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Preconditioning

Hi Everyone,
I am new, a "newby" as you refer to new owners of Tesla. I am enjoying my new Tesla model Y. I live in Coold coold New Hampshire, and I get about 70% of 316 full charge driving on a full charge, and this is expected.
The term "Preconditioning" keeps coming up in the forum, and I need to know how to precondition before a long trip, or even a short 40-50 mile trip. Does it mean to pre-heat the car for 10 minutes? I do this every morning before leaving for work, and I charge once or twice a week, but I don't need to plug it in every night. (240 plug) I took delivery last September and love it more and more each day.
Thanks - great forum by the way.
 

jcanoe

Well-Known Member
Oct 2, 2020
5,555
6,108
Maryland
Yes, what you have been doing is preconditioning the Tesla before you drive. There is no rule for how long but for maximum comfort consider preconditioning for 20 minutes or longer in cold weather.

At colder temperatures preconditioning will warm the battery pack. A cold battery pack cannot be charged, cannot accept power from regenerative braking. At colder temperatures the battery pack's ability to deliver full power is impacted. If you see one or more snow flake overlays on the battery icon on the Tesla app main screen then you will know that the battery should be warmed. If you see a red battery icon appear on the Climate Control screen within the Tesla app while preconditioning then the Tesla is actively warming the battery pack.

For passenger comfort set the HVAC to Auto and your preferred cabin temperature. You can turn on the seat heaters during preconditioning. If you have the latest version of the Model Y you would also have the steering wheel heater.

Since you have 240V charging at home you can precondition while still plugged in without using the battery charge to precondition the Tesla. You don't have to charge every day; when you do charge set the daily charging limit to no more than 80%, up to 90% is ok.

If you use Scheduled Departure the Tesla will automatically start charging early in the A.M. so that charging can complete shortly before you normally leave for work. The battery will be partially warmed up from charging. You can also schedule the Tesla to automatically precondition so that the battery has been fully warmed and the passenger cabin is warm when you leave in the A.M.
 
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Double-check your owner's manual because yours might be newer/older/different. What I read about Scheduled Departure is that it is programmed to stop at 600a (if possible to reach your charging limit before then) and then will heat up/cool down the interior shortly before your pre-set departure time. Look at page 160. I read somewhere that Tesla does this to take advantage of off-peak charging rates (which don't exist where I live).
 

jcanoe

Well-Known Member
Oct 2, 2020
5,555
6,108
Maryland
Double-check your owner's manual because yours might be newer/older/different. What I read about Scheduled Departure is that it is programmed to stop at 600a (if possible to reach your charging limit before then) and then will heat up/cool down the interior shortly before your pre-set departure time. Look at page 160. I read somewhere that Tesla does this to take advantage of off-peak charging rates (which don't exist where I live).
Tesla recently updated the Scheduled Charging and Scheduled Departure setting options. You can now start charging at the beginning of a desired charging window, i.e. 11PM; you can use Scheduled Departure and specify the time that the charging window ends so this is no longer automatically 0600 (your local time.) You can also schedule to precondition the vehicle whether or not the Tesla is plugged in.
 
That's great to know for those of us who don't have off-peak windows. I did not think it made sense to let the batteries cool down only to be heated up again.
Tesla recently updated the Scheduled Charging and Scheduled Departure setting options. You can now start charging at the beginning of a desired charging window, i.e. 11PM; you can use Scheduled Departure and specify the time that the charging window ends so this is no longer automatically 0600 (your local time.) You can also schedule to precondition the vehicle whether or not the Tesla is plugged in.
 

jcanoe

Well-Known Member
Oct 2, 2020
5,555
6,108
Maryland
That's great to know for those of us who don't have off-peak windows. I did not think it made sense to let the batteries cool down only to be heated up again.
I'm not convinced that charging does much to warm the battery beyond the minimum temperature needed to be able to charge. This A.M. I preconditioned my Model Y (not plugged in) for 20 minutes. The driving display showed 5 dots (reduced regenerative braking) after preconditioning. The outside temperature was 25F. I drove about 4 miles and plugged into a free public Level 2 charging station (200V/30A) while I had breakfast. The Model Y charged for 1 hour and 20 minutes. I preconditioned, briefly using the Tesla app, after charging completed. After I unplugged and headed for home there were twice as many dots indicating that the battery was colder than before charging. I noticed the reduced regenerative braking on the drive back home.
 
Hi Everyone,
I am new, a "newby" as you refer to new owners of Tesla. I am enjoying my new Tesla model Y. I live in Coold coold New Hampshire, and I get about 70% of 316 full charge driving on a full charge, and this is expected.
The term "Preconditioning" keeps coming up in the forum, and I need to know how to precondition before a long trip, or even a short 40-50 mile trip. Does it mean to pre-heat the car for 10 minutes? I do this every morning before leaving for work, and I charge once or twice a week, but I don't need to plug it in every night. (240 plug) I took delivery last September and love it more and more each day.
Thanks - great forum by the way.

If you have easy access to a plug, which it sounds like you do, it’s a bit better for the battery to charge nightly. It’s also just nice to know that every day your car is ready to go for any extra need. Since it sounds like you have a short commute, you can just set the charge level to 70 or 80 to be even a bit nicer on your battery.
 
Yes, what you have been doing is preconditioning the Tesla before you drive. There is no rule for how long but for maximum comfort consider preconditioning for 20 minutes or longer in cold weather.

At colder temperatures preconditioning will warm the battery pack. A cold battery pack cannot be charged, cannot accept power from regenerative braking. At colder temperatures the battery pack's ability to deliver full power is impacted. If you see one or more snow flake overlays on the battery icon on the Tesla app main screen then you will know that the battery should be warmed. If you see a red battery icon appear on the Climate Control screen within the Tesla app while preconditioning then the Tesla is actively warming the battery pack.

For passenger comfort set the HVAC to Auto and your preferred cabin temperature. You can turn on the seat heaters during preconditioning. If you have the latest version of the Model Y you would also have the steering wheel heater.

Since you have 240V charging at home you can precondition while still plugged in without using the battery charge to precondition the Tesla. You don't have to charge every day; when you do charge set the daily charging limit to no more than 80%, up to 90% is ok.

If you use Scheduled Departure the Tesla will automatically start charging early in the A.M. so that charging can complete shortly before you normally leave for work. The battery will be partially warmed up from charging. You can also schedule the Tesla to automatically precondition so that the battery has been fully warmed and the passenger cabin is warm when you leave in the A.M.
This statement runs counter to what Tesla recommends. Tesla strongly recommends leaving Model Y plugged in when not in use. In other words, leave the vehicle plugged in at all times. It's on page 160 of the manual in the section titled, Charging.
 

jcanoe

Well-Known Member
Oct 2, 2020
5,555
6,108
Maryland
This statement runs counter to what Tesla recommends. Tesla strongly recommends leaving Model Y plugged in when not in use. In other words, leave the vehicle plugged in at all times. It's on page 160 of the manual in the section titled, Charging.
Yes, this is counter to what Tesla states regarding leaving the vehicle plugged in. Many people either due to circumstances or personal choice do not plug in and charge their Tesla vehicle every day. Many Tesla owners have at some point left their Tesla vehicle parked while away on a trip, in some cases for a month or even longer with no ill effect.

What happens after the battery has been charged and reaches the charging limit that you have set? Nothing. The Tesla does not continue to charge the battery. Also, in cold temperatures the Tesla vehicle does not warm the battery until you initiate preconditioning. Even in warm temperatures if you have cabin overheat protection turned on this only remains active for 12 hours.

My experience with my 2020 Tesla Model Y has been that as long as I do not leave Sentry Mode activated the Tesla will use/lose no more than 1 to 2 % of the battery charge every 24 hours. The 12V battery is able to independently power the necessary 12V systems after the Tesla shuts down (goes to sleep) for ~30 hours. At that point the Tesla will connect the high voltage battery power to the vehicle's 12V power, for a time, and charge the 12V battery.

As far as reasons for not plugging in my Tesla every day these include not driving many miles each day, avoiding unnecessary wear and tear on the charging cord and the charging port. If I drive three short trips am I supposed to plug in each time I arrive back home? No. I have set up Scheduled Departure so that when I do plug in my Tesla vehicle charging will not take place until the early hours of the morning, complete shortly before my planned departure time. As long as I plug in the Tesla before I go to sleep charging will take place at the appropriate time. I always unplug my Tesla if there is a chance of electrical storms in my area.

Tesla wrote the statement about always leaving the vehicle plugged in perhaps 10 years ago when EV ownership was quite new to consumers and owners needed direction and guidance with this new technology. Times change, Tesla owners are much more savvy about charging and maintaining an electric vehicle. Platitudes such as "a plugged in Tesla is a happy Tesla" are just silly. Appliances don't have feelings although my refrigerator is definitely out to get me (can't turn my back on it even for a minute!)
 
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Tesla recently updated the Scheduled Charging and Scheduled Departure setting options. You can now start charging at the beginning of a desired charging window, i.e. 11PM; you can use Scheduled Departure and specify the time that the charging window ends so this is no longer automatically 0600 (your local time.) You can also schedule to precondition the vehicle whether or not the Tesla is plugged in.

Just be aware that if you deselect time-of-use (TOU) rates on the Charging display, the car will start charging as soon as you plug it in. It will still warm the cabin and precondition the battery for your departure time, but you lose any benefit of battery warming during charging. To get around this, select TOU option but set the end time for cheaper rates to be later than your departure. That will cause the charging to be delayed until the morning. The alternative is to select a specific time to start charging, and accept whatever charge level that reaches by departure time. If you do that, you can't select Scheduled Departure on the Charging screen, BUT it now seems that cabin heating can be scheduled on the Climate screen when the car is parked. This appears to be a new feature that I haven't seen any documentation for.
 

jcanoe

Well-Known Member
Oct 2, 2020
5,555
6,108
Maryland
Just be aware that if you deselect time-of-use (TOU) rates on the Charging display, the car will start charging as soon as you plug it in. It will still warm the cabin and precondition the battery for your departure time, but you lose any benefit of battery warming during charging. To get around this, select TOU option but set the end time for cheaper rates to be later than your departure. That will cause the charging to be delayed until the morning. The alternative is to select a specific time to start charging, and accept whatever charge level that reaches by departure time. If you do that, you can't select Scheduled Departure on the Charging screen, BUT it now seems that cabin heating can be scheduled on the Climate screen when the car is parked. This appears to be a new feature that I haven't seen any documentation for.
Heating of the battery during charging is minimal, i.e, the Tesla battery management system will only warm the battery enough so that the battery can be charged without damage. Charging will not warm the battery sufficiently so that regenerative braking will not be limited when you start to drive, almost as limited as if you had not charged at all. The only way to reduce how much regenerative braking is limited due to a cold battery pack is to precondition before driving. In my experience this will take 20 minutes, or longer, depending on the outside temperature if you want to have almost full regenerative braking capability when you start driving.
 

jcanoe

Well-Known Member
Oct 2, 2020
5,555
6,108
Maryland
I have left my Model Y plugged in for several days. After charging the first night to 80% the battery state of charge (SOC) dropped by 5% by the time I used my Model Y. I preconditioned before driving but at 240V/32A the battery SOC should not have dropped by preconditioning. (The battery SOC had dropped by this amount even before preconditioning.) I don't know the protocol but it appears the Tesla battery management system will not top up the battery unless and until the battery pack SOC falls by a specific amount.

I question the idea that when preconditioning while plugged in the Tesla will use mains power instead of using power from the battery pack to precondition. The front and rear drive unit motors are wired to power control modules. The power control module is wired to the high voltage battery. Also, the heat pump operates using a high voltage compressor that draws power from the battery pack. Neither the motors or the heat pump are wired to the onboard charger.

120V or 240V mains power enters the charging port and is sent to the on-board charger. The on-board charger has to step up the voltage to ~400V and then rectify the AC voltage to DC voltage. The rectified power can then flow into the battery pack.

I think of a bath tub analogy where when the Tesla's battery pack is fully charged the bath tub is full of water. When you use power from the battery pack to precondition the Tesla vehicle you are opening the drain and some of the water starts to run out of the bath tub. If the Tesla vehicle is plugged in when you start using a significant amount of power from the battery pack then the on-board charger will draw power via the charging cable, send power into the battery pack to replenish the battery. If you are charging at Level 1 (120V) the faucet is basically trickling water into the bath tub. If you are charging at Level 2 (240V) the water flows into the tub a higher volume. If you are using a Supercharger then the water gushes from the faucet into the bath tub (at least until the tub is more than half full, then the flow is reduced.)

So when preconditioning while plugged into Level 2 (240V and at least 32A) you can draw 7kW from the battery to warm the battery pack and warm the cabin and the on-board charger is able to send ~8kW into the battery pack. At the end of the preconditioning period the net SOC of the battery pack will be approximately where it was before preconditioning.

Also, partial charging and discharging of the battery pack will have an insignificant impact on the life of the battery. Otherwise regenerative braking would be something to avoid since under normal driving using regenerative braking power is continuously being drawn from the battery pack and returned to the battery pack.

The battery pack definitely has a limited number of full charge and discharge cycles before the capacity of the battery is reduced. Partial charging and discharging of the battery, i.e. maintaining the battery between 40% and 80% or similar can be performed many more times than full charge and discharge cycles. Drawing a couple of % of the SOC of the battery pack and then replenishing the battery has even less impact on the useful life of the battery.
 
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I have left my Model Y plugged in for several days. After charging the first night to 80% the battery state of charge (SOC) dropped by 5% by the time I used my Model Y. I preconditioned before driving but at 240V/32A the battery SOC should not have dropped by preconditioning. (The battery SOC had dropped by this amount even before preconditioning.) I don't know the protocol but it appears the Tesla battery management system will not top up the battery unless and until the battery pack SOC falls by a specific amount.

I question the idea that when preconditioning while plugged in the Tesla will use mains power instead of using power from the battery pack to precondition. The front and rear drive unit motors are wired to power control modules. The power control module is wired to the high voltage battery. Also, the heat pump operates using a high voltage compressor that draws power from the battery pack. Neither the motors or the heat pump are wired to the onboard charger.

120V or 240V mains power enters the charging port and is sent to the on-board charger. The on-board charger has to step up the voltage to ~400V and then rectify the AC voltage to DC voltage. The rectified power can then flow into the battery pack.

I think of a bath tub analogy where when the Tesla's battery pack is fully charged the bath tub is full of water. When you use power from the battery pack to precondition the Tesla vehicle you are opening the drain and some of the water starts to run out of the bath tub. If the Tesla vehicle is plugged in when you start using a significant amount of power from the battery pack then the on-board charger will draw power via the charging cable, send power into the battery pack to replenish the battery. If you are charging at Level 1 (120V) the faucet is basically trickling water into the bath tub. If you are charging at Level 2 (240V) the water flows into the tub a higher volume. If you are using a Supercharger then the water gushes from the faucet into the bath tub (at least until the tub is more than half full, then the flow is reduced.)

So when preconditioning while plugged into Level 2 (240V and at least 32A) you can draw 7kW from the battery to warm the battery pack and warm the cabin and the on-board charger is able to send ~8kW into the battery pack. At the end of the preconditioning period the net SOC of the battery pack will be approximately where it was before preconditioning.

Also, partial charging and discharging of the battery pack will have an insignificant impact on the life of the battery. Otherwise regenerative braking would be something to avoid since under normal driving using regenerative braking power is continuously being drawn from the battery pack and returned to the battery pack.

The battery pack definitely has a limited number of full charge and discharge cycles before the capacity of the battery is reduced. Partial charging and discharging of the battery, i.e. maintaining the battery between 40% and 80% or similar can be performed many more times than full charge and discharge cycles. Drawing a couple of % of the SOC of the battery pack and then replenishing the battery has even less impact on the useful life of the battery.

I have never pre-conditioned before driving the car but I have monitored what happens when charging the TB (traction battery) when the cell temps are at or below around 46F. My setup can deliver 6.24KW to the cars internal AC charger. When charging with a cold TB 3KW was sent to front motor stator winding and 3KW to the rear (via Scan My Tesla) with the remaining 240W for the awake cars overhead. So even though the motor windings could accept 7 to 8 KW, the car was smart enough not to use more than 6kW which is the max power the wall outlet could provide. This indicates to me it did not draw any energy from the TB. During the battery heating period no miles were added. I do not know if there is some method of turning off the current flow to the TB during this heating process or not? Since the TB, the motor stator windings and the output of the internal AC-to-DC car charger are all on the high voltage bus, I suspect Tesla simply keeps the car chargers high voltage DC output below the current TB voltage level which should keep any current from flowing towards the TB (ie.. no charging)?

Considering the above, I could believe the car probably is smart enough to only use wall power during pre-conditioning (and not draw extra power from the TB): however, if there were not enough wall power available (example 120V @ 12A) supplemental battery energy probably would be used (not enough wall power available to perform the requested pre-conditioning function)?
 

jcanoe

Well-Known Member
Oct 2, 2020
5,555
6,108
Maryland
I have never pre-conditioned before driving the car but I have monitored what happens when charging the TB (traction battery) when the cell temps are at or below around 46F. My setup can deliver 6.24KW to the cars internal AC charger. When charging with a cold TB 3KW was sent to front motor stator winding and 3KW to the rear (via Scan My Tesla) with the remaining 240W for the awake cars overhead. So even though the motor windings could accept 7 to 8 KW, the car was smart enough not to use more than 6kW which is the max power the wall outlet could provide. This indicates to me it did not draw any energy from the TB. During the battery heating period no miles were added. I do not know if there is some method of turning off the current flow to the TB during this heating process or not? Since the TB, the motor stator windings and the output of the internal AC-to-DC car charger are all on the high voltage bus, I suspect Tesla simply keeps the car chargers high voltage DC output below the current TB voltage level which should keep any current from flowing towards the TB (ie.. no charging)?

Considering the above, I could believe the car probably is smart enough to only use wall power during pre-conditioning (and not draw extra power from the TB): however, if there were not enough wall power available (example 120V @ 12A) supplemental battery energy probably would be used (not enough wall power available to perform the requested pre-conditioning function)?
You provided an interesting observation re charging when the battery is cold. At the beginning of a charging session the Tesla and the EVSE negotiate the charging rate, i.e. 120V or 240V and maximum amperage. My post concerned preconditioning. When preconditioning the Tesla does not need to be plugged in. Preconditioning periods are generally much shorter, i.e. less than 1 hour (often less than 30 minutes), than a charging session. The Tesla will draw as much power as needed to warm the battery pack and the cabin in the shortest possible time. In this case the power demand of preconditioning could exceed the power available to the on-board charger. It would be interesting to monitor the power draw while charging a cold battery pack with a lower power charging circuit, i.e. 240V/16A (~4kW). This is well above the power when using Level 1 charging but half of the power level when I charge at 240V/32A (~8kW.)
 

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