Batteries can be very complex systems, and all the various aspects work together to meet design intent. With an EV, one of the primary driving factors behind the design is a long life. Ideally the battery would last as long as the rest of the vehicle. In order to do this with current battery tech, its VERY common for manufactures to limit the absolute SOC window to something narrower than the battery can physically tolerate. Most batteries will tolerate a charge much higher than they see in service, but this can limit cycle life to a handful of cycles. Since people typically don't want a pack that's massively degraded after 1000 miles, nobody is doing this. So when the car indicates 100%, its never 'really' 100% of what the battery will physically hold. But rather, a software imposed limit. This is true for effectively any rechargeable lithium battery in consumer products. Now, with this software imposed 100% limit, it still means when you hit 100% SOC, the battery should not accept any additional charge of any kind. So you will have zero regen. Any ICE vehicle made within the past ~20 years most likely has fuel cut at speeds above when the torque converter can lock. So you do get some modest amount of deceleration on top of rolling resistance and drag. An EV with 100% SOC will most likely roll much more readily than an ICE due to the optimizations put in place to minimize the cost of the battery for the given range. And with most any modern EV, the battery most likely still has a fair bit of capacity left after it hits 0%. This does not mean you can keep driving past 0%, its intended to be there as a buffer so the car isnt a useless brick after a deep discharge. Discharge most modern lithium packs too low and you increase the risk of cells going into reversal or being damaged internally to the point where they will not tolerate a charge. Most EV's intentionally add a small buffer below the indicated 0% before it hits the minimum design SOC to account for error. This isn't free energy or some amazing technology, its just the manufacturer being unsure of how much energy is going to be left. It still will stop you from discharging past 0% of the design SOC even though energy is still available in the battery. This is mostly so if the car sits a long time and discharges to 0% design SOC, it can physically disconnect the pack and will be able to safely recharge for quite some time. Without these buffers on both ends, the battery would most likely fail very quickly for some people that charge high and discharge low on a regular basis. Having some buffer on the top end also means you can get higher charge rates at higher SOC without punishing the pack. So, really most any well designed battery has extra capacity you pay for but can't use. This is true for some better designed consumer products like laptops, cordless tools, and vacuums. It's a big part of how someone can design a battery to last 20 years when cellphones last 1-2. Just different priorities, chemistry, and design. And in a good pack design, there very well may be various tiers of SOC. The physical limits of the battery, the design limit, and then what you show to the consumer.
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How does Tesla limit range in the SR?
- Thread starter djroberts
- Start date
ucmndd
Well-Known Member
That’s a nice hypothetical, but it definitively doesn’t work like this on a Tesla.
Again, what is your real world experience in this matter?
Leafdriver333
Somewhat Active Member
darth_vad3r
Well-Known Sith
One reason I bought the SR+ over the SR is I thought I was getting something for the extra money I spent, and if I only ever charge to 90% and the SR is top locked, I could have just got that and charged to 98%, and saved a bunch of money. I also thought I was paying more for an upgraded interior.
pdx_m3s
Active Member
You also got Autopilot ($3,000 option). So the extra money you spent isn’t $4,500, it’s more like $1,500. I think you’ll be glad you went for SR+ when it comes to sell your car in terms of resale value... even if all the $1,500 got you was fog lights, 20 “more” miles of range, faster 0-60, and more speakers turned on (I may be missing something).
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darth_vad3r
Well-Known Sith
No, I didn’t. I bought before Autopilot was “included”. I paid something like $2k CAD plus tax for fog lights? and the ability to charge the SR above 98% and 100% up to 109% occasionally ... which does what? Save me 3 minutes at my first supercharger stop on a road trip? I never charge to 100%. I have Superchargers easily within reach in any direction by starting well below 90%.
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Celledral
Member
Can confirm the SR will Regen at 100% SOC, although my 100% only reads 218miles.
This is in contrast to an LR car which will not.
I’ve charged my LR at a Supercharger for 27 minutes while indicating 100%. This was after charging for 45 minutes to reach 100%. The power was initially 7kW and then diminished to 1kW. All this is to say, the battery was considered 100% full at the end. When I initially drove away, the dashed line representing reduced regen extended all the way to the middle and I had no discernible regen braking.
I'd think Tesla is one of the few to be willing to do whats best for pack life and customer experience. The capacity they are hiding from the consumer isn't that much, so its not really that big of a deal which end they put it on. The exact specifics of how and what they do are going to depend on what they're trying to do and how much overhead the SR+ config has over the regular SR.
Personally, i'd say they most likely have higher confidence and overhead in the SR/SR+ over the LR since they expect more cycles on those packs over the life of the car. And its also sold to a consumer looking for a lower cost vehicle, which oddly enough almost always is a more critical consumer. So this would mean they don't really 'need' to pad the low range of the pack since it has sufficient overhead anyways. And carrying around more capacity just adds to degradation and increases fire risk with no appreciable consumer benefit. Most likely they just clip the max cell capacity, which would slightly increase pack life, marginally reduce cell degradation, and give the ability to charge at slightly higher rates as SOC nears 100%. The last aspect is probably of particular importance to Tesla, where they are encouraged to ensure people spend less time at Superchargers. And the shortest range vehicles are the ones most likely to both require more frequent charging, as well as spend more time at a charger waiting for higher SOC. This would be the most logical outcome, since it technically has a marginal savings in the way of lower likelihood of pack failure and supercharger upgrades. It's possible they padded the low end a touch and added the rest to the top, but I think that's not as likely and would indicate somewhat lower confidence in the SR+ config.
It's very possible they just told the car to stop charging at a lower 'absolute' SOC than the SR+, and nothing else changed. That would be how you could still get regen at 100% indicated SOC, it would be easiest, and it would be the lowest effort to maintain software long term. This would mean you could charge the SR to SR+ levels by towing it and charging the last bit with regen. I suspect they're not too concerned with this, and simply prefer the better customer experience with maintain some regen at 100% SOC for the most critical consumers. The folks that charge to 100% on the top of a hill just get a little extra bump.
This is all speculation of course.
well reasoned speculation, my summary it's the top end b/c Tesla does the "right thing" for the long term. So I will charge my SR to 100% when I can till I upgrade to SR+. Hopefully they will have a price/sale soon for the upgrade.
darth_vad3r
Well-Known Sith
Who's to say "the right thing" isn't do do a little at the bottom and at the top? Do you really need the 100% range? 70% is healthier anyways, so set it to 80% of SR. I'd only charge an SR to 100% daily if I was using 80-90% of my battery daily, otherwise why keep it so high? 50% is ideal storage amount, does the SR slider adjust that point I wonder to do the right thing, since 50% of 220 will be <50% of actual battery? Hmm, maybe the right thing is to lock an equal amount on both sides.
darth_vad3r
Well-Known Sith
@Leafdriver333, here are those two posts for:
@Celledral confrims SR ALLOWS regens at 100%, @Zoomit confirms LR does NOT allow regen at 100%:
@Celledral confrims SR ALLOWS regens at 100%, @Zoomit confirms LR does NOT allow regen at 100%:
Leafdriver333
Somewhat Active Member
Probably Tesla gave a slight buffer on all Tesla cars on both ends.
And if SR has more room on both ends, it may be the one that will maintain the best condition for years to come compared to all other Tesla cars.
darth_vad3r
Well-Known Sith
Well that's debatable. Compared to an LR that drives the same number of lifetime miles probably no, because you will be using the batteries less on the LR. Compare to an LR that drives 50% more miles to keep with the ratio of 50% more battery? Ya, maybe.
Kognos
Member
I'll bite on this since this is related to a question I had in my head.
How much energy do you actually recharge, and is that measured anywhere? The energy graph only shows how you scale against EPA, but I've never seen me start at 80% on a drive then it becomes 81% through regenerative braking.
I would wager that if drive at 100% your Tesla would recharge because ... you're driving. You're spending energy just to light the screen, the brake lights, etc. The question I've posed to myself is this - can you actually recharge on a drive where you end up with more range than you started?
Even if so, when approaching full charge the M3 will say "Regenerative braking limited" so it probably only recharges what it consumes and still can't achieve a net-positive battery rate, even if it does charge.
I'm not saying it's impossible, I've just yet to see a net-positive recharge. So if the premise is that there's some kind of extra buffers at 100% and at 0% based upon this reasoning, I would be skeptical that this is true unless someone can say otherwise.
darth_vad3r
Well-Known Sith
The energy graph does not “only show how you scale against EPA”, it shows you Wh/mi or Wh/km over the last x, y, z km or mi, and if it’s green it’s adding energy to the battery (on the consumption tab). The trip meter can also show negative Wh/mi for a trip to show energy has been added in your trip, not used.
Just like supercharging tapers to protect the battery as SoC approaches 100%, so to does regen “recharging” have to taper to protect the battery at high SoC. Even if you drive and are using the screen, lights, etc, you are still at 99.5% SoC and thus can’t charge “fast” which is what full regen would be like.
Start at the top of a long hill or mountain and you can easily end a trip with more range than you started with. Or get someone to tow you while you regen ... there’s a YouTube video of this
Cued up at the end of 1.0 miles of towing with regen, you can see about 1kWh added (1.0 mi and -1000 Wh/mi) and 3-4 miles of range added (230 end, 227 start that dropped to 226 once they started moving):
The “extra buffers” above 100% or below 0% are most certainly there on the SR, since they’ve not actually sold a real “SR”, butt only the “SR+” and then updated the software to lock out part of the battery (at the top end, or a bit at the top and bottom possibly).
People have also posted about severely limited essentially zero regen after charging a non-SR to 100%, and others posted about having regen available with an SR charged to 100%. I quoted two of these 4 posts up.
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Kognos
Member
Start at the top of a long hill or mountain and you can easily end a trip with more range than you started with. Or get someone to tow you while you regen ... there’s a YouTube video of this
Seriously ... that is cool. Thanks so much! Every day a lesson...
I don't really monitor it, but my wall connectors energy is measured with a TED5000 and I glanced at it a few times. It puts back in basically exactly the energy id assume considering its a ~74kwh pack. The car very much will charge from regen, its just that you don't get some crazy amount of energy from regen. You're never going to gain energy from using regen unless you start off at the top of a hill or get towed. Accelerating and then decelerating with regen still wastes ~40-60% of the energy compared to sitting still. Theres losses drawing energy from the pack, losses from the motor and drive unit accelerating, and then more or less the same losses putting energy back in. How significant these losses are depends massively on cell temperature, age, SOC, and the rate at which it happens. If you accelerate up to a moderate speed and wait for the battery meter to just tick down 1%, and then regen a lot, it will go up briefly. The car consumes more power than you'd think even just sitting there awake, screen off or on. Especially when its in drive and running all the systems. Just like your battery meter dosent go down 1% every time you accelerate, it won't go up noticably either. But some people went down big hills and charge up several percent along the way. Its basic physics, the energy has to come from somewhere.
The battery has hard limits on what it is allowed to hold. Its both dangerous and damaging to the battery to charge beyond its design intent. Sure, a percent or two isnt a big deal, but they have no reason to allow this. Most battery management systems are very leery about overcharging and will ensure this never happens, so power tapers to near zero as SOC approaches 100%. So yes, you will likely have some non zero regen even at 100% indicated, but its going to be a few kW, so barely noticeable. And this is only going to be if the battery isnt at 100.00% SOC. Most likely whats going to happen is the car will terminate the charge immediately at, or just before 100.00% SOC. The charger will turn off, and the car will continue pumping coolant, consuming some energy off the battery. So by the time you get in the car the SOC might be 99.76% or something like that, but still indicate 100% on the dash. So there IS space left, just very little. It should be happy to allow regen up to 100.00%, but its going to be super weak. And as the gap increases between the max design SOC and current SOC, the regen power will go up. This is the very same reason why you get less regen when the battery is cold. The batteries internal resistance is higher, so it means the voltage will go up more for the same input power. The BMS most likely won't let the cell voltage go past some absolute value, so it tapers input to the battery to prevent this. This means reduced regen and charge power in some situations.
It's actually quite considerably more complex than this when all factors are taken into account, but the details don't matter so much here. The battery WONT let you overcharge it. It most likely has some failsafe system that will open the contactors if the SOC gets too high somehow. If they don't its theoretically possible a DCFC can overcharge the pack and this will almost certainly cause a very substantial nearly explosive fire. So if the car is allowing regen, its not at 100%. And as it approaches 100% its going to limit charge power/regen to be confident its not overcharged. Most consumer devices show 100% when they really are internally reading several percent less. Consumers would tend to think somethings wrong if it took an hour for their phone to charge that last 1%, even though it really might.
This thread has sold me on getting the SR vs. the SR+ as its like getting the first 3 or so years with 0 perceived battery degradation by effectively getting the larger battery for 5K less. Fantastic.
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