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Battery Heater failing to turn off after battery is warmed?

4.2K views 14 replies 8 participants last post by  garsh  
#1 ·
Hi, am new here but searching through the site didn't find any similar threads on what I'm experiencing.

I have a 2020 LRAWD M3 which I've owned now for 1yr; i previously owned a MR-RWD M3 for 12 months prior to upgrading to the LR.

On my MR, I would routinely get the rated 240Wh/mi on the car and range mileage consumed matched (within a narrow error band) the actual miles driving. The historical Wh/mi for the car over 18k miles, all in chill mode, with me driving was 237Wh/mi.

On my LR-AWD now however, I'm driving the same routes and again in chill mode exclusively but I am unable make but a rare trip below 290-300 Wh/mi. What is more interesting is that if I drive somewhere for 20-25 minutes, park the car for 10 minutes on an errand, the subsequent drive, on occasion, will operate at 240Wh/mi for the next trip as I would expect. Other times it returned immediately to a 300Wh/mi efficiency. I have one regular 205 mile trip I have to make (which was doable with the MR but other needs warranted the LR upgrade) which in Chill mode I have yet to arrive there with 40 miles range remaining and a 300Wh/mi trip efficiency. If I make a stop shortly into the trip, the next trip immediately after the stop I will see a more typical 240Wh/mi for a period and then the car returns to its same inefficient self. When I did this trip with the MR I regularly got ~240 Wh/mi in the various weather conditions (Central valley California, so no weather extremes) and would get there with 30 miles to spare, which was expected on a 240 mile range M3. I have yet to get past 230 miles with my LR M3 which now has a historical Wh/mi rating of 293.

The behavior I'm experiencing perhaps correlates to a battery heater that may not be turning off once the battery is contioned appropriately. thus impacting the range for the remaining portion of the trip.

I've tried to engage Tesla service to investigate, but so far they are only saying 'the faster you drive the less efficient the car will be' which while accurate, is discounting the other data I have presented them that appears to point to the battery heater temperature sensor or relay or some such causing an overactive heater. They say their diagnostic tests done remotely show no warrantable items to service, and promptly cancel the appt before it occurs. Has anyone ever experience this condition and gotten Tesla service to respond and investigate? I'm about to start CAN logging to investigate more, and appreciate any tips on what may be going on. No other M3 owner I know who lives in Chill mode is getting this terrible efficiency as I am, and my similar driving of my MidRange showed that I'm not the culprit...

TIA.
 
#2 ·
There is no battery heater in the Model 3. Heat is recovered from other operations such as the HVAC running, or from the traction motor windings.

Another thing you should keep in mind is that the optimal battery temperature is something like 83 degrees, and most of the time it's not that warm even in California, in winter.

Ironically, if your battery is cold (below 80 degrees), and it's not warm enough to use the air conditioning, and you're driving delicately, the car will warm up the traction motor windings by intentionally wasting energy on them so the battery can be warmed up. That could cause higher than normal Wh/mi readings.

A smaller but present issue is if it's colder outside, the tires become harder, which can affect energy consumption as well. I don't remember which direction it goes, but it's possible.
 
#3 ·
@JasonF’s response is great but I’ll add that the LR battery is heavier so you won’t ever be as efficient as you are in the MR and you have dual motors now which are a little less efficient.

Are the wheels and tires the same?
 
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#4 ·
@JasonF's response is great but I'll add that the LR battery is heavier so you won't ever be as efficient as you are in the MR and you have dual motors now which are a little less efficient.

Are the wheels and tires the same?
Yes, I would have expected the LR to have less efficiency than the MR, even tho Tesla reports the same rating for both. What I did not expect was 24% less efficient vehicle that can't get within 75% of its rated range.

yes, the cars are optioned exactly the same, including the aero wheel covers.

If the M3 has no heater, where is it spending its energy when 'predcondtioning for supercharging' and the Wh/mi jumps when about 15 minutes from the supercharger? I've also seen when charged to its target to draw current for scheduled departure. Where is this current being turned into heat in that scenario?
 
#7 ·
Ok, so if it has no heater, what could possibly be keeping it in that 'heating' or 'conditioning' mode longer than it should be on a 205+ mile drive? I expect the initial period of a trip to be inefficient as it conditions the batteries for use, but I never (or very rarely) see it drop back to ~rated efficiency like the MR I had for 18k miles did regularly.
 
#15 ·
Ok, so if it has no heater, what could possibly be keeping it in that 'heating' or 'conditioning' mode longer than it should be on a 205+ mile drive?
The fact that it doesn't have a dedicated heater, and therefore runs the front motor for a longer period of time to help heat things up?

As an experiment, the next time you're scheduled for this long trip, have your car charging for an entire hour right before you leave. Charging the battery heats it up quite well, and I find that this helps immensely with cold-weather-related issues (efficiency, reduced regen available).
 
#8 ·
If the car operates to consume more energy (kWh) to heat the battery (or anything else) that consumption is going to be reflected in the Wh/mile for the rest of that trip. You cannot get it back. If you start a drive and the battery needs heating for part of the first leg then you stop and charge and the battery stays warm from the short stop and supercharging, the next leg Wh/mile will show no effect of the battery being heated so it will be less Wh/mile than the first leg.
 
#9 ·
Yes, I understand conservation of energy theory, thanks. I was not expected to get it back. I am expecting the instantaneous efficiency to reach rated levels after it stops conditioning the battery and over the trip asymptotically reach its rated efficiency provided a sufficiently long trip. 205 miles in my mind is sufficiently long to see a similar efficiency compared to the MR on the same route and conditions.
 
#10 ·
Hi, am new here but searching through the site didn't find any similar threads on what I'm experiencing.

I have a 2020 LRAWD M3 which I've owned now for 1yr; i previously owned a MR-RWD M3 for 12 months prior to upgrading to the LR.

If I make a stop shortly into the trip, the next trip immediately after the stop I will see a more typical 240Wh/mi for a period and then the car returns to its same inefficient self. When I did this trip with the MR I regularly got ~240 Wh/mi in the various weather conditions (Central valley California, so no weather extremes) and would get there with 30 miles to spare, which was expected on a 240 mile range M3. I have yet to get past 230 miles with my LR M3 which now has a historical Wh/mi rating of 293.

TIA.
Are you sure that you haven't maybe seen cooler than summer temps? That's the simplest, most obvious answer.
 
#11 ·
I drove the MR from Dec 2018 through Dec 2019. The LR has been driving from Dec 2019 through now. So seasonality is similar for both cars. At first I indeed did write it off to 'winter' or whatever we get in CA requiring more pre-heating. Commuting is different in 2020 but I still have to do the 40 mile one way commute weekly and have done the 205 mile trip to the central valley multiple times with each car. When I get off at my exit to end the commute trip the MR would often show a trip efficiency of 225 Wh/mi whereas the LR is repeatedly 290.

Does a LRM3 spending its entire life in Chill mode with a historical 293 Wh/mi in a moderate climate seem odd to anyone else? If it was the driver, why was I so much more efficient in the MR?
 
#12 ·
Chill mode has very little impact to your usage. It is just as easy to go 80 in chill as one of the other modes.
Pre-heating isn't the issue with temperature, it's just battery efficiency. Most batteries do the same thing, they get cold and lose their capacity.
Many years ago, I took a camera skiing and the first time up the lift, it just wouldn't work. Came back to the bottom and it worked. Next time it worked perfectly. The difference, first trip I had it outside my jacket, the next time it was inside.
Tesla batteries seem to start losing their capacity around 70 degrees.