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Precondition car plugged in vs not plugged in

Darthbenji

Active Member
Mar 27, 2018
1,003
594
Ontario
Is there any difference between preheating the car while plugged in vs unplugged? In my experience the heating doesn’t run off of the wall power, it simply drains the battery. The battery doesn’t charge while heat is on. So if I want to leave with 90% and a warm car I need to actually charge to 92% and burn off 2% heating it. Being plugged in seems to make no difference. Is this the experience of others?
 

Darthbenji

Active Member
Mar 27, 2018
1,003
594
Ontario
Just warmed up for a drive. Started at 83%. Leaving and it’s at 81%. Plugged in the entire time. This notion of shore power seems to be a myth. Unless I’m doing it wrong. Me experience is you need to overcharge to compensate for preconditioning the cabin.
 

jalatontarzan

Member
Oct 27, 2019
17
33
Finland
When preconditioning from shore power the car can pull up to 11kW. So if your wall connector cannot supply that, the battery will supplement. I charge at 32 amps at 238v and lose 1% in 15 min preconditioning. I imagine if I charged at 48 amps I wouldn’t lose any.
It can pull more than 11kW, closer to 14kW. Because preheating from the app also activates battery heater which takes 7kW (LR models), cabin heater 6kW and rest for the computers, seat heaters and so on. Sucks if you need every last drop of range in colder climate and also need to defrost windows. Sucks extra hard if you have less than 11kW charger because even that cannot keep net draw positive. Only solution is to go and activate cabin heater from car since that doesnt activate the battery heater. Would be awesome to have option for battery heater in app.
 

Darthbenji

Active Member
Mar 27, 2018
1,003
594
Ontario
When preconditioning from shore power the car can pull up to 11kW. So if your wall connector cannot supply that, the battery will supplement. I charge at 32 amps at 238v and lose 1% in 15 min preconditioning. I imagine if I charged at 48 amps I wouldn’t lose any.

This is my setup as well.
 

sightman

Member
Jul 25, 2020
99
116
Quakertown, PA
It can pull more than 11kW, closer to 14kW. Because preheating from the app also activates battery heater which takes 7kW (LR models), cabin heater 6kW and rest for the computers, seat heaters and so on. Sucks if you need every last drop of range in colder climate and also need to defrost windows. Sucks extra hard if you have less than 11kW charger because even that cannot keep net draw positive. Only solution is to go and activate cabin heater from car since that doesnt activate the battery heater. Would be awesome to have option for battery heater in app.

thanks, didn’t realize it was that high. Another reason to convince the boss lady to let me buy the 48 amp wall connector
 

medphys3

Member
Feb 10, 2020
45
20
Northwest Ohio
Your experiences are different than mine. I use a 3rd party charger that only draws 16 amps. When the car is preconditioning (cabin and battery), the car display shows that the car is pulling 16/16 amps, but charging rate is only 1 or 2 mph. So the charger is clearly providing power to the car for preconditioning. And I always have my 90% ready to go.

This is with the new software 2020.48.30. I never really paid much attention to it before this version.

2019 LR RWD
 
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jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
7,777
8,596
Riverside Co. CA
@camalaio has the most knowledge around this specific topic that I have seen here on our boards. Tagging him here in the hopes he can copy / paste info he has posted on "shore power" before.
 

drtimhill

Active Member
Apr 25, 2019
1,610
1,919
Seattle
Is there any difference between preheating the car while plugged in vs unplugged? In my experience the heating doesn’t run off of the wall power, it simply drains the battery. The battery doesn’t charge while heat is on. So if I want to leave with 90% and a warm car I need to actually charge to 92% and burn off 2% heating it. Being plugged in seems to make no difference. Is this the experience of others?
Hmm whenever I preheat it certainly triggers the car to draw power from the wall.
 

Peteski

Active Member
Oct 2, 2017
3,517
2,275
UK, Milton Keynes
My 2018 MX seems to allow the battery to drop a few percent in the garage before starting to charge again from the mains. So if I charge to 80% and leave it sitting in the garage it will slowly drop to something like 77% before topping itself back up again to 80% from the charger. No idea if that still applies when pre-conditioning the cabin, or whether it immediately start to charge. I haven't paid enough attention, but I do set my target charge to around 83% to guarantee leaving with at least 80%. No data on our M3 to compare yet.
 

drtimhill

Active Member
Apr 25, 2019
1,610
1,919
Seattle
My 2018 MX seems to allow the battery to drop a few percent in the garage before starting to charge again from the mains. So if I charge to 80% and leave it sitting in the garage it will slowly drop to something like 77% before topping itself back up again to 80% from the charger. No idea if that still applies when pre-conditioning the cabin, or whether it immediately start to charge. I haven't paid enough attention, but I do set my target charge to around 83% to guarantee leaving with at least 80%. No data on our M3 to compare yet.
Yeah my guess is there is some hysteresis on charging triggering which is what is being seen here.
 

akenham

M3 LR AWD+ 2020
Sep 19, 2020
71
77
East Anglia, UK
[edit: for context, 2020 AWD with PTC / no heat pump, wall charger = 32A / 7kW ]

It depends on how you ask the car to preheat in my experience - there are two routes via the app:

  1. Climate on - either
    - hit the fan button on the front page of the app
    - hit the "climate on" button at the bottom of the climate page of the app
    => causes the climate to warm up to the current AC set point, 21 deg C for me
  2. Defrost - the screen heater symbol at the bottom of the climate page of the app
    => causes the climate to go to a "HI" setting and give it 100% - this even blows hot air out past the door handles to de-ice them.
Both cause my car to draw power from my tesla wall connector (chasing lights) which can supply up to 7kW / 32A

Using (1) very rarely consumes any battery in 30 minutes preconditioning at UK winter temps (-3 to +5 deg celsius)
Using (2) always uses a few % of battery.

Both cases warm the battery - I have full regen after preconditioning; if I skip doing it I have reduced regen and/or a snowflake symbol at present ~zero temperatures.

My interpretation is that my battery preconditioning is consuming most of the ~7kW shore power - using (1) just warms the cabin and isn't at 100% for very long whereas (2) goes all guns blazing and far exceeds what the wall can provide.

I have always found (1) sufficient except in very extreme conditions (snow, heavy icing) so that's my go-to.
 

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Peteski

Active Member
Oct 2, 2017
3,517
2,275
UK, Milton Keynes
Yeah my guess is there is some hysteresis on charging triggering which is what is being seen here.

Yeah, which I've always thought makes sense otherwise the charger would be constantly switching on/off. Which I imagine is not very good for it. With the 3% hysteresis, it basically just tops up briefly roughly every 24 hours if left parked up in the garage.

What I don't know is what happens when I switch on the heating. Does it still wait until the battery drops below the hysteresis level or does it immediately start charging to compensate for the heater? From the above post it sounds like the charger kicks in straight away.
 

android04

Member
Apr 1, 2016
347
325
Crete, Nebraska
Yeah, which I've always thought makes sense otherwise the charger would be constantly switching on/off. Which I imagine is not very good for it. With the 3% hysteresis, it basically just tops up briefly roughly every 24 hours if left parked up in the garage.

What I don't know is what happens when I switch on the heating. Does it still wait until the battery drops below the hysteresis level or does it immediately start charging to compensate for the heater? From the above post it sounds like the charger kicks in straight away.
In my experience, it seems like Tesla changed the behavior in a recent software update. I remember in the past if I turned on the heater or AC and the car was plugged in and already charged to it's set point, the contactors would close and it would draw power from the High Powered Wall Connector (shore power). Recently, I noticed that this was not the case. My guess is that Tesla updated the behavior to only draw power from the battery when it's cold so that the pack heats up faster and you get more regen.

BTW, I don't always precondition. But I've had my Model 3 since April of 2018 and have 53k miles on it.
 

akenham

M3 LR AWD+ 2020
Sep 19, 2020
71
77
East Anglia, UK
In my experience, it seems like Tesla changed the behavior in a recent software update. I remember in the past if I turned on the heater or AC and the car was plugged in and already charged to it's set point, the contactors would close and it would draw power from the High Powered Wall Connector (shore power). Recently, I noticed that this was not the case. My guess is that Tesla updated the behavior to only draw power from the battery when it's cold so that the pack heats up faster and you get more regen.

BTW, I don't always precondition. But I've had my Model 3 since April of 2018 and have 53k miles on it.

I precondition every drive and my car is way above its charge set point (I've reduced it due to covid lockdown) and it's still drawing from the wall connector as usual (2020.48.26).

I wonder if something else is going on - maybe the new "off peak hours" setting (I use the "begin charging at..." )
 

android04

Member
Apr 1, 2016
347
325
Crete, Nebraska
I precondition every drive and my car is way above its charge set point (I've reduced it due to covid lockdown) and it's still drawing from the wall connector as usual (2020.48.26).

I wonder if something else is going on - maybe the new "off peak hours" setting (I use the "begin charging at..." )
I also have been using the "Begin charging at" option. What have been the temps for you? Mine have been below the temp setting where the charging connector will not lock in if not charging.
 

SigNC

Active Member
Aug 23, 2017
1,466
1,278
NC
Your experiences are different than mine. I use a 3rd party charger that only draws 16 amps. When the car is preconditioning (cabin and battery), the car display shows that the car is pulling 16/16 amps, but charging rate is only 1 or 2 mph. So the charger is clearly providing power to the car for preconditioning. And I always have my 90% ready to go.

This is with the new software 2020.48.30. I never really paid much attention to it before this version.

2019 LR RWD

Your car also can't pull as much power for battery heating as an AWD as it only puts 3.5kW into the battery for heat instead of 7. However, 3.5+ the PTC heater for the cabin is still more than the ~4kW that wall charger can provide. However, once the cabin gets warm the power requirement for the cabin will drop off considerably and you likely have about 500w surplus.
 

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