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Nav Preconditioning vs max defrost

Is there a difference between the battery preconditioning the car will do while navigating to a supercharger vs turning on max defrost?

I've got a supercharger within 6 miles of home. I was thinking of setting the navigation destination to the supercharger and allow the car to do the preconditioning. The max defrost I use presently doesn't seem to work very effectively (30 min of max defrost does not reduce the "dots" indicating battery temp shown on screen.

My MY is parked in an unheated car port, covered but exposed to the weather.
 

jcanoe

Well-Known Member
Oct 2, 2020
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Maryland
Is there a difference between the battery preconditioning the car will do while navigating to a supercharger vs turning on max defrost?

I've got a supercharger within 6 miles of home. I was thinking of setting the navigation destination to the supercharger and allow the car to do the preconditioning. The max defrost I use presently doesn't seem to work very effectively (30 min of max defrost does not reduce the "dots" indicating battery temp shown on screen.

My MY is parked in an unheated car port, covered but exposed to the weather.
Using the Navigation system to navigate to a Supercharger will start warming the battery to a higher temperature than if you were preconditioning the Tesla while parked. Maximum defrost will defrost the windshield, autopilot cameras and the charging port. Six miles it not enough driving time to precondition for optimal use of a Supercharger. You could precondition at home for at least 20 minutes, then navigate to the Supercharger so the battery is more fully warmed for the Supercharger session. You have to be driving for the Navigate to a Supercharger to precondition the battery for the Supercharging session. If the Tesla remains parked after setting a Supercharger as the destination in the Navigation system the additional battery warming for optimal supercharging will not start until you start driving. You can drive anywhere, even around in circles, to start preconditioning before arriving at the SuperCharger.
 

pt19713

Active Member
Feb 5, 2020
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Delaware
Tip, if you want the battery to warm up faster, don't set the interior cabin temp to a high temp. Set it to something like 67-68F. The car will direct more heat/refrigerant to the heat pump for a longer period to heat the cabin. Once they temp is reached, more heat is directed to warm the battery.

Also note, the front Stator will pull 3.5 kW while parked and preconditioning. The Tesla nav to Supercharger, it only pulls 2.0 kW and does not get as warm while the car is in motion. While parked in my garage and turning the cabin heat on, I can see the front Stator motor getting to 210F. While driving, I don't see it going above 125F (in temps before 40F).
 
PT - does the max defrost not accomplish the preconditiong of the battery? Just heating the cabin will do the warming of the battery or do I need to do both?

It would be nice if Tesla had a button on the app that said - PRECONDITION BATTERY. Seems like a reasonable thing to have.

Just to clarify, the plan was NOT to go to the supercharger, just use it's proximity to my home as a way to get the car to precondition the battery.
 

pt19713

Active Member
Feb 5, 2020
1,062
1,394
Delaware
PT - does the max defrost not accomplish the preconditiong of the battery? Just heating the cabin will do the warming of the battery or do I need to do both?

It would be nice if Tesla had a button on the app that said - PRECONDITION BATTERY. Seems like a reasonable thing to have.

Just to clarify, the plan was NOT to go to the supercharger, just use it's proximity to my home as a way to get the car to precondition the battery.
It does, but it takes longer before the heat gets routed to the battery, and also requires around 4 kW of energy versus 500 watts by using the normal climate.

IMO, it's faster to turn on the heat to around 66-69F and if the ambient temps are around 30-45F, the cabin should be warm in 3-5 minutes. I never use the defrost HI just because it's a lot of energy.

I have a datalog and can plot the info in graph format tomorrow.
 

pt19713

Active Member
Feb 5, 2020
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Delaware
So I redid the graphs for comparison.

Scenario 1: 10 minutes, pre-condition via app, defrost setting to HI
Scenario 2: 18 minutes, pre-condition via app, cabin set to 67F
Since the duration is longer on the second scenario, I looked at just the battery inlet and battery pack temps at the 10 minute mark


In Scenario 1, the battery pack started at 54F, ended at 61F, net increase 7F in the 10 minutes.
In Scenario 2, the battery pack started at 52F, ended at 57F, net increase of 5F in the 10 minutes. This is not what I was expecting, as mentioned in my post above. Here's what I found interested.

In Scenario 1, the battery inlet temp (the temperature of the refrigerant before it enters the battery pack), started at 53F, ended at 75F, net increase of 22F.
In Scenario 2, the battery inlet temp started at 46F, ended at 72F, net increase of 26F.

I think if I were to do an 18 minute pre-condition with the defrost on HI, we can get a better comparison.
At some point I'll also test out how the car warms up if using the Tesla supercharger as the navigation point. I'm curious if the front motor will be using 3.5 or 2.0 kW since it only generates 2.0 kW of heat while it's in motion. I've never looked to see what it is while in Park.

But, comparing the two results, during a 10 minute duration, the temps are close enough that it's really insignificant unless you're comparing the energy requirement. Scenario 1 requires 11.8-11.9 kW. Scenario 2 requires 7.8 kW.

scenario1_high_defrost_10minutes.JPG



scenario2_normal_incabin_heat_18minutes.JPG
 
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pt19713

Active Member
Feb 5, 2020
1,062
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Delaware
I ran some errands so I was able to precondition the car before heading out, so I ran the defrost from the app on the HI setting for 18 minutes to compare against setting a cabin temp at 67F.

Long story short, there's not much difference in terms of battery temp increases. Defrost on HI, the battery increased in temp by 15F in 18 minutes. Cabin temp at 67F, the battery increased in temp by 17F in 18 min. Based upon the defrost on HI requiring about 11.8 kW and the cabin temp at 67 requiring 7.8 kW, the latter option would seem to be better.

Note, you can see in scenario 2 that the Octovalve initially is pulling some heat away from the battery but once the cabin is warmer after 2 minutes, it redirects more of the refrigerant back to the battery pack. This is shown with the green line (Battery inlet temp) on the 2nd graph.

020621_18minute_preconditioning_defrost_HI.JPG



scenario2_normal_incabin_heat_18minutes.JPG
 
A big thank you for those observations.

It would appear it is more cost efficient (kWh consumed) for the resulting warm up of the battery pack using the environment control rather than the max defrost. In my situation, with the battery being exposed to the cold temps (20-30F range), I think I'll run the cabin heat for about 30 min and see what the condition of the battery is.

I have noticed that when I waken the car, the car wants to recharge the battery pack back up to it's set level, but with the temps being as cold as it has been, the car wants to condition the battery first. For example this morning, with outside temps being around 30and the car's charge level set to 75%, when the car awoke, it reported 72% SOC. It took an hour to recover the apparent 3% difference. I suspect that those initial % readings are somewhat distorted by the low battery pack temp. I don't have the hardware you have to monitor that closely.

I'm wondering if that is even more efficient, waking the car and setting the charge level 5-10% higher and let the car handle the conditioning of the pack prior to it's starting the actual charging.

TeslaFi reported a use of 5.58kWh over 58 min doing conditioning this morning, reporting a net additional 1.15kWh which I presume went into the battery pack.

Gotta say, never went into this amount of detailed energy usage investigation with my Subaru!
 
Is there a difference between the battery preconditioning the car will do while navigating to a supercharger vs turning on max defrost?

I've got a supercharger within 6 miles of home. I was thinking of setting the navigation destination to the supercharger and allow the car to do the preconditioning. The max defrost I use presently doesn't seem to work very effectively (30 min of max defrost does not reduce the "dots" indicating battery temp shown on screen.

My MY is parked in an unheated car port, covered but exposed to the weather.

You want to keep all that heat IN the battery pack (coolant). With the new heat pump, pushing all that heat into the cabin might actually temporarily lower the battery temperature as it's pulling heat from all available areas (it's a shared coolant loop) and instead directing it into the cabin. The car will do it's job given enough time. A better option would be putting the supercharger into the nav and then driving around for 25 minutes before hitting the supercharger....

You probably could also hit a level 2 charger and maybe charge there for 15 to 20 minutes to get some heat into the battery and then navigate to the supercharger and plug in right away...
 

pt19713

Active Member
Feb 5, 2020
1,062
1,394
Delaware
A better option would be putting the supercharger into the nav and then driving around for 25 minutes before hitting the supercharger....

You probably could also hit a level 2 charger and maybe charge there for 15 to 20 minutes to get some heat into the battery and then navigate to the supercharger and plug in right away...
Waste of time to drive around to warm it up. Just go to the supercharger. It'll warm up faster while plugged in versus driving around pre-conditioning.
 
One of the points of this exercise is to NOT drive around. I'm trying to get the car as ready as possible before leaving home, doing all the preconditioning work while still plugged in (30a/220v service in my case). I had no intention of actually going to that close supercharger when I start out, just trying to see if using the nav precondition function works more effectively/efficiently at getting the battery temps up initially.

As for pushing all that heat into the cabin, I agree. That's why I'll be setting the cabin temp to only 62. Based on pt19713's report, once the cabin temp reaches the set point, the octovalve will direct more heat from the heat pump into the battery pack. No need to get the cabin up to a higher temp, especially since getting into the car at 62 will still feel warm compared to the outside temps.

Now I'm wondering, if you heat the cabin to 68, and turn on the seater heaters (my wife's term), will the octovalve redirect the excess heat generated by the seats into the system? Can the system actually utilize the cabin air in this manner? Probably not, just a hypothesis, not a theory.
 

pt19713

Active Member
Feb 5, 2020
1,062
1,394
Delaware
Now I'm wondering, if you heat the cabin to 68, and turn on the seater heaters (my wife's term), will the octovalve redirect the excess heat generated by the seats into the system? Can the system actually utilize the cabin air in this manner? Probably not, just a hypothesis, not a theory.
Typically this is done after you exit the vehicle. It'll pull the heat from the cabin to the battery to store it. It does seem to make a small difference if you're running errands, where you're out of the vehicle for 10-20 minutes at a time. In freezing or sub-freezing temps, the battery will start to drop in temp after 45-60 minutes (faster in colder conditions).

It'd be too hard to test while driving due to all the various sensors and what they're reporting. There's no easy way to show if the heat from the refrigerant to the battery is from the heat pump, motors, or cabin. There is a sensor reporting the "Five way valve angle" which could be something but I'm not sure if anyone knows how to interpret it. I'm guessing it's one of the valves and the position it's in and how it directs the refrigerant.
upload_2021-2-7_10-47-2.png
 
I think the goal of the car will always be to conserve energy. So I think as soon as it hits the set point it’ll back off the HVAC system instead of going full tilt still and just redirecting the heat.

I doubt the seat heaters could increase air temperature that much either. I suspect the loss to ambient temperatures outside the vehicle probably will be larger than the seat heaters can account for.

Again, the vehicle knows the best way to heat things up but also conserve energy. If you want to play the game, driving around and playing within the guidelines of the design is probably the most effective way.

One thing I have noticed is that you can start to precondition the cabin and then stop preconditioning it a moment later but the battery preconditioning icon will still show in the app for approximately 20 to 30 minutes. I don’t know if that’s a bug or a set cycle the battery conditioning runs on. Either way I don’t think this actually increases the speed at which the battery is heated up OR the final temperature, but at least you’re not using as much energy to do so.
 

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