New error message seen this week.

[meteosat007]

I have a PW3 with expansion pack and have started to see this error below and could not see anything on Google.
Does anybody know what it refers too?

Not thinking its a Powerwall Dashboard issue.

BMS_a021_SW_EOC_SOC_Correction

[meteosat007]

AI did find this but related to car BMS!

[jasonacox]

Nice! thanks for posting.

[mcbirse]

Hey @meteosat007

The BMS_a021_SW_EOC_SOC_Correction alert will be active when Powerwall 3 systems are performing a battery calibration.

I believe it will occur periodically (and automatically / aka out of our control) since a calibration is required for LFP battery chemistry to maintain accurate state of charge values.

When active, you should see something like below in the Tesla App:

And in Powerwall Dashboard, you will see your battery charge percent going down, and as below - likely it will discharge below your reserve all the way to zero.

So don't panic if you think your system has stopped charging when it should be! (like I did briefly the first time I saw this). Check for the alert or in the app for the calibration message.

[mcbirse]

You're welcome Jason.

My new Powerwall 3 system did the calibration almost exactly 2 months after the install.

So, you could possibly expect yours to the do the same around then. It seemed like a 2 month scheduled event to me.

[JohnJ9ml]

These are every two month events. Alas, they don't give you any warning: Surprise! We're calibrating! I wish I new in advance, because I would do things like charge the car and let it happen off the batteries - certainly a better budgetary use of the battery juice than selling it back to PG&E at a pittance and then buying it all back again.

The calibration also never feels like they think about doing the buy side / charge side of the equation when the electrical price is cheap - I've found myself at rock bottom when 4pm rolls around, or still charging back up from the grid during high side pricing.

[jasonacox]

Wow - this is no joke. The calibration can be pretty heavy! Push 13.4 kW from my two Powerwall 3's.

[mcbirse]

Wow - at least the calibration would have completed quickly?

Mine took a while (per graph) as it discharged slowly down to zero.

Guessing this is due to my settings restricting export to grid (except from solar)... might have to look for that setting. Or, it could operate differently depending on the mode, i.e. Self-Powered (my current setting) vs Time-Based Control?

[jasonacox]

Yes, it was fast! And good point. I'm using Self-Powered, but I do allow battery export to grid. All I can say is... it sure does! ;)

In my case, it drained the batteries to 8% and didn't start charging up to reserve setting for an hour.