Decreasing rated range.

[ckessel]

That explanation is great and all, but I still don't know what it means in the real world. If my pack says 250 rated miles on a full charge, how far can I really drive (assuming EPA rated usage)?

It doesn't matter if degradation is real or hidden in an imbalance if the end result is I can only go 250 miles either way. If the reality is 250 is really 260-ish when I'm actually driving due to a misinformed algorithm, that's different.

 

[gaswalla]

it does matter if it's degradation vs imbalancing b/c imbalancing can be corrected (but we don't have an official method from Tesla yet) vs degradation means it's a permanent loss of range

 

[gg_got_a_tesla]

With my 60, when topping off to 90% at 12A/16A at 110V, or 30A at 208V, I was consistently maxing out at 173 miles and very rarely 174.

However, for the past couple of weeks, I've been topping off to 90% at 40A at 200-ishV from new HPWCs installed at work.

With this, I've been hitting 175 miles with some regularity:

Not sure what to make of it... I did move up to 5.8.10 last week fwiw.

 

[apacheguy]

it does matter if it's degradation vs imbalancing b/c imbalancing can be corrected (but we don't have an official method from Tesla yet) vs degradation means it's a permanent loss of range

Yeah, up to a certain point. Have you seen islandbayy's video on degradation? He explicitly states why your pack will incur degradation through imbalance. It's fundamentally not good to run on an imbalanced pack. Here's a nice way to think about it:

I have a battery with 10 cells. 9 cells are at 4.1 volts, 1 cell is at 3.9 volts. I discharge all cells until the 9 cells are at 3.3 V, but that one cell is now at 3.1 V. Cycling that single cell down to lower voltages will result in permanent damage in the long run. You can't just think, oh well it'll pop back up the next time I balance the pack because it won't (It'll be degraded permanently). Furthermore, you're ultimately limited by the weakest cell in the pack so from a long-term battery health perspective the BMS really needs to keep all cells balanced.

 

[Dave EV]

Yeah, up to a certain point. Have you seen islandbayy's video on degradation? He explicitly states why your pack will incur degradation through imbalance. It's fundamentally not good to run on an imbalanced pack.

The amount of imbalance here is sooo small it's not going to affect anything unless you are regularly driving it down to zero miles. It's a non issue.

Yeah, the lower voltage module will be stressed a bit more when you get down to zero miles. But anywhere above that in your typical SOC range, there's nothing to worry about.

"100%" SOC will always be determined by the module with the highest voltage and "0%" SOC will always be determined by the module with the lowest voltage.

 

[ACDriveMotor]

@apache But I've read on this same thread that TM discharges based on the lowest cell voltage. If that is true then your scenario is avoided, at the cost of reduced range (because some cells remaining capacity goes unused). Would love to see us come to a consistent conclusion about whether imbalance is an annoying problem (less usable range) vs. a real problem (battery health due to excessive discharge).

I would also love to hear that TM has a service alert should a pack become dangerously imbalanced (however they would define that). Seems like a reasonably simple thing to do, define an imbalance threshold and throw a message.

For now I am avoiding both deep discharge and full charges on my vehicle until we get better clarity on this topic. I don't need a ton of daily range and so I don't care about loss of range due to imbalance as long as it is correctable and not causing permanent issues. I do worry about some here in TMC that are doing multiple full charges to try to achieve an arbitrary Rated range target. Full charges are not good for Li batteries. Am I the only one that sees the irony/catch-22 in doing full charges to increase reported capacity and as a result causing a permanent reduction in capacity?

 

[rlang59]

Which do you mean?
(1) algorithmically (bug/design change)
(2) due to users picking values other than 90% (max Daily) and 100% (max Trip)
(3) the switch from 92-93% (Standard) to 90% (max Daily)

Combination of 1 and 2.

 

[AmpedRealtor]

Maybe, but at any rate it is NOT healthy for the pack to be imbalanced. Reason is that some cells will be cycled to lower SOC than others which can be detrimental. So we shouldn't just say, "Oh well, my pack is out of balance so it's not a big deal. I'll recoup those miles when I range charge next time."

To be fair, there is no information to support your assertion other than hearsay from other owners and self proclaimed experts. Do you know, for a fact, that the Model S BMS doesn't individually monitor each cell in the pack? It would seem foolish not to do so, especially when an individual cell could overheat, leak, explode, etc. if not managed properly. I'm pretty sure that Tesla has to manage each cell individually or risk a conflagration, and as such, the balancing issues are nothing more than software estimation error that happens over time.

Max charging to recover a handful of miles on your display is not good for your battery. It never was. Any apparent benefit is psychological at best and is gained at the risk of reducing the long term life and range of the pack.

 

[qwk]

To be fair, there is no information to support your assertion other than hearsay from other owners and self proclaimed experts. Do you know, for a fact, that the Model S BMS doesn't individually monitor each cell in the pack? It would seem foolish not to do so, especially when an individual cell could overheat, leak, explode, etc. if not managed properly. I'm pretty sure that Tesla has to manage each cell individually or risk a conflagration, and as such, the balancing issues are nothing more than software estimation error that happens over time.

Max charging to recover a handful of miles on your display is not good for your battery. It never was. Any apparent benefit is psychological at best and is gained at the risk of reducing the long term life and range of the pack.

Sigh, There is plenty of information that Tesla doesn't monitor every single cell in the pack. Take a look at the BMS diagnostic menu. The cells are wired is such a way that makes monitoring each individual cell very difficult and would add more failure points. That's why each cell has a ultrasonically welded "wire fuse", to prevent cell runaway.

 

[AmpedRealtor]

Yeah, up to a certain point. Have you seen islandbayy's video on degradation? He explicitly states why your pack will incur degradation through imbalance. It's fundamentally not good to run on an imbalanced pack. Here's a nice way to think about it:

I have a battery with 10 cells. 9 cells are at 4.1 volts, 1 cell is at 3.9 volts. I discharge all cells until the 9 cells are at 3.3 V, but that one cell is now at 3.1 V. Cycling that single cell down to lower voltages will result in permanent damage in the long run. You can't just think, oh well it'll pop back up the next time I balance the pack because it won't (It'll be degraded permanently). Furthermore, you're ultimately limited by the weakest cell in the pack so from a long-term battery health perspective the BMS really needs to keep all cells balanced.

Islandbayy does not work for Tesla and has stated that he has no knowledge of how Tesla's BMS system works. While his opinions are interesting given his previous experience with batteries, I certainly would not take his recommendations as gospel given the fact that he doesn't really know how Tesla's battery and BMS systems work and interact with each other. His recommendations are nothing more than educated guesses. Tesla's battery warranty does not cover degradation due to use (that covers almost every situation), and as such, I would be very, very careful in experimenting with a $50,000 replacement part. Wouldn't it suck to be doing all of these max charges to recover 3 miles of range on the display only to discover, in two years, that you've lost 30% of your battery capacity which will not be covered by Tesla? It's possible, so why risk it?

Let's wait for an official solution from Tesla. So far, nobody that I know who has done the max charging has recovered more than 5-7 miles at the most. Hardly worth the effort or the risk, in my opinion. I max charged recently (and for the first time) to 301 ideal miles, then drove 10-15 miles at 75 MPH on the freeway without the range display budging from 301 miles. If anything, this proves to me that the algorithm has problems because it didn't know that it had another 10-15 miles of energy stored up. How else could I drive 10-15 miles and not have the range display budge a single mile? This was on flats and with the regen limited due to high battery state of charge.

 

[qwk]

Let's wait for an official solution from Tesla. So far, nobody that I know who has done the max charging has recovered more than 5-7 miles at the most. Hardly worth the effort or the risk, in my opinion.

While max charging(unless you need it)is probably not that great of an idea, it can get you your range back if you need it. The people that are only getting back 5-7 miles are either not doing it correctly, or don't have that much to gain back. Please read post #98 in the link provided.

Model s at 40,000 Miles - Page 10

 

[AmpedRealtor]

Sigh, There is plenty of information that Tesla doesn't monitor every single cell in the pack. Take a look at the BMS diagnostic menu. The cells are wired is such a way that makes monitoring each individual cell very difficult and would add more failure points. That's why each cell has a ultrasonically welded "wire fuse", to prevent cell runaway.

Well that's disappointing.

- - - Updated - - -

While max charging(unless you need it)is probably not that great of an idea, it can get you your range back if you need it. The people that are only getting back 5-7 miles are either not doing it correctly, or don't have that much to gain back. Please read post #98 in the link provided.

Model s at 40,000 Miles - Page 10

What concerns me is that in order to gain back those 33 miles, he has had to 100% charge every day since November 2013. He posted in February 2014. OMG!

 

[ecarfan]

Islandbayy does not work for Tesla... His recommendations are nothing more than educated guesses... Wouldn't it suck to be doing all of these max charges to recover 3 miles of range on the display only to discover, in two years, that you've lost 30% of your battery capacity which will not be covered by Tesla? It's possible, so why risk it?

And that is very sound advice. Obsessing about a few miles of range and doing multiple 100% charges to try to "get it back" makes no sense to me.

I plug my S in every night and charge it to 85%. I only do a 100% charge if I am going to need the range when I get up in the morning and drive it. Beyond that I don't worry about it.

 

[apacheguy]

@AmpedRealtor - I never explicitly stated that Tesla's BMS does not balance the pack. There are indications, however, that balancing only occurs on a 100% charge, but I agree that we do not know for certain what is occurring when the mobile app reads "1 minute remaining."

My recent posts were simply to make an argument for balancing the pack, but most certainly did not argue that the Tesla BMS does not do that already. I was responding to folks who were saying it's no big deal to operate an imbalanced pack. I'm of the camp that believes a pack should always be balanced, but that's just my view. Furthermore, let it be noted that I am NOT doing successive range charges. I average about 1 per month.

I second your motion for further info from Tesla on this issue. The email that has been floating around on the forums doesn't clearly address the balancing issue, IMO.

 

[AmpedRealtor]

To apacheguy and others, please don't misunderstand my posts as criticism in any way. I am as confused as the next person and also looking for answers regarding best practices for our batteries. I concur and agree that Tesla should communicate better regarding this issue and let us know what's going on. I am just sounding a word of caution to those out there who may be reading this for the first time that there are pros and cons to deeply cycling your battery. Since it is arguably the most expensive single component in the car, caution is advised before undertaking any regimen that is not officially endorsed by Tesla.

 

[qwk]

Well that's disappointing.

- - - Updated - - -



What concerns me is that in order to gain back those 33 miles, he has had to 100% charge every day since November 2013. He posted in February 2014. OMG!

Yeah, not something I would want to do to my pack, but I guess if one needs the range....

 

[Dave EV]

Well that's disappointing.

Why? Tesla would have to stick a coulomb counter on every single cell to be able to monitor the health of each cell. And even then, it would not get them anything since hundreds (or whatever the number of cells is in parallel) of cells are hard-wired in parallel. There is no point to monitoring at the cell level, only at the sheet level. Never mind that doing so would add a ton of cost to manufacturing.

Similarly, look at a LEAF's pack - the LEAF has 192 cells and 48 modules. Each module is in a 2P-2S configuration. Each paralleled cell-pair is monitored, but not individual cells.

 

[stopcrazypp]

Why? Tesla would have to stick a coulomb counter on every single cell to be able to monitor the health of each cell. And even then, it would not get them anything since hundreds (or whatever the number of cells is in parallel) of cells are hard-wired in parallel. There is no point to monitoring at the cell level, only at the sheet level. Never mind that doing so would add a ton of cost to manufacturing.

We already know there are 96 series cell groups (for 85kWh pack, 16 modules*6 per module) from the Model S diagnostic screen. It's those groups that need balancing. The cells in parallel will essentially self-balance (as they are all held in the same voltage and charge can move from the stronger cells to weaker cells).

In general, the drift for the Model S should not be that bad given Tesla buys these cells in huge batches from Panasonic and can have relatively good control over consistency. Obviously Tesla themselves decided it was not necessary to continuously have the pack balance itself rigorously all the time.

 

[wycolo]

> then completely discharge the battery to zero, [from TM email]

No one should read this as ZERO MILES, as I'm guessing TM means ZERO SOC. In other words driving down to '0 miles' then immediately charging back to a normal SOC is not particularly stressful to battery, but driving down to ZERO SOC is the thing that 'would not be good for the battery'.
--

 

[techmaven]

I spoke at some length with my Tesla Server Advisor about the battery balancing - I insisted that his old information about pack balancing was incorrect. He looked around at some things on his computer and came back with this answer:

1) Pack balancing only happens during a range charge
2) CAC recalculation only occurs with a deep cycle

Which means that you have to charge all the way up and let it sit long enough to balance... then discharge pretty much all the way down, and then possibly repeat once or twice and after a full range charge then, you should have a reading on capacity.

Now, there are still a questions about how fast to charge to avoid imbalance and how far to discharge to get an good CAC recalculation.