr5min
If I drive 70mph it will take 2hr51min
etc.

The faster you drive, the more time you save (duh) simple on an ICE as refuelling times are not much different from pumping 2 gallons vs 10 gallons.

But with an EV the next part of the puzzle is figure out power used per mile at the different speeds and charging times to replace the power and of course if I have enough power to drive that fast and still make it 200miles.

The chart below gives me some idea of what this is (for the model S). Then you need to mix in charge rate times.

If you crunched all these numbers you would end up with the ideal speed to drive and charging time combination.

You are correct but it turns out that it’s practically impossible to drive fast enough unless you’re willing to risk lives and jail time.

 

[Daniel in SD]

To put some math behind it.
At high speeds power consumption goes up with the square of speed.
Let's say you use 250Wh/mi at 60mph
V = velocity (mph)
D = Distance (mi)
T = Time (hours)
Ps = supercharger power = 120kW
Ec = Energy used (Wh) = (V/60mph)^2*250Wh/mi * D

T = D/V + Ec/Ps

Solve for minimum time: Wolfram|Alpha: Making the world’s knowledge computable
Optimal velocity is 95mph. I thought it would be a little faster. The true optimum will be a little slower. Superchargers may not be close enough together or empty enough to always get 120kW. You also have to factor in the time spent getting off the highway to the supercharger.

Going to a reference consumption of 300Wh/mi only brings the optimum down to 90mph.
Lowering the supercharger rate to 60kW brings it down to 75mph.

 

[ModelNforNerd]

Hmmm, using the trucker "sweet spot" of 50mph overall...I did pretty good on the way back from Christmas. 629 miles in 11 hours 52 minutes. 53mph overall average.

And it would have been slightly faster if I was able to get my own Supercharger pair at my last charging stop...but I ended up next to another 3, and I was only pulling 35kW until he reached his tapering point. Probably a difference of about 10 minutes overall, so only about .7mph difference over the whole trip.

 

[lolder]

Several people already did this. Their conclusion was drive as fast as you can and charge between about 10 and 50-60%. The least time on their graphs shows about 105 mph. 80 mph was still pretty good. Away from California and big cities and on non-holidays superchargers are not very busy.

 

[JeffK]

Let's say I have route with SC perfectly 200 miles apart.

haha I don't know for sure that I'd safely make 200 miles in a P3D as average speeds around here are 80 mph.

 

[ℬête Noire]

Are you referring to the "real time" trip consumption graph estimate, or the navigation estimate? I've not found the Navigation system estimate to be as good as the Better Route Planner, as the car's initial navigation estimate doesn't factor in temp, road conditions, excess vehicle weight, HVAC consumption, driving above posted limits, etc.

That particular item is because it is the upside down of the way it works. You assume fast and it tells you when you need to slow down. Also, it appears that the nav does use some of the other factors (I'm talking the car, not the www.Tesla.com trip planner) directly and some of it indirectly.

I found that the more I drive the better it gets, I suspect it is filling in that stuff with actual use data, 100% it is using current battery state. It shows me where I could go and then I do a translation to shorter hops for speed (and less fatigue by keeping per stop under 2.5hrs). As a bonus it also includes DC locations and gives warnings when you'll be stuck if you don't have a non-DC/SC option available to you.

Better Route Planner is just flat out too conservative I've found. It adds huge chunks of unnecessary time ad distance because it can't find viable routes. The only way I can coax it to make jumps the car is perfectly capable of doing is put in gonzo efficiency numbers, pin the max-min to 0-100. At that point I've lost confidence in it's output.

BRP probably ok to use in very dense SC, where it's easier to find a good enough route. But out here in the middle of the continent it comes up short.

 

[Galve2000]

i wonder why no one talks about EVTripPlanner anymore..

for me it's the gold standard.

 

[SageBrush]

To put some math behind it.
At high speeds power consumption goes up with the square of speed.
Let's say you use 250Wh/mi at 60mph
V = velocity (mph)
D = Distance (mi)
T = Time (hours)
Ps = supercharger power = 120kW
Ec = Energy used (Wh) = (V/60mph)^2*250Wh/mi * D

T = D/V + Ec/Ps

Solve for minimum time: Wolfram|Alpha: Making the world’s knowledge computable
Optimal velocity is 95mph. I thought it would be a little faster. The true optimum will be a little slower. Superchargers may not be close enough together or empty enough to always get 120kW. You also have to factor in the time spent getting off the highway to the supercharger.

Going to a reference consumption of 300Wh/mi only brings the optimum down to 90mph.
Lowering the supercharger rate to 60kW brings it down to 75mph.

Very elegant and pretty close to the actual numbers.
The thing is though, you don't want to hit the taper during charging so the practical solution is:

Drive as fast as allowed and safe, to arrive with a SoC of 10-20% at the next charging stop. Then leave when the car says to. Most of the time it works out to using 50% of battery capacity each leg in a Model 3 and averaging about 80 kW charging

 

[StellarRat]

Several people already did this. Their conclusion was drive as fast as you can and charge between about 10 and 50-60%. The least time on their graphs shows about 105 mph. 80 mph was still pretty good. Away from California and big cities and on non-holidays superchargers are not very busy.

Is jail time factored in?

 

[Mod3forMe]

To put some math behind it.
At high speeds power consumption goes up with the square of speed.
Let's say you use 250Wh/mi at 60mph
V = velocity (mph)
D = Distance (mi)
T = Time (hours)
Ps = supercharger power = 120kW
Ec = Energy used (Wh) = (V/60mph)^2*250Wh/mi * D

T = D/V + Ec/Ps

Solve for minimum time: Wolfram|Alpha: Making the world’s knowledge computable
Optimal velocity is 95mph. I thought it would be a little faster. The true optimum will be a little slower. Superchargers may not be close enough together or empty enough to always get 120kW. You also have to factor in the time spent getting off the highway to the supercharger.

Going to a reference consumption of 300Wh/mi only brings the optimum down to 90mph.
Lowering the supercharger rate to 60kW brings it down to 75mph.

Thanks this is what I was looking for

haha I don't know for sure that I'd safely make 200 miles in a P3D as average speeds around here are 80 mph.

If you are running heat it might be tough to do it.

 

[299792458]

I did a ~1200 mile trip from CO to CA and learned a lot while monitoring my energy usage and driving habits.

My advice: be aware of all the obvious factors that will reduce range more quickly (spirited driving, elevation, temperature, wind, etc), but the bottom line is to use a trip planner like the Tesla nav and the instantaneous range graph while being cognizant of the line that shows energy usage for rated range (corresponding to miles remaining, if you have it in that display mode). If you aim to keep it close to rated, you will be fine and avoid range anxiety for those long legs, if you have any. The in-car navigation with charging stops works well, despite being sort of limited.

Charging past 80% (when the charge rate slows down dramatically) is usually not worth the time, unless you really need the range. I may have added a couple of hours to my trip inadvertantly for extra charge that wasn't necessary.

Also, I found myself wandering and goofing off a bit while charging, spending more time than I needed at stops. In the end, athough the total trip time was longer (than driving straight through), it felt shorter and I was way more refreshed throughout the journey.

 

[lolder]

Is jail time factored in?

Not for autobahn users.

 

[e-FTW]

Also, I found myself wandering and goofing off a bit while charging, spending more time than I needed at stops. In the end, athough the total trip time was longer (than driving straight through), it felt shorter and I was way more refreshed throughout the journey.

Autopilot user I assume. That is a factor here: you can usually spend more time on the road without needing to stop because you are tired.

 

[Galve2000]

Autopilot user I assume. That is a factor here: you can usually spend more time on the road without needing to stop because you are tired.

I think he means goofing off at a rest stop. I find the same is true for me... the car was almost always done charging before I was ready to leave the rest stop. you just build in a little more of a buffer which allows you to have a bit of fun while you drive.

 

[ModelNforNerd]

I think he means goofing off at a rest stop. I find the same is true for me... the car was almost always done charging before I was ready to leave the rest stop. you just build in a little more of a buffer which allows you to have a bit of fun while you drive.

It's a little bit of both. I'm fresher when I arrive because I'm less stressed about the driving during each hop. Once you learn to just deal with the extra time for charging, it's a lot less stressful overall.

 

[RScottyL]

I was thinking about putting together the calculations on the optimum way to plan road chip charging and highway speeds. Before I do I am wondering if someone has already tackled this? If not I am also wondering were I can find the key data points?

The key thing I would like to figure out is how fast to drive on highway road trips. If I can nail down the average power consumption and different highway speeds and the average charge times, I can come up with calculations that tell you wether you will save more time by driving fast and charging longer or driving slow and charging less.

From what I have read, electric vehicles won't go as far on the freeway as they do in the city! This is obviously because you are doing stop and go traffic in the city and using your brakes more to regen.

As someone else said, if at all possible, stick closer to 55 or 60 to get longer range than if you were going 70+!

 

[hamtonp]

From what I have read, electric vehicles won't go as far on the freeway as they do in the city! This is obviously because you are doing stop and go traffic in the city and using your brakes more to regen.

As someone else said, if at all possible, stick closer to 55 or 60 to get longer range than if you were going 70+!

For EV, you actually get better range in the city. That's due to low drag and regen braking.
The below URL shows the city mpge higher than highway:
Gas Mileage of 2018 Tesla Model 3

I believe I can achieve rated range on the highway driving 70-75 mph. That's if temperatures are favorable.

 

[ℬête Noire]

I believe I can achieve rated range on the highway driving 70-75 mph. That's if temperatures are favorable.

I find I need optimal conditions (70F-80F), no HVAC, and sub-70mph to hit 310mi range with the AWD. IIRC I hit around or just above 290mi at 70mph in good conditions. RWD should be able to hit 310mi at 70mph though.

 

[Trailblazer]

Bjorn did a video on this topic a while back (using a Model S P100D in Germany) - he came up with 106mph as the optimal driving speed.