How does scheduled charging work?

[willow_hiller]

Last week, we decided to save a few fractions of a cent per kWh by setting our Model 3 to a scheduled charge at midnight with a limit of 90%. When we went to drive the car the evening of the next day, the battery was down to 88%. It was a hot day, so I figure it may have used some charge cooling off with Cabin Overheat Protection.

I was under the impression that the Model 3 used power from the mains as long as it was plugged in. (E.g. if you preheat your Tesla in the winter while it's plugged in, it won't have an impact on your battery). Is this true? And is it still true while scheduled charging is on?

 

[willow_hiller]

And maybe one addendum question, assuming a base amount of vampire drain per day, would leaving a Model 3 on scheduled charging mode cycle the battery faster than not?

 

[animorph]

It will usually let the battery run down to about 3% and then charge at the next scheduled time. Or it might start a few hours later than scheduled if it reaches that level just after the scheduled time. Some people have had it recharge at 1%, but mine's been very consistent.

It uses mains power only when you turn the car on or start the climate while plugged in. Not for normal vampire losses.

Typically my X does a scheduled charge every three days or so if I'm not using it. I haven't followed our 3 as closely, but I think they're the same.

 

[Mr Vader]

also have to consider at what time the charging time is scheduled to stop.
for example: if you have if from midnight to 7am, but you don't start driving the car until 8am, there will be some vampire drain for Sentry (if enabled), cooling or heating and plain and simple loss of energy...and since the scheduled charge was meant to stop at 7am, even with the cable connected, it won't self replenish.

 

[srs5694]

It uses mains power only when you turn the car on or start the climate while plugged in. Not for normal vampire losses.

I have a J1772 EVSE with JuiceNet software, so I can monitor how much electricity my car is drawing.

When my Model 3 had software version 2019.8.x, it would begin charging for a minute or so roughly every hour when plugged in. It would also not sleep when plugged in, which greatly increased vampire losses. My presumption was that the car was drawing electricity whenever the charge dropped far enough below the set charge rate, but I don't know that for a fact. I upgraded to 2019.12.1 this morning, and this behavior has changed; the car now sleeps after a charge is complete, even if it's still plugged in, so it's not drawing more power every hour. (I haven't yet left it plugged in but unused for the half-day or day I'd expect to be required for significant sleeping vampire drain to occur, though.)

Also and FWIW, after I took delivery (a month ago), I spent some time with the car plugged in, but with me sitting in the car studying the controls. The AC turned on, and when I later examined my JuiceNet data, I saw that the car was using electricity delivered from the EVSE at a lower rate (about 2kW, from memory) after charging was complete, presumably to power the AC and computer directly from the mains, rather than involving the battery.