Strange charging behaviour

Wol747 said:

After 2021.4.12 on my S I have an odd charging behaviour.
At home I keep it plugged into the HVWC and the SOC set to 70%. After the update there is the usual clanking of contactors and fan whirring about every three or four minutes, the car charges for a minute or so then stops until the next charge starts in three or four minutes.
I'm wondering if something's changed in the bug fix update which makes it keep at exactly the set charge state. I would expect that the program would allow the SOC to slip a little below that set before charging up to slightly over to avoid almost constant reconnection.

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You might want to confirm one thing. Do you have charging set to start at a specific time or the be charged by a set time for departure? In my case I do not have any of that turned on. It will start charging whenever I plug in and the SOC is below my set point. I used setting to start charging at a specific time for several years, but turned all that off several months ago when I started to get signs my MCU1 might be getting flaky (didn't want to get caught with a failed MCU and unable to charge at home).

I started noticing last year the behavior you describe where as soon as the SOC drops below the setpoint, so 1 percent SOC loss, it automatically starts charging again. I forget what release that was, but well before 2021.4.12. Previously it wouldn't trigger to start again unless it fell about 3 percent or so below the limit.

Personally, I don't care for the new behavior. This is one of the reasons that I've now gone to not charging every day, but manually control when I change by keeping the setpoint at 50%, then when I want to charge to say 70% - 90%, I manually raise the limit up, let the car charge, and soon as it finishes, reset back to 50%.

I know vampire drain increased significantly as a result of some of the changes/feature the past couple years which keep the car on more of the time (sentry, summon on demand, climate overheat protection, etc). I don't know if this change somehow is a way to mask vampire drain/loss when people are plugged in at home? Or counter all the people that I've seen complain that I had my car set to charge to 90%, but when I went to leave is was at 87-88% and complaining as if something went wrong and it wasn't charging to the correct value. Either way, I'm not a big fan of it personally, but I know how to manage it in a way that it doesn't impact me any more.

Hi All,

Check out this similar thread...


My wife's 2015 Model S will start to charge every 30 minutes or so without any decrease in displayed percentage.

I'm worried for an internal contactor that is chattering...

Shawn

@Wol747 I also wonder if this change where they appear to continually be topping up the HVB may also be related to change in strategy around how they manage the 12V battery. I've not done an extensive amount of digging, but my casual understanding is anytime the contactors would make contact and the HVB system is alive means that they also would be directly powering the DC to DC converter to supply other systems. That means not drawing from the 12V battery, and actually topping the 12V battery up. If that is indeed the case, then this would be eliminating the deep cycling of the 12V battery, greatly extending its life.

Not sure if that's an intended long term strategy, a short term one to mitiate current situation with 12V battery in very tight supply (not just a Tesla issue), or totally unrelated. However, it does seem like it would be another impact of this change in how frequently they top up.

I'm now have similar behavior with 2021.4.12 on my LR 2018 S. Every 1 to 2 hrs, I get charging started, then a minute later, charging completed. No change in available range. My local Tesla Service center replaced the onboard charging unit, but I still have the same behavior when connected to my Tesla Wall Charger.

The Service Technicians are stumped. I think it's a botched software update.
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RedSky said:

I'm now have similar behavior with 2021.4.12 on my LR 2018 S. Every 1 to 2 hrs, I get charging started, then a minute later, charging completed. No change in available range. My local Tesla Service center replaced the onboard charging unit, but I still have the same behavior when connected to my Tesla Wall Charger.

The Service Technicians are stumped. I think it's a botched software update.
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I've pondered since I first noticed this a couple months ago whether it was botched or potentially an intentional change in the charging strategy. I have no inside information to know this is why Tesla might have one this, but two reasons I can hypothesize are:

1) This would give the appearance of eliminating or reducing parasitic loss when car is parked and plugged in. The magnitude of parasitic loss is much greater now if you leave features such as cabin overheat protection, sentry, or summon enabled when at home. While the charging strategy doesn't actually reduce the loss, it make is not as obvious as when you go out to your car a day later it's still at the same level where charging stopped.

2) This may actually help reduce in stress/deep cycling on the 12V battery and prolong 12V battery life. That may have become a bigger priority given the number of 12V replacements which Tesla has likely been doing on warranty plus are issues with supply shortages at the moment. My hypothesis for how this helps the 12V is that any time the contactors engage to charge the HVB it will also be supplying power to top up the 12V battery.

Both of those could be reasons for this change being intentional, and not a botched software update. I also didn't track the exact update where I first started to see this, but is was a couple updates ago for me, so sometime latter part of last year.