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Is 100% really 100% and if not...
- Thread starter random155
- Start date
tonybelding
Active Member
100% has never been 100%. If you charge Li-ion cells to 100% you quickly ruin them. It's the same way if you let them discharge down to 0%. That's a ruined battery.
When your car says 100%, it means the maximum charge that the battery management system is programmed to allow, and when it reads out 0%, it means the minimum charge that the system is programmed to allow. Those values are a calculated compromise between available capacity and maximizing the battery's service life.
Over time Tesla have gotten more data on battery life and have adjusted their calculations accordingly.
When your car says 100%, it means the maximum charge that the battery management system is programmed to allow, and when it reads out 0%, it means the minimum charge that the system is programmed to allow. Those values are a calculated compromise between available capacity and maximizing the battery's service life.
Over time Tesla have gotten more data on battery life and have adjusted their calculations accordingly.
That’s kind my point. Why aren’t we regularly charging to 100% then? Especially now since batterygate, where Tesla has decreased the amount of power the battery can charge? I normally charge to 90% once a week, and I don’t necessarily need the extra 10% but I’m just curious that if we aren’t really ever maxing out the battery how can giving it a full charge on a regular basis (knowing it’s not a full charge) degrade the battery quicker?
Just because it isn’t really 100% doesn’t mean that charging higher won’t cause more degradation.
It’s a matter of degrees - Going from 80% cycles to 90% cycles increases wear, too, just not as much as going to 100%.
Ignoring the fact there was always buffer on both ends.
Battery gate cost me 10-15 miles that is 4-6% not 10. So essentially you are saying you want to now begin daily charging to the old 95%..............when 90% was always considered the max safe daily.
Tesla is in the wrong here but two wrongs don't make a right and their behavior doesn't make it a good idea for you to abuse the battery.
Battery gate cost me 10-15 miles that is 4-6% not 10. So essentially you are saying you want to now begin daily charging to the old 95%..............when 90% was always considered the max safe daily.
Tesla is in the wrong here but two wrongs don't make a right and their behavior doesn't make it a good idea for you to abuse the battery.
Lo
like I said, I don’t need the extra 10% regularly, and I charge once a week. I was just curious. So “essentially” I’m not saying I want to charge “daily” to 95%.
Understood. Does anyone know how many Kwh we can actually put into an 85 battery, since it’s obviously not 85kwh?
BigNick
Infamous Fat Sweaty Guy
All cells in the pack charged to 4.2V is a "true" 100%.
In reality, you'll never get every single cell out of 7104 (85/90) or 8256 (100) charged to 4.2V.
This is due to differences in the individual cells and the pack's construction, and that's even if your car allows charge to "100%" and you haven't been capped. You'll probably wind up at an average of 4.190V to 4.195V, with some cells a few mV higher and some cells a few mV lower.
The "85" pack when new had 81.5 kWh capacity, and 77.5 kWh of usable energy (the "bottom" 4 kWh is locked-out so you don't brick the battery).
In reality, you'll never get every single cell out of 7104 (85/90) or 8256 (100) charged to 4.2V.
This is due to differences in the individual cells and the pack's construction, and that's even if your car allows charge to "100%" and you haven't been capped. You'll probably wind up at an average of 4.190V to 4.195V, with some cells a few mV higher and some cells a few mV lower.
The "85" pack when new had 81.5 kWh capacity, and 77.5 kWh of usable energy (the "bottom" 4 kWh is locked-out so you don't brick the battery).
doghousePVD
My grandfather’s car
A lot of people misunderstand battery capacity. A liquid fuel tank has a very objective "full", say 10 gallons. This varies a little bit by temperature (tank and fuel), so the energy content of the tank varies a little. In practice the variation is too small to be noticed often. Very cold gasoline occupies less volume for the same amount of energy, so a full tank of sub-freezing gasoline contains more energy than tank at 100˚F. A very full tank of sub-freezing gas will overflow when it warms up.
Batteries are different. A nominal 100 kwh battery if discharged rapidly (lots of rapid acceleration, high speed gaining elevation, with maximum heat or a/c running) will likely only be capable of discharging 80 to 90 kwh, and if the battery is very cold, even less.
Conversely, a very slow discharge may have the battery discharge something like 120 kwh. Further complication is the change of temperature during use, and variation of temperature from cell to cell.
The answer to "How much does a 85 kwh battery hold" is it depends, and is complicated. Tesla changing the charging regimen is recognizing they are still learning about the optimal charging and storage parameters. As others have pointed out, the buffers built into the battery management system for safety and another complication.
BTW, the amount of energy needed to fully charge a battery will be significantly over the nominal capacity, due to inverter inefficiencies, waste heat generation, cooling if necessary, and charging speed. A fast charge will create more wasted heat, while a slow charge (like 32 A) will be much more efficient.
zanary
Active Member
Nice explanation. I think this explains why I see these values.
I have a September 2007 Model S P100D around 34000 miles.
Using one of those tools on Android to read diagnostics data from that special cable under the cubby, I see the following
- Nominal Full Pack = 90 kWh
- Usable Full Pack = 85 kWh
- Energy Buffer = 5 kWh
BTW, it shows the following which is very interesting as well
- Discharge Cycles = 202
- Charge Cycles = 214
- DC Charge Total = 6687 kWh
- AC Charge Total = 7596 kWh
- Regen Total = 4983 kWh
zanary
Active Member
I have often wondered about this. My Zoe charges to 100% indicated, but still gives 5-10 kW regen going down a long hill near my house. Regen does drop off eventually, but it must be pushing the battery over 100%.
Since the notion of 100% seems in reality just a measure of the limits the manufacturer is prepared to push the technology to, what are you actually entitled to? It seems you are just buying a certain design of battery with a certain number of cells.
So if Tesla subsequently decide you will get better service from your battery by changing the operating parameters, you would presumably be OK with that.
Since the notion of 100% seems in reality just a measure of the limits the manufacturer is prepared to push the technology to, what are you actually entitled to? It seems you are just buying a certain design of battery with a certain number of cells.
So if Tesla subsequently decide you will get better service from your battery by changing the operating parameters, you would presumably be OK with that.
Tesla batteries are degrading in the similar fashion like all the other manufacturers. The non existing degradation is a myth based on comparing rated miles at % charge. This number changes all the time with various updates and is useles when considering battery degradation.
Not all others, no. Certain companies decided they don’t need to thermally manage the pack, and those cars suffer far faster degradation than the companies that take proper care of the packs.
If Nissan sold your car with less than full volts at 100% so you can regen that's legal and OK - your car was EPA rated with a cap in place and sold with a cap in place, you have exactly what you bought on day 1.
Tesla rated and sold our cars with full 4.2v 100% charge. We bought them with those stats. They later de-rated them, which is illegal. Not just individual theft from each of us, but also federally EPA fraud illegal as well.
You are entitled to exactly what you purchased, as advertised. You are buying cells that were tested and advertised to charge to a specific voltage at 100% that was capable of meeting federally tested numbers. Volt capped batteries must be either tested with the cap in place and sold that way, it is theft and fraud to cap after the fact.
And these known crimes (established fact) were probably instituted for a reason. If that reason was fire mitigation like Tesla said the day it released 2019.16 and started downgrading us they committed some much more serious federal crimes in hiding dangers and concealing a recall notice from the NHTSA. If they did it to avoid warranty claims it's Magnusson Moss violation - yet another federal crime.
The best we can hope for from Tesla as far as the motivation behind them committing federal fraud and grand theft is that they did it out of malicious spite and nothing more. If they only did it to be mean to us, the criminal charges end with them being punished for the crimes they are already caught committing. It gets worse if they were telling the truth when they said they were "revising charge and thermal management" settings in response to fires because that public statement shows the downgrades were intended all along to be secret safety law dodging shenanigans and everything since has been lies to conceal some crimes that could rock the company's future.
doghousePVD
My grandfather’s car
I read of people checking their voltages as a indication of SoC, which can be very misleading. If a battery is being fully charged, the voltage is high, higher than the battery at rest. After the charging circuit is disconnected, a few hours later the voltage will drop to its resting full voltage, even if there is no vampire drain. Conversely, if the battery has been discharged very rapidly, the voltage will drop. A few hours later, the voltage will rise to its resting voltage.
Ideally, voltages should be measured after the battery has rested with no discharge or charge for several hours. That is impossible in a Tesla, since the battery is always discharging to maintain battery temperatures, recharge the 12 volt subsystem, data communication, and other vampire loads. These loads are quite volatile; listen to the changes in noise of battery cooling system after charging.
Optimal battery voltages are also temperature dependent. The SMS is measuring the cell temps, and adjusting the voltage for charging and full. Even with the thermal systems built into the packs, the temperature is not always constant, not necessarily uniform through the whole pack.
None of the chatter I see here seems to realize the "squishiness" of battery voltage and SoC numbers. Excessively focusing on precisely 4.2 V per cell is not a useful exercise, and is bad for your blood pressure.
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