M3 2021 Calculated charging time way off

[EV Promoter]

Charging from 60% to 80% limit.
That is from 320 km to 425 km.
Charging at 11A-220V = 16 km/hr shown on screen.

Remaining time 11 hr 10 min on screen.
But to charge 105 km @ 16 km/hr it takes just 6,56 hr.

Now, after a while, 330 km - 10h 15 min.

What's wrong?
2020.44.25

 

[SSedan]

Did it have to warm the pack first?
If you were sitting in it power get diverted to the HVAC reducing charge speed.
Once you get out full power goes to charging and it charges faster.

 

[EV Promoter]

No, the car was Parked in a garage, 11° C , and locked, no Hvac running or anything else.

But something changed: 1 hour after the start, suddenly the calculated time was spot on to the minute.

Why for one hour was off of +4 hours?
Not very pratical to always do the math by hand to know when the charge will end...

 

[camalaio]

No, the car was Parked in a garage, 11° C , and locked, no Hvac running or anything else.

But something changed: 1 hour after the start, suddenly the calculated time was spot on to the minute.

Why for one hour was off of +4 hours?
Not very pratical to always do the math by hand to know when the charge will end...

There's a bunch of reasons the time can vary and be "wrong", but usually the km/hr value would indicate this.

At 11C it's possible your battery was a bit colder and the car was indeed heating it. Problem with that theory is that it would show less km/hr then (because for AC charging, the displayed km/hr or mi/hr is the net positive power going into the battery). This could've been something they changed for 2021 models, but that would be a bit weird...

Not really sure, honestly. But you're correct anyways - going by time left can be pretty inaccurate in certain scenarios.

 

[EV Promoter]

@camalaio the km/hr was remarkably constant at 16 since the start to the end, and your consideration (interesting) that the consumption of some battery heating should have appered as a reduction in speed, rules out the thing.

I can add that the phenomenon is not occasional, but this is the first time i do some math on it.

Weird, the error in % on such a simple calculation doesn't make sense... 1 hour to correct it it's mysterious.....I have no history (brand new) to judge if is related to the update, unfortunately.

It would be interesting to know if anybody did similar checks.

 

[Gasaraki]

The BMS tries it hardest to calculate time to "fully charge" based on best guesses on the current battery level, the max battery level, the level that you want to charge to, etc, etc. When you first charge it's guesses might be way off. Your battery heats up as it charges, which causes the battery level to change. The input current might not be steady when you first plug in. And potentially million other reasons.

By one hour, it has a pretty good idea based on the conditions of the last hour.

 

[EV Promoter]

The BMS

Hard to understand the sense of such generic comments.

The BMS calculated, since the first seconds from the start, the correct charging speed, 16 km/hr.
And the same was shown during the entire charge.

Is this value that can fluctuate, but was spot to calculate a precise remaining time.

Starting and final charge in % were of course a fixed and known values.

4 hours of difference in projected time is out of any logic with this scenario and is not very logic outside a very large bug.

 

[EV Promoter]

It was a bug.

Updated to 2020.48.10
Reset 2 wheels + pedal
Shut-off from screen & locked the car
Left 1 hour without interference.

Problem solved. Precise prediction of charging time since the very start.

Notice that the problem was still there when the update was installed.
Only after the "procedure", it was sorted out.

 

[EV Promoter]

Joking.

Today again, after 1,30 hr charging, calculation 7 hrs off..... how to report to Tesla? Service will do nothing...