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boilerbots
Member
I see what you are suggesting.... probably all of Tesla engineering is in California and they have never experienced this "spike" either!
mknox
Well-Known Member
Yep. It's a pretty impressive amount of power consumption when pack warming and cabin heating all come on when you first set out. I got my car in March. Not exactly "winter" but we did have some cold and snow. I think I was seeing numbers over 1,500 Wh/mi for the first few miles, and the orange power meter could be sitting at (I think) 5-10 or more kW just stopped at a light.
I opted to not grab video, as it wasn't really necessary to document the "initial energy spike". A couple of pics illustrate:
This is sitting in my car this morning after unplugging the charge cable. At this point some energy is being used, as the systems have woken up and come online, the cabin HVAC has kicked in, dome lights are on, radio is on, etc... it was relatively cool this morning, so the sound of the thermal management was relatively modest. Initial pic:
And this picture is 90 second later, after I've backed down my driveway and rolled down the street for the first bit of distance. This spike is low today, as I mentioned it was rather cool (high 60's) this morning. The spike is in the 800's:
By the time I got to work ~33 miles later, my average usage was about 304Wh/mi... so the initial energy usage while the car is stationary is what seems to account for the initially reported "spike" once the "Since Last Charge" meter updates after the car moves a bit.
(I earlier thought it was tied to the first 0.1 miles having had to elapse, but apparently not as per the pics)
This is sitting in my car this morning after unplugging the charge cable. At this point some energy is being used, as the systems have woken up and come online, the cabin HVAC has kicked in, dome lights are on, radio is on, etc... it was relatively cool this morning, so the sound of the thermal management was relatively modest. Initial pic:
And this picture is 90 second later, after I've backed down my driveway and rolled down the street for the first bit of distance. This spike is low today, as I mentioned it was rather cool (high 60's) this morning. The spike is in the 800's:
By the time I got to work ~33 miles later, my average usage was about 304Wh/mi... so the initial energy usage while the car is stationary is what seems to account for the initially reported "spike" once the "Since Last Charge" meter updates after the car moves a bit.
(I earlier thought it was tied to the first 0.1 miles having had to elapse, but apparently not as per the pics)
mknox
Well-Known Member
Okay, I see what you're saying. I see that too. I just attributed it to the fact you haven't driven a mile yet, and the Wh/mi calculation doesn't have enough data points to be accurate. For me, it goes into the "normal" range pretty quickly.
Ben W
Chess Grandmaster (Supervised)
To address some of these issues... If the display shows that you've traveled 0.1mi and have a 1000Wh/mi "spike", that's really an insignificant amount of power in the big picture. (just 0.1kWh, or what a hair dryer uses in 3 minutes.) A more significant spike occurs when you get up to speed on the freeway, say; the Wh/mi will jump to 600Wh/mi for the first mile or two, then decrease to 300+ over the next several miles. This is simply because it takes a lot of energy to accelerate up to speed. I think it would be interesting if the kinetic energy of the car were considered in the calculations, so it wouldn't "count against" the power used. Consider that at 80mph, if the power died, you could coast for nearly a mile before coming to a stop. I wonder if anybody has actually tried/measured this.
Second, as far as how much energy is in a "Rated Mile": Keep in mind that the car does have a significant "Spare Capacity" below zero, which means that the "Rated" range from 265mi to 0mi corresponds to somewhat less than 85kWh. If there is 5kWh "in reserve" below the zero point, then the "Rated" display actually works out to 302Wh/mi. That's how you can drive for a long distance at 308Wh/mi and still "lose ground" versus the Rated display.
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I've also long suspected that the "Rated" display (at least in the Roadster) is nonlinear; it drops off quicker towards the beginning, and gets more conservative as you near zero. So each mile on the "Rated" display might represent 290Wh/mi toward the high end of the pack, and 320Wh/mi toward the low end. This is pure speculation, but corresponds to what I've observed in 4+ years of Roadster ownership.
Second, as far as how much energy is in a "Rated Mile": Keep in mind that the car does have a significant "Spare Capacity" below zero, which means that the "Rated" range from 265mi to 0mi corresponds to somewhat less than 85kWh. If there is 5kWh "in reserve" below the zero point, then the "Rated" display actually works out to 302Wh/mi. That's how you can drive for a long distance at 308Wh/mi and still "lose ground" versus the Rated display.
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I've also long suspected that the "Rated" display (at least in the Roadster) is nonlinear; it drops off quicker towards the beginning, and gets more conservative as you near zero. So each mile on the "Rated" display might represent 290Wh/mi toward the high end of the pack, and 320Wh/mi toward the low end. This is pure speculation, but corresponds to what I've observed in 4+ years of Roadster ownership.
While the amount of energy may not be great in the big picture, it illustrates one of the points I made in my initial post:
The trip meters account for energy used for things other than locomotion.
This is evident in that on a really hot morning when the the HVAC comes on full-bore... or if I sit in my garage for several minutes with the car "on", the initial spike is much higher... often time 1400+ Wh or more.
That leads to the questions I had above regarding why the rated miles on the dash and the actual distance driven don't match provided my entire energy usage is accounted for in the "since last charge" meter and my average energy usage is in the high 200's?
The trip meters account for energy used for things other than locomotion.
This is evident in that on a really hot morning when the the HVAC comes on full-bore... or if I sit in my garage for several minutes with the car "on", the initial spike is much higher... often time 1400+ Wh or more.
That leads to the questions I had above regarding why the rated miles on the dash and the actual distance driven don't match provided my entire energy usage is accounted for in the "since last charge" meter and my average energy usage is in the high 200's?
schueppert
Member
I have also noticed the spike and I agree with your conclusion that the trip meters account for energy used for things other than locomotion. But that does't mean the trip meters account for everything other than locomotion. For example, if the trip meter works by a continuous measurement of current and voltage delivered by the battery then it will not measure energy consumed by the internal resistance of the battery.
This is a really interesting thread. I see the spike every day: it's mildly downhill from my garage to the street and down the block, but the first reported value I see is usually above 700 Wh/mile.
As for Ben's suggestion, the geek in me would relish having an instantaneous 'total energy' range display that combines kinetic energy with the battery state. But KE is pretty small potatoes when compared to the energy stored in an 85 kWh battery pack. More useful would be a trip calculator tied in with the navigation system that factors in elevation changes, weather and driving style to give a running readout of predicted range remaining at the goal. If that number is holding steady or rising, all is well; if it's declining, time to look for a closer charging opportunity. My glider has had this capability for 15 years or more, and as I've pointed out before there are any number of parallels between cross-country soaring and EV road trips.
Now I'm not so sure what it is. I had been under the impression that he EPA 5-cycle testing that led to the revised distance estimates for the 85KW pack boiled down to 308Wh/mi... but I can't find that definitively anywhere now.
When you say your "car's display shows" 300Wh/mi for Rated, what are you speaking of?
1. 308 Wh/mi. = 85 kWh / 265 mi ... i.e. if the battery pack have exactly as much energy as advertised and none is used for buffer (or the buffer isn't included in the capacity advertised)
2. I believe mknox is referring to the "Rated" that is near the 300 Wh/mi line in the Energy chart.
schueppert
Member
The kinetic energy (1/2mv^2) of a 4,647lb (2,112kg) Model S at 70mph (31.3m/s) is 1.0MJ or about 300Whr. I suspect the margin of error on the rated range display is greater than this anyway. The potential energy (mgh) of Model S at the top of a 2,000m mountain is 41.4MJ or about 11.5kWhr. This is obviously very significant, and I guess you could adjust the rated range meter for it, but of course you only can use this range bonus if your are planning to come down the mountain!
schueppert
Member
How to you divide 85kWh by 265 miles and get 308Wh/mi??? My calculator says 321Wh/mi. But it works if you apply an efficiency factor for the battery of 96%, which is probably about right. That is, a 96% efficient 85 kWh battery actually delivers 81.6 kWh which at 308 Wh/mile gives a rated range of 265 miles.
Sorry guys, I spaced. 320ish is indeed the number you get from that math.
When I got 308ish, I think it was from doing calculations like these:
New Model S owner charging primer (US) - Page 6
When I got 308ish, I think it was from doing calculations like these:
New Model S owner charging primer (US) - Page 6
But, this assumes that we don't have 85kWh batteries, rather 90kWh usable batteries because at 0 there is really another 20 miles or so left (after artificial reduction of capacity by removing top 5% and bottom 5%, so the batteries are really 100kWh). Rolling this number further down, that would make the cells used ~3.9Ah cells. I don't think this correct.
Peter
Peter
mknox
Well-Known Member
I'm going to have to go back and look now, but I thought there was a horizontal line on the energy display that said "Rated" on one side and 300 Wh/mi on the other. (I keep my displays in "Rated Range" mode). There is another (dashed?) line that shows your average consumption over whatever miles you have it set to average over.
No worries... this stuff is hard to keep straight absent definitive documentation.
So in that regard, is there an authoritative definition of what a "Rated Mile" is on the model S?
Is this not an EPA/Gov't standardized thing?
Ah... that OK, that makes sense. I'll double check as well... I guess I'm not sure I ever connected that that line had a constant value.
So if that's the actual value, and I keep my average per trip under that value as per the trip meter....
A few months ago someone on the forums who ran their Model S battery until the car stopped noted that the energy consumed 'since last charge', as shown on the Trips display, was right around 80 kWh. I'll see if I can't find the reference.
[edit:]
I couldn't find the thread I was looking for, but I did find one from early autumn last year where the car displayed 0 when the 'since last charge' showed 76.9 kWh consumed. I believe it was a Range charge, too.
Battery reserve and real world range
[edit:]
I couldn't find the thread I was looking for, but I did find one from early autumn last year where the car displayed 0 when the 'since last charge' showed 76.9 kWh consumed. I believe it was a Range charge, too.
Battery reserve and real world range
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