Supra, just to make sure. Are you saying that when the car reads 0 SOC that the car shuts down because mine didn't and I drove about a mile back to the house. Also in TM-spy when my SOC was 0 the battery read 4kw left and did count down to 3 kw once I got parked. If you are correct and my car was a fluke then the total rated miles at 100 SOC would be a lie because to get the rated miles it needs to have the ability to use the 4kw of reserve. Maybe the term lie is a bit harsh but you get the point. For my S75 the 4kw is about 12 rated miles that I would be loosing. I understand if Tesla says hey your car can get 239 miles rated at 100 SOC but we reserve the bottom 12 because it's not a good idea. It's another thing to say your car could get 239 but we decided that you can't drive the last 12.
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This is why you can't get 'rated range'
- Thread starter David99
- Start date
Thr anecdotal we have seems to suggest otherwise. Multiple folks who’ve monitored their BMS have proven they’ve driven below 0% displayed when the BMS is still reporting 3-4 kWh remaining in the battery packs, and still >3.0 volts. From the videos I’ve seen, you’re extremely power limited as you get to these extremely low energy states such that you can’t demand a high draw. I do agree if there’s battery modules out of balance (beyond the limit that is considered normal), you could see a sudden shutdown prior to 0 displayed, but again, in my previous post I mentioned I’m assuming everything is balanced (i.e. normal).
To summarize my previous post (sorry it was so dang long):
- Displayed rated range is based on total usable capacity (this has been proven).
- Total usable capacity doesn’t include the anti bricking buffer (this is my theory).
- Total usable capacity does include another buffer of ~3-4 kWh (this is my theory).
- Displayed rated range will diverge from using total usable capacity to total usable capacity minus this extra buffer mentioned in the previous bullet (this has been proven).
mal_tsla
Member
Makes sense to me. I don't know too many ICE drivers that try to run their tank completely dry either. Most plan to refuel with 2-5gal remaining and many ICE car fuel gauges read Empty with 3 gals left in reserve.
Shred, this is my understanding how it seems to work also. I believe that the 3-4kw maybe linked to the cell pack voltage of 3.1v. We would need to have someone with a 100 pack let us know if their reserve was larger. If it isn't then this could be the reason those of us with 60-85 see a larger hit and power restrictions since we are closer to the 2.9-3.0v cut off voltage.
I think having a small buffer at 0% displayed SOC or 0 rated range makes sense. The issue is how the rated range is being calculated as you're driving. If you drive within the EPA assumptions (290 Wh/m for an 85D), the distance you're actually traveling should match the rated range. In other words, if I have 260 miles displayed and I drive 20 miles (within EPA assumptions), I should be seeing 240 miles remaining, which is not the case. Instead, you'll see something less like 230 miles remaining. It's basically decrementing faster than you're actually driving, which is misleading.
Yeah, it all seems to make sense to me. I just think this idea floating around that the 4 kWh buffer we're seeing is the "anti-brick buffer" is incorrect. That would mean folks are able to utilize the anti-bricking buffer which would make absolutely no sense; we would see a lot of bricked batteries I'm sure. It would make more sense the anti-brick buffer is to remain well above the levels where you would brick the batteries, and it does seem Tesla's will shut down around 3.0V, well above 2.5V where it appears lithium-ions will become bricks. There's several videos on YouTube showing folks driving beyond 0% displayed SOC and 0 displayed rated range. Here's one, here's another, and yet another, not to mention you've also proven this as well as several other members on this forum. Here's a video where someone actually was monitoring the BMS data using TM-Spy past 0% displayed SOC until the BMS reported SOC was 0%. Sure enough, it was on the verge of shutting down at 0% BMS reported SOC (0.0 kWh remaining), and the cells were right around 3.0V.
The interesting part is @wk057 CAN Bus deciphering PDF has a statement about the BMS reported energyBuffer value that says, "energyBuffer appears to be the antibrick buffer. This is NOT a below 0miles remaining value." Perhaps that energyBuffer value being reported is the no kidding anti-brick buffer, but it seems like there is another buffer that is also 4 kWh that exists at 0% displayed SOC or 0 displayed rated range, or perhaps that is what the energyBuffer actually is and the anti-bricking buffer value isn't even reported? All speculation obviously but perhaps @wk057 could provide more insight.
Interesting stuff for sure. I think the big take away for me is:
- Displayed rated range is how much you can drive under the EPA assumptions before the vehicle will completely shut down.
- Displayed rated range is misleading since it will decrement faster than how much you've actually driven, based on it trying to achieve a ~4 kWh buffer at 0% displayed SOC or 0 displayed rated range.
Edit: @lymex2018 mentions this in a post in the Scan My Tesla thread.
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Negative, not what I'm saying at all. The 4kw serves a two-fold purpose. At zero, it encourages the driver not to drive any further, thereby protecting the battery. As well as protecting the driver from the volatility or wide variation between modules in the pack below dash zero. You could have half the modules at 2.6v and the other half at 2.4, which would give you well under a safe 300v of total battery output. That's why zero is set where it is, to discourage the depletion below that number.
Again, you *can* drive below zero and get into that 4kw, but absolutely nothing is guaranteed. You could get 5 miles, you could get 20. It all depends how long the battery can give that bare minimum total high-voltage output to the drivetrain. My point has always been that the *only* way you can get EPA rated numbers are if you put that 4kw back into the equation, then the numbers actually make sense. But in reality, it depends on the car and the situation if you can use all or some of that 4kw. Tesla seems to think that it should not be unavailable to you or else 0 wouldn't be set where it is.
Why wouldn't the 4kw be the antibrick buffer? Tesla could set zero any place they wanted. And I believe they set it there because below zero, the car is basically unpredictable and dangerous to drive because the voltage just isnt there to move the car in a normal manner.
Ah okay, I think we’re saying the same thing.
However, all of the videos and posts I’ve seen about folks driving until the car is completely dead seems to suggest you can use all 4 kWh fairly consistently (based on the range they’re getting), assuming you’re driving under the EPA assumptions and your battery cells are balanced. But you will become very power limited the closer you get to actual 0 kWh, which makes sense from a battery stand point. Now, I’m not suggesting to drive below 0% displayed. In fact, I’d actually recommend staying well above it if you can help it. Who knows why Tesla choose a 4 kWh buffer but if I were to guess, so you have a more consistent driving experience/expectation before you hit 0% displayed (i.e. not power limited), battery capacity is an estimation so it’s better to have a pad so the indication doesn’t undershoot resulting in unexpected shutdowns, to give a bigger buffer to account for battery cells being imbalanced (older/higher mileage Teslas), etc.It’s really just semantics. To me, an anti-brick buffer suggests it’s a buffer to prevent bricking the battery, or the protection circuit in lithium-ion batteries that is commonly between 2.6-2.9 volts (or 3.0 which appears to be the case in Teslas). This buffer we’re talking about seems more like a “not very smart to drive” buffer, not necessarily that you will brick the batteries if you deplete it or that you’ve triggered the protection circuit (which would be the car shutting down).
Ah okay, I think we’re saying the same thing.
It’s really just semantics. To me, an anti-brick buffer suggests it’s a buffer to prevent bricking the battery, or the protection circuit in lithium-ion batteries that is commonly between 2.6-2.9 volts (or 3.0 which appears to be the case in Teslas). This buffer we’re talking about seems more like a “not very smart to drive” buffer, not necessarily that you will brick the batteries if you deplete it or that you’ve triggered the protection circuit (which would be the car shutting down).
I think you're right. There is an anti-stupid buffer and an anti-brick buffer.
Ah okay, I think we’re saying the same thing.
It’s really just semantics. To me, an anti-brick buffer suggests it’s a buffer to prevent bricking the battery, or the protection circuit in lithium-ion batteries that is commonly between 2.6-2.9 volts (or 3.0 which appears to be the case in Teslas). This buffer we’re talking about seems more like a “not very smart to drive” buffer, not necessarily that you will brick the batteries if you deplete it or that you’ve triggered the protection circuit (which would be the car shutting down).
Well now you have me wondering. On the one hand, if you had a very hidden super secret brick protection, why doesn't it show up in the CANbus as a line item? The owner would never know about it and it could be useful for diagnosis in the shop. However, on the other hand, I don't think they can have a super-secret hidden brick protection because the CANbus *does* report individual module and brick voltages. If you do the math, there just isn't anything on either the high-ned or the low-end that alludes to super-secret brick protection. Unless they've arbitrarily just said, don't let the car move if the lowest module is 3.00v, and then they say on the back-end, that anything between 2.99v and bricked, IS the brick protection.
This is way above my level of knowledge in the BMS but with my caveman understanding, I'm not sure why the anti-brick buffer would even need to show up in the CAN Bus data. It just seems like something that would be known by the BMS, similar to how it knows how to not let cell voltage exceed 4.2V, it's simply programmed/hardware limited to not allow the batteries to be utilized actively (i.e. driving) below 3.0V (+/- a small amount). The anti-bricking buffer is that remaining voltage from 3.0V to 2.5V (lithium-ion brick). If this is true, I would think the reported energyBuffer in the CAN Bus data is actually this "anti-stupid buffer", as ran349 put it, since we know the vehicle is adjusting rated range to achieve ~4 kWh at 0% displayed/0 rated range. It would need to know that value along with nominalEnergyRemaining to be able to have a target to shoot for.
This post by DB 2 is one of the most informative that I think illustrates this. At 0% displayed SOC, BMS is also reporting 5.3% SOC (aka SOC Min), 3.8 kWh remaining (nominalEnergyRemaining) and 3.199V for the lowest cells. After driving for 17 miles and using 4.0 kWh, BMS is reporting 0.0% SOC, 0.0 kWh remaining and 2.999V for the lowest cells. Of note, at 0% displayed/5.3% actual remaining, you can see he's being limited to 200 kW maximum (instrument cluster energy graph). When he gets to 0% actual remaining, it's down to 50 kW maximum. I think this goes to your point in a previous post, not a very safe condition to be driving in as you're extremely power limited. Any type of hill, acceleration, etc. is not going to happen. Very similar findings as well in this video I mentioned earlier as well as what @N..8 found monitoring his BMS data when at/below 0%.
Great post....In my reading it seems that early Tesla drivers didn't have this 0 SOC buffer and it was later added with a software update. Unlike an ICE car where you can drive it normally until it runs out of gas the battery goes into limp mode. So they added a buffer to keep you out of that but still being able to access it if case of emergency. Like posted above very few people ever drive their cars to empty so it was a safe bet for Tesla to do buffer. As I've stated before I think this effects smaller packs more because you become more power limited because you have less cell packs with 3.1v verses the larger 100 pack.
So they cheated. They adjusted the algorithm so that owners wouldn't see a decrease in range of 12-15 miles overnight. So *now* I'm wondering what happens when nominal_pack_remaining hits zero? Is that the actual car-shut down?
I will say this, the 2 times I went into the negatives, watts per mile was not matching the reduction of kw from the 4kw remaining (it was dropping a lot faster). While I'm starting to believe we all can use that anti-stupid buffer, I think everyone's results will be a little different based on temperature and driving conditions. That's just a theory.
I think mileage will vary depending on the pack condition. If a single cell pack were to be weak then it would hit the cut off "<3.0"?? even though you may have 1-2 kw total left.
It was exactly the opposite of that. There used to be some driving below 0 buffer a long long time ago, and it was removed in one of the software updates like sometime back in 2013 or so. It is the most common behavior now that right around plus or minus 1 or 2 miles of the 0 reading, the car will shut down.
That's what I think will happened based on the anecdotal data we have. But like N..8 mentioned, I think any abnormal imbalance in the battery packs could result in premature shutdown which we've also seen, or perhaps even the BMS being "out of sync" since it's my understanding the displayed SOC and rated range are more accurate the closer you are to 0% or 100%.
Hm, I don't think that's true based on everything we've mentioned in this thread. My previous post goes into some detail.
Do you have any data or sources you could share that shows that the most common behavior is the car will shut down 1-2 miles after the 0 displayed rated range? Everything I've seen suggest otherwise.
That's why I called it the anti-stupid buffer in my previous post. No one should assume they have any mileage past 0 rated miles showing on the dash. Many people do stop right at 0 miles, but others have reported driving several miles below zero.
I would agree with this statement as I think I tried to say the same thing above.
I'd like to mention a few things based on my experience with driving down close to 0 or below.
There is no hard limit. Its ambiguous. I have driven my car down to almost 0 countless times and the power limiter comes on at different times. It depends on temperature and SoC which makes perfect sense. But it also depends on how recent the battery has been used, how much it has been used and and how recent it was charged. Maybe that's partly explained by temperature but I think it doesn't explain it entirely.
Here is an example that illustrates it. On a road trip I drive and charge back to back. The battery gets cycled a lot in a short period of time. The power limiter comes on very late when I drive down low.
When I drive little and don't charge my car for days and then drive it down low, the power limiter comes on much earlier.
I also thought battery voltage would be the main determining factor but I see different behaviors at the same voltage depending on the previous use patterns.
In other words, yes SoC, temperature, power draw all play a role, but I see different battery health even when all the above are the same. The term 'recent cycle amount' would describe it best. The BMS definitely knows about it as it adjusts accordingly. It determines mostly the power limits and how deep into the buffer you can go. It definitely isn't balancing. My cells are alway closer together after long resting periods.
Battery capacity seems to be a complex issue with many variables.
There is no hard limit. Its ambiguous. I have driven my car down to almost 0 countless times and the power limiter comes on at different times. It depends on temperature and SoC which makes perfect sense. But it also depends on how recent the battery has been used, how much it has been used and and how recent it was charged. Maybe that's partly explained by temperature but I think it doesn't explain it entirely.
Here is an example that illustrates it. On a road trip I drive and charge back to back. The battery gets cycled a lot in a short period of time. The power limiter comes on very late when I drive down low.
When I drive little and don't charge my car for days and then drive it down low, the power limiter comes on much earlier.
I also thought battery voltage would be the main determining factor but I see different behaviors at the same voltage depending on the previous use patterns.
In other words, yes SoC, temperature, power draw all play a role, but I see different battery health even when all the above are the same. The term 'recent cycle amount' would describe it best. The BMS definitely knows about it as it adjusts accordingly. It determines mostly the power limits and how deep into the buffer you can go. It definitely isn't balancing. My cells are alway closer together after long resting periods.
Battery capacity seems to be a complex issue with many variables.
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