New Tesla Owner, battery range lower than expected

[menzic]

Pay close attention next time the Lexus self charging hybrid advert is on TV. It states that it can drive up to 50% on battery, if you read the small print that is based on driving at 27mph. Based on that a M3 LR can do 600 miles. So I don’t pay too much attention. The same way I don’t hold Apple accountable for how quickly I burn through my battery on Tesla forums . I just plug it in when I need to.

 

[Jeeves]

Ok so taking into account only using between 20 and 80% the real world range of SR+ is around 140 - 150 miles then. Had planned on around 180 miles but seems that was too optimistic.

Not a problem day to day but once a week I do 120 mile round trip with no time or facility to charge which if I keep to the suggested parameters, could be a bit tricky in the winter.

Sadly no Tesla SC’s near me until the ‘coming soon’ site for Dorchester is built.

You should be OK even in winter, but you may want the 90% then. Consider preheating or ev.energy to target charge completion by your departure time.

 

[Neilman]

Can't speak for the M3SR+ but my M3LR took me on a round trip to London from Southampton via M3 covering 159 miles with the battery starting at 90% dropping to 28% when I got back. There were a couple of shorter local trips included in that 159 mile total.

Started at 90% "trip" charge to make sure I had enough then afterwards it took 5.5 hours to recharge the battery back to 80% "weekly" charge.

 

[M3BlueGeorgia]

You should be OK even in winter, but you may want the 90% then. Consider preheating or ev.energy to target charge completion by your departure time.

Can't speak for the M3SR+ but my M3LR took me on a round trip to London from Southampton via M3 covering 159 miles with the battery starting at 90% dropping to 28% when I got back. There were a couple of shorter local trips included in that 159 mile total.

Started at 90% "trip" charge to make sure I had enough then afterwards it took 5.5 hours to recharge the battery back to 80% "weekly" charge.

Speed is the range killer, so you'll go much further on a congested UK motorway at 40-50 mph than cruising on a Midwestern US freeway at 85 mph.

 

[Glan gluaisne]

Speed is the range killer, so you'll go much further on a congested UK motorway at 40-50 mph than cruising on a Midwestern US freeway at 85 mph.

It is indeed. Energy usage increases roughly in proportion to the cube of speed, so going from 50mph to 70mph will very roughly use 2.744 times more energy per mile. This shows in the Wh/mile data. Comparing two recent drives I made shows this pretty well.

Last week I did a ~35 mile round trip to Amesbury and back, mainly on the fairly empty A303. I was hoofing it a bit, and the car used an average of about 330 Wh/mile. Today we drove a roughly 112 mile round trip to Gosport and back, and because my wife was in the car and I drove fairly sedately, despite the motorway run along the M27 (with it's 50mph limit for a fair bit of the journey), the car averaged about 222 Wh/mile.

The temperature and weather was much the same for both trips, but today the car only used about 67% of the energy per mile it used compared to my solo trip last week.

 

[MrBadger]

Great article from ABRP Tesla Model 3 Performance vs RWD consumption - Real Driving Data from 233 Cars

 

[Jason71]

It is indeed. Energy usage increases roughly in proportion to the cube of speed, so going from 50mph to 70mph will very roughly use 2.744 times more energy per mile. This shows in the Wh/mile data. Comparing two recent drives I made shows this pretty well.

Last week I did a ~35 mile round trip to Amesbury and back, mainly on the fairly empty A303. I was hoofing it a bit, and the car used an average of about 330 Wh/mile. Today we drove a roughly 112 mile round trip to Gosport and back, and because my wife was in the car and I drove fairly sedately, despite the motorway run along the M27 (with it's 50mph limit for a fair bit of the journey), the car averaged about 222 Wh/mile.

The temperature and weather was much the same for both trips, but today the car only used about 67% of the energy per mile it used compared to my solo trip last week.

From what scientific principle are you deriving the cubed relationship between speed and Energy?

 

[Glan gluaisne]

From what scientific principle are you deriving the cubed relationship between speed and Energy?

It's a bit rough (as mentioned) but the lion's share of drag is aerodynamic, and aerodynamic drag is proportional to the square of (air) speed (from 0.5.rho.Cd.A.V^2), so energy is proportional to the cube of (air) speed. The rough bit comes from the fact that rolling resistance also forms a part of the total drag, and that varies only slightly (in comparative terms) with speed. There will also be some impact from the terrain, although this tends to average out over longer journeys to some extent.

All a bit rough, but as an illustration of the significant impact speed has on energy consumption it's a reasonable approach, IMHO.

 

[mrobins64495]

Still rarely averaging over 220kw/h. I even had a trip (65miles) into the city where my LR averaged 192kw/h averaging 65 on the motorway and a little congestion into the city.

It’s now dropped to 220/240kwh with the colder weather.

 

[Jason71]

It's a bit rough (as mentioned) but the lion's share of drag is aerodynamic, and aerodynamic drag is proportional to the square of (air) speed (from 0.5.rho.Cd.A.V^2), so energy is proportional to the cube of (air) speed. The rough bit comes from the fact that rolling resistance also forms a part of the total drag, and that varies only slightly (in comparative terms) with speed. There will also be some impact from the terrain, although this tends to average out over longer journeys to some extent.

All a bit rough, but as an illustration of the significant impact speed has on energy consumption it's a reasonable approach, IMHO.

Based on that in your own example you should have gone from 222wh/m at 50 to over 600 at 70mph ( 2.7 times) so it doesn't seem to produce results that even come close to reflecting reality. so even if correct it clearly forms only one component and not the defining one.

 

[AndrewGR]

Based on that in your own example you should have gone from 222wh/m at 50 to over 600 at 70mph ( 2.7 times) so it doesn't seem to produce results that even come close to reflecting reality. so even if correct it clearly forms only one component and not the defining one.

I think you will find that it is power that goes up roughly as the cube of speed, not the energy used per mile. Energy used will go up roughly as the square of speed. If you go faster you get there faster so you use the higher power for a shorter time.

 

[DJP31]

Based on that in your own example you should have gone from 222wh/m at 50 to over 600 at 70mph ( 2.7 times) so it doesn't seem to produce results that even come close to reflecting reality. so even if correct it clearly forms only one component and not the defining one.

I wonder if a good practical non scientific test would be test the last 5 miles efficiency using the energy graph. So choose a motorway, enable the nav and then drive like a grandma for 5 miles, and note Wh/m from the energy graph. Then do another 5 miles like you stole it and compare the two.

 

[Jason71]

I think you will find that it is power that goes up roughly as the cube of speed, not the energy used per mile. Energy used will go up roughly as the square of speed. If you go faster you get there faster so you use the higher power for a shorter time.

obviously the E=1/2MV2 formula applies only while accelerating so when cruising at 70 vs cruising at 50 it is correct that it is air resistance that is the defining factor but since we were told to ignore that factor in most of the GCSE Physics I did a very long time ago I don't really have much insight to that though I was under the impression that that also was proportional to V squared.

 

[drtimhill]

Picture attached:-

Yeah you have charging set to about 90% by the look of it, so the range looks about right. As noted by others, to prolong battery life you should keep the car between 20% and 80% (or even 30% and 70%). However, dont fret it, and if you are going on a long road trip go ahead and charge to 100% (though you won't have regen braking until the battery discharges enough to allow the car to do regen).

You will find there is only a very indirect relationship between the miles range shown for the battery and what you actually get, since there are many variables (driving style, temperature, terrain) that the simple estimate does not allow for .. you need to think of the battery SoC as more like a gas tank level meter. The Energy graph gives much more accurate numbers, and is your friend if you really need to track mileage.

 

[Jeeves]

I recommend taking a look at ABRP to get good predictions on your likely use of the battery on that 120 mile journey.

 

[Glan gluaisne]

Based on that in your own example you should have gone from 222wh/m at 50 to over 600 at 70mph ( 2.7 times) so it doesn't seem to produce results that even come close to reflecting reality. so even if correct it clearly forms only one component and not the defining one.

Firstly, I'll repeat that I DID say it was rough (twice), it was just a rough illustration of the relationship between speed, drag and energy use per unit time. Secondly, we never drive at a constant speed for a whole journey, speed varies, along with many other variables. It is a fundamental fact that aerodynamic drag increases in proportion to the square of speed, and the energy used per unit time increases in proportion to the cube of speed.

The energy needed to accelerate to a given speed has some impact, but much of it will be recovered when slowing down, as the law of conservation of energy applies, with only a small amount of energy being lost as heat in the brakes and motors, etc. during regen. I'm pretty sure that aerodynamic drag accounts for probably the lion's share of the overall drag, hence the reason that lowering Cd and the projected frontal area has such a significant impact on fuel/battery energy consumption.

 

[Jason71]

Firstly, I'll repeat that I DID say it was rough (twice), it was just a rough illustration of the relationship between speed, drag and energy use per unit time. Secondly, we never drive at a constant speed for a whole journey, speed varies, along with many other variables. It is a fundamental fact that aerodynamic drag increases in proportion to the square of speed, and the energy used per unit time increases in proportion to the cube of speed.

The energy needed to accelerate to a given speed has some impact, but much of it will be recovered when slowing down, as the law of conservation of energy applies, with only a small amount of energy being lost as heat in the brakes and motors, etc. during regen. I'm pretty sure that aerodynamic drag accounts for probably the lion's share of the overall drag, hence the reason that lowering Cd and the projected frontal area has such a significant impact on fuel/battery energy consumption.

I was just being scientific. You proposed a theory that predicts 600wh/m then gave an experimental result that you said roughly supports your point that shows 330wh/m.
I'm just saying that for me personally "rough" doesn't cover that level of deviation from theory ( however many times you say it )
I am not denying that the relationship between speed and energy usage in an EV is non linear I'm just saying that your example does nothing to support your assertion that it is a cubed relationship when it does not even amount to a squared increase let alone cubed. ¯\_(ツ)_/¯.

 

[Glan gluaisne]

I was just being scientific. You proposed a theory that predicts 600wh/m then gave an experimental result that you said roughly supports your point that shows 330wh/m.
I'm just saying that for me personally "rough" doesn't cover that level of deviation from theory ( however many times you say it )
I am not denying that the relationship between speed and energy usage in an EV is non linear I'm just saying that your example does nothing to support your assertion that it is a cubed relationship when it does not even amount to a squared increase let alone cubed. ¯\_(ツ)_/¯.

I did no such thing. The two examples were entirely separate and unrelated; one referred to the unrealistic example of the way power varies in proportion to the square of speed, and energy per unit time varies in proportion to the cube of speed.

The other was just two real-world drives, wholly unrelated to the constant 50mph and constant 70mph theoretical examples.

I was at pains to highlight that there were rough approximations involved, and lots of variables that impact the real world outcome, other than just speed.

Not sure what's so hard to grasp, or why it needs arguing about, TBH. The laws of physics are pretty much proven beyond any reasonable doubt, (the first example illustrating the relationship between air speed and drag/energy). The modelling of real-world car performance is very much theory, with lots of variables that may be difficult to accurately measure, or impossible to predict in advance, one reason why the car display of range remaining may not be that accurate.

 

[GeorgeSymonds]

The car stores energy (measured in kwh) and the miles range available is just a translation of kwh to miles using the figure from the official test cycles and all as calculated by the BMS. Two things to note however, from what I can gather they use the US official test figures not the european ones so its never going to match the printed media. Secondly the BMS drifts out over time and there are various reports and articles on how to help it keep calibrated so it knows how many kwhs are available. Its also more a problem with the M3 than the MS and MX for various reasons I don't pretend to really understand due to internal resistance and balancing not that its important.

The other comment is about charge levels and various figures of keeping below 80% and/or 90% have been quoted. It always used to be 90% but its not really an exact number such that charge to 80% and you will be fine, charge to 81% and it falls off a cliff and the battery will self implode. I've always been happy with a middling charge level depending on what I'm doing - so if tomorrow I need to drive 140 miles I would charge to 90% and expect to get home around 20%, if the next time I thought I might need 10 miles I might just charge it to 50% or not bother if it was already over 40% SoC. I don't subscribe to the always be charging mantra. Its kind of like a petrol car for me - I don't fill up every day, I might brim the tank if I have a long journey, equally I never let it get too empty, I'm just not a slave to it either way.

 

[Jason71]

I did no such thing. The two examples were entirely separate and unrelated; one referred to the unrealistic example of the way power varies in proportion to the square of speed, and energy per unit time varies in proportion to the cube of speed.

The other was just two real-world drives, wholly unrelated to the constant 50mph and constant 70mph theoretical examples.

I was at pains to highlight that there were rough approximations involved, and lots of variables that impact the real world outcome, other than just speed.

Not sure what's so hard to grasp, or why it needs arguing about, TBH. The laws of physics are pretty much proven beyond any reasonable doubt, (the first example illustrating the relationship between air speed and drag/energy). The modelling of real-world car performance is very much theory, with lots of variables that may be difficult to accurately measure, or impossible to predict in advance, one reason why the car display of range remaining may not be that accurate.

agreed the physics is fixed and says Power varies in proportion to the cube of speed NOT the square as you have stated.
As such so does energy per unit time but no one cares about that since we drive for a fixed distance not a fixed time hense why we talk about wh/mile not wh/minute. And since at a higher speed you cover the distance more quickly your energy consumption over a mile is proportional to speed squared not cubed.
As such i cannot agree with your original statement:

Energy usage increases roughly in proportion to the cube of speed, so going from 50mph to 70mph will very roughly use 2.744 times more energy per mile. This shows in the Wh/mile data

The theoretical energy usage would be 2.744 time more energy per minute but only 1.96 times more energy per mile.
Still a lot and not what you would actually see since 100% of your energy use is not used to overcome drag.