Battery life seems way off?

[AlanSubie4Life]

Yesterday is was -12F I used 43% and went ~35 miles, in our LR AWD. It’s the heater.

What was your average speed (time on trip meter) and Wh/mi? What were your tire pressures?

Also if you want more range (less usage) keep it <60 mph.

However, going faster in these conditions may well reduce usage, for obvious reasons. Not saying it's a great idea to try to drive 80mph at -12F, but it would probably result in better efficiency.

 

[coleAK]

What was your average speed (time on trip meter) and Wh/mi? What were your tire pressures?
.

tire pressures 42 psi, I add air for winter temps. Average speed 45mph. The roads are unplowed loose snow which also adds a lot of usage. My Wh/mi over the last 2 weeks is >600 Wh/mi.

 

[AlanSubie4Life]

tire pressures 42 psi, I add air for winter temps. Average speed 45mph. The roads are unplowed loose snow which also adds a lot of usage. My Wh/mi over the last 2 weeks is >600 Wh/mi.

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

 

[jjrandorin]

Yesterday is was -12F I used 43% and went ~35 miles, in our LR AWD. It’s the heater. If you want less usage (more range) turn the heat down to 60-62F, if you don’t care like me and want to be warm with windows that aren’t frozen keep it 68-70F. Also if you want more range (less usage) keep it <60 mph. As per regen, if there is snow or ice keep it on low, dry roads normal is good.

Given your location, if there is anyone here that should have experience with "tesla ownership in the cold", you definitely are in the top tier there

 

[PACEMD]

What was your average speed (time on trip meter) and Wh/mi? What were your tire pressures?



However, going faster in these conditions may well reduce usage, for obvious reasons. Not saying it's a great idea to try to drive 80mph at -12F, but it would probably result in better efficiency.

What? I don't think so.

 

[AlanSubie4Life]

What? I don't think so.

Try it and see! While certainly conductive heat losses will increase somewhat at speed, the car is really not subject to wind chill factors like a human.

It’s extremely unlikely that heat output will double at 80mph vs. 40mph, and besides, at these temperatures, the heat may be running at maximum output power anyway. Remember that if you go double the speed a fixed power output device will half the Wh/mi consumption. So as long as the car is in the open loop heating mode where it is trying to get the car to temperature, for sure going faster will help. It’s just math.


@coleAK - curious if the car is able to maintain the cabin at a good temperature with these external temps? I found that I get chilly drafts from the windows due to combo conductive/convective loss when it is 40 degrees out so wonder what happens when it is 50 degrees colder.

 

[PACEMD]

Alan, I always pay attention to your post but that's not the way that works. Or I'm not understanding what you are saying. I've been monitoring this for 5 months now on my routine 150-mile highway commute here in Montana. The biggest efficiency hits for me are from highway speed and temperature. Of those, speed is the big enemy, or at least the one I can control. Our speed limit here is 80 mph, above 60-65 mph efficiency drops, really taking a big hit when I cruse my usual 85 mph. This effect is much worse when the temperature is below freezing. This has been a common discussion here with no evidence I have read disputing my empirical observations. So perhaps I'm missing what you are trying to say........

 

[AlanSubie4Life]

Alan, I always pay attention to your post but that's not the way that works. Or I'm not understanding what you are saying. I've been monitoring this for 5 months now on my routine 150-mile highway commute here in Montana. The biggest efficiency hits for me are from highway speed and temperature. Of those, speed is the big enemy, or at least the one I can control. Our speed limit here is 80 mph, above 60-65 mph efficiency drops, really taking a big hit when I cruse my usual 85 mph. This effect is much worse when the temperature is below freezing. This has been a common discussion here with no evidence I have read disputing my empirical observations. So perhaps I'm missing what you are trying to say........

Of course aero losses will increase at speed, as we all know with the square. I am just saying that fixed losses (like heat) actually likely go down with speed. There is a crossover speed where at a high enough speed consumption will go up (and range will begins to decrease) but if you have a very high fixed load, the optimal cruising speed for range (optimal speed is about 25-30mph neglecting any of the huge effect of heat) increases. The higher that fixed load the higher the optimal speed.

Three primary elements can be modeled:

1) Fixed watts (accessories and overhead). HVAC is not necessarily fixed but can be in the right conditions. Wh/mi goes down with increasing speed.

2) Power (W) linearly proportional to speed. Rolling resistance for example. Wh/mi constant with speed roughly.

3) Power (W) proportional to the cube of velocity. Like aero losses. Means Wh/mi goes up with square of velocity.

There may be losses proportional to the square of speed related to drivetrain efficiency, but not aware of what those would be or how to model them.

Simple way to think of it in relation to heating losses in isolation is that the faster you get there, the less time you are running the heat. So you will use less energy to heat the cabin for a fixed trip distance.

 

[PACEMD]

So some isolated theoretical heat efficiencies not seen in real life? If you can show me how my Wh/mi will decrease at 80+ mph versus 65 mph in temperatures of -15 degrees f I will buy you free supercharging for life. If that were true it would solve all my commute worries. The truth is it doesn't work that way. I monitor my Wh/mi on the energy graft and the odometer every week on my 150-mile commute and look at that versus speed and temperature. Why? Because I want to understand the variables when the temperature drops to -25. I do not have a plot of that data but I can tell you that the Wh/mi increase with speed as I said, and increase with low temperatures. The two together ain't pretty.

 

[AlanSubie4Life]

Wh/mi will decrease at 80+ mph versus 65 mph in temperatures of -15 degrees f I will buy you free supercharging for life.

I was comparing 40mph and 80mph. 65mph may well be better than both of those speeds. But 80mph may still be better than 40mph. It depends. It’s a curve with a peak. The peak moves around depending on conditions. Snow on the road, for example, dramatically increases rolling resistance, and likely simply makes the whole Wh/mi vs. velocity curve uniformly higher. Whereas higher accessory use moves the peak of the curve to higher speeds.

 

[Dr. J]

Thank you for your feedback! I was expecting a bit of a drop and the range as an estimate but over 30% will make it hard to plan trips.

Use abetterrouteplanner.com to plan trips. You can set all kinds of variables.

Your battery will gradually degrade, so over several thousand miles you will see a small reduction in range. OTOH, as your brand new tires get worn in, you should see a slight improvement in actual range (i.e., lower Wh/mi consumption). HTH.

 

[PACEMD]

I was comparing 40mph and 80mph. 65mph may well be better than both of those speeds. But 80mph may still be better than 40mph. It depends. It’s a curve with a peak. The peak moves around depending on conditions. Snow on the road, for example, dramatically increases rolling resistance, and likely simply makes the whole Wh/mi vs. velocity curve uniformly higher. Whereas higher accessory use moves the peak of the curve to higher speeds.

Ok, now that's just obfuscating the fact that higher speeds and lower temperatures decrease efficiency. And in particular that the combination does nothing to improve that.

 

[TMThree]

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.

Battery is not as happy when cold. But if you use cabin heat, it can burn 6000W of power, so using seat warmers instead is recommended.

 

[S4WRXTTCS]

I think there are a few things to keep in mind.

Tesla is really optimistic about rated range. Like I have the P3D, and there is no way I'm ever going to get 310 miles.

Why won't it happen?

Temperature - On average day the Seattle area is around 40-50F
Rain - The rated range assumes there isn't any additional drag or resistance
Wheel/Tires - I have the 20" Summer Performance Tires and I've heard people who swap with 18" or 19" wheel/tires have a lot better efficiency
Speed - The speed limits are typically far higher than what Tesla does the rated range for. Like I can probably get close to rated range at 65mph which is fine in a 60mph zone, but 65mph is too slow for a 70mph zone.

In my experience with a 90% charge I can make a 190-200mile journey without stopping to charge as long as I keep the speed to 70mph or less. This assumes there isn't much elevation change or any rain. It also assumes that I'll arrive with about a 10% battery charge.

That works out to being around 80% efficient.

It's not what I was hoping for, but instead of worrying too much about it I simply assume the rated range is 250 miles.

I find it hard to believe that its 310 miles because then the TeslaFI leaderboard would be full of LR Model 3s with trips over 290 miles, but it's not. I'd only have to do 261 to make it onto their top 50 list for the Model 3.

I think the reason people aren't doing long stretches without charging is that the speed required to get rated range is less than the driving speed they want to go at.

I typically modulate my speed to give me 10% or more remaining range on my road trip to/from Portland. Sometimes I'll combine this with pulling behind a Semi where I'm still a decent amount of distance away from it, but close enough to get efficiency gains. If that's not enough I'll turn off the heat. If for some reason if it's still not working out I'll stop at the Supercharger in Centralia halfway through the journey.

 

[TMThree]

I think there are a few things to keep in mind.

Tesla is really optimistic about rated range. Like I have the P3D, and there is no way I'm ever going to get 310 miles.

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:

280 mile range for P3D
296 mile range for AWD with 18" aeros
331 mile range for LR RWD with 18" aeros

The breakdown for driving at 80 mph is:

231 mile range for P3D
254 mile range for AWD with 18" aeros
273 mile range for LR RWD with 18" aeros

At 55 mph, you can go over 400 miles on the LR RWD.

I have the LR RWD. If I'm using aftermarket 19" rims and driving 90 mph, I get around 310ish Wh consumption. Today I took a leisurely drive with my 18" aeros and this is the result. I got over the EPA numbers needed to hit 325 mile range:

 

[coleAK]

I think there are a few things to keep in mind.

Tesla is really optimistic about rated range. Like I have the P3D, and there is no way I'm ever going to get 310 miles.

Why won't it happen?

Temperature - On average day the Seattle area is around 40-50F
Rain - The rated range assumes there isn't any additional drag or resistance
Wheel/Tires - I have the 20" Summer Performance Tires and I've heard people who swap with 18" or 19" wheel/tires have a lot better efficiency
Speed - The speed limits are typically far higher than what Tesla does the rated range for. Like I can probably get close to rated range at 65mph which is fine in a 60mph zone, but 65mph is too slow for a 70mph zone.

In my experience with a 90% charge I can make a 190-200mile journey without stopping to charge as long as I keep the speed to 70mph or less. This assumes there isn't much elevation change or any rain. It also assumes that I'll arrive with about a 10% battery charge.

That works out to being around 80% efficient.

It's not what I was hoping for, but instead of worrying too much about it I simply assume the rated range is 250 miles.

I find it hard to believe that its 310 miles because then the TeslaFI leaderboard would be full of LR Model 3s with trips over 290 miles, but it's not. I'd only have to do 261 to make it onto their top 50 list for the Model 3.

I think the reason people aren't doing long stretches without charging is that the speed required to get rated range is less than the driving speed they want to go at.

I typically modulate my speed to give me 10% or more remaining range on my road trip to/from Portland. Sometimes I'll combine this with pulling behind a Semi where I'm still a decent amount of distance away from it, but close enough to get efficiency gains. If that's not enough I'll turn off the heat. If for some reason if it's still not working out I'll stop at the Supercharger in Centralia halfway through the journey.

I get rated Wh/mi all summer in Alaska. Well the 4 months of it, when like you said it isn’t raining.

 

[AlanSubie4Life]

Ok, now that's just obfuscating the fact that higher speeds and lower temperatures decrease efficiency. And in particular that the combination does nothing to improve that.

Not really! Just pointing out that it’s not always more efficient to go more slowly. Of course, it is always a negative to use the heat as far as range goes, and the lower temperatures probably reduce drivetrain efficiency a bit as well.

 

[PACEMD]

Not really! Just pointing out that it’s not always more efficient to go more slowly. Of course, it is always a negative to use the heat as far as range goes, and the lower temperatures probably reduce drivetrain efficiency a bit as well.

Right, it's all cool, Alan. Nevertheless, the fact remains, higher highway speeds, meaning 70s/80s+, and lower temperatures decrease efficiency. The combination does nothing to improve that. Of course, it's not as simple as faster always equals less efficient. The original statement I questioned was that driving 80 mph with an external ambient temperature of -15f would improve efficiency over driving 40 mph at -15f. It may warm the battery faster but I'm willing to lay some money down says the Wh/mi go way up. I've seen those numbers as can anyone else.

 

[AlanSubie4Life]

The original statement I questioned was that driving 80 mph with an external ambient temperature of -15f would improve efficiency over driving 40 mph at -15f. It may warm the battery faster but I'm willing to lay some money down says the Wh/mi go way up. I've seen those numbers as can anyone else.

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

You can see the efficiency rapidly improves as speeds increase (gets lower) before starting to get worse again, but only gets worse gradually from there. It’s only modestly higher at 80mph vs. 40mph (by about 20-30Wh/mi). Optimal speed is around 55mph.

Compare to the original curve with no big base load:
https://www.wolframalpha.com/input/?i=Plot+350%2Fx+%2B+101.494+%2B+0.0300833+x%5E2+with+x+from+10+to+80

No heater:

Optimal speed is around 20mph. 80mph is a lot worse than 40mph of course, by about 140Wh/mi - there is nothing to counterbalance to the extra aero loss in this case.

So putting some actual numbers to it, you’re almost certainly right that 40mph is still more efficient than 80mph even in these very cold conditions. But 40mph is about the same as 70mph.

So I’ll retract my original statement and rather than say “80mph may be more efficient than 40mph,” I will say:

...that efficiency will improve under these conditions the faster you go, up to about 55mph.

I could also say (clearly correctly) that 80mph is very likely more efficient than 20mph, under these conditions (see the plot)! I guess where I was wrong is that at 40mph, you’ve already really got most of the benefit to moving right along, as far as the static load goes. Somewhat diminishing returns at that point to going faster. Looks like I would have been barely right if I had said 80mph is more efficient than 30mph (they are similar).

 

[PACEMD]

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