Cold weather trip; Considering avoiding Nav directly to SC to avoid preconditioning

[SilverStar]

First properly cold weather trip. I’ve driven in below freezing with my 3, but not this cold & also it’s a 2018 so no heatpump involved.

Temp is -16C (just above 0F), and I’m seeing the pre-conditioning come on nearly as soon as I depart from the last SC. Pulling up the Energy readout it says I’m blowing about 15% on pre-conditioning & another 15% on cabin.

That’s a lot.

Tried dropping from 20C/68F to 19C, couldn’t casually see a difference.

So took it one step further trying things out, I set my destination to the restaurant near the charger (dropping off passenger there anyway). Bingo, obviously no preconditioning cost but also Cabin then dropped to where I expected, negligible (two people generate a lot of heat, just need to dry it, which heatpump design does very efficiently).

Sooooo…besides somewhat slower charging & the nag that I should precondition next time, what’s the drawbacks here?

Note: I’m traveling into the teeth of winter, here. Headed to Saskatchewan & forecast has overnight down to -30C, maybe lower. I’m hoping to be off the road by the coldest but expect I’ll see -25C.

PS I’ve found some discussions here sort of dancing around this, a mention of the effect, but not quite coming out & saying this is a valid technique.

 

[EVer Hopeful]

I saw this bit: "I’m traveling into the teeth of winter, here"

then I saw this bit:

so I thought this:

but then I also saw this "Headed to Saskatchewan & forecast has overnight down to -30C"

so then I added this:

to your post


Interesting idea. Sorry that I don't have anything (sensible) to add, but it sounds like a feasible approach. My expectation is that it'll simply take longer to charge

 

[SilverStar]

I saw this bit: "I’m traveling into the teeth of winter, here"

then I saw this bit: View attachment 1007918

so I thought this:

but then I also saw this "Headed to Saskatchewan & forecast has overnight down to -30C"

so then I added this: View attachment 1007919 to your post


Interesting idea. Sorry that I don't have anything (sensible) to add, but it sounds like a feasible approach. My expectation is that it'll simply take longer to charge

Go big or go home? Why not both?

 

[David99]

I monitored the temperature on my battery yesterday as it was preconditioning going to a Supercharger. It heated up the battery to about 45 C. That's pretty warm. You need a lot of energy to heat a battery from 0 C to 45 C. I did the math, it is around 25 kWh of energy. That is 1/3 of the entire battery capacity. I'd say it is unreasonable. I assume the car would limit the amount of battery heating in those situations to not run out of battery before you arrive.

Preconditioning is not my favorite feature and I wish I could turn it off easily (other than using a different destination). It wastes energy to save just a few minutes of charging time. It really isn't much as you now have to recharge the extra energy you just used to heat. Additional energy is now wasted as the battery needs to be cooled sooner and more as we started with a rather warm battery. The BMS will never allow a harmful charge rate. If you arrive with a battery that is cooler, it will just charge a bit slower.

On longer road trips with multiple Supercharger stops, it doesn't matter much. The battery temperature is close to ideal due to the longer driving time anyways and each supercharging stop heats up the battery even higher.

 

[mcsenerd]

I think "preconditioning" is the single point where there could be some serious "monkey business" going on with Teslas...especially since SCs are no longer at-cost or loss leaders and are and/or are becoming an ever-increasing source of income for the company. Not saying that theyr'e certainly doing anything that's not on the up and up at this moment, but the temptation for a company has to be very high, and I could easily see it happening. As in..."look, we're looking out for you by wasting a bunch of billable electricity to increase your charging speed so we can pump all of it that we wasted right back in when you finally get to a Supercharger!"

 

[SilverStar]

I think "preconditioning" is the single point where there could be some serious "monkey business" going on with Teslas...especially since SCs are no longer at-cost or loss leaders and are and/or are becoming an ever-increasing source of income for the company. Not saying that theyr'e certainly doing anything that's not on the up and up at this moment, but the temptation for a company has to be very high, and I could easily see it happening. As in..."look, we're looking out for you by wasting a bunch of billable electricity to increase your charging speed so we can pump all of it that we wasted right back in when you finally get to a Supercharger!"

I’m gonna disagree with this. It has its place. When the feature first came out, around 2020, it clearly could wait too long to matter in cold weather. I suspect this is result of overkill to avoid incidents of waiting too long.

It’s a complex problem, and contingent of context that may not be readily apparent, at least somewhat depending on driver’s preference in the moment.

 

[Acps110]

There is no reason to avoid preconditioning. If you charge a Lithium Ion battery when it is too cold, it will damage itself by creating short circuits inside.

The preconditioning process was lengthened to allow the battery to warm up more slowly.

It is not wasting energy by preconditioning for 1 to 2 hours prior to a Supercharger stop. If preconditioning is not done, you could end up with a large replacement cost for your now non-working battery pack.

 

[mcsenerd]

I’m gonna disagree with this. It has its place. When the feature first came out, around 2020, it clearly could wait too long to matter in cold weather. I suspect this is result of overkill to avoid incidents of waiting too long.

It’s a complex problem, and contingent of context that may not be readily apparent, at least somewhat depending on driver’s preference in the moment.

I'm not saying it doesn't "have its place" and insinuating that I am is a misconstruing of ideas. What I AM saying is the whole process is nebulous, sometimes mind-boggling, and also easily manipulated...even in manners that would allow for easy plausible deniability. Maybe it's the cynic in me, but I trust profit driven companies about as much as I trust my teenagers... I can love em...but still have a wary eye.

 

[boulder.dude]

There is no reason to avoid preconditioning. If you charge a Lithium Ion battery when it is too cold, it will damage itself by creating short circuits inside.

The preconditioning process was lengthened to allow the battery to warm up more slowly.

It is not wasting energy by preconditioning for 1 to 2 hours prior to a Supercharger stop. If preconditioning is not done, you could end up with a large replacement cost for your now non-working battery pack.

That’s a pretty big assertion! “Plugging into a SC without preconditioning may damage your battery back.”

I have not seen anything official that would suggest this.

 

[Acps110]

That’s a pretty big assertion! “Plugging into a SC without preconditioning may damage your battery pack.”

I have not seen anything official that would suggest this.

Any charging (Supercharger, Level 2, even regenerative braking) is dangerous for a cold Lithium Ion battery. Google Lithium plating and dendrite formation. Dendrites are very bad for a battery because if they grow big enough, they can cause internal short circuits. Once they begin to form, it is an irreversible chemical process. The colder the pack, the greater the likelihood of them forming, Luckily, there is an easy solution to greatly reduce them forming, heat.

Every winter, there are posts here about, “Why is my car pulling 32 Amps from the wall, but showing 0 miles of range added per hour?“ Because the pack is too cold to charge without damaging it. “Why is my regenerative braking reduced?” Also because the pack is too cold to charge without damaging it. The car will heat the pack in both situations to allow for charging. There were some Model S in China a few years back that had runaway thermal events and large fires caused by internal short circuits in the battery pack. Tesla quickly released software updates to keep it from happening to the rest of the fleet. Those software updates worked, because cars stopped catching on fire.

There are no upsides to avoiding preconditioning, and all downsides. Cold pack, Lithium plating, dendrite formation, longer & slower charging sessions, longer Supercharger lines waiting for a stall to open up, and large cost for a replacement pack. If the car wants to precondition for an hour or 2 before arrival, it needs that much time to heat the pack up to keep from damaging it.

 

[David99]

Every winter, there are posts here about, “Why is my car pulling 32 Amps from the wall, but showing 0 miles of range added per hour?“ Because the pack is too cold to charge without damaging it. “Why is my regenerative braking reduced?” Also because the pack is too cold to charge without damaging it. The car will heat the pack in both situations to allow for charging.

You gave yourself the answer. The BMS limits charging and discharging to make sure the battery is safe and doesn't get damaged.

 

[fholbert]

You gave yourself the answer. The BMS limits charging and discharging to make sure the battery is safe and doesn't get damaged.

I’d think that’s correct. Tesla brags about how advanced the charging system is, can’t believe it would let the SC destroy the battery.

In the OP’s situation, what about changing the navigation system to the SC 15/20 minutes out? Is that enough time to condition the battery? That’s a question, not a statement.

Been really cold in SoCal too, we got down to 34* this week.

 

[David99]

In the OP’s situation, what about changing the navigation system to the SC 15/20 minutes out? Is that enough time to condition the battery? That’s a question, not a statement.

Been really cold in SoCal too, we got down to 34* this week.

That's a good question. I believe, based on observation in my two Teslas, it will adjust heating based on how much time it has. I recently had it start preconditioning 45 min before the supercharger. Then the message came on and off a few times until I arrived. On short trips to a supercharger I noticed the car was working much harder to warm up the battery. The compressor was running, the motors were running louder (to produce heat).

 

[Acps110]

You gave yourself the answer. The BMS limits charging and discharging to make sure the battery is safe and doesn't get damaged.

Slower charging doesn’t help the dendrites, only heat does. The car is charging slower to allow it to be used. If it is charging slower, then still in the danger zone.

It’s a cumulative effect. Charging when the pack is cold will form small dendrites, but you as a user won’t notice because you can’t see inside the cells. Then more charging when cold and the existing dendrites get bigger. Then one day, it all comes to an end and you need a new pack or at worst case, the car burns to the ground.

 

[mcsenerd]

Slower charging doesn’t help the dendrites, only heat does. The car is charging slower to allow it to be used. If it is charging slower, then still in the danger zone.

It’s a cumulative effect. Charging when the pack is cold will form small dendrites, but you as a user won’t notice because you can’t see inside the cells. Then more charging when cold and the existing dendrites get bigger. Then one day, it all comes to an end and you need a new pack or at worst case, the car burns to the ground.

The BMS heats the battery at the SC if need be. Unlike the preconditioning behavior during navigation/driving, this is clearly shown and explained directly by the car itself during charging sessions.

 

[Marsh25]

I've noticed this when towing and have advised people the not navigate to the supercharger if they think their range might be borderline. When you might not make it, a few extra minutes of supercharging is nothing to an hour on a J1772.

Now when I'm not towing, I don't worry about it. The long range has enough spare juice to cover it.

 

[mcsenerd]

I've noticed this when towing and have advised people the not navigate to the supercharger if they think their range might be borderline. When you might not make it, a few extra minutes of supercharging is nothing to an hour on a J1772.

Now when I'm not towing, I don't worry about it. The long range has enough spare juice to cover it.

That's likely excellent advice and I can certainly see how someone not paying attention could be easily bitten by that. I can't speak for everyone, but myself, I don't discount the needs or benefits of preconditioning. My only concerns are those that I've stated. One, it's a process that has NOT been fully explained, communicated, and/or described by Tesla. Furthermore, I don't believe in perfection...and this whole process follows this belief. As in, I do NOT believe that the current algorithm or calculations are ALWAYS appropriate and in many cases they're just outright wasteful. Lastly, I completely and unequivocally believe that this behavior has HIGH potential for abuse, either via active intent...or through inaction and/or indifference if such action would reduce potential financial benefits to Tesla. The motivation is too high and growing, IMHO.

 

[SilverStar]

In the OP’s situation, what about changing the navigation system to the SC 15/20 minutes out? Is that enough time to condition the battery? That’s a question, not a statement.

This is exactly what I had ended up doing. In the -20C to -30C range I found setting Nav to the SC at 15 min out from arrival wasn’t quite enough, it was on the edge of maybe or maybe not needing to heat at the SC. 20 min out used more energy of course, but it was very close to normsl
full speed charging immediately off the bat.

I was get the overhead back down into the 15-20% range area.

Keep in mind that a big reason why I’m doing this is for safety. Windchill was substantially lower, sub -40C. And I’m traveling through relatively empty areas. I want to maintain way more than the typical buffer, in case I’m help up along the way.

 

[SilverStar]

Oh, and the Nav energy use estimating understands this to some extent. You can see this by comparing the estimated arrival SOC when set to a SC vs set to a waypoint in the SC’s parking lot.

What it doesn’t seem to get right is how much extra heating the cabin & pre-conditioning at the same time costs. There’s clearly an inherent limitation of the octo-valve setup that doesn’t allow you to do both efficiently at the same time.

My guess is needed both amounts of heat pushes the system to heavily use running the compressor motor in heat generation mode, which is effectively resistive heating.

 

[boulder.dude]

That's likely excellent advice and I can certainly see how someone not paying attention could be easily bitten by that.

My experience is that it will only precondition if there is enough juice to do so before the reaching the SC. If not, it won’t precondition.