GHammer
Dark Star
Maybe a moderator can change the title of this thread.
"Supercharging to 100% is unbearable"
"Supercharging to 100% is unbearable"
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Supercharging to 100% is unbearable...
- Thread starter random155
- Start date
Even charging to 80% on my pack is pretty unbearable... 90/100% is now a complete joke
@Random, the solution is to switch from % to miles... then you will never have to see it’s stopping at 97. Kidding aside, it may not be worth worrying about those 3%. Tesla won’t address something that minor and you are clearly going through a lot of frustration trying to “balance” when it likely won’t make any real world difference.
That would be due to Tesla crippling your battery. If it does not charge beyond 97% press them for a warranty.
See the Batterygate/Chargegate sticky in the forums.
LOL - my first post got two "agree" and two "disagree"'s
This is not about superstition or magic, but basic knowledge of the science behind this.
Let's do some adult education: From what I read, Service-center employees could use some too.
SoC= State of charge
full design capacity = The designed capacity of a cell, like 3Ah
full actual capacity = the actual capacity, lower than design due to degradation/age.
A fictive 100KWh pack may be basically 96 batteries in series (about 403v at the maximum allowed voltage of 4.2v per cell * 96 )
Let's say each part of this series consists of 86 cells in paralell, those 86 cells act as one big cell with higher capacity and current capability than fewer cells. If the chemistry goes bad in one cell, or it shorts, and the interconnect burns up, you lose the capacity of that cell.
The Battery is then a S96P86
Since 4.2v is the maximum allowed cell voltage once a cell(or any amount of parallel calls) holds 4.2v, one defines that as 100% actual SoC
Balancing happens at any SoC, you can verify it with Scan My Tesla app, as you will see voltages to be balanced after a while at ANY
Balancing is simply to load on the cells with highest voltage(SoC) - if this is done during charging, and you charge a cluster with 10A current, then load the same cluster with 10A, the SOC will not go anywhere. You dissipate all the energy that otherwise would charge the cell.
Balancing cannot compete with high charging currents, the balancing cannot dissipate 10KW from a cluster of better cells.
Now, imagine one of the 86 battery clusters to have a few bad cells, or being in worse shape.
The current during charge is equal across all serial-connected components (batteries) and all are charging, but the "cluster" of 86 cells is has a 5% lower actual capacity , so it's chemistry is "full" while the other cluster of batteries in series can still absorb 5% more energy.
Since all have the same current, the current is now lowered to whatever the fullest member of the series can accept, and since it is full, it means the charge current is lowered to when this one balancer can dissipate in heat (also limited by hot pack/coolant)
And so .... you may wait for many hours for the remaining 95 members of the series to get their full charge, at the current limited to the poorest/already done parallel cluster.
Now imagine if each balancer (96 in total) could output 1kW in heat - that would mean you could complete the other packs at 1kW input - right ? - but what happens when 90 of the 96 series is full? 90kW heat production to maintain a charge current to maintain a 1kW energy on those last 6 cell-groups?
If one plan to go to 100% - Supercharging is just stupid, as slow charging will eventually get there too, but not with you looking at paint dry.
There is no need to go to 100% - if you get to 100% for all cells, ... remember that the LOWEST discharge allowed is defined by the worse cell, the BMS will not let you destroy the poorest cells by deep discharge, so once the 5% reduced cells get to their 0% (minimum allowed voltage) then it is perfectly irrelevant if the remaining 95 cells in series still hold 5% more energy.
So in short: While charging to 100% over xx hours ,the cell groups with lowest actual capacity are charged fully first (absorb all the energy they can hold), then they are held 100% just to let the better cells reach their maximum voltage(and capacity) ... which you will never spend, as you are limited by the worst cell(clutser) in series
Hance: Long 100% charge is abusing the poorest cells in the battery,
Physics, chemistry, engineering ... not magic & superstition.
This is not about superstition or magic, but basic knowledge of the science behind this.
Let's do some adult education: From what I read, Service-center employees could use some too.
SoC= State of charge
full design capacity = The designed capacity of a cell, like 3Ah
full actual capacity = the actual capacity, lower than design due to degradation/age.
A fictive 100KWh pack may be basically 96 batteries in series (about 403v at the maximum allowed voltage of 4.2v per cell * 96 )
Let's say each part of this series consists of 86 cells in paralell, those 86 cells act as one big cell with higher capacity and current capability than fewer cells. If the chemistry goes bad in one cell, or it shorts, and the interconnect burns up, you lose the capacity of that cell.
The Battery is then a S96P86
Since 4.2v is the maximum allowed cell voltage once a cell(or any amount of parallel calls) holds 4.2v, one defines that as 100% actual SoC
Balancing happens at any SoC, you can verify it with Scan My Tesla app, as you will see voltages to be balanced after a while at ANY
Balancing is simply to load on the cells with highest voltage(SoC) - if this is done during charging, and you charge a cluster with 10A current, then load the same cluster with 10A, the SOC will not go anywhere. You dissipate all the energy that otherwise would charge the cell.
Balancing cannot compete with high charging currents, the balancing cannot dissipate 10KW from a cluster of better cells.
Now, imagine one of the 86 battery clusters to have a few bad cells, or being in worse shape.
The current during charge is equal across all serial-connected components (batteries) and all are charging, but the "cluster" of 86 cells is has a 5% lower actual capacity , so it's chemistry is "full" while the other cluster of batteries in series can still absorb 5% more energy.
Since all have the same current, the current is now lowered to whatever the fullest member of the series can accept, and since it is full, it means the charge current is lowered to when this one balancer can dissipate in heat (also limited by hot pack/coolant)
And so .... you may wait for many hours for the remaining 95 members of the series to get their full charge, at the current limited to the poorest/already done parallel cluster.
Now imagine if each balancer (96 in total) could output 1kW in heat - that would mean you could complete the other packs at 1kW input - right ? - but what happens when 90 of the 96 series is full? 90kW heat production to maintain a charge current to maintain a 1kW energy on those last 6 cell-groups?
If one plan to go to 100% - Supercharging is just stupid, as slow charging will eventually get there too, but not with you looking at paint dry.
There is no need to go to 100% - if you get to 100% for all cells, ... remember that the LOWEST discharge allowed is defined by the worse cell, the BMS will not let you destroy the poorest cells by deep discharge, so once the 5% reduced cells get to their 0% (minimum allowed voltage) then it is perfectly irrelevant if the remaining 95 cells in series still hold 5% more energy.
So in short: While charging to 100% over xx hours ,the cell groups with lowest actual capacity are charged fully first (absorb all the energy they can hold), then they are held 100% just to let the better cells reach their maximum voltage(and capacity) ... which you will never spend, as you are limited by the worst cell(clutser) in series
Hance: Long 100% charge is abusing the poorest cells in the battery,
Physics, chemistry, engineering ... not magic & superstition.
Over-worded but appreciated. While I understand your point, I"m only doing what a service tech asked me to do to determine what Tesla's next step is to correct my problem. It sounds like I may have some issues with a pack in my battery that is preventing my car to charge to 100%, so I will jump through a few hoops to get it fixed.
dhrivnak
Active Member
You should really do that at home as it is best for the car to sit a while to balance.
This is one of the points I don't understand. Everything else in your post I get and agrees with my understanding, although exactly how charge is shuttled around I do not yet understand.
If multiple cells are wired in parallel with just a basic fuse device to drop individual bad cells out of the parallel group, how can those parallel cells 'balance'? It must be that they are taken to be identical and the cells 'force' eachother to follow exactly the same voltage even though the current through each cell could be different.
Once you put bricks (parallel packs of cells) in series, I can see how you balance one brick with another as the voltage across each pack of cells can be different from others compared with parallel cells that are forced to have the same voltage for all those cells.
Thank you for reading, then I did not completely waste my time
Yes. All parallel-connected cells are balanced as a group. Nor is there any reason for a more individual charge, as they work together, the ones with more ready ions will provide a little more current, than some of them with higher internal resistance, but in the big picture, they are balanced in terms of the chemical state of the cells. Also, should you sneak in one defective cell with 1Ah, while the rest are 3Ah each.... it will contribute less, but still not be destroyed, as the voltage of the group never goes that low.
A cell with low SoC increase it's internal resistance, thus "working less" while the rest does work normally.
Think of parallel connected cells as if it instead making one big sheet of the battery material, you just split it up across many containters.
What is extremely important, it to balance between the different groups. Otherwise, the worn cells with lowest capacity to absorb the power, would be deep discharged while the rest might be good. , or if a few groups were bad, internally shorted, a full charge would mean that the rest would get higher voltage than is good for them.
the rest is up to the software:
The BMS may lie to the user and tell the user that 100% SoC is achieved when some most are at 100% , or just tell the truth, it is all about how anal the user is, and what makes him happy.
Samsung had a few for Galaxy phones for a while that charged to only around 4.1v (liead about 100%) in order to prolong the life, if user dis, then reconnected the charger at 4.1v, , it went to the usual 4.2v - some users were unhappy about that too.
Galaxy Note8 ? mine charges to 4.3v - #1 priority is short term is then good reviews in term of battery life.
It is very hard to make users happy, if they got hung up in numbers with complex reasons.
The short answer is: do not be obsessive about stuff like that, for the user, only one number is truly important: "Actual Capacity" or "Usabel Full Pack" in Tesla terma, (kWh)
If people nag to get to see 100% while some cell group is hanging behind and charging slowly, then Tesla can say "100%" and keep charging, then somebody will complain about power usage with no apparent charging,... then the solution is to ... ? stop charging at 96% ? it's hard to please everyone.
I am designing right now a very small but rather complex BMS, (did better before)
attaching a photo, you can see it's WIP as no of the main connectors have been soldered on.Thanks. Yes, that's exactly what I needed - multiple parallel cells just like one cell with large surface area.
In my opinion it's really more useful from a technical view to consider energy system overall because if you isolate one small view you can make a useless system seem great in just one narrow respect. Many owners seem to think that because Ev's are 'maintenance free' that nothing is wearing out and you can't abuse the car.
Slamming a battery from 300kw discharge to 75kw charge with multiple hard accelerate / decelerate cycles is bound to take a toll on the battery, as is any other use that pushes the battery chemistry to its limits.
The whole concept of 100% is not really absolute as there are trade-offs of course. But with EV that already pushes battery very hard, there is bound to be big temptation to push a little harder if you can sell at higher price. You just have to learn about your warranty and failure costs the further you push.
What I would love to get clear is if it is possible / meaningful to talk about cell (brick) balancing except at the point you go to constant voltage (at whatever limit you decide to use) and allow the cells to absorb energy slowly until they balance.
That is, can you 'force' balance and keep bricks balanced under high current charging conditions? I could see that setting your preferred SoC and allowing the car BMS to charge (current) then balance (constant voltage) would be fine as long as balancing gives time for cells / bricks to absorb energy fully.
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AjrUleZ
MS and MX Long Range Plus 21" and 22" OEM
boonedocks
MS LR Blk/Blk 19”
Well said @Ande
I always supercharge 20 - 80 or 88 max & run. Time is money
which is why we don’t use supercharging at all and do all of our charging at home.
Ande is definitely well versed in this area, thank you. Along with not being able to charge to 100%, I noticed that my 90% went from 233 miles to 226, in what seems like overnight (post "batterygate"). I understand what you're saying about how we perceive our packs whether 97% or 100%, and big picture it doesn't matter as long as the "usable full pack" remains constant (minus normal degradation). But I thought this might be a little more than that considering the small drop in miles along with the inability to charge to 100%, hence my inquiry with Tesla. If there is an issue with a module in my pack, I obviously want it addressed before my warranty expires. Thanks again for your input, it was very comprehensive.
The balancing is happening at all times, probably only except when the battery goes into deep discharge prevention mode/disconnects.
Let's imagine charging at 110A @ 374V (3.9v/cell), that is 1.28A/cell (or less than 0.5C as one say in terms of charge current per cell)
Now imagine one of those blocks have some defective cells, and the remaining absorbed more energy, and are getting full at 4.2v/cell , while other cells are still at 3.9v now the balancer starts to put a load on them.
to maintain a charge current of 110A with one full cluster, one would need to put a load on that full cell cluster of 110A*4.2V 462W
This, with some balancing power of the other 95 series, would pose a ridiculous amount of heat that the car would need to get rid of.
Hence the balancer is not capable of dissipating up to 462W in each of the 96 cells (as everyone need a balancer.)
So let's say the balancer MAY be designed to dissipate only 60W per cell.
60/4.2= 14.2 A would be the is the maximum charging current with one cell getting full.
Again; this does not mean you could/would maintain a 14.2A charge if 90 of those 96 batteries are full, as 90*60W =5.4KW heat energy that needs to be dissipated... and you would gain at best 6(remaining modules) *4.1v * 14.2A = 350W .... so at the end, in this scenario .. .you would use 5.4kW to gain 350W charging effect, charger/rectifier losses not included.
So let's say that is a great idea, and you had BMS charge to absolutely EVERY of those 96 in paralell were 100% full. Huge losses, long time, and a true SoC of 100%.
Now you drive, but you can only drive till the weakest of those 96 in series has only 70% of the capacity of the rest - BMS cannot allow deep discharge to any of those the rest, so the car stops at first cell being "empty" (having only it's safety margin left)
You are now stranded til 1 cell cluster being empty .. it does NOTHING GOOD that the 95 others are at SoC 30%
Hence, obsessive charging to "100%" is pointless, unless the BMS lie a bit to us and say 100% is reached when the charge process becomes ridiculous due to many cells getting full..
Hugh Mannity
Mediocre Member
awesome stuff in here; @Ande would you recommend cranking down the amperage for a nice long charge/balance cycle ? My home charging is 240V @ 32 Amp. Assume that is mostly fine for balancing the pack; else would you think bringing the current down to 10A or something would be a good idea ? Have a nice long charge once in awhile for time for balancing ?
I always have my charge setting @ 89% with a run up to 100% every few months or so when we road trip.
I always have my charge setting @ 89% with a run up to 100% every few months or so when we road trip.
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