Preconditioning energy usage - plugged in vs. unplugged

[silverstoned83]

I thought it might be useful to share what I’m able to see using my Juicebox charger when it comes to preconditioning before departure. The screen shot below was taken after 17 min of preconditioning, while plugged into the charger obviously, and the battery was already at its charge setpoint. The MY was parked in a 50F garage.

When preconditioning first starts, you can see that it consumed my chargers entire 10kW of output power, but only for a couple of minutes, and then it starts ramping down to around 8 - 9kW. Then, after 15 minutes exactly or 2 kWh of energy spent, the motors stop generating heat and the power draw drops to around 800w, which is how much power it takes to continue running the heat pump alone to maintain cabin temps.

To compare, when you precondition without being plugged into the charger, it only preconditions the cabin, not the battery. In fact, it’s actually cooling the battery off since the heat pump is scavenging heat from it, assuming there is heat there to recover.

 

[silverstoned83]

I just noticed that the graph's time axis is inaccurate. The data on the graph was collected over 17 min, but the time axis makes it appear as if it lasted like an hour.

 

[jcanoe]

I precondition in the A.M., for 10 to 20 minutes, whether or not the Model Y is plugged in. The overnight temperature inside my garage is typically at or below 42F. I leave the climate control set to 70F and the seat heater for the driver's seat set to medium heat. When I precondition using the Tesla app the battery warming indicator will illuminate. This is telling me that the Tesla BMS does warm the battery pack as required whether or not the Model Y is plugged in.

 

[silverstoned83]

I precondition in the A.M., for 10 to 20 minutes, whether or not the Model Y is plugged in. The overnight temperature inside my garage is typically at or below 42F. I leave the climate control set to 70F and the seat heater for the driver's seat set to medium heat. When I precondition using the Tesla app the battery warming indicator will illuminate. This is telling me that the Tesla BMS does warm the battery pack as required whether or not the Model Y is plugged in.

I can assure you that it did not warm the battery when I tested this yesterday morning after the car had sat all night long, but I didn't check the app to see if the battery warming icon was present or not. Even though I didn't check for the battery warming icon in the app, its still very easy to determine if in progress by listening for the distinct high-frequency sound that is created by the motors when they are producing heat to warm the battery quickly, which it wasn't making when unplugged.

When preconditioning, it could be that it will only use battery power to heat the battery if the cell temp falls past a certain point. Or, it could be that it is only using the heat pump to generate the heat for both the cabin and the battery so that it doesn't use as much energy.

 

[jcanoe]

I can assure you that it did not warm the battery when I tested this yesterday morning after the car had sat all night long, but I didn't check the app to see if the battery warming icon was present or not. Even though I didn't check for the battery warming icon in the app, its still very easy to determine if in progress by listening for the distinct high-frequency sound that is created by the motors when they are producing heat to warm the battery quickly, which it wasn't making when unplugged.

When preconditioning, it could be that it will only use battery power to heat the battery if the cell temp falls past a certain point. Or, it could be that it is only using the heat pump to generate the heat for both the cabin and the battery so that it doesn't use as much energy.

On Monday I preconditioned while plugged in for 20 minutes and the battery heating icon was illuminated. I was interrupted did not leave as expected and stopped preconditioning. A half hour later I resumed preconditioning and this time the battery heating icon did not illuminate. I will repeat double preconditioning when the Model Y is not plugged in and observe the battery heating indicator. I am going to test the assumption that whether or not the battery is heated has to do with the temperature of the battery pack and not whether the Model Y is plugged in.

Wouldn't the heat pump scavenge heat to send to the cabin from the heat source with the greatest temperature gradient? Not sure if that is the battery coolant inlet/outlet or the front and or rear motor outlet coolant.

 

[silverstoned83]

Wouldn't the heat pump scavenge heat to send to the cabin from the heat source with the greatest temperature gradient? Not sure if that is the battery coolant inlet/outlet or the front and or rear motor outlet coolant.

The heat pump scavenges heat from a combination of heat sources, including the battery, motors, computer, and outside air condenser coil. A hydronic loop flows through each of these components and this is how the heat is recovered/sent to the heat pump. This is my understanding at least..

 

[alexcue]

latest update notes...

"Scheduled Departure can now precondition your battery and cabin even when your car is unplugged. To account for different utility rate plans, you can now set the time when your off-peak rates end to save on charging costs."

 

[silverstoned83]

latest update notes...

"Scheduled Departure can now precondition your battery and cabin even when your car is unplugged. To account for different utility rate plans, you can now set the time when your off-peak rates end to save on charging costs."

The important part to note is that it will only do so as needed, and this may be dependent on cell temp in combination with whether or not you’re plugged in.

I would like to know when the BMS does or doesn’t warm the battery, especially since the heat pump will suck heat from the battery by design whenever it isn’t trying to warm the battery. This means that one could be cooling the battery when they thought they were warming it before departure, which would be quite impactful when trying to prepare to supercharge.

 

[silverstoned83]

So I confirmed this morning that the MY does warm the battery when unplugged and preconditioning is active. However, I did learn some differences about how it goes about this when compared to being plugged in.

When I first started preconditioning, the battery warming icon did not illuminate on the app at the same time. At first I thought it wasn't going to warm the battery, but after 2 minutes or so, the battery warming icon appeared. However, it wasn't the same as when plugged in, and it was obviously being much more economical with its energy usage. I did confirm that the high frequency sound was present, indicating that the motors were in the process of heating up.

Also, the battery warming only ran for 5 minutes, compared to 15 minutes when plugged in. I confirmed that the motors were no longer heating and the sound was no longer being emitted.

My guess is that it will turn the battery warming back on after some period of time when unplugged, if the outside air temps and cell temps are low enough.

Bottom line, battery warming is far more aggressive when plugged in.

 

[meh_]

So I confirmed this morning that the MY does warm the battery when unplugged and preconditioning is active. However, I did learn some differences about how it goes about this when compared to being plugged in.

When I first started preconditioning, the battery warming icon did not illuminate on the app at the same time. At first I thought it wasn't going to warm the battery, but after 2 minutes or so, the battery warming icon appeared. However, it wasn't the same as when plugged in, and it was obviously being much more economical with its energy usage. I did confirm that the high frequency sound was present, indicating that the motors were in the process of heating up.

Also, the battery warming only ran for 5 minutes, compared to 15 minutes when plugged in. I confirmed that the motors were no longer heating and the sound was no longer being emitted.

My guess is that it will turn the battery warming back on after some period of time when unplugged, if the outside air temps and cell temps are low enough.

Bottom line, battery warming is far more aggressive when plugged in.

This is just anecdotal evidence.

here is my anecdote - I had my car unplugged at 75% SOC and turned on the climate prior to leaving, both the cabin and battery preconditioner turned on - it was 41 in the cabin and likely the same in the garage. I got caught up with something and left if running for 35 min. When I got in I only had 1 regen dot - indicating to me that the battery was substantially warmed up

 

[alexcue]

This is just anecdotal evidence.

here is my anecdote - I had my car unplugged at 75% SOC and turned on the climate prior to leaving, both the cabin and battery preconditioner turned on - it was 41 in the cabin and likely the same in the garage. I got caught up with something and left if running for 35 min. When I got in I only had 1 regen dot - indicating to me that the battery was substantially warmed up

Good info, but what was the SOC when you got in after running for 35 minutes?

 

[silverstoned83]

I had my car unplugged at 75% SOC and turned on the climate prior to leaving, both the cabin and battery preconditioner turned on - it was 41 in the cabin and likely the same in the garage. I got caught up with something and left if running for 35 min. When I got in I only had 1 regen dot - indicating to me that the battery was substantially warmed up

How long did the car sit in the garage prior to preconditioning?

 

[pt19713]

To keep things simple, the car will require anywhere from 7.5- 7.8 kWh to 11.8-12.1 kWh to precondition. 7.8 kWh if you use a lower cabin temp, 12.1 if you have the defrost set to high. Each motor draws 3.5 kWh. In trying to figure out why there's an additional ~4 kWh when the defrost is set to high.

The Stator motors don't care if it's plugged in or not. It'll be 3.5 kWh per motor regardless.

Note, this is for forced preconditioning. I have not messed with the scheduled departure/ conditioning.

 

[silverstoned83]

To keep things simple, the car will require anywhere from 7.5- 7.8 kWh to 11.8-12.1 kWh to precondition. 7.8 kWh if you use a lower cabin temp, 12.1 if you have the defrost set to high. Each motor draws 3.5 kWh. In trying to figure out why there's an additional ~4 kWh when the defrost is set to high.

The Stator motors don't care if it's plugged in or not. It'll be 3.5 kWh per motor regardless.

Note, this is for forced preconditioning. I have not messed with the scheduled departure/ conditioning.

I bet the extra energy is going to the heat pump so that it can focus on scavenging heat from the air, which would explain all of the condenser fan noise you can hear from outside.

To clarify, the energy I think you’re referring to is the instantaneous rate of energy consumption, not the total amount of energy consumed. If so, the units should be kW since you’re describing the instantaneous power draw, time not being a factor. The unit kWh is used if describing the total energy consumed over a duration of time.

 

[pt19713]

I bet the extra energy is going to the heat pump so that it can focus on scavenging heat from the air, which would explain all of the condenser fan noise you can hear from outside.

To clarify, the energy I think you’re referring to is the instantaneous rate of energy consumption, not the total amount of energy consumed. If so, the units should be kW since you’re describing the instantaneous power draw, time not being a factor. The unit kWh is used if describing the total energy consumed over a duration of time.

yeah, you're right. Should be kW. I post too much, constantly bouncing back and forth between battery pack sizes and talking about consumption lol.

Another possible explanation for the huge spike with the defrost on HI is a small heated filament to be used when temps are too cold for the heat pump to be effective. Something like this would've been found during the Munro Y teardown, though.

 

[silverstoned83]

Another possible explanation for the huge spike with the defrost on HI is a small heated filament to be used when temps are too cold for the heat pump to be effective. Something like this would've been found during the Munro Y teardown, though.

Yeah, I watched all of the Munro teardowns, which were all very informative. The heat pump can definitely consume a decent amount of energy if it wants/needs to.

 

[Madsen203]

I did a simple test and rather than posting a new thread I thought I would bump this.

Garage temp was 60° and set scheduled departure but forced the charge the afternoon before so it had a night of cooling off the battery.

It consumed 2kwh of energy similar to the results listed above. I wonder if charging the battery before departure naturally preconditions versus the added energy added by this process as stand alone.

 

[jcanoe]

I did a simple test and rather than posting a new thread I thought I would bump this.

Garage temp was 60° and set scheduled departure but forced the charge the afternoon before so it had a night of cooling off the battery.

It consumed 2kwh of energy similar to the results listed above. I wonder if charging the battery before departure naturally preconditions versus the added energy added by this process as stand alone.

It depends on the temperature of the battery pack. The Tesla vehicle's battery management system will only charge the battery if the pack temperature is at or above 50F (10C). If the battery pack is colder than 50F the Tesla vehicle will first warm the battery pack before charging.

Preconditioning the Tesla vehicle in cold temperatures will further warm the battery pack to 68F (20C). If the battery pack is already at 50F from having just completed charging then less energy will be needed to bring the battery pack temperature to 68F than if the battery pack temperature was at 40F, 30F, etc. from sitting overnight.

If charging completes by 06:00 A.M. and you don't leave in the morning until 7:30 or 8:00 A.M. the battery will still be warm from charging when you start preconditioning the Tesla vehicle before you leave.

If you are on a TOU rate plan that has an off-peak rate period that ends at 06:00 A.M. preconditioning after 06:00 A.M. is going to use more expensive peak rate period grid power during the peak rate period. The only way I am aware to prevent using grid power during the preconditioning period is to unplug the Tesla vehicle after charging has been completed, before preconditioning or maybe lowering the charging limit by ~4% or 5% so that the Tesla vehicle will not immediately begin charging during the preconditioning period.

 

[Madsen203]

It depends on the temperature of the battery pack. The Tesla vehicle's battery management system will only charge the battery if the pack temperature is at or above 50F (10C). If the battery pack is colder than 50F the Tesla vehicle will first warm the battery pack before charging.

Preconditioning the Tesla vehicle in cold temperatures will further warm the battery pack to 68F (20C). If the battery pack is already at 50F from having just completed charging then less energy will be needed to bring the battery pack temperature to 68F than if the battery pack temperature was at 40F, 30F, etc. from sitting overnight.

Makes total sense. Probably why it waits to schedule charging until just before your departure time set - naturally warms battery in the process. I was curious how much it took and will be more interested to see how to mileage fares with no preconditioning on a similar temperature morning.

 

[jcanoe]

Makes total sense. Probably why it waits to schedule charging until just before your departure time set - naturally warms battery in the process. I was curious how much it took and will be more interested to see how to mileage fares with no preconditioning on a similar temperature morning.

If you don't precondition before driving what you will notice most (besides the passenger cabin being cold) is that you will have very little, effectively no regenerative braking available. When you precondition before driving, for 15 minutes or longer depending the temperature, your Tesla vehicle will have some amount of regenerative braking available.