Precondition car plugged in vs not plugged in

[drtimhill]

In my experience it never "pays" to Preheat cabin or battery. Especially on a very short commute. But even on long ones it doesn't "pay" (it's a net loss on energy for more comfort).

No-one was discussing net energy usage, or costs thereof for that matter. The OP was asking about preheating plugged vs unplugged, and trying to understand if there was a befit to doing this while connected to a charger.

And of course there is a net energy loss, otherwise you have perpetual motion.

 

[mswlogo]

Oops

 

[mswlogo]

No-one was discussing net energy usage, or costs thereof for that matter. The OP was asking about preheating plugged vs unplugged, and trying to understand if there was a befit to doing this while connected to a charger.

And of course there is a net energy loss, otherwise you have perpetual motion.

I was replying to drtimhill that flat out said it’s “worth it” to preheat. And basically that Tesla has done the math to prove it’s worth it. It might be “worth it” to keep his ass warm. But it’s not going be more efficient or extend the life of your battery. Read what I was replying to.

If you need a bit of extra range it can help with that. At of some cost of course.

 

[drtimhill]

I was replying to drtimhill that flat out said it’s “worth it” to preheat. And basically that Tesla has done the math to prove it’s worth it. It might be “worth it” to keep his ass warm. But it’s not going be more efficient or extend the life of your battery. Read what I was replying to.

If you need a bit of extra range it can help with that. At of some cost of course.

And so Tesla preheat the battery for no reason then?

 

[JCtx]

So, what is mostly happening, is people are recalibrating the BMS to more accurately measure the battery, they are not "healing" the battery at all .. it stays with the capacity its had all along .. its just that the car is more accurately reporting it. There is a slight overall health benefit in the form of cell balancing (making sure all the cells have the same approx charge level), which probably has a small beneficial effect on long-term health since it makes wear slightly more even across cells, but I've never seen any clear data about such an effect.

the very high level version (TL ; DR version) is to do that "occasionally" to allow the battery maintenance system (BMS) to calibrate properly. There was never any advice to do that as a general charging practice.

So they aren’t really going off manual. They don’t ask you to do it constantly. Once a week or so.

That was exactly the kind of counter-argument I was looking for . Thank you very much for your detailed explanations. And yes, now I believe it's better to leave it connected all the time, and that's exactly what I plan to do after I get the 220V 14-50 outlet in the garage. In the mean time, I won't let it drop below 50%. I might get the outlet next week before that happens, so no issues. Charged it today for the first time (car is 6 days old) at a supercharger from 29 to 90% (35 minutes). I might let the battery run down once a month or two the way explained above (with 3-hr 'sleep' time). Thanks again guys; greatly appreciated.

 

[mswlogo]

And so Tesla preheat the battery for no reason then?

It’s strictly for comfort. You will never gain/save energy by more regen than you spent heating the battery. But you will be warmer and more “comfortable” with one foot driving. But it is not “worth it” to me. Too expensive to my wallet and the environment.

 

[sightman]

I was replying to drtimhill that flat out said it’s “worth it” to preheat. And basically that Tesla has done the math to prove it’s worth it. It might be “worth it” to keep his ass warm. But it’s not going be more efficient or extend the life of your battery. Read what I was replying to.

If you need a bit of extra range it can help with that. At of some cost of course.

I read your posts and I was also under the impression that Tesla figured it all out for me. Why then does preconditioning turn on battery heating (in winter)?

while I don’t use it on short trips I generally precondition for 10-15 min. I definitely like the feel of stronger regen. My car is garaged but going to work in the morning if I don’t preheat I find I end up using the friction brakes more even on a 50 min commute.

By preconditioning for 15 min using the mobile connector I’m consuming just shy of 2kW (this includes losses and cabin heat). And I like knowing the initial load of the cabin heater doesn’t come from the main pack. But I’m interested to read your thoughts.

 

[hgmichna]

When the battery gets too cold, indicated by a blue snowflake, it cannot provide its full capacity. That's the most important reason to warm up the battery. Secondary reasons are better regenerative braking and faster charging.

 

[mswlogo]

When the battery gets too cold, indicated by a blue snowflake, it cannot provide its full capacity. That's the most important reason to warm up the battery. Secondary reasons are better regenerative braking and faster charging.

Snowflake is another story. But the energy is not lost and if you do normal driving, the pack will warm up on its own without extra heating.

Now if it’s -20F then yeah, I’d probably want to warm my pack some.

 

[drtimhill]

It’s strictly for comfort. You will never gain/save energy by more regen than you spent heating the battery. But you will be warmer and more “comfortable” with one foot driving. But it is not “worth it” to me. Too expensive to my wallet and the environment.

From Wikipedia (on Lithium-Ion batteries): "Degradation is strongly temperature-dependent, with a minimal degradation around 25 °C, i.e., increasing if stored or used at above or below 25 °C."

So its not "strictly for comfort".

 

[mswlogo]

I read your posts and I was also under the impression that Tesla figured it all out for me. Why then does preconditioning turn on battery heating (in winter)?

while I don’t use it on short trips I generally precondition for 10-15 min. I definitely like the feel of stronger regen. My car is garaged but going to work in the morning if I don’t preheat I find I end up using the friction brakes more even on a 50 min commute.

By preconditioning for 15 min using the mobile connector I’m consuming just shy of 2kW (this includes losses and cabin heat). And I like knowing the initial load of the cabin heater doesn’t come from the main pack. But I’m interested to read your thoughts.

Your still putting load on the pack. It’s just replenishing it as fast as it’s draining it, assuming you have enough shore amps to cover the load.

If I put my X in “Range Mode” it does not heat the pack if I precondition the cabin (it might if there was a snow flake, which is rare on the X). If I don’t put it in Range Mode it will heat the battery when I preheat the cabin.

If you lived on top of a mountain it might be worth preheating your pack. Otherwise how would it know how much regen your going to use to make it “worth it”? My commute might be all up hill or short and I gain no regen for preheating the pack.

It does it for “comfort”. People generally like the car not changing behavior based on weather.

 

[mswlogo]

From Wikipedia (on Lithium-Ion batteries): "Degradation is strongly temperature-dependent, with a minimal degradation around 25 °C, i.e., increasing if stored or used at above or below 25 °C."

So its not "strictly for comfort".

Degradation INCREASES as temperature goes above 25C in your own quote.

It says nothing about below 25C.

I’ll tell you what does degrades anything. Temperature cycling !!!

Accelerated heating the pack once or twice a day is more likely going to age it. And don’t forget there is no battery heater on the 3/Y your putting load on the whole system to accelerate what it will do more gradually when you drive. How can putting MORE load on the system every day help decrease the degradation of the whole system.

Also your not STORING it at 25C as your quote is talking about unless you propose you heat 24/7?

There is no way heating the pack every day is good for it.

 

[Brock-WI]

As others have mentioned, preheating is primarily aimed at occupant comfort. If you have a longer trip and preheat you are basically using power from the wall and not from the battery. If you look at a 30 mile trip in winter that might consume 10 kWh of battery if the car is cold. Now if you preheat that same car it might consume 11kWh total but 3 kWh came from the wall. So at the end of your trip the cars battery will have consumed only 8 kWh instead of 10 kWh.

Strictly from an energy standpoint preheating consumes more energy but leaves more energy in your battery. I believe this would also cycle the battery LESS than if you didn't preheat. In the grand scheme of things I think this is less than anything measureable on the batteries life. Again going back to occupant comfort.

The time it is beneficial (beside comfort) is if your going on a long trip, essentially adding 3kWh to you pack size, only becasue you consume it from the wall rather than from the battery once your moving down the road.

 

[Gasaraki]

It is not worth it to preheat if you are not going to a supercharger to charge or don't have snow you need to melt on your car. The heater is so fast that in 3 mins the interior gets warm so you can just do that when you start driving.

Sure the battery might be more efficient if it's warmer but is it worth it to use 3% of battery just to get it slightly warmer and then gain 1% in efficiency? No. (just an example, it take way more than 3% to warm up the battery from a really cold state)

 

[drtimhill]

Degradation INCREASES as temperature goes above 25C in your own quote.

It says nothing about below 25C.

I’ll tell you what does degrades anything. Temperature cycling !!!

Go read it again .. it says "if stored or used at above or below 25 °C".

Tesla dont preheat the battery for fun or comfort, they do it for battery health.

 

[camalaio]

Go read it again .. it says "if stored or used at above or below 25 °C".

Tesla dont preheat the battery for fun or comfort, they do it for battery health.

You're making a very strong claim Tesla has never made when all the evidence points to it being for comfort/feel reasons, especially since this was a frequent feature request (the cars did not originally do this! They added this at the end of winter last year IIRC).

Using Wiki articles or other publicly discoverable information on general Li-ion battery health recommendations doesn't lead you to the same behaviour Tesla does. For example, it normally lets the battery float around 35C passively if it can, choosing not to actively cool it. That's definitely hotter than that 25C number.

Further, they do some things as a trade-off. Charging at hot temperatures isn't normally good for battery health (you'll note most chargers for phones, tools, etc. don't allow charging when hot, even other EVs), yet Tesla actively heats the battery for Supercharging. This isn't "healthier" - the benefit they're getting from this is faster charging. The health would be better by not actively heating it so much and charging slower. Keep in mind the preheat temps range from about 25C to about 60C, increasing with the SoC you start charging at (lower percentage being cooler).

Preconditioning the battery in cold conditions is a trade-off: it takes a lot of energy, but it gives you stronger regenerative braking.

Don't take my word for it though, it's also on Page 78 of the current owner's manual, section "Regenerative Braking" under "Cold Weather Best Practices": https://www.tesla.com/sites/default/files/model_3_owners_manual_north_america_en.pdf. This is the only explanation I could find for the suggestion of preheating the car (other than the obvious cabin/windshield benefits).
You'll also see the mentioned preheating for Supercharging just below, under "Warming the Battery Before Supercharging".

This is partly why they also recommend a ridiculous 30-45 minute precondition time. To make an actual difference, it needs to run for a while. The battery is big and has a lot of thermal mass, requiring a lot of energy to heat.

Lastly, this is a choice Tesla has left to owners. If it was something ultimately important and worth doing to the battery health, the car would just do it. An example of this is it doesn't let the pack get too far below freezing temperature at any time, even when parked.

---

There are battery chemistries we have today (some very similar to what we already use) that last much longer, the caveat being that their operating and storage temperatures need to be very tightly controlled. We don't do this because it would be extraordinarily wasteful for EV battery packs, and/or lead to even smaller capacities (cooling/heating/insulation needs).

 

[mswlogo]

You're making a very strong claim Tesla has never made when all the evidence points to it being for comfort/feel reasons, especially since this was a frequent feature request (the cars did not originally do this! They added this at the end of winter last year IIRC).

Using Wiki articles or other publicly discoverable information on general Li-ion battery health recommendations doesn't lead you to the same behaviour Tesla does. For example, it normally lets the battery float around 35C passively if it can, choosing not to actively cool it. That's definitely hotter than that 25C number.

Further, they do some things as a trade-off. Charging at hot temperatures isn't normally good for battery health (you'll note most chargers for phones, tools, etc. don't allow charging when hot, even other EVs), yet Tesla actively heats the battery for Supercharging. This isn't "healthier" - the benefit they're getting from this is faster charging. The health would be better by not actively heating it so much and charging slower. Keep in mind the preheat temps range from about 25C to about 60C, increasing with the SoC you start charging at (lower percentage being cooler).

Preconditioning the battery in cold conditions is a trade-off: it takes a lot of energy, but it gives you stronger regenerative braking.

Don't take my word for it though, it's also on Page 78 of the current owner's manual, section "Regenerative Braking" under "Cold Weather Best Practices": https://www.tesla.com/sites/default/files/model_3_owners_manual_north_america_en.pdf. This is the only explanation I could find for the suggestion of preheating the car (other than the obvious cabin/windshield benefits).
You'll also see the mentioned preheating for Supercharging just below, under "Warming the Battery Before Supercharging".

This is partly why they also recommend a ridiculous 30-45 minute precondition time. To make an actual difference, it needs to run for a while. The battery is big and has a lot of thermal mass, requiring a lot of energy to heat.

Lastly, this is a choice Tesla has left to owners. If it was something ultimately important and worth doing to the battery health, the car would just do it. An example of this is it doesn't let the pack get too far below freezing temperature at any time, even when parked.

---

There are battery chemistries we have today (some very similar to what we already use) that last much longer, the caveat being that their operating and storage temperatures need to be very tightly controlled. We don't do this because it would be extraordinarily wasteful for EV battery packs, and/or lead to even smaller capacities (cooling/heating/insulation needs).

I love your last couple responses. Thank you !!

 

[mswlogo]

It is not worth it to preheat if you are not going to a supercharger to charge or don't have snow you need to melt on your car. The heater is so fast that in 3 mins the interior gets warm so you can just do that when you start driving.

Sure the battery might be more efficient if it's warmer but is it worth it to use 3% of battery just to get it slightly warmer and then gain 1% in efficiency? No. (just an example, it take way more than 3% to warm up the battery from a really cold state)

Exactly. That’s how I always felt. The 3 heater was so damn fast why does anyone need to preheat. Unless you’re frozen out, like that ever happens

 

[RheesB]

I have had my M3 plugged in and sitting for two months so far, in temps as low as -10 and it does wake up and charge a bit every day. Local mobile service guy said better to leave it plugged in and keeping battery up and allowing updates to load than to unplug the battery and store it inside. Indoor storage at hometown has no outlets available and they will not install any, just to show me how lousy customer service is in America in 2021.

I sure hope I have FSD complete when we get home in April.

 

[MikeHolliday]

thanks, didn’t realize it was that high. Another reason to convince the boss lady to let me buy the 48 amp wall connector

I charge my Model Y with the Gen 3 Wall Adaptor at a full 48 Amps. If it is set to charge to 80%. When I leave my house it will have a full 80% charge. If you are only charging at 32 Amps it will draw the battery down a little, because the Wall Connector does have the ability to put out the amount of power needed for pre-conditioning.

The Gen 3 48 Amp Wall Connector (Connected to a 60 Amp Breaker) can pull no more than 11,520, 240 volts times 48 Amps = 11,520 Ohm's Law. Tesla publishes 11.5 Kilowatt.

Gen 3 Features (Copied from the Tesla website. Wall Connector)

· Up to 44 miles of range per hour of charge

· Compatible with Model S, Model 3, Model X and Model Y

· Up to 11.5 kW / 48 amp output

A standard range Model 3 can only charge up to 32 mile/hour, but a LR Model 3, LR Model Y, Model S & X can charge up to 44 miles/hour.