Warm charging vs. Off-peak in winter

[clack]

Wanted to share an observation that caused me to switch from off-peak charging (middle of night) to charging immediately after parking. It's nearing winter in New England, so temps are dropping to 30-35 degrees F at night. When set to off-peak charging, with scheduled departure at 6:45am, charging starts between 2:30am and 3am. I typically have 20-30 miles of range to charge up, so maybe 6-8kW needed to charge up. If I charge immediately after parking during the day, I get 95-98% efficiency. If I let it wait until off-peak hours and charge in the iddle of the night, I get 50-55% efficiency. A lot of wasted power warming up the battery to get ready to charge off-peak.

Long story short, if you live in a colder climate, charging after a drive when the battery is already warm may be much more efficient. Highly recommend trying both and seeing what works better for you!

 

[Sophias_dad]

In that position I'd charge once a week or something, in the middle of the night.

Where in New England are there TOU rates?

 

[jcanoe]

Wanted to share an observation that caused me to switch from off-peak charging (middle of night) to charging immediately after parking. It's nearing winter in New England, so temps are dropping to 30-35 degrees F at night. When set to off-peak charging, with scheduled departure at 6:45am, charging starts between 2:30am and 3am. I typically have 20-30 miles of range to charge up, so maybe 6-8kW needed to charge up. If I charge immediately after parking during the day, I get 95-98% efficiency. If I let it wait until off-peak hours and charge in the iddle of the night, I get 50-55% efficiency. A lot of wasted power warming up the battery to get ready to charge off-peak.

Long story short, if you live in a colder climate, charging after a drive when the battery is already warm may be much more efficient. Highly recommend trying both and seeing what works better for you!

The missing part of the equation is what happens after charging completes. If you charge immediately upon returning home then the battery will warm from driving. If you normally precondition in the A.M. before leaving home the battery pack will have cooled overnight. Depending on the temperature preconditioning will require additional power to warm the passenger cabin and warm the battery pack (Tesla has tweaked the preconditioning routine in version 2021.40.6 to be more efficient with battery warming, i.e. "when using climate controls on the Tesla App, automatic battery pre-conditioning has been optimized to consume less energy.")

If you charge using Level 1 then you should probably start charging immediately upon arriving home, especially in winter, as charging will take more time and you have relatively little power available (1.4kW) on a 120V/15A circuit with which to charge so you don't want to be using power to warm the battery if you can avoid it.

 

[andaconda]

I usually let the car get down to around ~40% - then after a drive and I get home I'll plug it in right away. Charge up to about 80~85% and then on my next drive I unplug it. It may be a day or two or three before its unplugged. Rinse / Repeat...

 

[clack]

In that position I'd charge once a week or something, in the middle of the night.

Where in New England are there TOU rates?

After seeing your comment, I did a search and looks like residential has the same delivery charged around the clock where I live, so no financial benefit to charging off-peak.

In any case, I'm now letting it charge immediately when plugging in and seeing 96% efficiency on average. Curious to see what happens when the temps get lower into the 0-10 degree F range.