Liz
You should have asked to charge at the shop! I've even stopped at Toronto service for a charge when not booked in for service. You'd think they would have offered.
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Scary range anxiety day!
- Thread starter Jgdixon
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- Canada Range Anxiety
You should have asked to charge at the shop! I've even stopped at Toronto service for a charge when not booked in for service. You'd think they would have offered.
Raffy.Roma
Rome (Italy)
Hi guys. I would like to add two further recommendations.
11. Never pass up a charging opportunity!
12. Always plug in!
;-)
11. Never pass up a charging opportunity!
12. Always plug in!
;-)
I'm going to extend my 'pilots know in their bones' theme to 'glider pilots know in their bones'. Classic cross-country thermal soaring is a pretty precise analog for driving an EV on a road trip with charging stops along the way: you 'charge the battery' of a glider by being towed aloft, cruise along on course (draw from the battery) while looking for a thermal (charging station). When you find a thermal you stop cruising and circle to gain altitude (charge the battery). At some point you decide to continue on course (stop charging and drive on). Lather, rinse, repeat.
The problem of optimizing thermalling cross-country speed in a glider was solved in a theoretical sense a long time ago. As a historical aside, much of the theoretical work was done in the early 1950s by Paul McCready, the late founder of AeroVironment, which makes EV charging stations, among other things. Two aspects of cross-country thermal soaring are particularly relevant here: the question of how fast to cruise between thermals (charging stations) and when to leave a thermal and continue on course.
Without going into detail, the basic concept is simple: to optimize cross-country speed, minimize the time to the top of the next thermal (minimize the time to the end of your next charging stop). Seems pretty self-evident when you put it that way, right? But what guidance does that give us as EV drivers?
First: the slower the next charge, the slower you should drive to get there. If you imagine a time plot of SOC over several charging stops, what you want to see is a sawtooth pattern with equal slope on either side of each valley, where the valley represents the start of a charging session. If your next charging stop delivers a 20kW charge, you should drive so as to average a draw of 20kW en route to the charge stop. If it's a Supercharger, you 'should' drive at a 90kW draw (safety and speeding tickets aside). If it's a 10kW L2J1772, better hope it's an overnight stop. If it's a 15A 120V wall outlet...well, that sucks.
So that's the ideal: but the practical reality is different in several interesting ways. Remember our cross-country glider pilot? The first complication arises when you consider that in order to continue making progress, our pilot must find the next thermal before reaching the ground (depleting the battery to zero SOC). In a glider, you never really know where you'll find the next thermal, whereas in an EV you should always know where your next charge stop is located. When a glider pilot becomes concerned about finding a thermal and goes into survival mode (i.e., is no longer interested in maximizing cross-country speed), he slows down to a speed that maximizes his search radius; the EV driver slows down to a speed that brings the charging station within range.
When does our glider pilot decide to leave a thermal and head back out on course? If the thermal is stronger than average, he'll stay there and get as much altitude as possible, only leaving when the rate of climb starts to diminish. If the thermal is weaker than average and there is a reasonable expectation that there is a stronger thermal ahead on course, he might choose to stop climbing at a lower altitude and press on in the expectation of climbing faster in the next thermal. Similarly, an EV driver sitting at an L2 charger delivering 6 or 7 kW might choose to leave for a 20kW charger farther down the road as soon as they felt comfortable that they had sufficient range to get there, with reserves. The more experience you have and the better you can anticipate the conditions ahead, the smaller your reserves can be. The decision about when to leave the last charging stop for your final destination is based on the charge rate: the faster the charge, the higher the SOC you'll want before leaving, and the faster you'll be able to drive to your destination.
There's more to this subject, but I think that's plenty to chew on for now.
The problem of optimizing thermalling cross-country speed in a glider was solved in a theoretical sense a long time ago. As a historical aside, much of the theoretical work was done in the early 1950s by Paul McCready, the late founder of AeroVironment, which makes EV charging stations, among other things. Two aspects of cross-country thermal soaring are particularly relevant here: the question of how fast to cruise between thermals (charging stations) and when to leave a thermal and continue on course.
Without going into detail, the basic concept is simple: to optimize cross-country speed, minimize the time to the top of the next thermal (minimize the time to the end of your next charging stop). Seems pretty self-evident when you put it that way, right? But what guidance does that give us as EV drivers?
First: the slower the next charge, the slower you should drive to get there. If you imagine a time plot of SOC over several charging stops, what you want to see is a sawtooth pattern with equal slope on either side of each valley, where the valley represents the start of a charging session. If your next charging stop delivers a 20kW charge, you should drive so as to average a draw of 20kW en route to the charge stop. If it's a Supercharger, you 'should' drive at a 90kW draw (safety and speeding tickets aside). If it's a 10kW L2J1772, better hope it's an overnight stop. If it's a 15A 120V wall outlet...well, that sucks.
So that's the ideal: but the practical reality is different in several interesting ways. Remember our cross-country glider pilot? The first complication arises when you consider that in order to continue making progress, our pilot must find the next thermal before reaching the ground (depleting the battery to zero SOC). In a glider, you never really know where you'll find the next thermal, whereas in an EV you should always know where your next charge stop is located. When a glider pilot becomes concerned about finding a thermal and goes into survival mode (i.e., is no longer interested in maximizing cross-country speed), he slows down to a speed that maximizes his search radius; the EV driver slows down to a speed that brings the charging station within range.
When does our glider pilot decide to leave a thermal and head back out on course? If the thermal is stronger than average, he'll stay there and get as much altitude as possible, only leaving when the rate of climb starts to diminish. If the thermal is weaker than average and there is a reasonable expectation that there is a stronger thermal ahead on course, he might choose to stop climbing at a lower altitude and press on in the expectation of climbing faster in the next thermal. Similarly, an EV driver sitting at an L2 charger delivering 6 or 7 kW might choose to leave for a 20kW charger farther down the road as soon as they felt comfortable that they had sufficient range to get there, with reserves. The more experience you have and the better you can anticipate the conditions ahead, the smaller your reserves can be. The decision about when to leave the last charging stop for your final destination is based on the charge rate: the faster the charge, the higher the SOC you'll want before leaving, and the faster you'll be able to drive to your destination.
There's more to this subject, but I think that's plenty to chew on for now.
That is an excellent summary, stevezzzz, and what a great analogy.
I "discovered" your rule of thumb very quickly after getting the Roadster. "Don't drive faster than you can charge."
The slowest charge point I ever use is 235V, 24A, or about 5.5 kW. That's good for only 40 Ideal km per hour (Roadster). Painful! The fastest trip time requires me to drive as slowly as I possibly can! It actually makes sense to drive below the speed limit, and pull over occasionally to let everyone pass!
The fastest charge point I've ever used is 238V, 70A, or about 16.5 kW. That's almost 120 kph (Roadster) or 90 kph (Model S). When going there, I drive as fast as possible without getting a ticket or running out of juice. (Annoyingly the very best location is in my garage... I can sometimes get over 240V @ 70A!)
Tesla has promised a 401 Supercharger this year. That will really change the equation. You want to arrive there "on fumes". The question on when to leave will come down to the ramp-down as it approaches full, and how long your next leg is. The optimization exercise might get a little more complicated. If the Supercharger is still charging faster than you can at the next stop, and there's still room in your pack, it might make sense to top up more before leaving.
Having both cars presents another interesting optimization challenge. In areas where charging opportunities are few and lower power (e.g. upstate New York) it will be faster to take the Roadster since it effectively charges 30% faster on a range basis. On the other hand, when Superchargers are available it will be much faster to take the Model S.
I "discovered" your rule of thumb very quickly after getting the Roadster. "Don't drive faster than you can charge."
The slowest charge point I ever use is 235V, 24A, or about 5.5 kW. That's good for only 40 Ideal km per hour (Roadster). Painful! The fastest trip time requires me to drive as slowly as I possibly can! It actually makes sense to drive below the speed limit, and pull over occasionally to let everyone pass!
The fastest charge point I've ever used is 238V, 70A, or about 16.5 kW. That's almost 120 kph (Roadster) or 90 kph (Model S). When going there, I drive as fast as possible without getting a ticket or running out of juice. (Annoyingly the very best location is in my garage... I can sometimes get over 240V @ 70A!)
Tesla has promised a 401 Supercharger this year. That will really change the equation. You want to arrive there "on fumes". The question on when to leave will come down to the ramp-down as it approaches full, and how long your next leg is. The optimization exercise might get a little more complicated. If the Supercharger is still charging faster than you can at the next stop, and there's still room in your pack, it might make sense to top up more before leaving.
Having both cars presents another interesting optimization challenge. In areas where charging opportunities are few and lower power (e.g. upstate New York) it will be faster to take the Roadster since it effectively charges 30% faster on a range basis. On the other hand, when Superchargers are available it will be much faster to take the Model S.
Al Sherman
It's about THIS car.
Fascinating analogy but I think it all comes down to reserve fuel. In my airplane, it's in the tank. In my Model S it's in the battery. I can even create extra by slowing down/turning off accessories.If there's noway you'll exceed your fuel supply, good. If you set a min fuel number(I think ChadS may have come up with 177? in another thread) then you plan your charge stop to be under that number. Your reserve (additional SOC) should be planned to get you to your alternate. If you can't do that; it's risky. Seems to me the planning is simpler than you're making it.
The only "accessory" that has any significant impact is the cabin heater. The rest is really small stuff. To put it in perspective, it takes around 20 kW to keep the car moving on the highway. That's a LOT of power! If you plug something into the USB port to charge it, at most it can consume 2.5 Watts. That's almost a thousandth of what it takes to keep the car moving!
Turning off headlights or the seat heater might save you a couple of dozen watts, not thousands. It's really not worthwhile! You can do more just by easing your speed down 1 kph.
So I don't worry about "accessories". I only concern myself with #1 my speed, and #2 the cabin heating/cooling. And not so much the air conditioner - it consumes a fraction of what the heater takes.
Al Sherman
It's about THIS car.
Sure. I always drive to maintain a certain reserve margin. I watch the "distance to go" on the GPS, and the "projected range remaining", and drive to keep things in positive territory.
When driving the Roadster, I aim for a 40 ideal km buffer, and try very hard not to ever go under 30 km. If I still have over 40 near the end of a trip, I'll often speed up a little or use some more heat as required to arrive with 30. I've only gone under 30 km Ideal on two occasions, and they were both caused by unexpected trip "interruptions" (in one case my GPS invented a non-existent highway off-ramp, and the other was caused by a TV reporter).
I'm still getting used to the Model S, so to be conservative I've been aiming for a 30 km Projected Range buffer, and never go below 30 km Rated Range. (I'm using Projected for planning purposes because I'm not used to the power draw in various driving conditions yet.)
When driving the Roadster, I aim for a 40 ideal km buffer, and try very hard not to ever go under 30 km. If I still have over 40 near the end of a trip, I'll often speed up a little or use some more heat as required to arrive with 30. I've only gone under 30 km Ideal on two occasions, and they were both caused by unexpected trip "interruptions" (in one case my GPS invented a non-existent highway off-ramp, and the other was caused by a TV reporter).
I'm still getting used to the Model S, so to be conservative I've been aiming for a 30 km Projected Range buffer, and never go below 30 km Rated Range. (I'm using Projected for planning purposes because I'm not used to the power draw in various driving conditions yet.)
Al Sherman
It's about THIS car.
Exactly. Just as in aviation you initially set your reserve based on performance data,and others experience. Then as time goes by you can adjust that number based on actual experience and comfort level.
I agree with you, Al. My aim was not to complicate anyone's planning exercises, but to give people different tools to use when thinking about what it means to drive an EV. When you start with a baseline of decades of ICE experience (400+ miles range, 10 minute fill-ups any place you want), it's useful to have a little help making the conversion to EV-think.
Liz G
P03056
Had it been a Tesla shop I would have but it was a 3rd party shop and I didn't have my UMC...which leads to another rule.
13. Always have your UMC in the car
14. Always plug in when you can.
LOL - I've used that "range extender technology" in my Roadster. The Model S with its extra range and "Range Mode" has so far been able to keep me comfortable without resorting to that!
For my 2nd trip to the city in the S, 180 miles total, I decided to forego cabin/seat heat since it was a mostly sunny day. Indeed there was solar gain thru the windows, but I suspect the glass all around is the 0.32 factor IR-rejecting kind. Enough gain to keep the dog & my upper body warm, but the legs & feet were cool. Not enough to cause shivering but it took the long walk across the WalMart lot & more inside to normalize. So I grabbed the leggings & muklucks to keep in the S at all times.
Roadster: need the leggings as well as heated boots, if such even exist. And the cabin insulation/soundproofing upgrade.
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Roadster: need the leggings as well as heated boots, if such even exist. And the cabin insulation/soundproofing upgrade.
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Awesome 
I was laughing in my chair but wife just didn't get it, even when I tried to explain.
I was laughing in my chair but wife just didn't get it, even when I tried to explain.
colinb
Member
What we saw today is that a 110V/12A did little to nothing to increase range for at least 2 hours of being plugged in when temps are -15C or below. In retrospect it might have been better for us to just get in the car and drive rather than wait the 2-3 hours with the car sitting idle, cold weather and slow charge fighting to come out on top. I also think it may be sensible for Tesla to state that the 110V/12A option is useless below a certain temperature. We'll certainly rethink any trips into sub zero that don't have at least a 30-40A charging point available.
Al Sherman
It's about THIS car.
No question. When your reserves are augmented anywhere (ICE gas stations) you really have never worried about reserves. You need gas, you get gas. Much different thought process for excess range trips in an EV. I definitely see where you're going. AND, as a lifelong aviator without a glider rating, I lobed the insight into the thought process. I actually read it over two or three times. Very interesting.
If you stopped expressly to plug in, I agree it probably did little or nothing to extend your range. OTOH, if you had to stop for another reason, plugging in certainly helped you to avoid a loss of range due cold temps and pack heating.
ig_epower
Member
Along the same lines - I pack several towels in the back of my car (for washing/drying, cleaning up potential spills or as a liner for dusty cargo that may have to go in my car). If it gets really chilly, the seat heaters work great but covering my legs with the towels does an amazing job to retaining a little heat where the seat heaters cannot reach. Of course the heater should work but sometimes the 35 - 40 kph consumption rate may be needed for range rather than cabin comfort. I find the Range Mode really not that effective in long distance winter driving that I cannot accomplish with my own control of my heating accessories.
