25% slower Supercharging due to degradation

[hacer]

Maybe an insignificant amount, but doesn't the BMS mitigate some of this?

Not really. The balancing circuit can provide a current bypass path shunting a bad cell, however this can handle only quite small currents and is only activated when the battery is nearly fully charged. It does nothing during discharge. It does provide the ability to prevent overcharging of the 71 good cells but that neither changes the max current the string is capable of nor the ability to extract energy from the other series elements once the bad segment has reached its low voltage limit.

 

[David99]

Quick update.
I've added several Supercharging sessions to a chart. The top blue line is an 85 battery when it is relatively new. the other lines are various charging sessions with much higher mileage on the battery. There is some variations but clearly it is slower than it was. It starts at about the same power level, then drops faster and earlier. The difference is 10-15 kW. As the battery fills up the difference gets a little smaller. Again, what I used to calculate the time difference was how long it takes to add 40 kWh (the typical average amount of energy needed between two Superchargers).

Here is the same graph but I added the Model 3 LR (blue line). Looking at it this way shows that the Model 3 has a huge advantage in terms of charge speed. It doesn't draw more power, but it keeps that power level for much long adding energy into the battery much quicker! Awesome job Tesla!

 

[David99]

David,

Nice to hear that it's not that. One other thought on how Tesla might be calculating the taper. I know you showed your graph of the charge rate against %charge. What if the formula they use uses remaining capacity of the battery rather than %charger to decide on the taper. It would almost make sense for them, they would have one formula that could work for all the various battery sizes without worrying about keeping separate specialized ones. With your capacity loss, it almost feels like those curves might overlay after being re-normalized, )I would do it but I don't have the raw data you do.) -Peter

That's a great idea. I did a quick calculation on a paper and as I expected, it accounts for aprox 10% difference. So yes the reduced capacity requires me to charge to a higher level where charging is slower. The other part is Tesla reducing the rate due to battery aging. Maybe it's the internal resistance that is increased or them just being more careful after having more data from the batteries out there. The only way to test this is there was a new 85 pack available. But it's been discontinued for a while now.

In 4 years we will know if the new 100 packs of the Model 3 will show similar behavior.

 

[oaito]

Hi!

I'm aware that this thread was dormant for a long time. Nevertheless, were you successful in determine whether battery degradation (slow and linear changes) or updates to the BMS/firmware (sudden changes post f/w) had have which impact over time?

I'm asking for experience before the so called #chargegate or #batterygate, since I'm trying to establish a baseline before these more recent changes.

I myself started logging data through teslalog.com in May 2017 at ~81385km or ~50570,4m though I've a lack of comparison data.

BR, Patrick.

 

[David99]

Hi!

I'm aware that this thread was dormant for a long time. Nevertheless, were you successful in determine whether battery degradation (slow and linear changes) or updates to the BMS/firmware (sudden changes post f/w) had have which impact over time?

I'm asking for experience before the so called #chargegate or #batterygate, since I'm trying to establish a baseline before these more recent changes.

I myself started logging data through teslalog.com in May 2017 at ~81385km or ~50570,4m though I've a lack of comparison data.

BR, Patrick.

It happened over a long period of time, gradually, not suddenly. Recently the charge rate has been reduced even more.