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New Charging Regime on Home Wall-Charger

Testicle

Member
Jan 12, 2020
7
2
England
I have a 2014 P85, recently at the Service Centre for over a month, for an MCU-1 repair/replacement.
Current firmware: 2020.32.5
I have noticed that the car now does a top-up charge every 3:16hours, instead of the usual two day period.

This seems like a good idea, since it should prevent the 12V battery from being hammered and needing replacement every two years. I'm on my third battery and have an imported lithium unit for the next failure.

Has anyone else noticed this new behaviour?
 

Testicle

Member
Jan 12, 2020
7
2
England
Powerwall1.jpg
 

beatle

Member
Aug 31, 2019
991
472
Springfield, VA
I'm still on 2020.32.3 and have not noticed that behavior. The HV pack has nothing to do with the charge of the 12v. The 12v will charge up from the HV pack whenever its voltage gets low, and the HV pack seems to only charge up when it's a little more than 3% off its desired charge capacity.
 

Testicle

Member
Jan 12, 2020
7
2
England
I'm still on 2020.32.3 and have not noticed that behavior. The HV pack has nothing to do with the charge of the 12v. The 12v will charge up from the HV pack whenever its voltage gets low, and the HV pack seems to only charge up when it's a little more than 3% off its desired charge capacity.

The HV contactor has to close to charge the 12volt battery and only did so when the 12volt battery was fairly-well discharged. It is this heavy cycling of the battery that is responsible for its very short lifetime. The battery in an ICE vehicle has to withstand heavy cranking currents and yet still lasts ~5 years. Now that the HV battery is accepting charge every 3.25 hours, the 12volt battery should receive more of a float charge and hence a longer life.
 
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beatle

Member
Aug 31, 2019
991
472
Springfield, VA
Are you saying that the 12v battery charges whenever the HV pack charges? I realize the HV contacts have to close to charge the 12v, but I don't believe the 12v charges at the same time unless it drops below its low voltage threshold.
 

Testicle

Member
Jan 12, 2020
7
2
England
Are you saying that the 12v battery charges whenever the HV pack charges? I realize the HV contacts have to close to charge the 12v, but I don't believe the 12v charges at the same time unless it drops below its low voltage threshold.
The purpose of my post was to draw attention to the new charging behaviour and ask if others had noticed it. I don't know why Tesla has changed their strategy, but since the contactor must be closed to charge the HV battery, it follows that the 12 volt battery is now able to be charged. It makes sense to do this, but I don't know. By alerting others on this list, maybe we can determine if this is indeed the case.
 

serendipitous

Member
Sep 10, 2019
342
496
Maryland, USA
I have a 2014 P85, recently at the Service Centre for over a month, for an MCU-1 repair/replacement.
Current firmware: 2020.32.5
I have noticed that the car now does a top-up charge every 3:16hours, instead of the usual two day period.

This seems like a good idea, since it should prevent the 12V battery from being hammered and needing replacement every two years. I'm on my third battery and have an imported lithium unit for the next failure.

Has anyone else noticed this new behaviour?

I noticed this recently as well on my 2019 Raven MSP. I hear the HV contactors and wall connector relay click every few hours now (my office shares a wall with the garage). TeslaFi does not report this as Charging - it just looks like an idle - however the app shows Charging (e.g. from 80% -> 80%). My car has never slept for very long, though - I have noticed for many months that my car will sleep for exactly 1 hour, wake up for a few minutes, and then go back to sleep for 1 hour.

And to answer the other poster's question - yes, when the HV battery contactors are closed (in other words, when the car is not asleep), the DC-DC converter powers all of the 12v accessories, and charges the 12v battery. When the car goes to sleep, the contactors open and the 12v system is on its own, drawing from the 12v battery.
 

Testicle

Member
Jan 12, 2020
7
2
England
Since reading how Tesla are actively discharging batteries held at SoCs greater than 78%, I've dropped my SoC setpoint to 76%. I now notice that the cycling period is 7 to 8 hours, with a very tight tolerance on the setpoint. I think they have significantly reduced the hysteresis, which results in far more frequent charging; altogether a good thing.
 

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