The EV fact thread

[markjay]

"EV power usage at 70 mph is irrelevant/unrealistic as average speeds are much lower than that".

Gets quoted all the time.

That's nonsense said by people who never studied basic math and never heard of Variance....

 

[markjay]

I see kidney stones in your future! That's not good for you at all and you clearly don't drink enough fluid.

It's one thing that ExCell do not have EV chargers... but I hope they have toilets!

 

[poormansporsche]

I see kidney stones in your future! That's not good for you at all and you clearly don't drink enough fluid.

I drink a identical amount each day which includes 2 litres of squash. Strangely if I work a morning shift I "go" a good 3 times but on evening / night shifts I usually go the whole 10 hour shift without "going".

My original post was tongue in cheek though, you really wouldn't want to drive 10 hours without some form of break.

 

[tode]

Precisely - drag (which we know accounts for most of the power usage when cruising) is based on the square of the speed - it doesn't go up linearly.

I think you'll find that drag is proportional to the cube of the speed . . .

 

[ChipChop]

People with hundreds of thousands of pounds spare are not stupid though, likely ‘on paper’ the vehicles are owned by a foreign entity. They know what they are doing.

After the recent publicity anyone driving a Tesla Cybertruck on UK roads is guaranteed to be pulled over by the police and rightly so. That particular vehicles sharp edged panels are plainly very dangerous for pedestrians and cyclists in an accident.

 

[BTB 500]

As per my previous post, the expectation of having an EV charger next to each parking slot at the destination is unrealistic, and will become more so as more people drive EVs.

Fast superchargers at motorway services on the way there and back are the only realistic option. That, or leaving your car (EV or ICE) at your local train station car park and catching an early train into London.

As for convenience.... we should keep in mind that there are around 10m people living in Greater London, it's nigh on impossible to accommodate everyone's convenience needs, and compromises will have to made. Of course, people can choose to live in a rural area or a small village or town and only ever travel to other rural areas or to the nearest town, and they can use their car to their heart's content.

The other point made a week or so ago is that ultra-rapid charging relies on only a few of the Superchargers (or whatever) at any given site being in use.

E.g. a location with 20 x 250 kW chargers would require 5 megawatts from the grid to run them all at their rated output. It's pretty unlikely it would have a connection supporting that - if it had a 1 megawatt supply then each outlet would run at just 50 kW ... so a '10 minute charge' would be out of the question at busy times.

 

[190]

I think you'll find that drag is proportional to the cube of the speed

Ok semantics but the exact wording is important because it confuses the debate of whether is squared or cubed. My understanding was that drag increases by the square of the speed but the power needed to overcome that drag increases by the cube of the speed.

 

[Bobby Dazzler]

And driving at 60mph instead of 70mph would make a difference to EV range.

Has anyone done a test and observed the miles/kWh at 60 and then at 70 ?

I haven’t but I’ll try to remember to do it.

It's only a 14% increase in speed but you would expect to see the power requirements increase by a larger figure due to the aero drag.

And unless the journey starts at one motorway junction and ends at another - and the motorway is completely free flowing - the journey won’t be anywhere near 14% shorter door to door.

 

[BIGDOG]

The other point made a week or so ago is that ultra-rapid charging relies on only a few of the Superchargers (or whatever) at any given site being in use.

E.g. a location with 20 x 250 kW chargers would require 5 megawatts from the grid to run them all at their rated output. It's pretty unlikely it would have a connection supporting that - if it had a 1 megawatt supply then each outlet would run at just 50 kW ... so a '10 minute charge' would be out of the question at busy times.

Reading your comments on this thread is like listening to a nagging wife.

‘And another thing’…

 

[Bobby Dazzler]

E.g. a location with 20 x 250 kW chargers would require 5 megawatts from the grid to run them all at their rated output. It's pretty unlikely it would have a connection supporting that - if it had a 1 megawatt supply then each outlet would run at just 50 kW ... so a '10 minute charge' would be out of the question at busy times.

I follow your logic but I’ve never heard any Tesla drivers complaining that the charging speeds are woefully low at Supercharger sites compared to what is claimed. Tesla Supercharger sites tend to be well utilised at peak times too - other charging stations tend not to be. Someone like @clk320x might know from experience Tesla forums.

 

[markjay]

The other point made a week or so ago is that ultra-rapid charging relies on only a few of the Superchargers (or whatever) at any given site being in use.

E.g. a location with 20 x 250 kW chargers would require 5 megawatts from the grid to run them all at their rated output. It's pretty unlikely it would have a connection supporting that - if it had a 1 megawatt supply then each outlet would run at just 50 kW ... so a '10 minute charge' would be out of the question at busy times.

"They said is couldn't be done" can be used to describe almost every aspect of modern life.

Trains and railways, cars and motorways, planes and airports, radio, TV, mobile phones, Satellite Navigation, the Internet - at evey home and soon in every car..... the list is endless.

Anyone suggesting at the turn of the twentieth century that we will drill for oil in the Arabian desert or North Sea or Venezuela, pump it out of the ground, shipped it in big ships around the world, then process it and deliver it by road haulage to millions of local petrol stations around the globe to power 1.5 billion cars, would have been declared clinically insane.

The other obvious issue is that you are extrapolating on current technology.

 

[BTB 500]

I follow your logic but I’ve never heard any Tesla drivers complaining that the charging speeds are woefully low at Supercharger sites compared to what is claimed. Tesla Supercharger sites tend to be well utilised at peak times too - other charging stations tend not to be. Someone like @clk320x might know from experience Tesla forums.

Superchargers were just an example, but I would be interested to know what the grid supply to their sites is rated at (I tried to find out, without any luck). A 5 megawatt connection is unlikely I think - that would supply 270 UK houses all simultaneously running at maximum possible consumption (normal domestic supplies are 80A, so at 230V that's 18.4 kW).

I've certainly read a fair few comments from EV drivers about getting much less than the rated maximum power from ultra-rapid chargers, even with the relatively light usage most sites have now. I don't recall whether that was Tesla or not though.

 

[BTB 500]

"They said is couldn't be done" can be used to describe almost every aspect of modern life.

Trains and railways, cars and motorways, planes and airports, radio, TV, mobile phones, Satellite Navigation, the Internet - at evey home and soon in every car..... the list is endless.

Anyone suggesting at the turn of the twentieth century that we will drill for oil in the Arabian desert or North Sea or Venezuela, pump it out of the ground, shipped it in big ships around the world, then process it and deliver it by road haulage to millions of local petrol stations around the globe to power 1.5 billion cars, would have been declared clinically insane.

The other obvious issue is that you are extrapolating on current technology.

The ability of the power generation & distribution infrastructure to support close to 100% BEV usage in future is something else though. I'm just looking at the operation of existing sites now - each charger can't supply any more than the total power coming into the site (which isn't infinite - it will have a hard limit) divided by the number of chargers there. Obviously as batteries get bigger and chargers more powerful and EVs more plentiful the more of an issue this will become.

 

[clk320x]

I follow your logic but I’ve never heard any Tesla drivers complaining that the charging speeds are woefully low at Supercharger sites compared to what is claimed. Tesla Supercharger sites tend to be well utilised at peak times too - other charging stations tend not to be. Someone like @clk320x might know from experience Tesla forums.

Even with V3/V4 sites being full I have always got the max power output. The sites have sufficient power supplies but if this isn’t possible they are supported by ‘Mega Pack’ batteries for peak use.

 

[Will]

Certainly 6 hour etc. non-stop trips are exceptional, but something like two hours out and two hours back isn't a particularly unusual case for many people. And I think most people can drive for a couple of hours without needing to stop. So a suggestion that EVs are just as convenient on longer runs all hinges on being able to charge at the destination.

Obviously on motorways a much higher proportion of drivers really are making long runs (including vans/coaches/trucks ... not just private cars), so rest/comfort breaks are probably more of a requirement. Certainly historically (when most motorway service stations were built) cars were a lot slower and not really capable of long high speed runs anyway. When I was a kid driving from Surrey to Nottingham to stay with my grandparents took most of a day - the family car we had then was theoretically capable of 72 mph, but certainly not all day long! We always stopped a couple of times. Now I wouldn't dream of it - while we still lived down south I drove up to Nottingham for a funeral and was back home again by late afternoon.

I definitely think it’s worth remembering that even in 2025 there’s plenty of EVs out there with quite respectable ranges already. Perhaps not Vito vans with room for several dogs etc - totally understand your specific example which is very niche for the type of journeys etc but this is hardly representative is it?

As time goes by (and a relatively short time too!) EVs are getting better in terms of performance, range, charging speed etc and the infrastructure for charging is improving all the time too.

The excuses for not being able to use one are weak already and as you mention, compared to a few decades ago the expectations have changed already.

In other words, the preference for not stopping is minor. You’d have had to stop in the past and if you happen to live just a little beyond the current range for being able to do a 400 mile round trip without stopping at all (and with no changing facility at the exact arrival location too) then you would just have to change your habits.

And no doubt in the future there will be more changing infrastructure - including at the Excel centre - and hopefully they’ll have a Vito equivalent with a 500+ mile range so you might be able to not have to stop at all for even 30 minutes on the way back if you don’t have any way to charge at your destination

 

[ToeKnee]

I think you'll find that drag is proportional to the cube of the speed . . .

Are you sure it's not the square of the speed?

 

[Bobby Dazzler]

Ok semantics but the exact wording is important because it confuses the debate of whether is squared or cubed. My understanding was that drag increases by the square of the speed but the power needed to overcome that drag increases by the cube of the speed.

This ^^^^

For those interested. I copied this off some bloke on the Internet, but I hear that he’s devishly handsome - and that’s important - and he seemed to know what he was talking about so it must be right.

Motive power is a function of running resistance and vehicle speed, and running resistance is a function of the square of vehicle speed, and so motive power is a function of vehicle speed cubed.
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Speed is maintained when the power output of the engine is equal to the running-resistance power (Pw):

Pw = Fw * V

where,
Pw is motive power (kW)
Fw is running resistance (N)
V is vehicle speed (km/h)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

The running resistance is calculated as (Fw):

Fw = Fro + Fl + Fst

where,
Fw is running resistance (N)
Fro is rolling resistance (N)
Fl is aerodynamic drag (N)
Fst is climbing resitance (N)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

The rolling resistance (Fro) is the product of deformation processes which occur at the contact patch between the tyre and the road surface:

Fro = F * M * G

where,
Fro is rolling resistance (N)
F is coefficient of rolling resistance [0.025 for preumatic tyre on tarmac]
M is vehicle mass (weight) (kg)
G is gravitational acceleration [9.81m/(s*s)]
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Aerodynamic drag (Fl) is calculated as:

Fl = 0.5 * Ro * Cw * A * (V + Vo) * (V + Vo)

where,
Fl is aerodynamic drag (N)
Ro is air density [at 200m altitude: 1.202 kg/(m*m*m)]
Cw is drag coefficient (also commonly referred to as Cd)
A is maximum vehicle cross section (m*m)
V is vehicle speed (km/h)
Vo is headwind speed (km/h)

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

The climbing resistance (Fst), or downgrade force (Fst), are calculated as:

Fst = M * G * sin(Alpha)

where,
Fst = Fst is climbing resitance (N)
M is vehicle mass (weight) (kg)
G is gravitational acceleration [9.81m/(s*s)]
Alpha is gradient angle (degrees)
_______________________________________

 

[markjay]

....The other obvious issue is that you are extrapolating on current technology.

Like the famous prediction made in 1900 that in 50 years the height of the horse manor pile covering the streets of New York will be 1' high.......

 

[SmartAmg]

This ^^^^

For those interested. I copied this off some bloke on the Internet, but I hear that he’s devishly handsome - and that’s important - and he seemed to know what he was talking about so it must be right.

Motive power is a function of running resistance and vehicle speed, and running resistance is a function of the square of vehicle speed, and so motive power is a function of vehicle speed cubed.
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Speed is maintained when the power output of the engine is equal to the running-resistance power (Pw):

Pw = Fw * V

where,
Pw is motive power (kW)
Fw is running resistance (N)
V is vehicle speed (km/h)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

The running resistance is calculated as (Fw):

Fw = Fro + Fl + Fst

where,
Fw is running resistance (N)
Fro is rolling resistance (N)
Fl is aerodynamic drag (N)
Fst is climbing resitance (N)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

The rolling resistance (Fro) is the product of deformation processes which occur at the contact patch between the tyre and the road surface:

Fro = F * M * G

where,
Fro is rolling resistance (N)
F is coefficient of rolling resistance [0.025 for preumatic tyre on tarmac]
M is vehicle mass (weight) (kg)
G is gravitational acceleration [9.81m/(s*s)]
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Aerodynamic drag (Fl) is calculated as:

Fl = 0.5 * Ro * Cw * A * (V + Vo) * (V + Vo)

where,
Fl is aerodynamic drag (N)
Ro is air density [at 200m altitude: 1.202 kg/(m*m*m)]
Cw is drag coefficient (also commonly referred to as Cd)
A is maximum vehicle cross section (m*m)
V is vehicle speed (km/h)
Vo is headwind speed (km/h)

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

The climbing resistance (Fst), or downgrade force (Fst), are calculated as:

Fst = M * G * sin(Alpha)

where,
Fst = Fst is climbing resitance (N)
M is vehicle mass (weight) (kg)
G is gravitational acceleration [9.81m/(s*s)]
Alpha is gradient angle (degrees)
_______________________________________

Thanks. That's cleared it up, for me.

 

[ChipChop]

Even with V3/V4 sites being full I have always got the max power output.

At what state of charge % range?