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Supercharging, does it wear it out or not?
- Thread starter mrobins64495
- Start date
pdk42
Active Member
Fast charging will cause more rapid battery degradation. I don't know what the severity of it is, but I think there are many owners who do a lot of supercharging without issues However, Ymmc
Tam
Well-Known Member
The problems with most answers are: There is no definite authoritative reference of harms done by Fast DC or Supercharging.
Depending on how long do you want to keep your car, Tesloop taxi fleet is only charged by Superchargers with mostly setting their charge limits at 95 to 100% and its eHawk Tesla Model S 90D has driven over 445,000 miles and had to change its main battery at 194,239 and 324,044 miles.
Logically, if it hurts, Tesla should document it somewhere such as the Owner's manual or the web but there's no discouragement of using Tesla Superchargers at all!
The only time there was a question of using Superchargers were when Elon Musk complained in an annual stockholder that some locals were abusing the free unlimited Supercharging which caused long lines.
It's about the inconvenience wait for others in line and not about the battery's health.
Occasional supercharging _is_ good for the battery - it can counteract one of the ageing processes in the cells.
Excess heat is bad for the cells - but the charge profile probably counteracts this.
The software limitation on charge profile is a bit of an unknown in terms of what triggers it, I think.
I'm intrigued by this quote from tesloop's history:
Maybe it only applies to supercharging, or cell balance stress, but I'd been assuming that rest at low SoC was not ideal.
Excess heat is bad for the cells - but the charge profile probably counteracts this.
The software limitation on charge profile is a bit of an unknown in terms of what triggers it, I think.
I'm intrigued by this quote from tesloop's history:
Maybe it only applies to supercharging, or cell balance stress, but I'd been assuming that rest at low SoC was not ideal.
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Glan gluaisne
Active Member
I've been playing around with lithium batteries is EVs for some years now, and the only real issues that tend to shorten their life are high temperatures (not a problem with the Tesla pack as it's actively cooled) high numbers of charge discharge cycles using the whole capacity of the battery and failure to allow multiple cell packs to balance properly, occasionally leading to cell, or cell module, failure.
It's only really the latter issue that might, possibly, give some cause for concern after lots and lots of rapid charging, with no AC charging. When rapid charging, the battery management system in the pack doesn't really do cell balancing, as the charge current is too high. This doesn't normally matter, as in practice Tesla cell modules tend to remain in balance for long periods of time without intervention. It is possible, though, that if a car was never AC charged, it might eventually end up with the pack out of balance.
I'm certain that the BMS can not only detect this, but probably show some sort of warning message, or just reduce the rapid charge rate. If you think about it logically, the battery pack can happily deliver over 300 kW when driving, and get charged at around 70 kW or so from regen, so it's operating in the same sort of current range as a rapid charger all the time it's being driven, albeit not for prolonged periods of time.
From what I can gather, from monitoring AC charge current, the BMS seems to do most of the cell module balancing at the end of an AC charge, over a period of maybe fifteen minutes to half and hour. This bit of housekeeping keeps the pack in good enough order that it can then tolerate a few rapid charges without getting out of balance.
If planning to rapid charge a lot, I'd try and arrange to have an AC charge to 90% plus maybe once a month or so, just to give the BMS a better chance to do its thing.
It may be that the BMS will switch to being able to balance any time the car is parked before long. I have a BMS unit that does just this, actively balances the pack when it's neither charging or discharging and for the month or so I've been playing around with it I'm impressed at what a good job it does. It wouldn't surprise me to find Tesla start using this technique before long.
It's only really the latter issue that might, possibly, give some cause for concern after lots and lots of rapid charging, with no AC charging. When rapid charging, the battery management system in the pack doesn't really do cell balancing, as the charge current is too high. This doesn't normally matter, as in practice Tesla cell modules tend to remain in balance for long periods of time without intervention. It is possible, though, that if a car was never AC charged, it might eventually end up with the pack out of balance.
I'm certain that the BMS can not only detect this, but probably show some sort of warning message, or just reduce the rapid charge rate. If you think about it logically, the battery pack can happily deliver over 300 kW when driving, and get charged at around 70 kW or so from regen, so it's operating in the same sort of current range as a rapid charger all the time it's being driven, albeit not for prolonged periods of time.
From what I can gather, from monitoring AC charge current, the BMS seems to do most of the cell module balancing at the end of an AC charge, over a period of maybe fifteen minutes to half and hour. This bit of housekeeping keeps the pack in good enough order that it can then tolerate a few rapid charges without getting out of balance.
If planning to rapid charge a lot, I'd try and arrange to have an AC charge to 90% plus maybe once a month or so, just to give the BMS a better chance to do its thing.
It may be that the BMS will switch to being able to balance any time the car is parked before long. I have a BMS unit that does just this, actively balances the pack when it's neither charging or discharging and for the month or so I've been playing around with it I'm impressed at what a good job it does. It wouldn't surprise me to find Tesla start using this technique before long.
I’m at 5500 kWh of DC Supercharging on my 2019 M3. Pulled 210 kW on an Ionity the other week with no battery preconditioning...
Glan gluaisne
Active Member
He's partly right, but the bit about resistors across the cells is a bit confused. The BMS only ever switches in cell shunts when it's balancing, and it needs charge current in order to do that (as it's charge current it shunts across each cell module to stop its terminal voltage getting too high). There is a balance (no pun intended) between excessive BMS dissipation (i.e. wasted power when charging) and speed of balancing, though. A high shunt current BMS can balance a pack more quickly, but it wastes a lot more charge power when doing so. Higher values of switched cell module shunt resistors reduce this wasted power, but then cause the pack to take longer to balance at the very end of an AC charge.
From experience and readinging many varied posts on TMC and general Web research, I would say there are three main areas to consider:
Age related
Energy throughput related
Use related
All of these factors can change their behavior with slight tweeks to battery chemistry, so not all comments relate specifically to all batteries.
Also, the impact of different use can change as a battery changes with age.
Simplest is to just assume that Tesla have a reasonable approach that will give you decent battery performance whatever you do.
Second, you could take an ultra conservative approach that would likely make for a less satisfactory ownership experience probably without guaranteed significant benefit. Only AC (slow) charge, don't accelerate or regen hard, maintain 20 to 80% SOC.
Or you can try and learn about your own battery in detail with a tool like SMT and other online software which, if you find that stuff interesting, might have some benefit and if nothing else, you are more likely to spot if anything goes awry with your battery.
As batteries age, their electro chemical structure changes. Temperature also has an effect - at low temps the battery doesn't work (well) and at (excessively) high temps it can become unstable.
From what I have read here, M3 (and MY?) adopt different approach to battery maintenance / balancing, and MS changed over the years. What is likely to apply to all cars (because they have cells wired in parallel) is that ideally they should have some time for charge to equalise between the cells after use especially at the lower limits which is where the BMS can 'learn' about the state of the pack. This 'settling' or 'equalising' of charge is not the same as balancing - in which energy is bled off from higher performing cells so that energy is evenly spread through all cells to optimise energy storage of all cells.
So, does Supercharging wear out the battery faster than slow charging? With a healthy battery and allowing Tesla's management systems to do their job, for a given amount of energy through the battery there is likely minimal detrimental effect. If a battery has issues (due to age or other defect) then fast charging and at high SOC MIGHT accelerate degradation or even lead to a more dangerous situation, but I don't see how you can spot this kind of situation reliably without being a bit OCD about your car. In any case, such situations shouldn't arise.
The harder you push the car, the more load it puts on components and that includes the battery and the balancing system, but the car is designed to deal with those loads, so on its own, I don't feel that some Supercharging is a bad thing at all. I do believe that some slower charging sessions, while less efficient, do help maintain good energy balance between cells and hence keep your battery performing optimally.
Age related
Energy throughput related
Use related
All of these factors can change their behavior with slight tweeks to battery chemistry, so not all comments relate specifically to all batteries.
Also, the impact of different use can change as a battery changes with age.
Simplest is to just assume that Tesla have a reasonable approach that will give you decent battery performance whatever you do.
Second, you could take an ultra conservative approach that would likely make for a less satisfactory ownership experience probably without guaranteed significant benefit. Only AC (slow) charge, don't accelerate or regen hard, maintain 20 to 80% SOC.
Or you can try and learn about your own battery in detail with a tool like SMT and other online software which, if you find that stuff interesting, might have some benefit and if nothing else, you are more likely to spot if anything goes awry with your battery.
As batteries age, their electro chemical structure changes. Temperature also has an effect - at low temps the battery doesn't work (well) and at (excessively) high temps it can become unstable.
From what I have read here, M3 (and MY?) adopt different approach to battery maintenance / balancing, and MS changed over the years. What is likely to apply to all cars (because they have cells wired in parallel) is that ideally they should have some time for charge to equalise between the cells after use especially at the lower limits which is where the BMS can 'learn' about the state of the pack. This 'settling' or 'equalising' of charge is not the same as balancing - in which energy is bled off from higher performing cells so that energy is evenly spread through all cells to optimise energy storage of all cells.
So, does Supercharging wear out the battery faster than slow charging? With a healthy battery and allowing Tesla's management systems to do their job, for a given amount of energy through the battery there is likely minimal detrimental effect. If a battery has issues (due to age or other defect) then fast charging and at high SOC MIGHT accelerate degradation or even lead to a more dangerous situation, but I don't see how you can spot this kind of situation reliably without being a bit OCD about your car. In any case, such situations shouldn't arise.
The harder you push the car, the more load it puts on components and that includes the battery and the balancing system, but the car is designed to deal with those loads, so on its own, I don't feel that some Supercharging is a bad thing at all. I do believe that some slower charging sessions, while less efficient, do help maintain good energy balance between cells and hence keep your battery performing optimally.
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Doesn't fast charging tend to create dendrites in the batteries, which can then lead to more disastrous failures in the cell, including fire. I think this was the cause of some of the Model S fires which lead to the whole ChargeGate throttling of certain older battery packs.
Tesla's cell chemistry and battery management is designed to reduce likelihood of Dendrites I gather. Just fast charging alone should not be a problem for the cells as long as the battery as a whole is in reasonable shape and especially at SOC where max cell voltage is below say 3.9v. Of course specific voltages, charge rates, temperatures etc will apply to individual cars / models.
In an older / compromised / faulty pack, you are likely to have increased stresses in the cells.
Lithium plating is one effect that I believe happens before Dendrites form. There are other effects relating to the electrolyte (hence the interest in dry / more stable electrolytes) and formation of partial short circuits in the cells (that I don't really understand) that are something different from Dendrites.
The worst combinations are:
Compromised battery (some cells with blown individual fuses, some high internal resistance cells, some 'shorty' cells, some lithium plating, some electrolyte degradation, some other fault - maybe balancing circuits or general electronic component)
Sitting at high SOC (big increase in chance of Dendrites)
High cell voltages.
High temperatures.
Some of these factors can appear simultaneously with different causes due to different cells experiencing different 'aging' effects within the 1000's of cells in each pack.
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Balancing COULD be done by taking charge from strong / high energy cells (active balancing) or by just wasting energy as heat from the same high energy cells. Resistors can dissipate energy at any time as long as the battery pack and control electronics are active - so not during sleeping AFAIK.
The need for balancing comes from inevitable slight electro chemical differences between cells. The closer to identical the cells are, the less need for balancing.
Older cells are more likely to have ended up with bigger electro chemical differences so balancing circuits will have to work harder to keep energy shared uniformly across all cells.
Glan gluaisne
Active Member
Yes, I've built a few dozen packs of varying capacities and lithium cell chemistries over the years, and tried a number of different cell balancing techniques, from the well tried and tested shunt balancing method, through a home brew "flying capacitor" system and am currently testing an off-the-shelf active balancing BMS from China, of all places.
Over the years I've found the fairly dumb switched cell/cell group shunt method to be very reliable, but it does waste charge power and does limit the charge current during the balancing phase of a charge (due to heat dissipation from the switched shunts). My home brew flying capacitor system worked OK, and had the advantage that it could balance the pack when it wasn't being charged, but was severely limited by the effective charge that could be transferred , due mainly to the realistic limit on the size of the capacitors.
The active system I've been testing shows a great deal of promise, though. They seem to reliable balance cell groups to about 5mV, and will shift up to 5 A when dealing with a big cell/cell group imbalance. As with all active balancing systems, balancing slows down a lot as the pack becomes better balanced, but it still seems an impressive system. As far as I can measure, there seems to be virtually no energy loss during balancing (I can't see any temperature changes at all on the balancing circuitry). This, together with the fact that there's no need for the BMS to reduce charge current during the balancing phase, and the fact that the pack will start charging with the cells/cell groups always in balance, seem to be definite advantages of this approach.
It strikes me there are multiple potential benefits of active balancing.
I haven't quite thought through all the implications, but there would seem to be a big potential benefit of not requiring such accurate cell matching and also being able to get much better use from older batteries with mismatched cells.
The first post here How I Recovered Half of my Battery's Lost Capacity has some interesting info (true or not who knows...) about how balancing happens slowly during deep sleep on the model 3. like all these discussions there is much hearsay and speculation and disagreement in the whole thread...
Glan gluaisne
Active Member
My experience so far is that the active balancer works exceptionally well. It just sits there keeping all the cell/cell group terminal voltages very close matched all the time, with only a very tiny vampire drain. Overall, it seems to be significantly more energy efficient than the traditional switched cell shunt type balancing system, which is what I believe Tesla still use.
In theory, such an active cell balancing scheme doesn't need individual cell monitoring, in terms of triggering shutdown in the event of one cell/cell group reaching a critically low, or dangerously high, voltage, and should allow charge and discharge to be controlled solely by the whole pack terminal voltage. I'm not sure I'm brave enough to try that approach for unattended charge/discharge, but from the testing I've done so far I'm coming around to the view that it may well be very safe. It's just the paranoia from years of working with lithium cells, and the strong memories of the hazardous behaviour of some early cell chemistries, that makes me a bit nervous about this approach.
The op is a pretty knowledgeable poster, and imo there is quite a lot of decent content in that thread, but as always it's not obvious what is gospel and what mere conjecture.
I'm not sure how a battery can 'balance in deep sleep' since it at least needs the hv circuits to be active in order to operate the balancing controls. There appears to be be some differences of opinion regarding if the M3 only balances above certain SOC and if it attempts to maintain balance at all times.
My thought on that is that if Tesla allow you to set SOC limits as low as say 50%, then so doing would likely end up with quite a high level of charge imbalance if balancing only takes place above say 79 or 80%. The only requirement I can see for balancing to take place is for the necessary circuits to be energised and active.
For balancing to be effective, the balancing system needs a decent 'picture' of which cells store / absorb / release most energy and which are not as effective, and for that purpose I can see that the idea of letting a battery 'settle' with no current flow (as in deep sleep) is a necessary part of the process.
The misconception I have picked up many times in these discussions is that energy balancing happens in two very different situations - one controlled by the BMS using bleed resistors to 'waste / use' energy from specific bricks of parallel cells, and the other is an intrinsic and uncontrolled equalisation of charge between all the cells wired in parallel. Even when all systems are shut down, every cell remains connected in parallel with other cells in its 'brick' so current can flow from one cell to another, so 'balancing' charge within each brick. This is not the same as BMS controlled balancing, but it is necessary that it happens in order for the BMS to fully 'understand' the condition of the battery and so be able to manage it correctly.
I guess if your balancing capability is high enough, then you will NEVER have to deal with imbalance and can therefore assume voltage is even across cells as a proportion of battery terminal volts. I guess you need to monitor for 'error' contions though!
I wonder if this could be one of Tesla's million mile battery technologies, maybe using Maxwell caps to maintain near perfect balance even under heavy instantaneous loads.
I suspect that early model S owners suffering from all the 'gates are seeing what happens when all the control systems can't exert enough feedback control to keep systems on the rails. The only option then is to impose external controls that ensure there is enough headroom such that the internal controls (bms) can function well enough to keep the pack adequately controlled.
