How I Recovered Half of my Battery's Lost Capacity

[camalaio]

I have a different impression.

Given that over time the BMS can easily learn which bricks are lazy, at any point in time it knows how much energy needs to be bled off and where from to keep things balanced. All those things you mention are going on some of the time, but bleeding off energy is what it is any time of day. Even if you are drawing energy from all cells / bricks, you can always draw a little extra from some to keep them in line. Likewise, when charging, you can give the current a parallel path through a resistor so that not quite as much flows through the brick. As long as you have good data about the battery overall, you can apply balancing for as long as the balancing circuits can be powered on. I think this requires the battery to be active as I think the balancing circuits are powered by the modules themselves. This is a guess - assuming need to keep HV connected circuits as isolated / self contained as possible.

The open circuit state where the only currents in the battery are between the cells themselves is when the voltages settle and become a meaningful indicator of each brick's soc.

I think your idea is a combination my "improvement" thing and the "different" view of imbalance (or that's how I'm seeing it), plus an extra bit. (edit: I see after you did indeed say "like this" to what I wrote, hah)

It's very possible it would work that way, which would be an incredibly novel approach to my understanding. It's a far more sophisticated approach than leaked documents previously posted on these forums would suggest (which isn't impossible at all, the leaked stuff is not overly descriptive). I do kind of doubt they've gone to all that effort though. This is the sort of thing I'd like to see in papers and research (perhaps it exists!) to see what benefits and drawbacks there are to the approach.

A quick rabbit trail on Wikipedia showed me that this isn't an entirely novel concept, though I don't think it's been applied to Li-ion packs before. See "Milking booster", which seems to have been used under load (for a similar but not exact reason).

As some older S's do more pack heating and cooling - almost simultaneously in some cases! - and older cells have higher levels of internal heat generation - the parasitic dissipation can evidently become quite huge. Having to heat the whole pack before charging, then cool it down again when done must waste huge amounts of energy.

Model 3 is very lackadaisical when it comes to thermal management. The thresholds are far apart, and far away from where many fans expect them to be. I have heard that the Model S is much more aggressive on cooling, which is perhaps where some of those ideas come from.

Model 3 doesn't really cool the batteries after Supercharging, for example. You'll sometimes hear the fans rip like a hurricane for a minute or two, sometimes hear the AC compressor engage, but it's really brief. Thankfully that means it's not wasting much energy (and you need to heat it less for the next charge, hooray?), but the batteries are still quite hot for a very long time (probably until it rests overnight).

Thankfully with Model Y, in winter, that otherwise "wasted" energy to heat the battery can now be siphoned to heat the cabin via the new heat pump. One of the more effective use-cases of the heat pump in the winter.

Anyhow, I feel like I'm just adding more rabbit trails at this point so I'll stop there

 

[camalaio]

I'm trying to relate this procedure to my personal situation. I am retired so don't have the daily commute pattern, but I do usually go out some every day, whether for shopping, doctor appointments, day trips, or whatever. I'm rarely home no later than 6-7PM and often much earlier. I plug in every day, and charge to 80% at midnight. So it sleeps at least 5 hours at some reduced SOC, charges to 80%, then sleeps typically another 6-8 hours. And since it sleeps a lot at home, Sentry mode is not enabled. Also I've changed how I interpret 80%. Since I have a SR+ with 250 mile initial range, I used to charge to 200 miles. But after 8 months, the range is reduced to about 225 so now I charge to 180ish. Anyway, I don't see a lot of difference between your logic, which is good, and my usage pattern. Do you?

You have a pretty ideal situation already, don't need to change anything!

Most people will be in line with the core recommendations already. The main exceptions will be if using Sentry Mode or Summon Standby a lot, or if charging just barely covers your daily usage (e.g. long commute on just a 120V charging setup).

The only thing you're not doing that they are is not plugging in every day. The benefits of this are mostly unclear, and very very small if there are any (at the risk of not having enough charge to go somewhere).

 

[AlanSubie4Life]

The only thing you're not doing that they are is not plugging in every day.

Presumably if the relay on the UMC/WC is open for a long enough time, it is indistinguishable from being unplugged. It’s really a question of how long people feel it is necessary to not be doing any charging or drawing of any power from the wall to get that “benefit,” whatever that may be. Obviously once the relay closes, for any reason, that is distinctly different than being unplugged.

Seems to me it is fairly common to have 3-4 hour intervals where the car is sleeping even when plugged in, and the UMC relay is open at those times. Seems like a lot of balancing and adjustment could take place in 3-4 hours.

However, I’ve never paid super close attention to the relationship between closed contactors and the UMC relay, so not sure when a car is plugged in and is at the target charge level, and closes the contactors - does it always also energize the UMC? I don’t think so, but I could be wrong.

 

[EvanLin]

If I'm going to take a long drive i.e. road trip, then I charge to 100% to balance the battery

You don't need to do that.

The car balances all the time whenever its needed. (by wk057)
Tesla's 85 kWh rating needs an asterisk (up to 81 kWh, with up to ~77 kWh usable)

 

[camalaio]

You don't need to do that.

The car balances all the time whenever its needed. (by wk057)
Tesla's 85 kWh rating needs an asterisk (up to 81 kWh, with up to ~77 kWh usable)

Huh. After reading a few posts beyond that one, I have a few admittedly disappointing takeaways. Normally am a big fan of their content but this is just messed up.

1. For one, the linked post is regarding Model S/X BMS. This thread is on Model 3. While it would be cool if the Model 3 did all that (honestly, I can't refute it at this time), I don't think it does. We are really lacking on info here for Model 3 though.
2. The linked post was the start of a tirade against Model 3 battery capacity, charge efficiency, and CAN data
   • Model 3 is actually stupidly inefficient at charging, especially at low powers. He's correct that the actual charger is somewhere in the range of 92-96% efficient, but he's not accounting for the fixed overheads for computers, pumps, etc. (which are routinely 300W on my car). The claim that Model 3 can't be worse than S/X because it's newer is unfortunately just wrong.
   • He's claiming EPA numbers (charge efficiency and capacity) are faked numbers, but my own local group has basically reproduced the charging efficiency numbers. As well as so many people on these forums.
   • He seems to be misunderstanding the EPA numbers in general, while pointing at everyone else saying they don't understand?
   • Finally CAN data shows up that makes a lot of sense, then he just claims that data is false and not actually used for the range calc (it... it definitely is. It 100% is.)

Ugh. That was just really disappointing. Can we trust what he said about balancing amidst that bewildering argument? I'm really not entirely sure anymore.

I've been intentionally vague about things I've learned too, but I definitely haven't gone off the deep end of "everything you see is actually a lie and only I know the truth, which btw I won't share".

Anyhow. If any of that linked BMS stuff if true, that would give credit to the theory that balancing would potentially take a lot of energy. Imagine a single brick that discharges faster than others - by that post's theory, you'd actively and also pre-emptively drain every better brick, so all bricks but one, just to keep the whole pack balanced at all times and all SoCs. Balance is good, but is it that good? Worth all that expenditure? That's like 38W on the S/X. Jeez. And the only thing it can do to bring balance is drain.

This actually makes the OP start to make more sense. This is a clearly wasteful "evolution" of balancing. Model 3 probably does have a less wasteful balancing mechanism, though maybe not exactly as was communicated. Maybe Model 3 just goes back to the dark ages with a simpler balancing scheme that isn't so wasteful (balancing only at the top), but allows the pack to be imbalanced at low SoC. This gives the highest recoverable energy (in most cases), if not the ultimately longest-lasting pack.

I'm no battery expert, but I can't really understand the benefit of keeping balance throughout the SoC range at the cost of waste energy. Maybe, since the S/X have Ludicrous (or whatever the new fastest thing is) requiring huge draws, balance is more important. But the comparably tame Model 3 isn't expected to perform these Lud launches - it's the "mass market" EV, fit for a daily driver, but with some extra oomph over your last gasser.

But if Telsa wants to keep battery packs so tightly balanced (at least on the S/X as linked), why aren't they using active balancing? Much less wasteful.

 

[Battpower]

why aren't they using active balancing?

Really, this is where my journey started a couple of years ago when I revisited the idea of getting a Tesla model.

One of the things I find difficult in places like this forum is that 'authority', 'knowledge', 'experience', 'making sense' and 'certainty' are only loosely connected, and the fact that (hopefully) understanding does improve over time needs to be taken into account when looking up even fairly recent past posts.

Are we agreed that:

To some extent inevitable mismatches between cells means charge imbalance exists and will increase if not kept in check.

The factors that cause mismatching of cells, while mitigated through excellent manufacturing, are likely to increase with age and energy throughout as well as accelerated by 'abuse'.

Increase in mismatching leads to increased imbalance of charge through charging and discharging.

Increased imbalance must be addressed to keep the battery viable, and if of a passive design, by implication has to dissipate more energy to maintain balance. Indeed, balancing dissipation should relate primarily to mismatching of cells if everything else is working correctly.

In addition to the above, older cells become compromised from an electro-chemical perspective such that the maximum safe voltage is likely to need reducing to minimise tendency for formation of dendrites.

Other aging effects may include cells staring to self-discharge through slight internal shorting effect. I do not know where Tesla's chemistry is at with M3, but since the batteries do have finite life spans, these factors likely apply as much as to any other current technology.

?

 

[Battpower]

misunderstanding the EPA numbers in general

Slightly ot, but with all this discussion about range issues, I am not clear what EPA tests are actually focussed on. The idea of a 'range' figure that also looks 'better' just because you have a huge gas tank strikes me as odd. In the case of EV's, the EPA forms I have seen don't even attempt to record an EV equivalent to gas tank volume. Do they measure energy into the vehicle? If so, by AC or DC ? And if pre-heating of the battery is needed to achieve full / optimal charge and discharge (excuse that slightly invalid question) then do you count the heating energy too?

If computers are powered up during charging, then slower charging surely has a negative effect on real efficiency, but could be completely missed / ignored by test procedure.

 

[Battpower]

energy throughout

Sorry, typo!

"The factors that cause mismatching of cells, while mitigated through excellent manufacturing, are likely to increase with age and energy throughPUT as well as accelerated by 'abuse'."

 

[SomeJoe7777]

Ah, ok. Since it was coming from Tesla service folks, I had assumed "vampire drain" would include all user-observable drain since they field those concerns.

I was definitely presenting the impossibility of the claims as-is. I know the ~60W number is due to various other reasons (the car being routinely "awake" is the actual primary factor, in which many other things use far more power). So yeah, my calculations shouldn't reflect reality - they were to demonstrate that the appearance of the claim cannot be true.

It looks to me like they're in parallel, so 39.5 Ohm, implying 0.4W dissipation (~100mA). This appears to be much more reasonable. There's also nearby transistors (labelled Q) that are probably (dis)engaging those balance resistors. That is, they are not engaged full time, but engaged as necessary and individually (each group of components seems to go to a different group of cells in parallel).

I can't find the post anymore (sorry!), but someone rightly pointed out that when being switched on/off anyways, the resistor value only serves to change the amount of time needed to balance, but the same amount of energy will be used since dealing with a certain amount of imbalance via discharge requires removing a certain amount of energy. One reason to increase the resistance could be to give a more accurate reading while balancing though, as less current would lead to less voltage sag (we're talking tiny amounts though, not sure this is a problem in reality at these values).

I strongly suspect this is confirmation bias, but read on.

I fully believe there was something else goofed up with your case. In fact, though I've been avoiding the topic, I think your pack is (only) the second case I've read on that it appears balancing may have been the result of your range recovery.

Our current understanding of balancing outside of this thread is that the battery needs to be at rest and above approximately 73% (I'll have a thread on this later today). You appear to have been consistently using Sentry mode, which would mostly not allow balancing (or at least decrease the total time it can spend balancing).

So in my mind, the BMS was actually being very good at energy estimation. It was probably accounting for your (lightly) imbalanced pack. When given the opportunity to balance (you stopped using Sentry, etc.), it then correctly reported you can extract more energy before it needs to cut off the supply.

The finding is significant for that reason. It shows a case where doing "the bad thing" (e.g. Sentry 24/7 in an extreme case) could lead to reduced range, but also have that "lost range" be recoverable. Again, it's something we knew about, but it just doesn't matter to many people. Most people's charging habits and battery health will result in well-balanced packs, by design.

This is just one of many oversights and side effects, IMO, regarding flashy features like Sentry Mode.

I guess it's just easier to keep the numbers going eh?

1. I will still state that balancing and calibration are separate concerns. But it can only balance after charging is done, and balancing itself is a bit of a slow process.
2. I pointed out "stranding" because you have the burden of a stickied post in which you implied a recommendation by stating what worked for you. The internet sucks, doesn't it? Suddenly you're on the hook for everyone's personal cases without even having given context to your own.
3. See previous chunk of my post. You probably ended up balancing it (and thus increased extractable energy), not necessarily made it more accurate. Significant yes, but potentially not the cause you are thinking.
4. I will very strongly disagree here, elaborating below. Even the official app (but not car) gets this wrong!

The third-party tools use the Tesla API data which, yes, is the very same data you see in the app (and thus in the car as well to some extent). There are higher inaccuracies at lower states of charge - you cannot assume the "absolute error" for range at a lower SoC is the same at higher SoC.

Let's take my car's data, right now, from the API. In-app it's displaying 262km of range, which is about 162.8mi, thus the 162.85 below.

'battery_level': 55,
'battery_range': 162.85,
'est_battery_range': 236.2,
'ideal_battery_range': 162.85,
'usable_battery_level': 55,​

There are a few very important things to note here:

• Any representation of percentage is rounded. This is the primary source of error. At 20%, this could be either 19.5% or 20.49%. Since you divide by this to estimate range at max, this introduces huge variance at lower percentages (note how at 1%, it ranges from 0.5% to 1.49% - that's a 50% swing, showing where this increased variance comes from).
• I have no idea what "est_battery_range" is. Assuming it's miles that's ~380km, far too low for representing the 100% state and far too high for its current state. Assuming it's somehow in km, it doesn't jive with anything else.
• The numbers the apps use are the temperature-varying ones. For tracking actual battery health, this is unfair. Lower capacity is reported in cold, though this is not an actual indicator of degraded battery health.

So let's do the math these services would do. Take the current range (162.85) and divide by the percentage (0.55). That comes out to 296.1mi, or 476.5km. Also, in the app, if I drag the slider to 100%, reports that my 100% range is also about 476km, because it's doing the exact same calculation on the exact same data. So far so good, right?

Now recall the issue I mentioned with rounded numbers. I happen to know via the CAN bus that the actual SoC right now is 54.5%. If I use that instead, I get about 481km (and this is pretty much the actual 100% range of my car right now). But had it actually been 55.49% (and still reported "55"), that would falsely indicate 472km. That's already a 9km (5.6mi) spread.

At lower SoC, it gets even worse. Say at 10%, it was reporting 48.10km. But that "10" could be 9.5 or 10.499, which would indicate 100% ranges of 506km and 458km respectively. That is now a ridiculous 48km (~30mi) spread. In other words, that's 10% of the max range.

100% range estimates are estimates, whether it's a third-party service or the Tesla app, and their accuracy is worse at lower SoC.

Now, that is not to say the current range number in the car is inaccurate. That one is a pretty dang accurate representation of the current energy in the pack. The error is introduced when using a rounded, low significant digit percentage to estimate the 100% capacity.

These services have their place and can provide value, but the recommendation to throw away data for <90% SoC (if the service allows this) is absolutely warranted. Anything much below that has too much error for discussion on single-digit percentage degradations.

Very well done and fair points, and I agree with most of them.

I want to perosnally thank @camalaio, @Battpower and @AlanSubie4Life for their contributions to this thread, I think this has turned into one of the most informative and useful battery discussions I've seen on this forum in a long time.

I'd love to contribute more, but my options at this point are limited. I run my own business which takes up most of my time, leaving me with little room for tinkering like I used to do many years ago. But let me know if there's anything else you'd like from me. I have full TeslaFi records for this car, and I have SMT as well.

 

[AlanSubie4Life]

Do they measure energy into the vehicle?

Yes.

If so, by AC or DC ?

They measure AC energy added to the vehicle. They also measure DC energy put out by the vehicle (so they can measure actual driving efficiency).

And if pre-heating of the battery is needed to achieve full / optimal charge and discharge (excuse that slightly invalid question) then do you count the heating energy too?

In the cold cycle tests they do show that substantially less energy is available from the battery. And climate is set to a set point so they additionally get some overhead from that which hurts efficiency. However, for the recharge event, the numbers are way off on the cold cycle, and generally I think these are ignored (the exact treatment is explained in the publicly available EPA doc).

If computers are powered up during charging, then slower charging surely has a negative effect on real efficiency, but could be completely missed / ignored by test procedure.

I assume that they do their recharge events using the UMC at maximum amperage. But it is not specified, last I checked. Usually charging efficiency measured (meaning energy out over energy in) is about 90%. (It's about 88-89kWh to add ~78kWh to the battery.) Seems about right for a UMC at 32A.

Of course, all efficiencies quoted by the EPA are wall-to-wheels. But they definitely make the assumption that you are charging at a decent rate (120V 12A charging would give way worse results).

 

[camalaio]

Really, this is where my journey started a couple of years ago when I revisited the idea of getting a Tesla model.

One of the things I find difficult in places like this forum is that 'authority', 'knowledge', 'experience', 'making sense' and 'certainty' are only loosely connected, and the fact that (hopefully) understanding does improve over time needs to be taken into account when looking up even fairly recent past posts.

Are we agreed that:

To some extent inevitable mismatches between cells means charge imbalance exists and will increase if not kept in check.

The factors that cause mismatching of cells, while mitigated through excellent manufacturing, are likely to increase with age and energy throughout as well as accelerated by 'abuse'.

Increase in mismatching leads to increased imbalance of charge through charging and discharging.

Increased imbalance must be addressed to keep the battery viable, and if of a passive design, by implication has to dissipate more energy to maintain balance. Indeed, balancing dissipation should relate primarily to mismatching of cells if everything else is working correctly.

In addition to the above, older cells become compromised from an electro-chemical perspective such that the maximum safe voltage is likely to need reducing to minimise tendency for formation of dendrites.

Other aging effects may include cells staring to self-discharge through slight internal shorting effect. I do not know where Tesla's chemistry is at with M3, but since the batteries do have finite life spans, these factors likely apply as much as to any other current technology.

?

Agreed on all points, I think. Tight balancing could do well to extend the otherwise "dying" phase of a battery pack, which we wouldn't have much visibility into right now for Model 3.

The big unknown, to me, is if active balancing is actually "worth it" in the end. If my hunch is right that Tesla abandoned their "perfect balance at any SoC" approach claimed to be used on S/X and went with a simpler top-balanced mechanism for Model 3, perhaps Tesla themselves saw that it isn't worth it. Especially in range marketing, it's more effective to top-balance than engineer an active balance system that works at any SoC while driving. ROI or something like that. There are cases where this could result in earlier battery deaths I guess, but I don't know if it would be significant.

Slightly ot, but with all this discussion about range issues, I am not clear what EPA tests are actually focussed on. The idea of a 'range' figure that also looks 'better' just because you have a huge gas tank strikes me as odd. In the case of EV's, the EPA forms I have seen don't even attempt to record an EV equivalent to gas tank volume. Do they measure energy into the vehicle? If so, by AC or DC ? And if pre-heating of the battery is needed to achieve full / optimal charge and discharge (excuse that slightly invalid question) then do you count the heating energy too?

If computers are powered up during charging, then slower charging surely has a negative effect on real efficiency, but could be completely missed / ignored by test procedure.

A few points that weren't mentioned:

The EV equivalent of fuel volume is energy, measured in kWh. @AlanSubie4Life covered the rest regarding AC and DC numbers. Marketing fuel volume was not as important for ICE vehicles.

---

The EV equivalent of fuel efficiency is energy per distance, measured in-car as Wh/mi or Wh/km. On fueleconomy.gov, it's listed as kWh/100mi. The main thing to note is that the car is showing you DC efficiency, while the government website is showing AC (wall-to-wheels) efficiency. One is more useful for figuring out range, one is more useful for figuring out the cost of driving.

---

Regarding pre-heating of the battery, this is less clear to me. It's routinely said that the car runs different software and behaves differently from a consumer vehicle, but that just has to be mostly false (see: Volkswagen). So one can assume it behaves like a consumer vehicle in the cold, but there are many conditionals. For one, I don't know if they "cold soak" the car for this testing (though it seems they do, so I'll continue with that assumption). The battery pre-heating behaviour actually varies by year and software version. For driving, it didn't exist at all until this last winter!

Funny enough, (make your own conspiracies here now) the 20F temp I found for the cold tests is just above the threshold where the car is thought to heat the battery in standby. A degree lower and it would've been heating the pack.

Very well done and fair points, and I agree with most of them.

I want to perosnally thank @camalaio, @Battpower and @AlanSubie4Life for their contributions to this thread, I think this has turned into one of the most informative and useful battery discussions I've seen on this forum in a long time.

I'd love to contribute more, but my options at this point are limited. I run my own business which takes up most of my time, leaving me with little room for tinkering like I used to do many years ago. But let me know if there's anything else you'd like from me. I have full TeslaFi records for this car, and I have SMT as well.

Joke's on me, I'm currently unemployed

But in seriousness, thanks for giving a thread where the discussion didn't devolve into bickering about balancing for once... even if it appears that's what actually happened with your car in the end!

In the cold cycle tests they do show that substantially less energy is available from the battery. And climate is set to a set point so they additionally get some overhead from that which hurts efficiency. However, for the recharge event, the numbers are way off on the cold cycle, and generally I think these are ignored (the exact treatment is explained in the publicly available EPA doc).

Thanks for responding to the rest, but I have a question about this point. I'll have to dig it up again, but the 20F test I found showed less energy extracted on discharge and less AC energy going in for recharging. The math was such that the charge efficiency was almost the same as warmer conditions. To me this implies you genuinely cannot add enough energy to "fully charge" the battery if it was brought up to temp post-charge. Is that a correct interpretation? Or perhaps some energy is effectively "left behind" due to the cold, so that's why less energy was also needed to recharge it. That might make more sense? I'm thinking out loud here.

The only alternate explanation I can think of is that it's way more efficient charging at low temps, which seems impossible to me.

 

[Phlier]

Thankfully with Model Y, in winter, that otherwise "wasted" energy to heat the battery can now be siphoned to heat the cabin via the new heat pump. One of the more effective use-cases of the heat pump in the winter.

That just answered one of my questions... I was wondering if the only heat source the heat pump used to supply the cabin with warm air was outside ambient air. It's good to see that they're using additional sources of heat, as I just couldn't see how a heat pump using external air could ever meet the heat requirements of cabin warming in cold climates.

Man, there's a lot of smart guys on this forum. Thanks for sharing your knowledge with us, gents.

 

[camalaio]

One of the things I find difficult in places like this forum is that 'authority', 'knowledge', 'experience', 'making sense' and 'certainty' are only loosely connected, and the fact that (hopefully) understanding does improve over time needs to be taken into account when looking up even fairly recent past posts.

Actually, wanted to call out this part of your post specifically.

The reason I continue to contribute here is exactly this. There's constant statements (probably even by me) that everything has already been said regarding the battery. But not only does our collective understanding continue to evolve, the dang car changes behaviour via software updates! And then we have to unlearn, re-educate, etc. and figure out the differences. That's no small task, especially given that searching for a topic can lead to even recent posts with now-incorrect information (which is where "experience" can start to cloud things for sure, and "making sense" requires a changed perspective [not something humans are well known for, self included]).

Knowledge of implementations here is a moving target, and we're always behind the reality while dealing with the baggage of being a very human community.

Too philosophical? Bah, whatever, I'm leaving it!

That just answered one of my questions... I was wondering if the only heat source the heat pump used to supply the cabin with warm air was outside ambient air. It's good to see that they're using additional sources of heat, as I just couldn't see how a heat pump using external air could ever meet the heat requirements of cabin warming in cold climates.

Man, there's a lot of smart guys on this forum. Thanks for sharing your knowledge with us, gents.

Hang on, don't take my understanding as 100% accurate haha. I'm 99% sure this is how it works for various reasons, but I could be wrong. The air would be a bad thermal exchange source for heat - it's too cold for when you want heat, has low thermal conductivity, and you'd result in the system being "too cold" at that end for various reasons I'm sure an HVAC technician could explain far better than myself. Rejecting heat into the air (as they do for AC) works better for various physical reasons which I otherwise won't claim any knowledge of.

The document I read from... an EPA filing I think? does call out scavenging heat from the coolant system (motors and battery pack), and this is what other EVs with heat pumps appear to do as well. That's the bulk of confidence I have on the topic, coupled with the knowledge that the battery is heated to very high temps for DC Fast Charging.

 

[Phlier]

I'm sure an HVAC technician could explain far better than myself

I'm not exactly an HVAC tech, but I do have a bit of understanding about such things... I'm an airline pilot. And yeah, just using the outside air as a heat source for a heat pump just ain't gonna cut if for heating the cabin in cold weather. They'd need to have some other source. I wasn't sure if there was a backup resistive heater, or what. I was *hoping* that they'd scavenge heat from other places in the car. Maybe that's one of the functions of the famous "Octovalve?" It's at this point that I start getting in over my head.

The problem with being an airline pilot is that we know a little bit about a lot of things, and not very much about one thing in particular. Jack of all trades, master of none. But we *think* we know a lot more than we really *do*.

I may not be a very smaht man, Jenn-ay, but I do know what a Boe'ing is.

 

[camalaio]

I'm not exactly an HVAC tech, but I do have a bit of understanding about such things... I'm an airline pilot. And yeah, just using the outside air as a heat source for a heat pump just ain't gonna cut if for heating the cabin in cold weather. They'd need to have some other source. I wasn't sure if there was a backup resistive heater, or what. I was *hoping* that they'd scavenge heat from other places in the car. Maybe that's one of the functions of the famous "Octovalve?" It's at this point that I start getting in over my head.

The problem with being an airline pilot is that we know a little bit about a lot of things, and not very much about one thing in particular. Jack of all trades, master of none. But we *think* we know a lot more than we really *do*.

I may not be a very smaht man, Jenn-ay, but I do know what a Boe'ing is.

At the risk of derailing this thread (hey, it's all sort of range related in the end)...

They do have a backup "resistive" heater. They borrowed their concept of running the drive units in waste mode to generate heat for the battery, but applied that to the compressor (I think) so they didn't have to introduce a dedicated part for that function.

Because of this, I expect some use-cases of the Model Y are still going to be ultimately as inefficient as the Model 3 (the waste mode might be technically less efficient at getting that generated heat into the cabin than the Model 3's PTC heater). Those that park outside in the cold, for example, will have no heat to scavenge on their way to work. Anything heat dumped into the coolant loop via the motors is best used for the battery, and the cabin heat will need to be "inefficiently" generated.

Even if parked in a somewhat-insulated garage in winter, there's very little heat to scavenge. Keep in mind it wants to keep the battery a bit warm for other reasons (e.g. regen, which it wastes energy to provide already!), so only so much can be drawn for cabin purposes. Everything wants some warmth.

I think in the 10+C/50+F range of temps, the heat pump will be very effective (especially for garage-kept Model Ys). Below this, I expect any daily usage to be near equivalent to Model 3. At especially cold temps, I expect Model 3 would actually be the winner for range, if not practicality (the omission of wiper heat strips on the 3 is mildly infuriating, for example). Well, until Supercharging, then the Model Y wins for the original reason you quoted.

Problematically, a heated garage would make the Model Y look more efficient in winter because the battery gets warmer and can be used for heating the cabin, but all you're doing is moving that heat generation to something outside the car's measurement. This is effective and a good thing, but perhaps a bit dishonest to oneself about whole-picture energy usage. Weird to think about.

Oh. Product idea. Garage floor heating pad for the Model Y. Heats the battery to 35C. Not a win for efficiency at all, but would increase your effective range to be able to make it somewhere!

I may not be a very smaht man, Jenn-ay, but I do know what a Boe'ing is.

Looking at your location made reading this much more amusing, personally.

 

[Phlier]

Looking at your location made reading this much more amusing, personally.

Ah, but my location doesn't give away who I work for, although it seemingly would give that information away. Airline crews have a tendency to commute from anywhere they want to live to where they actually have to report for work. We have some guys that commute from Brasil to go to work!

As for regional accents, we don't talk like Forest Gump here... it's actually much, much worse.

OK, sorry for going so off topic, and thanks for the additional heat pump system information.

 

[timk225]

Back to the OP's first posting here. Since keeping the car charged to 90% all the time wasn't helping (plug in every night), I'm going to try this way. Sentry Mode off, and let it sit for at least 3 hours undisturbed at a time, 6+ hours when possible and overnight.

I began by letting it sit overnight at 22 miles range, then charged to 95% - 280 miles indicated, let that sit overnight, and as this charge is used during this week, I'll let it have its 3 or 6 hour times as much as I can, then when it needs a charge, I'll go to 90% and see what I get. I was at 266 miles for 90% before this experiment.

 

[Arctic_White]

One of the most helpful posts I've seen and I have read a lot of them. I have a 2 month old LR Model Y and my battery range readings don't make any sense and the Tesla folks don't seem to know how to answer my questions. I have provided a bunch of data, charts, spreadsheets and basis analysis related to drop in range and no answers/explanations have been provided. Frankly, its been very frustrating. I am going to try what you are suggesting and hopefully it will help. Attached is my chart from Teslafi. My EPA range is 316 but reported max range has mostly been between 305 and 309 since I've owned the car. My gut says not likely I've lost that much range in 2 months. Hopefully this exercise will get me back to a reported 316 mile range. Fingers crossed.

It doesn't make any sense because you keep on changing the amount it charges to. That is why there is so much inconsistency in your graph.

My recommendation would be to charge it to 90% each night and keep it plugged in. Every single night.

The variation then would become much more smooth.

 

[AlanSubie4Life]

I have SMT as well.

Pretty sure you don't have it, but basically I would like results from SMT from the car for capacity when it was brand new, and also as it ages, correlated with 100% range rated mile numbers. The sticking point of course are the results when the car was brand new - very few people have a bunch of datapoints *from SMT* for max kWh capacity correlated to 100% rated range numbers *from the car* from when the car is brand new AND as the battery loses capacity through the threshold where range loss starts to show. Need all the datapoints on both sides of that threshold (which I believe is 76kWh for 2018/2019 AWD Model 3s and 77.6kWh for 2020 Model 3s) - I've never seen them anywhere from anyone, so my theory about inflated (more energetic) rated miles prior to reaching the threshold has to remain pure speculation for now.

Thanks for responding to the rest, but I have a question about this point. I'll have to dig it up again, but the 20F test I found showed less energy extracted on discharge and less AC energy going in for recharging. The math was such that the charge efficiency was almost the same as warmer conditions.

I didn't want to dig up that detail for my post (since I couldn't remember the treatment off the top of my head), so I was deliberately vague, but here is what Tesla does for cold recharges - they don't measure the cold recharge energy! It's not important for 5-cycle range calculations. They simply take the measured DC discharge energy for the cold cycle and divide it by the general MCT (multicycle test?) test charging roundtrip efficiency number. That result gives the cold AC recharge number (which was 82kWh rather than a typical 88kWh, as you say - but also as you would expect since they extracted substantially less energy from the battery when cold - ~72kWh vs. a normal ~78kWh).

So they really don't measure how much energy it takes to charge at cold, as far as I can tell, as I interpret it (I'm sure they do, but I'm not sure it's published in the documents - and it doesn't need to be per regulation). The EPA just wants to know the DC driving efficiency, and they want to know the AC charging efficiency under "typical" conditions, as far as I can tell. The DC efficiency measured is used for the range calculations (in conjunction with the battery capacity), and the AC numbers are used to provide the MPGe values on the sticker (with appropriate other required pieces of data to do those calculations).

This is all in my "magical" spreadsheet (it's not magical, it just uses the formulas...), and I just plug in the cycle results and it invariably produces the same values as the EPA stickers (and as a side effect it produces the predicted charge/discharge constants for each vehicle type, which is not relevant for EPA stickers but is very relevant for owners).

Anyway, that's my take on it. Getting a bit far afield from the rebalancing discussion/rated range recovery discussion so that's the last from me on this; can always take it up somewhere else.

 

[G78M3]

"If the battery has a large depth of discharge to a low state of charge (Red zone), allowing the battery to rest for a few hours before recharging will minimize stress on the cells..."

This part needs to be highlighted because it is precisely the opposite of what the car asks us to do.

Last month came back from a road trip with about 5% left, as soon as I press PARK the car gives me a warning to charge it ASAP to minimize the risk of going below zero. I obeyed and started charging immediately vs. letting it start at 1am as scheduled. In hindsight, I lost a good opportunity for the BMS to take a battery snapshot at 5%, plus the aforementioned cell stress avoidance.