kuttakamina
Member
^^ the above to be printed, framed, and taught in schools all across the United States of America.
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^^ the above to be printed, framed, and taught in schools all across the United States of America.
stopcrazypp
Well-Known Member
To be fair, the 85 vs 85D numbers both include charging efficiency numbers and the 85 numbers are from 2012 (the EPA allows using old numbers even after car is updated to be better). So the 85 numbers don't reflect any software/hardware updates that may have been done to the car since then, and a large part of the difference in MPGe is charging efficiency.
From the EPA numbers you can calculate:
85D takes 34kWh/100mi * 270mi = 91.8kWh to charge full.
S85 takes 38kWh/100mi * 265mi = 100.7kWh to charge full.
http://www.fueleconomy.gov/feg/Find.do?action=sbs&id=36009&id=35980
If you look purely at battery to wheel, the 85 is rated at 265 miles, 85D is rated at 270 miles. Assuming the same usable capacity, the most you can expect is around 2% better efficiency, not anywhere near 18%.
breser
AutoPilot Nostradamus
From everything I've seen you can't reverse the numbers like that. There's too much fudging in the numbers to do that. They are a mathematical formula on based on the results of several tests. They are only intended to be used to compare like for like numbers. Any calculations on the numbers start producing a lot of garbage.
I have a hard time believing that Tesla has improved the efficiency of the chargers by 8.9 kWh on a 100% charge. That's 84.4% efficient for the S85 vs 92.5% efficient for the 85D. Maybe it's possible but I'm deeply skeptical. Especially since it really is possible to measure this. The car tells you how much energy you put into the battery on a charge. You can measure the energy use at the wall for the charge. So where are the people talking about how much better the newer cars charging efficiency is? I know we have people around here that are certainly measuring this information and would be posting about a difference like you're suggesting.
stopcrazypp
Well-Known Member
The reason why a lot of people get "garbage" out of the numbers is because they assume the MPGe number is from battery to wheel and then do their math based on that. They also try to use that number to match with the number on the energy display. The math obviously doesn't work out that way because the energy display does not include charging losses.
A FOIA request by a Leaf owner lays out the EPA test procedure, and shows the MPGe (and equivalent kWh/100mi) number measures AC electricity from the wall:
http://www.smidgeindustriesltd.com/leaf/EPA/EPA_test_procedure_for_EVs-PHEVs-1-13-2011.pdf
So while the way I did the math may not be 100% correct (because of rounding differences in the formula between the combined range vs combined kWh/100mi), it's going to be very close.
The S85 does measure to about 85% from measurements in 2013:
http://www.teslamotorsclub.com/show...-120V-charging?p=283815&viewfull=1#post283815
How many people have measured their energy use/charging efficiency at the wall for the 85D? I didn't see a figure for that yet. Everyone is stressing over the battery-to-wheel number, very few care about the wall to wheel number.
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breser
AutoPilot Nostradamus
Nobody needed to do a FOIA request to find out that the EPA test procedure is from wall to wheel. It's in the SAE standard referenced by the CFR. This should be old news to everyone. We discussed it to death when the P85D window stickers first showed up.
I don't believe you can do math based on the range and efficiency numbers. I'm not 100% clear on how the range number is derived. Strangely there is no explanation anywhere on exactly how it's derived. I couldn't find any formulas for it in the SAE standard. I'm skeptical that a charging efficiency difference between the S85 and 85D exists. But if such a large difference exists, then yes it could explain the discrepancies we've noted in the window sticker numbers from the S85 to 85D.
The OP of that thread has a P85D now. Unless you're going to suggest that there's some significant difference in charging efficiency between a P85D and an 85D. Then I'd be surprised if he hasn't already tested his charging efficiency with the P85D. I take the silence on the issue to be a lack of any interesting difference.
But maybe you're right and nobody has bothered to look for this difference.
Uncle Paul
Well-Known Member
Analysis may prove less than meaningful, as Tesla has an on going process of continuing improvement.
Things could change with the next software update.
Things could change with the next software update.
The 85 takes closer to 80kwh, from ~10 miles to range charge, from an L2 ChargePoint. I know that because ChargePoint emails the "wall" kwh provided. I'm sure there are others who can also vouch for how much lower than 100.7kwh the S85 takes to range charge. That is why many of us use the forums. They true up (or down) what's found at EPA, or the Design Studio.
AFAIK, the EPA's protocol has always included charging losses at the wall. If you have a link that says it didn't in 2012, please provide it. I believe Nissan's not doing so would simply have been their bad.
I'm especially skeptical that a charging efficiency difference exists between the 85D and an S85 built contemporaneously, rather than one built in 2013. There can't be many different parts, other than the obvious.
stopcrazypp
Well-Known Member
The EPA test procedure is as follows:
1) fully charge the car
2) unplug and leave car parked overnight
3) drive the car on EPA test cycle until it can't keep up with the cycle anymore (given the Tesla doesn't really have a "turtle" mode like the Leaf, this is when the car completely stops)
3) fully charge the car and measure AC consumption at the wall
So you must factor in overnight vampire loss and also drive the car until it stops completely to replicate those numbers. Absent of this, a charging efficiency approximation is sufficient, and so far 85% seems to be the number people get and it matches the EPA results.
I'm not saying that it didn't include it in 2012, but that the main difference in the efficiency numbers are the charging efficiency and no other explanation (assuming the usable capacity didn't change).
Anyway ignoring the charging efficiency issue and just looking at range numbers (assuming usable is the same): 265 for S85 and 270 for 85D will already give you the battery to wheel efficiency difference of 2%, not 18%.
llavalle
Member
I measured around 92% on my 85D when charging at 80Amps with my dual charger (HWPC). When my Efergy monitor report 50kWh, the car usually reports around 92% of that (46kWh in that case).
I'm pretty sure my charger is no different that a 2015 S85... but they did change the chargers 2 or 3 times so maybe that bad efficiency is actually from an older version of the charger?
stopcrazypp
Well-Known Member
Your data point supports the EPA numbers:
Your 2015 85D gets 92%.
Others have measured the 2013 S85 getting ~85% back in 2013.
So that matches the EPA numbers of 92.5% for 2015 85D and 84.4% for 2012-2015 S85.
Keep in mind the numbers for the 2015 S85 is the same as for the 2012 S85 (I suspect some confusion about my point is from this):
http://www.fueleconomy.gov/feg/Find.do?action=sbs&id=32557&id=35980
The charger likely went through some revisions. Updates to existing cars to address the vampire draw and sleep mode will also help the numbers. However, Tesla likely chose to not recertify the car with the new changes since 2012 (just like how GM didn't recertify the 2015 Volt even though it had more battery capacity, resulting in the 2015 having the same EPA numbers as the 2014, even though in reality it has more range).
So the 2012-2015 S85 EPA numbers are unlikely to reflect what a 2015 S85 measures in reality. And the same numbers also might not reflect 2012/2013 S85 models today due to software updates since then. So even if you compare a 2012 S85 (with the latest updates) vs a 2015 85D *today* it likely won't show that charging efficiency difference. We have to look back at tests done on older software versions from the 2012 time frame.
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breser
AutoPilot Nostradamus
Doesn't prove anything. His 85D is getting 92% on a HPWC at 80A. The 85% was on 120V at 12A (stated to be a standard 120V outlet so I'm assuming a NEMA 5-15 and not a 5-20). The very same thread and poster showed 87% at 240V at 40A. You also need to match the environmental conditions (50 °F) when charging because that'll change the energy spent for pack temperature management. You need a like for like test to really mean anything.
For all you know nobody ever had a car with the same software and hardware conditions to match the conditions that the S85 tested with (or for that matter the 70D, 85D and P85D). Manufacturers are allowed to test with prototype hardware. The standards are entirely silent on software. So you can basically discount every comparison test. Meaning your theory is impossible to prove without Tesla's help.
However, the CFR do require that vehicles be re-tested if certain pieces of hardware on the car change. Unfortunately, those rules are entirely written with ICE vehicles in mind and don't talk about chargers or batteries. In my opinion if there are significant hardware changes (as in the Volt example you give) then they really have to re-test. Maybe it's not violating the letter of the regulations, but it's certainly violating the spirit. I'll point out that Ford got fined for a spirit but not letter of the regulation situation here not that long ago. They used tests from one body style to report the numbers for another body style but that had the same hardware otherwise. The rules don't stipulate that body changes require re-testing. But Ford still got slapped down for that after customers started complaining about actual mileage.
Ultimately, you're basically suggesting that Tesla is implying that the D vehicles are better than they really are by not re-testing the S85 and passively sandbagging the numbers on the RWD vehicles. You haven't come right out and said that but you've danced around it. That's a pretty damning thing to say with such little evidence at this point.
Ohh and I forgot to mention the SAE standard requires that the charging be done with the charging equipment that comes with the car. Which means the mobile charger as far as I can tell. The HPWC wasn't available when the S85 was tested and you couldn't order the car with it since it wasn't available so even if you want to dance around the optional equipment situation, I don't think you can use the HPWC for the test. I have no idea if they can get away with 120V or 240V charging or what amperage. Based on the charge time on the window sticker I'd bet on 120V at 12A. Which is what I would guess is what you need to test with to compare the results against the window sticker numbers.
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stopcrazypp
Well-Known Member
Well it doesn't prove anything other than that both numbers are within the range of what 85D and S85 can get, which makes the EPA numbers entirely plausible (rather than impossible). And while the 85% is at 120V, it was also in a 2013 S85 with updated software with sleep.
I don't see it as sinister as that. I think in general if the changes result in higher efficiency and you choose not to retest, that will not sound the alarm for EPA (as the EPA likes the results being as conservative as possible). So doing so in that situation matches both spirit and letter of the regulations. Your Ford example was the opposite: they knew the numbers would be lower if they retested so they chose not to (officially I know they said their engineers weren't aware of the aero efficiency differences between the two body styles, but that was taken to be BS by most people). After all, people don't sue because of getting better than the EPA numbers, they sue when they get worse than EPA numbers.
SAE standard specifies testing with the highest AC power available. The EPA site lists the following under specs:
2012 S85:
12 hrs at 240V
2015 S85:
12 hrs at 240V
(standard charger)
4.75 hrs at 240V
(80 amp dual charger)
I'm pretty sure an optional EVSE doesn't matter, since no EV other than the Tesla comes with a standard 240V EVSE, but the standard still says to test at highest power available (don't have time now, but will dig up exact wording when I have a chance).
So it's entirely possible/valid for S85 to be tested at 240V (or even 120V) and for 2015 S85 to be tested with HPWC.
And putting aside this whole charging efficiency argument, how do you account for the fact the range numbers of 265 vs 270 showing only a 2% efficiency difference, while MPGe combined shows a 11% difference? Are you suggesting the usable capacity went down for the 85D, since otherwise, given the same usable capacity, the 265 vs 270 numbers directly reflect the battery-to-wheel efficiency difference?
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Breser, What is the real difference between the cars? Aren't you helping lay that bare, yourself? Most people are less concerned with where fault lies in discrepancies, than with what they're gonna get. For 85 / 85D, they can run with 313Wh/mile vs. 316Wh/mile, or 90 MPGe vs. 106 MPGe (Hwy). Pointing that out, a comparison of 70D, to 85D, on a MPGe basis, might raise additional questions.
Speculating, I'd guess that since the highway drive cycle still has accelerations in it, the 85D should do worse than the 70D. It's heavier. OTOH, if both motors are tuned to have less power in the 70D, it may have less ability to remain in single-motor mode on the highway. In my opinion, 70/85 D isn't an efficiency decision. It's a 15 kwh of storage decision.
My father recently traded in his 2013 85 for an 85D and says that the D gets around 310 Wh/m or even less where his 85 got just over 330 Wh/m on the same routes. So the D is about 5-6% more efficient.
breser
AutoPilot Nostradamus
Look let me be clear. I don't doubt there has been some improvement. I doubt the improvement is from 85% to 92% efficiency (in well controlled tests). The efficiency differences we're talking about here as seen in anecdotal tests are probably well within the range of normal charging efficiency differences based on climate, equipment differences, current differences, etc...
The thread you're pulling from also clearing shows that he was removing vampire drain. So that's the pure charging efficiency. The EPA test procedure is obviously going to include some vampire drain since they let the car sit. Your theory suggests that a 2012 car was doing better than that 2013 car with the improved software. Because it was hitting 85% after the vampire by your calculation. Of course the 2013 car was hitting 87% charging efficiency on 240V/40A. So maybe the difference there is just the charging rate differences in efficiency. I'll get to that later.
That's only viewing things form the perspective of an S85 buyer. Consider it from the perspective of an 85D buyer who spent more money on the idea that they're buying a more efficient car. If the amount of efficiency improvement between an S85 and 85D is less than provided in the EPA numbers that's going to make people upset.
Not bothering to update the numbers when all the cars had the same EPA economy information and all of them were presumably improved by the same amount doesn't do much. But once you're providing some of your models with updated ratings and some without and you're actually advertising the car to some degree on the improved efficiency. I do think that rises to an actionable situation.
So yes the Ford situation was different. Clearly people in that case were buying cars and getting less than the window sticker. In this case, presuming your theory, nobody is getting a car with less efficiency. But it is distorting the purchasing decisions in the market place and doing so in a way the encourages people to give Tesla more money. I'd also say this is somewhat tilted against Tesla since for all practical purposes their cars are just competing against each other.
Tesla may have not bothered to update the S85 rating because they don't expect to be selling it for much longer. Which would help mitigate this issue.
Just to be clear, the SAE standard doesn't specify how to come up with those charging rate numbers that go on the window sticker. As best as I can tell we have no idea how they come up with those. The old stickers were practically useless since they didn't even mention the dual charger bit. It's obvious that 12 hours at 240V is not 240V at 40A, so that's not maximum charging.
The SAE standard is terribly vague on the charging stuff. But it does specify that you can only use charging equipment that's included with the car. In my opinion that excludes the HPWC and requires the use of the UMC. I'd like to think that the interpretation of the standard means that they should be testing at 240V/40A. But even though the charging rate numbers aren't necessarily based on the SAE standard tests, the 12 hour rate gives me pause on accepting that.
The standard is far from clear cut. Even then it's pretty clear that the EPA has authority to permit deviations form the test procedure based on their own decisions. So without specific information about how these tests are conducted (not in general, but for the specific results) it's hard to know what the heck they did.
I don't think any of the supposed reasons make a lot of logical sense. Largely because Telsa published a blog post about the range on the AWD vehicles. If Tesla really did improve charging efficiency and that made up some of the difference I'd expect them to say that much. But they didn't mention it. Same with the usable capacity going down.
So I don't have a pet theory accounted for that difference. I spent a lot of time coming up with reasons during the P85D range debates. Without some good data I'm not going to bother to speculate on what the differences are actually caused by.
I've pondered doing FOIA to ask for all correspondence internally and externally about Tesla's testing of the Model S (old and newer tests both). But haven't sat down and spent the time to write it up. To get all the useful information I'd need to make it fairly broad and I'd probably also need to find a partner more clearly involved in media to avoid paying for the disclosure.
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Of course I'm interested in the actual differences. I haven't tried to explore the reasons for the differences because it's really hard to explore outside of Tesla. Just exploring the difference alone is hard to do with real world tests.
In fairness I don't think the EPA test results are particularly applicable to a lot of people. The average speed over the test cycle is still something like 45 mph (this is based off memory and the exact number might be a little off, but I'm pretty sure it's around 40-50 mph). Yes even the highway drive cycles have that low of an average speed. But they are still useful to compare models.
But stopcrazypp's theory here is that the numbers are distorted by a significant improvement in charging efficiency. Which makes those numbers useless to compare because the Wh/mile and MPGe are wall to wheel.
I think there is obviously some efficiency gains in the 70D. The question though in 70D vs 85D is really about the trade offs between the extra range vs the extra efficiency. Everyone is going to have different answers there because everyone has different use cases.
Also keep in mind that charging at higher rates (dual charger) is usually more efficient (to a point). This is because in addition to the conversion losses, there is also a fixed overhead. I haven't calculated the Model S (yet), but in the LEAF there was about a 350w-400w overhead which was the pumps running, computers, DC-DC converter, sometimes cooling fans, etc.
If you are charging from 120v @ 12A (1.44kW) in a LEAF then this is around 25% overhead! This is also another reason not to charge at L1!
If we assume similar overhead numbers for the model S, (I bet the MS has more) charging at 240v @ 40A is about 9500w (after power factor hit), so this would make the overhead around only 4%. If we bump up to 80A with dual-chargers then we get 19kW and only about 2% of that is overhead.
I'm not including conversion losses. These can vary a lot, and most chargers have a sweet spot where the conversion efficiency is best. At some point I'll run some tests.
If you are charging from 120v @ 12A (1.44kW) in a LEAF then this is around 25% overhead! This is also another reason not to charge at L1!
If we assume similar overhead numbers for the model S, (I bet the MS has more) charging at 240v @ 40A is about 9500w (after power factor hit), so this would make the overhead around only 4%. If we bump up to 80A with dual-chargers then we get 19kW and only about 2% of that is overhead.
I'm not including conversion losses. These can vary a lot, and most chargers have a sweet spot where the conversion efficiency is best. At some point I'll run some tests.
stopcrazypp
Well-Known Member
I found the reference that I remembered. It's from J1711-2010 which is testing for HEVs including PHEVs (not quite the J1634 for EVs, but I imagine it's similar) and it specifies:
The "charger" part refers to either on onboard or off-board charger, not the EVSE. It makes no mention of standard or optional, only that if it has a charger onboard it must use the onboard charger, not an external one (like a DC charger). It also explicitly say "highest power level". So perhaps you can interpret that to exclude the dual chargers (although it doesn't mention standard equipment), but you can't interpret it to exclude the HPWC (or better example is excluding a 220V EVSE for a Leaf for example).
My point there is, assuming the drive cycle didn't change (which appears to be true, given in 2012 Tesla already was forced to switch to the 5-cycle test), there's really only two reasons to explain the discrepancies:
1) Charging efficiency went up (note this includes vampire improvements)
2) Usable capacity went down
I can't think of a third reason able to explain the numbers (unless you count a mix of both being a third reason).
The range blog you mention refers to the EPA range number 265 vs 270 (2% difference), it says nothing about using the MPGe number to compare efficiency (in fact it does not mention that number at all). So there is absolutely no reason to bring up charging efficiency in that blog, since that has nothing to do with range. And it also pointed out 65mph range of 295 vs 285 (4% difference), 75mph range 249 vs 242 (3% difference).
http://www.teslamotors.com/blog/driving-range-model-s-family
So Tesla never claimed range (aka battery-to-wheel efficiency) is anywhere near 18% improvement as the highway MPGe number shows. Tesla only claimed a difference of about 2-4% depending on which number you use. Where that 18% comes from is people assuming the MPGe number is a battery-to-wheel number, rather than a wall-to-wheel number. My main point in the original comment was that this assumption is what makes that 18% battery-to-wheel improvement expectation invalid and that people should rather look at the range numbers to set their expectations, as Tesla's own blog on this subject does in the first place!
My best guess for the discrepancy is charging efficiency went up rather than usable capacity went down, but if you don't want to guess, that doesn't really change the main argument.
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