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Actual rated wh/mi

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
11,670
15,155
San Diego
Isn't the buffer the 4.2 kwh between 77.8 and 82kwh or is there an additional bottom end buffer? I assume that the extra 4.2kwh are top end buffer..

No. The link above shows for the LR Non-Performance Model Y they drew 78.5kWh from the vehicle (including basically the entire buffer). That's all the pack has, period. There's nothing else. The Model Y Performance 2021 has a larger pack (closer to 81kWh available - the data is available on the above linked site).

The buffer is always located below 0%, and for Model 3 it is 4.5% of the nominal full pack (and I THINK it is 4.5% for Model Y as well - SMT would tell you and I'm sure someone has posted the data for a Model Y). So at 0% your car will be very upset, but the BMS will think that you have a bit over 3kWh left before you're done. And if you're extremely lucky you might be able to use some or all of that. I wouldn't try though (see above test for the variability).

There is no top end buffer, though if you look at one of my other posts today Tesla does apparently have a way of "squeezing" extra energy into a fixed number of rated miles when the car is brand new with a very energetic pack that exceeds their expectation of the design capacity. But even in that scenario, your rated miles will start clicking down immediately...they'll just click down more slowly (slower by 1-2%, so imperceptible) when the car is brand new. No top buffer.
 
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AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
11,670
15,155
San Diego
My buffer is 3.1 kWh per scanmytesla.
So the % is likely lower than Model 3 then (not surprising since the Model Y is less efficient so they're going to want you to use more of the pack in "typical" scenarios even though this has no effect on EPA range). What is your nominal full pack?

You just take the ratio for the %. (Buffer / Nominal Full Pack) is always 4.5% for Model 3.
 

MY-Y

Active Member
Mar 4, 2020
1,313
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MD
It's 4.5% on mine. 3.1 buffer, 68.5 battery capacity. I need some more deep cycles to recalibrate my BMS.
Screenshot_20210524-163231.jpg
 
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AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
11,670
15,155
San Diego
3.1 buffer, 68.5 battery capacity.

Thanks. 4.5% it is then, just like Model 3. Also confirms the 77.8kWh when new used for the calculations above.

I need some more deep cycles to recalibrate my BMS.
Hmm...I know how that story goes. Anyway, good luck with that! Maybe you'll get a couple kWh back or maybe you're a special case where it's whack. Rare though.
 

MY-Y

Active Member
Mar 4, 2020
1,313
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MD
Thanks. 4.5% it is then, just like Model 3. Also confirms the 77.8kWh when new used for the calculations above.


Hmm...I know how that story goes. Anyway, good luck with that! Maybe you'll get a couple kWh back or maybe you're a special case where it's whack. Rare though.
Actually, it's already going pretty good. The screenshot from my post above was 1 week ago. I've let the car sleep at different charge levels for two deeper charge cycles this past week and I've already moved from 68.5 kWh to 69.4 kWh (just grabbed my scanmytesla screen now). I'll be at 100 kWh by Christmas. 😉
Screenshot_20210602-205808.jpg
 
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No. The link above shows for the LR Non-Performance Model Y they drew 78.5kWh from the vehicle (including basically the entire buffer). That's all the pack has, period. There's nothing else. The Model Y Performance 2021 has a larger pack (closer to 81kWh available - the data is available on the above linked site).

The buffer is always located below 0%, and for Model 3 it is 4.5% of the nominal full pack (and I THINK it is 4.5% for Model Y as well - SMT would tell you and I'm sure someone has posted the data for a Model Y). So at 0% your car will be very upset, but the BMS will think that you have a bit over 3kWh left before you're done. And if you're extremely lucky you might be able to use some or all of that. I wouldn't try though (see above test for the variability).

There is no top end buffer, though if you look at one of my other posts today Tesla does apparently have a way of "squeezing" extra energy into a fixed number of rated miles when the car is brand new with a very energetic pack that exceeds their expectation of the design capacity. But even in that scenario, your rated miles will start clicking down immediately...they'll just click down more slowly (slower by 1-2%, so imperceptible) when the car is brand new. No top buffer.
All the EV's I know have a top end buffer.. For example, on my Hyundai Kona Electric, the battery is 67 kwh and there is a 3kwh buffer at the top end and 64 kwh is available.. The top end buffer is there to prevent overcharging. I would be very surprised if Tesla is not concerned about overcharging the battery. The Kona has regen at 100%. This would not be possible if there was no top end buffer. Once the Kona reaches 0%, it stops.. On my wife's BMW i3, it has a gigantic buffer (as percent of the battery). The battery is 33kwh and only 27.2 kwh are available. The rest is top end buffer. 17.5% top end buffer and no bottom end buffer.
I understand that the chemistry of Tesla (Panasonic) cells are different but they are still Lithium Ion Polymer batteries.. Lower cobalt content..
 

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
11,670
15,155
San Diego
would be very surprised if Tesla is not concerned about overcharging the battery.

I’m sure they are. I have no idea how much “top buffer” there is of that type (there are various interpretations of the meaning of that term). There is maybe some buffer, but Teslas have basically zero regen at 100%, but that still doesn’t tell us what the buffer is - we’d have to look at voltages of other EVs and similar cells, and guess.

But that does not change the fact that there is ~77.8kWh available when new (again, for a pack of “x kWh” capacity - no one knows - but it does not matter). With a 4.5% buffer on the low end, before guaranteed shutdown (and shutdown may well occur WELL before using the entire buffer). That is straight from the EPA.
 
I’m sure they are. I have no idea how much “top buffer” there is of that type (there are various interpretations of the meaning of that term). There is maybe some buffer, but Teslas have basically zero regen at 100%, but that still doesn’t tell us what the buffer is - we’d have to look at voltages of other EVs and similar cells, and guess.

But that does not change the fact that there is ~77.8kWh available when new (again, for a pack of “x kWh” capacity - no one knows - but it does not matter). With a 4.5% buffer on the low end, before guaranteed shutdown (and shutdown may well occur WELL before using the entire buffer). That is straight from the EPA.
On my Hyundai Kona Electric, there are 2 readings for SoC (with OBD2 tool). One is SoC BMS and SoC Display. When the car is at 100% Display, the SoC BMS is at 96.5% indicating a 3.5% top end buffer.. That buffer was 4.5% when new, so the Kona's BMS moves degradation to the buffer so that you don't lose range until the buffer is used up. My Kona has 52k miles and no range loss at all. (LG Cells with high Cobalt)
I'm ordering the OBD2 harness for the Y... I'm very interested and the details from the BMS on the Model Y..
 
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AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
11,670
15,155
San Diego
On my Hyundai Kona Electric, there are 2 readings for SoC (with OBD2 tool). One is SoC BMS and SoC Display. When the car is at 100% Display, the SoC BMS is at 96.5% indicating a 3.5% top end buffer.. That buffer was 4.5% when new, so the Kona's BMS moves degradation to the buffer so that you don't lose range until the buffer is used up. My Kona has 52k miles and no range loss at all. (LG Cells with high Cobalt)
I'm ordering the OBD2 harness for the Y... I'm very interested and the details from the BMS on the Model Y..
Yes, this is pretty common. This is not the way the Tesla will work. You CAN lose capacity (about 1kWh or so - depends on how healthy a battery you started with) with no impact on indicated range, yet you are losing available energy of that ~1kWh. This continues until your energy goes below the 77.8kWh cap value and then you start showing a reduction in rated miles (which are a unit of energy).

Again, this initial loss is hidden, by Tesla inflating the rated mile energy content, if your initial nominal full time pack energy exceeds the cap value.

You’ll see this happen if you get SMT before your capacity loss brings you below the cap.

For Teslas, 100% is 100% - unless they software update to unlock capacity later (which could be an unlock of the top or the bottom) - but this is pretty rare - it happened for the LR RWD 3 most recently (I think). There is also the weird Model 3 battery situation in Europe for 2021 where for some battery types, 100% is 96% or so. But that is just because they are installing different capacity batteries in the same vehicle model and they want them to be all the same energy content. There is also the SR (not SR+) of course which has 8.5% capacity locked out - but all the above still lose usable capacity immediately when the battery loses any capacity.
 
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AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
11,670
15,155
San Diego
When the car is at 100% Display, the SoC BMS is at 96.5% indicating a 3.5% top end buffer.. That buffer was 4.5% when new, so the Kona's BMS moves degradation to the buffer so that you don't lose range until the buffer is used up
From this info alone, you also don’t know it is a top buffer. It probably is. But you would have to track the minimum and maximum pack voltages. For a pure top buffer, you would see the max voltage increase as the battery loses capacity, with no change on the voltage at 0-1% SoC. Etc. Or alternately, you observe that regen at 100% UI disappears over time...which means at least it is partially top buffer.

Anyway, for Tesla AFAIK the max voltage never changes as capacity loss occurs. Starts as high as Tesla is comfortable with (402-403V, unless it is one of the SoC limited vehicles like the SR or other special case) and that is it.
 
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Rocky_H

Well-Known Member
Feb 19, 2015
7,838
9,861
Boise, ID
All the EV's I know have a top end buffer.. For example, on my Hyundai Kona Electric, the battery is 67 kwh and there is a 3kwh buffer at the top end and 64 kwh is available.. The top end buffer is there to prevent overcharging. I would be very surprised if Tesla is not concerned about overcharging the battery.
It's taking two different tactics:
1. Most EVs go very simple on the charging limit interfaces and it always goes to "FULL". You don't get to adjust a granular slider to select your charge limit. So they really have to lock out a top end buffer so that sitting at "full" most of the time isn't actually 100% and constantly killing the battery.

2. With Tesla, they do allow access to all that, but they manage this with information and warnings. They mark the 90% to 100% area for "TRIPS", and if you use that a few days in a row, it will display a warning on the screen that it is unhealthy and damaging for the battery to use that too often. So they can allow it without a top buffer by telling people to not go up that high all the time.
 
From this info alone, you also don’t know it is a top buffer. It probably is. But you would have to track the minimum and maximum pack voltages. For a pure top buffer, you would see the max voltage increase as the battery loses capacity, with no change on the voltage at 0-1% SoC. Etc. Or alternately, you observe that regen at 100% UI disappears over time...which means at least it is partially top buffer.

Anyway, for Tesla AFAIK the max voltage never changes as capacity loss occurs. Starts as high as Tesla is comfortable with (402-403V, unless it is one of the SoC limited vehicles like the SR or other special case) and that is it.
Yes, pack voltage has been increasing with age.. but range remained unchanged. It's interesting that pack voltage doesn't change on Teslas.. Completely different way how the Tesla BMS manages the pack..
 

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
11,670
15,155
San Diego
Yes, pack voltage has been increasing with age.. but range remained unchanged. It's interesting that pack voltage doesn't change on Teslas.. Completely different way how the Tesla BMS manages the pack..

Yeah, it's totally different. They charge it to max at 100% (whatever they feel is max for safety and longevity, which turns out to be 402-403V with 96 series cells, again with the caveat that certain software-limited vehicles (e.g. Model 3 SR) will not do this). And that's it. As various people have described in various ways here, there is a rationale for this. The intent is to only very rarely charge to 100%, with 90% the default upper limit. Side comment: There's been massive controversy in Model S forums due to voltage limiting that was introduced at some point in some vehicles (without explanation from Tesla). The conversation has been going on for over a year now I think.

The thing you need to know for Model Y/3 is that the buffer is at the bottom, and it's 4.5% of your full pack capacity, at any time. So it reduces in size in conjunction with your pack capacity loss.

My Kona has 52k miles and no range loss at all. (LG Cells with high Cobalt)
Do not expect this with your Model 3 or Model Y. It'll be interesting to see if the new 2170L cells (which are currently only consistently available in Performance trim) are any better than the 2170 cells.

I would expect 10-15% capacity loss, roughly, at 52k miles, with 2170 cells (not 2170L, we have no long-term data on those). If you do better (you may), great. But it's a good expectation. I have ~10% loss at 25k miles.

Anyway, getting a bit off the Wh/mi topic here...probably should steer it back to that sort of question which is where we started (though battery capacity is an important part of understanding that Wh/mi rating).
 
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Yeah, it's totally different. They charge it to max at 100% (whatever they feel is max for safety and longevity, which turns out to be 402-403V with 96 series cells, again with the caveat that certain software-limited vehicles (e.g. Model 3 SR) will not do this). And that's it. As various people have described in various ways here, there is a rationale for this. The intent is to only very rarely charge to 100%, with 90% the default upper limit. Side comment: There's been massive controversy in Model S forums due to voltage limiting that was introduced at some point in some vehicles (without explanation from Tesla). The conversation has been going on for over a year now I think.

The thing you need to know for Model Y/3 is that the buffer is at the bottom, and it's 4.5% of your full pack capacity, at any time. So it reduces in size in conjunction with your pack capacity loss.


Do not expect this with your Model 3 or Model Y. It'll be interesting to see if the new 2170L cells (which are currently only consistently available in Performance trim) are any better than the 2170 cells.

I would expect 10-15% capacity loss, roughly, at 52k miles, with 2170 cells (not 2170L, we have no long-term data on those). If you do better (you may), great. But it's a good expectation. I have ~10% loss at 25k miles.

Anyway, getting a bit off the Wh/mi topic here...probably should steer it back to that sort of question which is where we started (though battery capacity is an important part of understanding that Wh/mi rating).
Thanks for the information! This is very interesting!!
 
On my Hyundai Kona Electric, there are 2 readings for SoC (with OBD2 tool). One is SoC BMS and SoC Display. When the car is at 100% Display, the SoC BMS is at 96.5% indicating a 3.5% top end buffer.. That buffer was 4.5% when new, so the Kona's BMS moves degradation to the buffer so that you don't lose range until the buffer is used up. My Kona has 52k miles and no range loss at all. (LG Cells with high Cobalt)
I'm ordering the OBD2 harness for the Y... I'm very interested and the details from the BMS on the Model Y..

Interesting topic. My daughter just got a Kona, my advice was based on my MY habits. I guess these don't translate to the Kona. I rarely charge above 80%, only time i do is because of the lousy slider on the screen. In just under 10k miles my pack has lost about 3.5% based on the best mileage according to TeslaFi. When I tell people they kinda freak out.
 
Interesting topic. My daughter just got a Kona, my advice was based on my MY habits. I guess these don't translate to the Kona. I rarely charge above 80%, only time i do is because of the lousy slider on the screen. In just under 10k miles my pack has lost about 3.5% based on the best mileage according to TeslaFi. When I tell people they kinda freak out.
Degradation is not linear on Teslas.. There is an initial drop and then it slows down. Got a former co-worker (just retired at age 56) with a Model S and he has 140k miles on his 2014 Model S and he still has around 90% remaining capacity (he was the first one in the office to have a Tesla and now there is 5 of us) .. He said that the first 5% dropped fairly quickly but it stabilized after that.. Teslas can't "HIDE" degradation in the buffer because the buffer is at the bottom end..
 
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Getting closer, I think ;) So why does EPA say both 280 Wh/mi combined and 316 rated miles? (Original mid-2020 Y LR numbers)

Wouldn't that mean the battery needed to hold 88.4 kWh?
I think I have your answer, I was just wondering the same thing on my vehicle. The EPA stated 280 wH/mi INCLUDES charging losses. The real EPA wH/mi target while driving is about 40 wH/mi less. So your solid grey line should be around 240 wH/mi and that should be your target efficiency if you want to get to the EPA rated miles. You can verify this number by making your dashed line overlap your solid line while driving efficiently (going downhill really helps).
 

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
11,670
15,155
San Diego
I think I have your answer, I was just wondering the same thing on my vehicle. The EPA stated 280 wH/mi INCLUDES charging losses. The real EPA wH/mi target while driving is about 40 wH/mi less. So your solid grey line should be around 240 wH/mi and that should be your target efficiency if you want to get to the EPA rated miles. You can verify this number by making your dashed line overlap your solid line while driving efficiently (going downhill really helps).
Yes that is basically true. As mentioned above.

Note that for “reasons” the rated line is 5Wh/mi higher than the actual charging constant.

And because of the buffer you have to be 4.5% lower than that constant for mile-for-mile rolloff.

And because of heat losses you have to be about 1% lower than that as measured on the trip meter.

So for the non-P Model Y take 77.8kWh or so and divide by the rated miles on the Tesla website (whatever the true adjusted max rated range is for the vehicle). That will give you the charging constant.

When the vehicle is new and the energy exceeds the degradation threshold, you’ll be able to use a little more per mile and still achieve parity, since the rated mile energy content will be slightly inflated. (For example you might have 78.5kWh at 100% rather than 77.8kWh, in which case your rated miles will have 1% more energy than later in life, to hide initial capacity loss.)

So for Model Y with 77.8kWh battery with rated range of 326mi initially the constant is about 239Wh/mi. Line on energy screen is probably about 244Wh/mi.

And if you show some rated range loss, you need to get about 226Wh/mi on the trip meter for mile-for-rated-mile “parity.”
 
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