Battery life seems way off?

[AlanSubie4Life]

Interesting. Alan. I would not have even questioned the original statement if the speeds discussed had been in the 40 to 70 range. Where I see my Wh/mi take off is above that. My point of bringing this up was to not have new folks thinking higher speeds are not an efficiency loss in the winter. What I see in my ongoing trials to maintain my commute during the Montana winter is that the best way I can improve efficiency on very cold days is to keep my speed under 70, if I need the range. Otherwise, I drive my usual Montana 85 mph. Anyway, thanks again for that input. I appreciate it.
Phil

Agreed. The rough plots above bear out your empirical results. Seems like something around 55-60mph is best, and that is what you are finding it seems. You’d see very little difference between 55 and 70mph (maybe 5%) so may as well go faster. But by 80mph the impact becomes a bit more concerning, probably 10%, and takes off rapidly for speeds above that.

I guess the corollary to this, which is obvious from above, is in winter you REALLY don’t want to be going slow or stuck in traffic. Your range will be destroyed! It’s pretty clear that speeds below 30mph are not good in extreme cold. You need to be moving along at around 40mph or higher. The “knee of cold winter range destruction” appears to be around 30mph to 40mph. Stay above the knee!

 

[taraquin]

So at those speeds the 7kW or whatever (not sure exactly) would be a 155Wh/mi adder.

Max output of heater is 7kW if that is what you meant. From what I understand it will only operate at that if climate is set to HI. Atleast in Model S climate rarely uses more than 5kW, but turn on HI and it can use almost 7kW. Remember that batteryheating of 7kW can kick in aswell if very cold and no precharge/preheat.

 

[taraquin]

A problem with 3 is the glass roof. Getting sunblock kit from ebay and adding some insulation can help. Watch Teslabjorns videos. He only insulated top roof. Kits from ebay can be used to insulate almost all of the glass roof at the back aswell.

Turning of rear heating might help a bit aswell if there are no passengers.

 

[AlanSubie4Life]

Max output of heater is 7kW if that is what you meant.

Yeah that is what I meant. I would assume that at -17F or whatever it would have to run at pretty close to 7kW no matter what the setting. I know from ChargePoint data that it uses 2kW or so steady state when I leave my car preheating for hours, with a 50 degree outside temp, with temp set point of 70. The AC would add to that I assume. Battery heating would also add.

To the extent those factors apply and depending on how large they get, it is possible that 80mph would be about as efficient as 40mph (once all the numbers are known just modify the formulas and replot them). But I have no idea how long the battery heating would run for - it’s likely not as much like climate control where it just has to run constantly.

A problem with 3 is the glass roof.

Driving on a chilly but sunny day the other day, and then observing what happened when the sun went down, I was actually wondering if the glass roof HELPS in cold, clear, daytime conditions. That winter sun radiant heat is still pretty hot, at least at my latitude.

 

[taraquin]

Yeah that is what I meant. I would assume that at -17F or whatever it would have to run at pretty close to 7kW no matter what the setting. I know from ChargePoint data that it uses 2kW or so steady state when I leave my car preheating for hours, with a 50 degree outside temp, with temp set point of 70. The AC would add to that I assume. Battery heating would also add.

To the extent those factors apply and depending on how large they get, it is possible that 80mph would be about as efficient as 40mph (once all the numbers are known just modify the formulas and replot them). But I have no idea how long the battery heating would run for - it’s likely not as much like climate control where it just has to run constantly.



Driving on a chilly but sunny day the other day, and then observing what happened when the sun went down, I was actually wondering if the glass roof HELPS in cold, clear, daytime conditions. That winter sun radiant heat is still pretty hot, at least at my latitude.

If temps are above freezing and it is sunny then probably yes, problem is heat loss through glass which occurs most of the time unless temp in sun close to what your preferred interior temp is. In winter, sun is liw and insulation of roof would do little to hinder heat from sun through glass since almost all of it comes through front, back or doorwindows, not roof

 

[TMThree]

I did some work a while back to fit some data I gathered with my car at a few speeds. Lots of variables and not too scientific so would not wager too much on it, but here it is:

A Primitive Model

This gives a 0.035 coefficient for aero. I actually think that’s a bit high since it seems that at 80mph 300Wh/mi is about what an AWD gets. Not 330Wh/mi. 0.03 works better.

Using that 7kW number for max heating (I think with AC it may be possible to get to 9kW though...it is possible to measure, but I don’t have a full 11.5kW charger (only 9.6kW) so I can’t check this).

So, I converted the formula to Wh/mi and added 9kW base load to the ~350W normal base load:

https://www.wolframalpha.com/input/?i=Plot+9350%2Fx+%2B+101.494+%2B+0.0300833+x%5E2+with+x+from+10+to+80

Can you add air density to the calculation?

For a turbocharged ICE vehicle, the colder temps bring more horsepower because of the increase in air density, same thing as driving in the mountains vs sea level.

For an EV, denser air just means more resistance when driving, so cooler temps harm range. I just don't know how much of an effect it has.

 

[AlanSubie4Life]

Can you add air density to the calculation?

Drag increases linearly with air density. At these extremely cold temps, the density is about 20% higher than at the temperatures (60 F) assumed in my model above.

So it might well make sense to increase the coefficient to 0.035 in extreme cold like this. This can easily be done by following the link and adjusting the coefficient yourself. It sounds like battery heating could be pretty significant so perhaps the load coefficient should be made higher than 9.35kW as well. As I said, it has to be measured with a high power wall connector and the limit of that measurement is about 10.5kW so it might not be enough. I guess the CAN bus readbacks provide the needed information on battery kW, if you have that access. That’s probably the best way to figure out the correct value for this coefficient in extreme cold.

Using 12.3kW base load and a higher air density, the optimal speed becomes 56mph with 430Wh/mi consumption (remember this model does not have a modified coefficient for increased rolling resistance due to snow on the road - still using that 101Wh/mi number - obviously this just shifts the entire curve upwards). 80mph is about 10-15% higher consumption:

https://www.wolframalpha.com/input/?i=Minimum+value+of+12300/x+++101.494+++0.035+x^2+with+x+from+10+to+80

 

[S4WRXTTCS]

This isn't accurate. It's not about being optimistic... Tesla applied a 310 mile range to their model 3 long range fleet, but that is not what a performance model 3 would ever get on the EPA test:

I agree that it's not exactly accurate because like you said what Tesla really did was they used the same EPA range for all LR variants. But, I'd argue that Tesla was also being optimistic because they posted ranges that were way more reflective of Summer conditions than Winter conditions in large parts of the country. They also posted numbers that are from lower speeds than most people travel at on the freeway. In addition to those two things they used the Aero hub caps with 18inch wheels that make the car look ugly. I don't believe I can even put those wheels on my P3D+ unless Tesla modified them from the last time I checked.

The chart you posted is very good for SUMMER conditions in Seattle. Its pretty reflective of the consumption I've had at various speeds during the summer. It doesn't fit the TeslaFI numbers I get for the winter though.

Now I don't necessarily blame Tesla for this because Porsche did the opposite, and Porsche is getting slammed in various forums for having poor range despite actual testing showing freeway ranges at speed over 250 miles. Which puts it on par with my P3D.

Going forwards I'm still going to advise people that Tesla inflated the ranges, but I'll use the chart you posted. The chart you posted is really good when it comes to showing the impact of speed. Maybe someone will create the same type of one, but showing the impact of outside temperature.

There is this calculator that could prove useful if I could figure out which numbers to plug in.
Tesla 3 Calculator

 

[TMThree]

I'd argue that Tesla was also being optimistic because they posted ranges that were way more reflective of Summer conditions than Winter conditions in large parts of the country.

All cars will suffer in range in winter.

You can read about the EPA test procedures on their website:

Detailed Test Information

 

[garth_angst]

Thank you for the feedback. I assumed a small drop in cold climate but 30% seems very excessive? I can get used to it if that is the way but still very unexpected.

You might be lucky to get only 30% drop.
I live in NY. I was averaging 208 Wh/mi from May when I got the car, until mid October. Always got over my rated miles.
Since then, I have been around 300 Wh/mi and about 30% range decrease WITHOUT even using the heat. I'm not looking forward to Jan-Feb range. It's actually been quite mild up here in December.

 

[S4WRXTTCS]

All cars will suffer in range in winter.

You can read about the EPA test procedures on their website:

Detailed Test Information

That's correct, but there are a few things to keep mind.

The EPA test for ICE vehicles does take into account temperature

From the link you posted:

"Beginning with 2008 models, three additional tests are used to adjust the city and highway estimates to account for higher speeds, air conditioning use, and colder temperatures."

I don't see where the EPA rating for EV's takes into account temperature.

Here is this info:
https://www.fueleconomy.gov/feg/pdfs/EPA test procedure for EVs-PHEVs-11-14-2017.pdf

And there is also this info:
Tesla Range Table - Teslike.com

For an EV temperature is critically important for so many reasons. Like for example if you have a short commute, and then temperature is lower than 50F then chances are you'll have zero regen during your entire commute to work.

For road trips it doesn't appear like the temperature drops that are common in the PNW region really impact range from the perspective of drag. It does impact EV range because of the heater power consumption.

The other thing that impacts only EV's/hybrids is energy loss while its sitting unused.

I've also experienced much higher sleep power consumption during the winter than the summer especially if I leave my car outside. Like over the last 16 hours my car has been sitting outside, and TeslaFI shows it sleeping. The starting range went from 145.55 to 136.6 so that's 9 miles in range loss.

Why did that happen?

Sentry Mode is off
Stay in Standby for Summon is off
TeslaFI makes sure the car goes to sleep

So what's causing the battery drain? I can only assume a battery heater is turning on.

That would account for why it doesn't happen during the summer, and it seems to scale with outside temp. I don't use any preconditioning, and I don't check in on it much (so no waking it from sleep).

I'm going to leave it in the garage tonight to see how much different the drain is. The garage is warmer than outside by about 10 to 20F. So I'm expecting to have a smaller per hour loss. If it's the same well then my theory goes out the window.

 

[AlanSubie4Life]

Tesla uses the 0.7 factor with the two-cycle test AFAIK.

“The introductory text of 40 CFR 600.115-11 states that manufacturers may alternatively use a factor of 0.7 in lieu of applying the derived 5-cycle equations. However, 0.7 is based on, and a direct mathematical result of, the pre-2017 slopes and intercepts and the now-outdated data that were used to develop those values, and its use should be discontinued for new gasoline and diesel vehicles. The new data used to generate the new slopes and intercepts is far more representative of today’s new gasoline and diesel vehicles, and the resulting slopes and intercepts (and the statistical strength of those coefficients) demonstrate that 0.7 is an inappropriate value to apply to new gasoline and diesel vehicles, in lieu of the derived 5-cycle equations. Use of the 0.7 factor would likely result in misleading label values for new gasoline and diesel vehicles. Thus, for the 2017 and later gasoline and diesel vehicles, it would not be appropriate to use the 0.7 factor. Rather than using the 0.7 factor, manufacturers should use either the derived 5-cycle equations with the new slope and intercept values or the vehicle-specific 5-cycle method. Because the updated data and regression equations do not inform EPA any further regarding advanced technology vehicles, the use of the 0.7 factor remains appropriate for certain vehicles and may continue to be used for electric vehicles, plug-in hybrid electric vehicles (charge- depleting operation only, based on an evaluation of cycle-by-cycle fuel efficiency), and other advanced technology vehicles, such as fuel cell vehicles.”

Most likely 0.7 is a bad factor to use for EVs as well. They just don’t know it yet, possibly.

 

[taraquin]

You might be lucky to get only 30% drop.
I live in NY. I was averaging 208 Wh/mi from May when I got the car, until mid October. Always got over my rated miles.
Since then, I have been around 300 Wh/mi and about 30% range decrease WITHOUT even using the heat. I'm not looking forward to Jan-Feb range. It's actually been quite mild up here in December.

Do you use winter tires or all season? Many summer and all season tires becomes really stiff at low temps which often increases rolling resistance a lot. Several consumption comparisons between Nokian R2 winter tires and Goodyear RS-A2 all seasons on my Model S showed that at 15C+ (55-60F+) there is only 5% difference in consumption (Nokians most efficient), but at 0-5C (30-40F) the Goodyears are really stiff and consumption is 10-15% higher compared with Nokians. At short trips it's the worst since tires heat up after driving a few kilometers. Also, tirepressure drops when temps drop so that must be taken into account aswell In general wet roads also increas3s consumption a few percent, snow on road is far worse.

 

[tna9001]

Owning a Tesla is like using a Windows computer, to get it to work like it’s supposed to, you’re got to know all the right “hacks”. If you want to just get in the car and drive just count on getting 70% of rated range.