SageBrush
REJECT Fascism
Not so. The kWh used during driving is the energy pulled from the battery; it does not care whether the energy is used to turn the wheels or make noise or run a heater
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Trying to Understand Efficiency
- Thread starter Nate977p
- Start date
Dmagyar
Member
I’m sure your problem will be greatly mitigated when you can add some 240 volt charging at home. I also was relying on the 120 volt plug charging method, when I added a 14-30 receptacle that changed from a possible 4 miles of charge per hour, to 22 miles per hour of charging...
SageBrush
REJECT Fascism
Ah .. sorry. Then I think it is still a mystery why the Wh/mile does not match up well with the range
yeah, I don't see much discrepancy in the efficiency reading vs miles consumed in my own car. Only thing I can think of is battery conditioning. It's really a black box (AFAIK) in terms of how the car decides when to precondition and whether it's a flat or variable power draw.
I would have assumed that in the OP's situation of starting in a moderately warm garage that the battery would not need to condition, but who knows. Maybe if outside ambient is cold, the battery proactively draws power from the motor to maintain temps....
AlanSubie4Life
Efficiency Obsessed Member
I don't see an answer to your question here, so I'll give you some math which gets close, but not quite.
First, the assumption (which may not be EXACTLY correct, but is close):
Battery with 75kWh will give you 310 rated miles. That means 242Wh/ rated mile. This is an assumption. The thing in question is whether the usable capacity is 75kWh - there is some debate. But it is CLOSE.
You used 72-46 = 26 rated miles.
You ACTUALLY used 26 rmi * 242Wh/rmi = 6.29kWh - This is what the rated miles delta tells you.
Your trip meter said you used 316Wh/mi * 18.1 mi = 5.72kWh (23.6 rated miles)
So, you have a discrepancy of 6.29kWh - 5.72kWh = 0.57kWh to explain.
This really is not that much, as it is just above 2 rated miles (0.57kWh/0.242kWh/mi = 2.4 rated miles). You could have been JUST above 71 miles when you started, and JUST under 47 miles when you ended - there is SOME rounding error on those numbers.
Second, the trip meter does not count ANY use while the car is in PARK. So even if you sat in the car for a minute or two with the climate control/battery heater on at those temperatures, you could explain the 0.57kWh (which may be a little less due to rounding error on the rated miles). The climate control + battery heating can easily take 12kW with a cold-soaked vehicle (I know yours was not, but if you have your climate control on by default, remember it turns on as soon as you open a door). To use 0.5kWh at 12kW would take 2.5 minutes. I've seen 7kWh use by the heater when the ambient is 60 degrees and the car is not cold soaked. So even one or two minutes of sitting in park (or even with a door open but not in the car) explains much of the remaining discrepancy.
The other thing to keep in mind at relatively low SoC like this is that battery state estimation is HARD. At the low end of the range, you may not be able to EXPECT that the range estimation is perfectly linear. There may be some errors as it calculates remaining available energy. This is a complicated problem, and in this case we're again only talking about a discrepancy of 2 miles rated range, so it would not take much of an error (less than 1%). I'm definitely waving my hands here, and I think this could be a contributing factor, but is not NECESSARY to explain the math, for the most part.
Unlike others, I do not recommend to switching to percentage, as % reading on the range indicator does not give you any indication of whether your battery is degraded (it will read 100% when fully charged, while a degraded battery which is at 100% will display less than 310 miles - so I feel like it is good to be aware of this). The miles indicator is the only way to know how much energy you have left in your pack - the % does not tell you this directly, you have to ASSUME that the pack is healthy. Again, don't worry about this much, of course - because battery state estimation is hard. You really will only know there has been degradation if you start to see several % change in the 310 rated miles full charge (so, when you start to see extrapolated numbers below 300 miles). And even seeing something like that could be a software issue.
Really the miles indicator is more useful in a catastrophic degradation case (there haven't been many for the Model 3, but there have been one or two that I know of), where the fully charged range goes to 150 or 200 miles. It will blissfully say it is 90% charged or whatever you set your charge limit to, but if you don't have it set to miles of range, you may not notice the degradation right away.
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No chance of 220. Currently have 110 if I get the spot, but it's in an apartment building. Talked to the parking management company and they said the quote to add was $70k so they are not doing it...
Do we know for fact what it rates? So it rates everything while in drive, but not in park? So it should get while stopped at a light?
It starts counting everything once you take it out of park. If you're stopped at a light, presumably, you're not putting the car into Park, so it's still counting. If you don't have HVAC running and the car is stopped at a light, then there's generally very low drain on the battery, unless the battery is conditioning. However, recalling some threads from the summer, it's not 100% clear if conditioning usage is reflected in the Wh/mi measurement. My own observations seem to indicate that it IS included.
If you put it in park in mid-drive, it will pause the count until you resume driving. If you leave your seat while the car is in park, it will zero the "gauge" and start a new measurement once you start driving.
AlanSubie4Life
Efficiency Obsessed Member
Yes, it should count it as long as you are driving normally and not putting the car in park.
Basically your described scenario is nearly completely accounting for all the energy (looks like less than 8% unaccounted for), and much of that may be due to rounding errors (most likely, as range numbers can bounce around +/-1 mile very easily) or losses while parked.
Yes. I concur with all of this. It will not reset the trip meter unless you leave your seat, but it will stop counting as soon as entering park.
So you can make your efficiency numbers look really great if you just do all your warming while you're in park! Sadly, of course, this does not actually save any energy.
For your quoted use scenario, your wall-to-wheel efficiency is about 316Wh/mi / 0.87 = 363Wh/mi (compare to EPA expectation of 290Wh/mi). (And will be probably closer to 390Wh/mi after accounting for static losses, based on your annual mileage.)
Thank you for replying to my main point
I do agree with your point on the range vs %, but I understand the other side and each to their own. Neither is wrong!
I would say though 10% is a big discrepancy if that were true, but you are right of many variables.
As for the Wh/Mi, that is a good point for lack of granularity. I thought of that and did two more tests today. I'm both cases the care never went to park. I also ensure I noted thme mileage down the second it turned to the next kWh.
Trial 1:
Distance: 64.4 miles
kWh: 23
Wh/Mi: 350
Calculated Wh/Mi: 357
Trial 2:
Distance: 29.2 miles
kWh: 11
Displayed Wh/Mi: 360
Calculated Wh:/Mi: 376
Thus it is not very off, but I am seeing about 5%.
I just am surprised, I would expect it to be pretty spot on. And not calculating while in P or vampire is just down right wrong I feel.
AlanSubie4Life
Efficiency Obsessed Member
Thank you for replying to my main point
I do agree with your point on the range vs %, but I understand the other side and each to their own. Neither is wrong!
I would say though 10% is a big discrepancy if that were true, but you are right of many variables.
As for the Wh/Mi, that is a good point for lack of granularity. I thought of that and did two more tests today. I'm both cases the care never went to park. I also ensure I noted thme mileage down the second it turned to the next kWh.
Trial 1:
Distance: 64.4 miles
kWh: 23
Wh/Mi: 350
Calculated Wh/Mi: 357
Trial 2:
Distance: 29.2 miles
kWh: 11
Displayed Wh/Mi: 360
Calculated Wh:/Mi: 376
Thus it is not very off, but I am seeing about 5%.
I just am surprised, I would expect it to be pretty spot on. And not calculating while in P or vampire is just down right wrong I feel.
So I assume in above for the "kWh" lines, you calculated that from (delta rated miles (rmi) ) * 0.242Wh/rmi ? On the trip meter, you should never use the stated kWh (the middle number) because it has rounding error (only 2 significant digits); it's always better to multiply miles traveled * displayed Wh/mi, and assign 3 significant figures to the result (not much point in even calculating the kWh value for a trip of less than 10.0 miles). The only relevant comparison here is Wh/mi * miles traveled, compared to (delta rated miles) * 242Wh/rmi.
Anyway, in your first case you're only off by 2%.
For the rated miles delta, yes, you should be able to do a better test and a better check if you do this VERY carefully with a separate trip meter.
Reset a trip meter RIGHT as a rated miles change occurs (make note of the miles)
Stop counting the rated miles change RIGHT as the end point rated miles change occurs.
Calculate the delta in rated miles (start - end). At the same time capture the trip meter reading (picture at the exact moment, and hope it has updated recently - really only an issue for shorter trips). This way you can get rid of some of the rounding error. The trip meter does not update continuously (another source of error), so it may not dump the latest efficiency number. The longer the trip the more accurate the result, due to this issue.
Use the delta rated miles * 242Wh/mi to calculate total energy used. Compare to the trip meter, but not the middle number - use the calculated number (first number * third number).
If you use the 242Wh/mi constant you might get pretty close if you do the experiment that way. Like I said, that constant "242Wh/mi" is really the thing in question here - it all depends on what Tesla thinks is the required energy to go 310 rated miles. Rated miles are really just energy with different units (they have nothing to do with distance).
I've gotten pretty close to a "match" to 242Wh/mi when I've paid attention to this, but I can really only say within a couple % (so somewhere between 237Wh/mi and 247Wh/mi). I wouldn't expect it to ever be exactly correct due to battery state estimation non-linearities and inaccuracy.
I agree Tesla's energy monitor (the trip meter) is garbage.
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My numbers were based on exactly when the kWh changed and grabbed the miles. But that being said, you are right it was pretty darn close and that could be rounding. I actually lost sight of my original point of this post
So back to my original point The trip meter is wildly off the real world and indicated range. I know it only factors in while in drive, but that is horribly in accurate. Let me take my recent example I have all my data for. I SC last night from very low (5% i think?) to 296 rated miles at about 10PM. It was cold last night (30 ish). I unplugged, drove about 3 miles, and parked in my garage last night (3 stories down). It was 57 when I left this morning in the garage, 30 outside, at 8:30am (was a bit behind today...). I drove to our office, parked from about 10am to 6pm, in temperatures ranging from 25-40. Left and went pretty much straight home and parked.
Start range: 296 miles
End range: 103 miles
Distance traveled: 123.1 miles
Used Range: 193 miles
Actual Efficiency (123.1/193): 63.8%
Now, using 242 kWh as the rated for the car (this is what I found by getting as close as possible to the rated bar in the Energy Graph (P3D)) I found this:
Battery Capacity (.250*310): 75.02 kWh
kWh at 296 Start Range: 71.63 kWh
kWh at 103 End Range: 24.93 kWh
Battery Used: 50.09 kWh
This math leads to an actual Wh/mi of 407 (50.09 kWh/123.1 distance traveled) vs the indicated 318 Wh/mi. This is crazy how far off it is. This was only for a daily commute, where it sat in a warmish garage (57) for 10 hours, drove for 2 hours, sat for 8 hours (in the cold to be fair), then drove for 2 more hours. The car did not sit idle in park for more than a few minutes at most. That means for a normal day, the indicated is only 78% accurate and i lose 22% efficiency from just sitting....
Am I missing something?
The trip meter is wildly off the real world and indicated range. I know it only factors in while in drive, but that is horribly in accurate. Let me take my recent example I have all my data for. I SC last night from very low (5% i think?) to 296 rated miles at about 10PM. It was cold last night (30 ish). I unplugged, drove about 3 miles, and parked in my garage last night (3 stories down). It was 57 when I left this morning in the garage, 30 outside, at 8:30am (was a bit behind today...). I drove to our office, parked from about 10am to 6pm, in temperatures ranging from 25-40. Left and went pretty much straight home and parked.Start range: 296 miles
End range: 103 miles
Distance traveled: 123.1 miles
Used Range: 193 miles
Actual Efficiency (123.1/193): 63.8%
Now, using 242 kWh as the rated for the car (this is what I found by getting as close as possible to the rated bar in the Energy Graph (P3D)) I found this:
Battery Capacity (.250*310): 75.02 kWh
kWh at 296 Start Range: 71.63 kWh
kWh at 103 End Range: 24.93 kWh
Battery Used: 50.09 kWh
This math leads to an actual Wh/mi of 407 (50.09 kWh/123.1 distance traveled) vs the indicated 318 Wh/mi. This is crazy how far off it is. This was only for a daily commute, where it sat in a warmish garage (57) for 10 hours, drove for 2 hours, sat for 8 hours (in the cold to be fair), then drove for 2 more hours. The car did not sit idle in park for more than a few minutes at most. That means for a normal day, the indicated is only 78% accurate and i lose 22% efficiency from just sitting....
Am I missing something?
AlanSubie4Life
Efficiency Obsessed Member
In short, I cannot explain this, if the meter really showed 318 Wh/mi. There are some issues with your numbers though:
1) First, the line on energy graph on the P3D is actually closer to 250Wh/mi I think but that still doesn't necessarily suggest we should use that as the constant for these calculations. I don't think that it's particularly relevant to this discussion since the battery on all LR cars are identical and they are rated at the same ~310 miles, though the RWD and AWD version dramatically differ on efficiency (and the line on the energy graph is actually in a different place on the two cars). So the constant to use for calculations is decoupled from this line on the energy graph.
2) Battery Capacity (.250*310): 75.02 kWh (actually equals 77.5kWh)! I would say 0.242*310 = 75.02kWh - I think that is more likely correct. But that is subject to debate.
193mi * 0.242 Wh/mi = 46.7kWh (not 50.09kWh)
But beyond that, if your trip meter TRULY showed 318Wh/mi and you did not spend any time in park (especially when the car was cold), then your overall result is hard to explain. The trip meter SHOULD show closer to 46.7kWh/123.1 = 379Wh/mi
When I have looked at this closely, doing the same calculations, I have been able to get it to show close agreement. However, you have been driving in colder conditions than I have, and perhaps that somehow throws things off. But I can't think of any particular reason why it would.
I originally had 250Wh/mi as I had seen that when I tried to observe it on my own, but that and 242Wh/mi are so close. And it is weird they are not the same as the battery is the same...
Good catch on the 46.7kWh; I had accidentally subtracted the full capacity of 75 instead of the capacity at charge of 296 miles of 71.63 kWh.
But as you said, 379Wh/mi vs 318 Wh/mi is still a 16% delta....
This is where my confusion lies.
My math says i used 46.71 kWh, but the car says 39kWh (pic coming in next post).
Can I really burn almost 8kWh by parking overnight in a garage at about 60, and then outside for 8 hours in 30? That would mean if I left my car sitting in an outside lot for a day, it would fully drain.....
I have to be off on math somewhere, no?
Thanks!
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