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Did you know the 3 heats the battery (actively) constantly while DC charging at any speed or temp?

I bet you didn't. I'll bet you're thinking right now, "no, that's nonsense, that can't be right, let me get in this thread and tell this idiot off". Or maybe "what makes you think that, where'd you get that data?". Perhaps "no, that's just because DC charging causes the battery to heat up"? Maybe even "Tesla knows best, you're thinking too hard about this". Finally, "what's it matter?". Well, those are all reasonable thoughts from reasonable people that once tread here.

Let me break down these thoughts to help make this long post more digestable.

**First, an update**
Since writing this, a few points have been made. Yes, this is Scan My Tesla. I have seen cases of information being hidden to "Solve" the problem via obscurity, so not saying how I got the info is to protect the access to that info. Second, it doesn't heat constantly - it can eventually decide to stop heating - but there is a very hard-to-reach threshold of heating that it finally reached after a long period of heating (often the entire session). Third, it still stands, especially at slower DC charging stations and arguably at 72kW SCs, that this heating does more harm than good by wasting energy and becoming less efficient than a gasser (in extreme slow DC charging cases).
**We now resume the original post, unedited**

No, that's nonsense, that can't be right
Sadly, it appears that Tesla's battery heating logic is quite simple - "if DC charging, run the battery heater". At least, from the sessions I've run at various existing battery temps and with both CHAdeMO and Supercharging, at 150kW, 72kW, and at 40kW (CdM), while logging data and observing.

What makes you think that, where'd you get this data?
How'd I find this? I hesitate to reveal my methods (though they are publicly available), by the fact that this complaint/observation isn't already documented (I tried searching, believe me), and just like white-hat hacking, revealing the method can expose undesired side-effects - like disabling that access completely, or (in the case of hacking) letting n'er-do-well's do bad things. The data I see, though, correlates closely with one another with multiple sources (e.g. motor power -> cooling loop mode -> inlet temperature -> cell temperatures), such that I can say with fair certainty that this is what's going on, though admittedly I don't have a LARGE number of samples; I'd be interested if anyone with the logging tools to also correlate or refute my findings.

So, the battery heater in the Model 3 is achieved through the motor/controller, by stalling it and making it emit waste energy but not turning. Clever trick. When the battery heating function is active, I can see the motor gets quite hot (181F is the hottest I found it, I think), and that follows into the battery inlet coolant temperature (being hotter than the hottest cell by a few degrees, meaning it's heating the pack), and in turn, the cell temperature rises.

That's just because DC charging causes the battery to heat up
You can tell for absolute certain that it's heating the pack, not cooling it, by the inlet temperature always being higher than the cells. Also, the motor heats up (quite significantly) while parked and "off", which means the heater is active. You can also see this happening while "conditioning battery for Supercharging" while navigating to a Supercharger - it starts the heater "early" and continuously heats from the moment you start navigation until you're done charging. We're talking about heating a 110 degree (F) pack, not a 40 degree pack.

Shockingly, this heating consumes 4kW of energy, constantly. In a 40kW (100A limit x 400V max batt V) CHAdeMO station, that means you only get ~34kW of input to the battery, because the motor is consuming the rest of it, needlessly heating the battery. You effectively get a 10% tax on your energy/time bill for owning a Tesla and heating the battery, endlessly (possibly until 55C, a number found in a Tesla patent during research on this).

It's also quite possible that this discrepancy - the battery heating - is partly responsible for the discrepancy between the Supercharger vs. the in-car billing that was noted earlier, that Tesla later refunded for many owners in bulk. The SC dispenses a certain amount of energy, but the battery logs less than that full amount of energy entering the battery, so the in-car display is based on "kWh into pack" while the station measures "kWh into car".

Tesla knows best, you're thinking too hard about this
There's something to be said for "Tesla knows best", and "the battery is probably happier to charge warm", but not at these extremes, with no control logic thinking "well... maybe we ought to not heat the pack when it's not peaking cell voltages", or "well... maybe it doesn't need heating if it's within human-happy temperatures". But again, I'm seeing it heating the battery well past 110 F, and yet it keeps the heater running. On a Leaf, this would be darn near 11 or 12 temp bars, if I recall correctly. Except the car's *actively* doing this to itself.

I recently read a bit about lithium battery degradation - the mechanisms of degradation, or at least the primary ones for voltage abuse, are electro-plating (ripping apart the copper materials) at low voltages, and acidic reaction (ripping apart the separator material) at high voltages and high temperatures. There's also cycle life, as lithium ion migration punches little molecular holes in the material with each cycle. Knowing these mechanisms, it seems terribly counterproductive to punch the voltage higher (causing voltage/temperature-based acidic decay) while charging, though it does indeed move molecules around faster (thus allowing faster charging rates) for high-current Supercharging.

There just seems to be no need to do this at lower speed charging, like 72kW charging or ultra-sluggish CHAdeMO rates. The battery is basically just being cooked that way.

Oddly, right after you're done charging and unplug it, the temp parameters go back to normal, the heater turns off, and the active cooling kicks in (if it's overheated the pack by its blind heating, you'll hear the radiator fan turn into a vacuum cleaner). So it cools right back off after it's done in the oven, throwing away all that energy.

What's it matter?
Well, if Tesla's mission is sustainable energy, then an unnecessary energy tax is, at bare minimum, undesirable and avoidable waste. Despite their best efforts to the contrary, many people still can't have home charging - particularly those in apartments or other shared housing (#bayarea). In particular, I've never had home charging in my one-car-one-EV-household since 2014 (briefly had it from 2013-2014, though). So, many people use Supercharging regularly. In all but the fastest V3 stations, this unwanted battery heating takes away from peak energy, and even at the fastest charging (250kW, but let's say 200kW for realism), 2% of that being "loss" ends up being 4kW, which is exactly the same as what's being input as battery heater energy - so why would it even be necessary? It's a bit self-defeating, and has a narrow band of utility that's disputable from both directions - useful or not useful - but seems to bias toward "not useful" to me.

It's also potentially harmful to the batteries, given the nature of temperature-based high-voltage degradation (a fully charged, hot battery - especially under charging load where voltage distribution may be internally uneven).

So why do it? Is this just an overlooked side-effect of "welp it worked once, ship it" and then forgetting about filling in additional logic for other cases (e.g. the heater was originally 2.5kW, I think I read elsewhere)? Other thoughts?
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Active Member
Apr 25, 2019
I'm not going to support or refuse your post, but:

(a) You are presumably working from observations on a sample of ONE (your car). How do you know its not faulty?
(b) "I have all the evidence and reasoning, but I'm not going to tell you what it is" clearly suggests that in fact you do NOT have such evidence. To be scientific you must also be transparent.
(c) You spend 90% of your post defending yourself against potential (not actual) detraction, but almost none explaining your claim.

If you think you have found a design flaw or issue, state it clearly, explain the evidence and reasoning that supports your claim, and only then worry about how others will interpret it.
It sounds like you are using scan my tesla, when talking about battery inlet and cell temperature?
Here is a video from teslabjørn regarding this. The heating actually stops when the battery reaches about 40 degC (on 50kW charger).

I remember in another video when he charged at 11 kW AC with a cold battery, the model 3 still used 7 kW for heating, leaving only 3-4 kW for charging. If this brings down the total charging time when you have your charing limit set to 90%, it is good. But this should be disabled when you set a low charging limit, and you only need a little juice to continue driving.
Well, it may not be a bug. Recently, I read an article in the science section of a quality newspaper here in The Netherlands about researchers that noted that a very warm battery during charging may actually limit the degradation process as a result of that charging. Research was done at the Pennsylvania State University and published in the science magazine Joule. Funny part is that they don't seem to know Tesla is already using this method. Main take-away (translated by me):

DUTCH: De onderzoekers hebben echter een optimum gevonden: als je alleen tijdens de tien minuten extra snel laden de batterij opwarmt tot 60 graden, valt de schade aan de batterij mee en behoud je grotendeels de lange levensduur. Het concept dat je kan spelen met dit compromis is hier erg belangrijk.” Na tien minuten wordt de batterij weer afgekoeld, en dat lijkt in de proeven van de onderzoekers zonder al te veel problemen te gebeuren.

ENGLISH: The researchers found an optimum: if you quickly heat the battery to around 60 degrees celsius during a short 10 minute charging session only, the battery damage will be very small and the longevity of the battery will be preserved. The concept of playing with this compromis is very important. After 10 minutes, the battery will be cooled again, and that method seems problem free.

https://www.nrc [dot] nl/nieuws/2019/10/30/even-de-accu-opwarmen-om-snel-te-kunnen-opladen-a3978544
BTW, to clarify the principle I would like to note the following (I'm a masters student electrical engineering, so I understand more and more of physics principles, but also I make mistakes, so please correct me if I'm wrong). In normal language: higher temperatures make it easier for ions to move (higher mobility). Part of the degradation is the fact that the ions are 'pushed' through the resistance. That is also why ludricous mode heats the battery, since that makes it easier to extract electrons from the battery (so less voltage drop and less degradation because of use). On the other hands, the high temperature accelerates chemical degradation processes (dendrite forming, etc), but apparently the one effect outweighs the other.


Well-Known Member
Aug 27, 2018
I didn’t read the whole thing but did you test this with with a “hot” battery. I can believe a warmer battery charges better/faster. Why do you think they added pre conditioning recently?

Also I’ve seen SC taper down to 1Kw when charging to 100% (which I’ve only done a few times just to check and balance the battery). Are you saying another 4kw is being charged and not displayed at that point in the charge?

Be curious what Model S/X does.
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REJECT Fascism
May 7, 2015
New Mexico
Are you talking about Li plating when you say 'electro-plating' ? If so read some more about the problem
Bjorn Nyland's videos are very informative regarding battery heating during charging. Highly recommended. I'm not sure about all the control laws in operation during charging in cold weather but my impression is that it is at least in part Amp dependent
>> Hesitate to reveal my methods

This makes it unscientific and just more blah blah.
The error is seldom with the results, it is almost always with the method.
"Hesitate to reveal my methods" that's a funny line. Why so secretive about having the CANBUS adapter that's widely known about? Anyone who watches that Bjorn guy on YouTube have probably already noticed this active heating phenomenon.
Because Tesla could decide "oh this is too much info for people to know" and do things to block access to this method, thank you very little. It wouldn't be the first time a company would fix a problem by making the information invisible once they found out how someone saw it. Yes, it's Scan My Tesla, and judging by the fact that I can find precisely dick on the subject, it seems that's not an incredibly widespread tool. (sorry, I'm not interested in watching every Joe that posts a Tesla video on YouTube - and most Tesla-related YT videos are pretty trashy and basic, but this particular guy might be worth watching if it's not an hour-long unscripted ramble-fest).

But I will take this one:
I'm not going to support or refuse your post, but:

(a) You are presumably working from observations on a sample of ONE (your car). How do you know its not faulty?
How could software be faulty in only one copy? I can see the battery heating target, see the heating energy, see the heating effect. There's no physical problem here, all the sensors report the same thing. If I were flying an aircraft, I'd see one sensor saying something strange, look at another and see it reporting the same thing, then another, and another, all the sensors agree that something wrong is happening. If I have no controls to change this myself, the proper thing to do would be to document it and try to see it fixed.

(b) "I have all the evidence and reasoning, but I'm not going to tell you what it is" clearly suggests that in fact you do NOT have such evidence. To be scientific you must also be transparent.
See above.

(c) You spend 90% of your post defending yourself against potential (not actual) detraction, but almost none explaining your claim.

If you think you have found a design flaw or issue, state it clearly, explain the evidence and reasoning that supports your claim, and only then worry about how others will interpret it.
Did I really? Because I look back at what I wrote, and I broke it down into potential detraction as a way to organize the data that supports my claim, clearly stated as both a summary at the beginning and end, explained the evidence throughout. I'm pretty sure you just skimmed it and didn't actually read it, but oh well, can't peel your eyes open and shove words into it.

So, if either of you could actually address literally any of the words I actually wrote, not merely attacking the way that I wrote them, that would be amazing.

Thanks, though, to the people that actually wrote insightful and constructive responses, not just trolling.

I didn’t read the whole thing but did you test this with with a “hot” battery. I can believe a warmer battery charges better/faster. Why do you think they added pre conditioning recently?
I agree, it definitely does charge faster, when possible. However, most of the time when there's a power limit, the battery isn't at its limit. I've seen a "hot" battery (thanks to overzealous pre-heating by navigation) still get power-capped, while at an un-paired 150kW SC. In fact it seems like most of the time I'm not getting full power, it's not at all related to battery temperature, and preconditioning thus has no effect. It's probably a site limit due to grid demand (I suspect Tesla works closely with PG&E in my area to dial back demand when needed). In most cases I'm seeing this just being an unnecessary energy tax, when the heating is not needed and would have no sensible effect at the rate I'm charging, which is limited by the station, not the battery, and to have that energy going into the battery instead would be more beneficial.

And yeah, from what I've seen, literally any time it's DC charging (and not at its maximum temperature, whatever that may be, because it keeps moving the "active heating" target value up as it heats), it's heating at 4kW. So that means for a 1kW full charge, it's dumping 4kW on the ground. I'd also be curious what the S/X platform does as well.
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Or just charge after a drive, before the battery cools
The battery never gets even remotely that warm - indeed it never even goes above 86 - when driving.

Well, anyway, I'm back to add more evidence of senselessness.

Today, I set out to see if the charging target (SOC limit) has an affect on whether it heats the battery or not, in a situation where it is completely senseless to heat the battery.

Before starting:

Battery is not being heated. Motor is cold.


Immediately after plugging in, set for 70% limit:

Calls for heating.

(inline image pasting is acting weird...)

10 minutes later, it's heating, but the target keeps rising (instead of using the target even remotely sensibly, it keeps "moving" the target, effectively making it heat forever).


Motor is getting quite warm, and it's warming the batteries.

4kW? Did I pull that number out of my arse?
You're right, those numbers are real and your car seems to heat the battery. As donkemaen said, you should look at a few of Tesla Bjorn's videos. It's possible that after the battery has heated up, the charge will be faster and the overall time will be lower (even though initially it's slower). Could also be to preserve the battery as jeroenjx indicated. I would assume Tesla have a good reason to do so.
I'm eager to get my M3 and buy the adapter to see all the data.
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4kW? Did I pull that number out of my arse?
View attachment 481420
If you actually took the time to watch the video I posted (30 seconds would be enough from the timemark i posted), you would know that the front AND the rear stators are used for heating. Usually, 7.5 kW combined. And you will see where they both stop heating.
My guess why Tesla is doing this:
Having a battery at the optimal temperature for the given charging speed increases the battery life, even if it's not needed to get the actual charging speed.
Yep, it heats the battery until it doesn't need to heat the battery anymore...then it cools the battery if it is too hot...and cools it till it doesn't need to cool it anymore...Heating power up to ~7.5kW. Been there done that but good that you have come to the came conclusion as all the others before.

Ohh and you know that you can make a custom page in the app so that we all don't have to look at things like your steering angle...etc?
So it doesn’t heat it up when charging with AC at home? If that’s the case I wonder why or why not?
It does, but it stops at a much lower temperature. I don't have this device but you can observe it if you start a charge on a cold battery and watch the numbers. At around 0C my car will pull the full [email protected] for ~10 minutes and charge at ~3km/h. That is the battery heating. After this it goes to the full ~48km/h.
OP, do you have anything new to add to Bjorn Nyland's findings ?

@GtiMart - Yes, Tesla is preventing irreversible Li plating.

Yeah, I'll add everything I said in OP that's been ignored. Particularly, that it doesn't help speed charging in most cases. If you're waving around this "Li plating" theory as the only defense for this unconditional heating behavior, you're standing on pretty shaky ground given that it doesn't do this with AC charging (it gets the battery above freezing, and that's it - basically it never happens for AC charging, but it happens pretty much constantly with DC charging), but AC charging is not fundamentally different from DC charging.

I still fail to understand where the wild responses of defense are coming from. This is incredibly wasteful behavior that just puts a tax on your energy bill and slows down charging. It's bad from every angle except the highest speed Supercharging. Bjorn's video worked from "see symptom" to "try to explain cause", while I'm working from "see symptom" to "try to explain how to make it better".

There needs to be more logic to prevent this heating when it's not necessary or helpful. My theory is that this is still just something that was programmed and forgotten, left unrefined after it worked once. There's significant room for improvement -- like not heating the battery if the station reports under a certain power, or if you've selected a lower charging limit.
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