Big Preconditioning Change

[zannman]

What's up with the big Preconditioning for Supercharging change?

My last big road trip in cooler weather was in April, but I just had preconditioning on for 80% of a 110 mile gap between superchargers last week. That's maybe 10kWh of power used for a small charging speed benefit at the next Supercharger.

Why was it necessary to make this winter weather change (it was around 50 degrees ambient) and is it possible to turn this off easily? I can't imagine how it will be on a true 15 or 20 degree F winter road trip.

 

[ottawam3]

I believe you can tap the message saying that it's preconditioning and it will stop doing so.

But wouldn't it be better being able to precondition and charge more efficiently and get you on your way rather than the extra time needed to get up to a particular temperature once you plug in? I guess it becomes a question of how much range is lost preconditioning vs how much time it takes to do it at a charger.

 

[GtiMart]

I'm not sure it used 10kWh. I believe only the front motor was used to generate heat as the rear one drives the car. I've seen around 3kW of power sent to the front motor when that happens (using ScanMyTesla). If your 110 miles took 1.5h, that would be 4.5kWh of energy. Maybe there's a bit in the back but really not much.
When the pack is cold, it really takes a long time with such a small source of heat to bring it up to 100F. I'm not surprised it starts so early. What happened before is that the pack was not hot enough at SuC arrival.

 

[Kevy Baby]

If it is preconditioning too much, cancel heading to the SuC and just put the address into the nav. When you are closer, cancel that and re-select the SuC.

Not the most elegant solution, but it should work.

 

[Kevy Baby]

I believe only the front motor was used to generate heat as the rear one drives the car.

What about an a RWD vehicle?

 

[GtiMart]

rwd tries to precondition too but I'm not sure waste heat can be generated while the motor drives the wheels. It's tough to tell even with ScanMyTesla since the power value fluctuates as you drive. The reports I've heard seemed to show rwd cars heating the battery pretty slowly. Hopefully someone will have more precise info.

 

[nayr14]

What about an a RWD vehicle?

I've watched ScanMyTesla over the years when it comes to preconditioning my RWD. When it shows preconditioning while traveling on the interstate, the battery inlet temperature immediately begins to rise and the stator temperature drops.

Depending on conditions, my theory is they bump up the flow from the rear stator (which they normally let sit at higher temp) into the battery to help raise the battery temp, and maybe run the motor in a slightly less efficient configuration. It definitely works, at least in the summer. Not as well as an AWD I'm sure. I'll have to keep an eye on it this winter. Previously in the winter I didn't see much improvement with preconditioning, but they might have made some changes.

I took a trip from Chicago to Denver and back this summer, I actually faced issues with the battery overheating and reducing charge rate! Driving into a SC at 110F battery temp doesn't take long to overheat it, along with the handles on v2 chargers.

 

[DaveRZ]

I could be wrong here (I'm not a Tesla expert), but "pre-conditioning" doesn't have to mean active generation of heat. It could also mean turning off active COOLING of the battery (continuing to circulate coolant to keep the pack an even temp, but not actively venting the heat to the outside air, or the A/C). Can anyone confirm that when you see "pre-conditioning" for a long trip that it is actively burning a bunch of extra electrons to heat the battery the whole time?

I'd like to think that people far more knowledgable than myself on the subject decided the correct "break-even" point where burning extra electrons is worth it prior to charging. I seriously doubt charging speed was their only metric when programming pre-conditioning.

 

[AZAV8R]

I could be wrong here (I'm not a Tesla expert), but "pre-conditioning" doesn't have to mean active generation of heat. It could also mean turning off active COOLING of the battery (continuing to circulate coolant to keep the pack an even temp, but not actively venting the heat to the outside air, or the A/C). Can anyone confirm that when you see "pre-conditioning" for a long trip that it is actively burning a bunch of extra electrons to heat the battery the whole time?

I'd like to think that people far more knowledgable than myself on the subject decided the correct "break-even" point where burning extra electrons is worth it prior to charging. I seriously doubt charging speed was their only metric when programming pre-conditioning.

Reading this thread, I've been thinking similarly. Interested in educated responses as well!

 

[zannman]

I'd be thrilled if I had the extra time to get ScanMyTesla running when these events happen, but it just isn't a priority. Heat in the battery makes a difference in cooler temperatures when you have a heat pump that can take advantage of (some would say NEEDS) the excess battery heat to work effectively. That's not my case with a pre-heat pump car, and I believe this was a case of optimizing performance for newer cars while reducing performance of older cars due to lack of consideration.

My efficiency for the drive in question was 60% when it would have been closer to 75% like every other leg of this trip. Last year and historically the efficiency of this drive in 55 degree F temperature was less efficient than my historical drives in 10 degrees F. Does that mean my sub 10 degree efficiency will drop to 45% and less for the first hop?

That's not exactly a winter weather enhancement.

 

[GtiMart]

The gain from heating the battery for supercharging is in time to charge. Hot, the battery can take 250kW. Cool/warm, you might get 60... Big difference in time to charge

With that said, you can cancel the preconditioning if you don't want it, or don't navigate to the supercharger

 

[Gasaraki]

I could be wrong here (I'm not a Tesla expert), but "pre-conditioning" doesn't have to mean active generation of heat. It could also mean turning off active COOLING of the battery (continuing to circulate coolant to keep the pack an even temp, but not actively venting the heat to the outside air, or the A/C). Can anyone confirm that when you see "pre-conditioning" for a long trip that it is actively burning a bunch of extra electrons to heat the battery the whole time?

I'd like to think that people far more knowledgable than myself on the subject decided the correct "break-even" point where burning extra electrons is worth it prior to charging. I seriously doubt charging speed was their only metric when programming pre-conditioning.

When it's 50 or 30, etc, the car doesn't need to actively cool the battery. The battery does not heat that much in normal driving in those temperatures. If you hard accelerate and lift off regen over and over again is when some heat will get generated. The auto preconditioning runs the front motor to generate the extra heat when it should be off in normal driving.

So yes, "pre-conditioning for supercharging" is active generation of heat.

 

[snikt]

I've only used a supercharger recently on my first road trip, so I don't know about what changed, but on one of my legs I noticed it did start preconditioning about 50 miles away from the supercharger. That didn't really make sense to me, surely it doesn't need that much time or distance.

For some it started maybe 10-15 miles, but one was at least 50-60 miles away. 60-70F outside and traveling at 75-80MPH

 

[derotam]

I'll add my two cents here... Based on my SMT testing with my 2018 RWD Model 3... The preconditioning available on the RWD basically goes to zero above about 30MPH. I did extensive testing on specific sections of road using cruise control. Basically you can only induce so much inefficiency into the motor while it is being used for propulsion.

On an AWD vehicle, you should be able to get full heating capability on the forward motor as long as it isn't being used... Based on various Bjorn videos from at least a year ago, the front motor basically isn't used in normal driving conditions until you hit about 90MPH.

For those using SMT now, watch out with testing this because in the past after an SMT update, the power values went flaky in regards to activating pre-conditioning while driving. I think it was the overal power usage went DOWN bay about 3kW when pre-conditioning was activated which is obviously wrong. I noted the error to the developer but it wasn't really addressed during the 6 months that I was bringing it up. I haven't used SMT in a while since I haven't been driving as much lately so I need to test again.

 

[GtiMart]

That is my understanding as well @derotam . It's possible that RWD cars get some additional heat by changing the way the heating/cooling system runs (superbottle/octovalve) but I also think the rear engine/circuits cannot generate extra power through inefficiencies while driving the car forward. In preconditioning I see my front engine consume 3kW (or 3.5kW?) and that engine's temperature go up unless I floor it in which case that engine temporarily drives the car instead.
Even in an AWD, heating the battery takes a long time. A RWD would take forever, which explains why it now starts so early.

Note that SMT just got an update very recently to fix some power values.

 

[Gasaraki]

I've only used a supercharger recently on my first road trip, so I don't know about what changed, but on one of my legs I noticed it did start preconditioning about 50 miles away from the supercharger. That didn't really make sense to me, surely it doesn't need that much time or distance.

For some it started maybe 10-15 miles, but one was at least 50-60 miles away. 60-70F outside and traveling at 75-80MPH

Pre-conditioning doesn't produce as much heat as you think it does. Supercharging likes the battery temperature to be 45-50C. So your 60F battery temp needs to be brought close to 50C (122F). That is why pre-conditioning starts so early.

This is even worst for the RWD cars. They pre-condition VERY slowly.

 

[derotam]

That is my understanding as well @derotam . It's possible that RWD cars get some additional heat by changing the way the heating/cooling system runs (superbottle/octovalve) but I also think the rear engine/circuits cannot generate extra power through inefficiencies while driving the car forward. In preconditioning I see my front engine consume 3kW (or 3.5kW?) and that engine's temperature go up unless I floor it in which case that engine temporarily drives the car instead.
Even in an AWD, heating the battery takes a long time. A RWD would take forever, which explains why it now starts so early.

Note that SMT just got an update very recently to fix some power values.

Yeah, the whole pre-conditioning WHILE DRIVING is pretty overrated, even with an AWD in my opinion. Really it probably is only measurably useful when starting a low speed drive(non-highway) drive with a cold battery and where it still takes a while to get to the supercharger.

Pre-conditioning while still at home parked and waiting to leave is really the most useful case for any kind of battery pre-conditioning in my opinion.

I'll have to check out SMT again and see if the power values are fixed for that issue I found in the past.

 

[GtiMart]

I don't use superchargers much so I don't have a lot of experience. I remember one drive where it started maybe 40 minutes before arrival on my AWD and the battery gained maybe 10C, so going from 25C to 35C approx... Not exactly sure of the numbers but I think it's in that ballpark. It was enough to get good SuC speed on a V2. I would say it works well while driving on a AWD, but I wouldn't think on a RWD it does much. On the bright side, even if it starts 2h away, it's not costing much battery on the RWD