Is it just me?

[Mactech]

It's a very silly thing to do... acceleration is the no 1 range killer on EVs... they should have read the manual.

I have to disagree with that!
Acceleration changes electrical energy into potential energy. Braking changes that energy into heat, to warm the planet and disappear from the vehicle.
I believe braking is the no 1 range killer on a EV's, it's just a waste of energy, and worse still, I slows you down!
Observation and anticipation is the key to hone on the range... spelling mistake intentional...this time!

 

[markjay]

I have to disagree with that!
Acceleration changes electrical energy into potential energy. Braking changes that energy into heat, to warm the planet and disappear from the vehicle.
I believe braking is the no 1 range killer on a EV's, it's just a waste of energy, and worse still, I slows you down!
Observation and anticipation is the key to hone on the range... spelling mistake intentional...this time!

That's not how EVs work... braking doesn't generate heat because there's no (or very little) friction, other than between the road and the tyres. EVs have regenerative braking. That's why driving an EV in city traffic is very economic, the more braking the more energy goes back into the battery. I get back into the battery about 25% of the electriity used, when driving around central London. And, when driving downhill, the car actually charges the battery as it is slowing down the car, increasing the remaining mileage. Acceleration is the big killer here. That, and high speed (70mph) motorway driving due to little braking and also due to air resistance.

 

[Mactech]

That's not how EVs work... braking doesn't generate heat because there's no (or very little) friction, other than between the road and the tyres. EVs have regenerative braking. That's why driving an EV in city traffic is very economic, the more braking the more energy goes back into the battery. I get back into the battery about 25% of the electriity used, when driving around central London. And, when driving downhill, the car actually charges the battery as it is slowing down the car, increasing the remaining mileage. Acceleration is the big killer here. That, and high speed (70mph) motorway driving due to little braking and also due to air resistance.

I’m only 3 weeks into EV driving, but on my very first day I drove from Canterbury to Norfolk at an average of almost 60mph and bettered the manufacturer’s range figure by 25 %. I didn’t once touch the brake pedal after leaving Canterbury.
So I must be doing it all wrong

 

[MikeInWimbledon]

high speed (70mph) motorway driving

Gawd I feel old. I can remember doing 70 on Park Lane and Embankment.

Someone else would have been driving, of course. A SAAB 900 Turbo, methinks.

Different times.

 

[markjay]

Gawd I feel old. I can remember doing 70 on Park Lane and Embankment.

Someone else would have been driving, of course. A SAAB 900 Turbo, methinks.

Different times.

Ha ha Park Lane is now 20mph.......

 

[MikeInWimbledon]

Ha ha Park Lane is now 20mph.......

You'll be telling me next that you can't just feed a West End parking meter with coins all day any more,
before heading off somewhere in the evening.

 

[markjay]

You'll be telling me next that you can't just feed a West End parking meter with coins all day any more,
before heading off somewhere in the evening.

When our office moved to York Way, just outside the Kings Cross train station, parking along York Way was free and unrestricted.

Who would have beloved it, free unrestricted parking in Central London, just outside one of the busiest train stations...

 

[ALFAitalia]

I’m only 3 weeks into EV driving, but on my very first day I drove from Canterbury to Norfolk at an average of almost 60mph and bettered the manufacturer’s range figure by 25 %. I didn’t once touch the brake pedal after leaving Canterbury.
So I must be doing it all wrong

From your background you must realise that accelerating something quickly uses more energy and has more losses than accelerating slowly ......the fuel used, derv, petrol or electricity is irrelevant. But yes of course, regardless of fuel used, the less you brake the better the economy.

 

[Mactech]

From your background you must realise that accelerating something quickly uses more energy and has more losses than accelerating slowly ......the fuel used, derv, petrol or electricity is irrelevant. But yes of course, regardless of fuel used, the less you brake the better the economy.

Yes, if we assume we are going to travel, then we must move, therefore acceleration is mandatory. The rate we accelerate is discretionary. Because we travel on roads, slowing down and stopping is something that happens. In an EV driven with some forward observation, the kinetic energy in the moving car can be returned to the battery with a reasonably efficiency. Using the brakes just completely wastes that energy as heat.
So I maintain that it is braking that is biggest danger to the range, as it is a complete energy loss.

 

[Bellow]

From your background you must realise that accelerating something quickly uses more energy and has more losses than accelerating slowly

Are you sure about that?
It takes more power but the energy expended is the same. And, in some instances it will be more fuel efficient to accelerate harder eg, a SI engine which is more efficient at higher loads and accelerating more swiftly enables earlier engagement of higher gears further reducing throttling losses.

 

[Mactech]

Are you sure about that?
It takes more power but the energy expended is the same. And, in some instances it will be more fuel efficient to accelerate harder eg, a SI engine which is more efficient at higher loads and accelerating more swiftly enables earlier engagement of higher gears further reducing throttling losses.

Ek = Mv squared.
Whilst there is some discussion to be had as the the efficiencies of motor and regeneration of the kinetic energy (Ek), putting that energy into the moving vehicle is 'very similar' at whatever rate you put it in. Chassis and aero drag, road surface and level are all small factors but the theory of conservation of energy and of momentum, broadly applies.

 

[Bellow]

Ek = Mv squared.
Whilst there is some discussion to be had as the the efficiencies of motor and regeneration of the kinetic energy (Ek), putting that energy into the moving vehicle is 'very similar' at whatever rate you put it in.

Yep, it takes a finite amount of energy to accelerate a mass to a specified velocity. Whether that is done with a small force over an extended period or a large force over a contracted period doesn't really matter.
Similarly, when it comes to slowing a mass the energy dissipated is the same whether the 'braking' force is large or small - only the time (and distance travelled during the event) varies. More obvious than the case for acceleration but deceleration is only acceleration with reversed polarity.

Chassis and aero drag, road surface and level are all small factors but the theory of conservation of energy and of momentum, broadly applies.

No cheating physics!

There is confusion I think because the mantra of 'harsh braking costs fuel' is never explained. An accompanying sentence on 'husbanding momentum' would go along way to aid an understanding that the problem with braking is that fuel consuming acceleration is required immediately after it - unless you've arrived at your destination that is. The canard that a block of wood under the throttle pedal will save fuel is frequently uttered. It likely will. But one placed under the brake pedal will be more effective still. That, will really focus the mind to deploy the throttle sensibly.

 

[Mactech]

Yep, it takes a finite amount of energy to accelerate a mass to a specified velocity. Whether that is done with a small force over an extended period or a large force over a contracted period doesn't really matter.
Similarly, when it comes to slowing a mass the energy dissipated is the same whether the 'braking' force is large or small - only the time (and distance travelled during the event) varies. More obvious than the case for acceleration but deceleration is only acceleration with reversed polarity.

No cheating physics!

There is confusion I think because the mantra of 'harsh braking costs fuel' is never explained. An accompanying sentence on 'husbanding momentum' would go along way to aid an understanding that the problem with braking is that fuel consuming acceleration is required immediately after it - unless you've arrived at your destination that is. The canard that a block of wood under the throttle pedal will save fuel is frequently uttered. It likely will. But one placed under the brake pedal will be more effective still. That, will really focus the mind to deploy the throttle sensibly.

The Newton cradle is a good example of conservation of energy.

File:Newton’s_cradle_slo_mo.webm

You will note that the balls at each end have impacts and acceleration in multiple 'g's indicating that the rates of acceleration we see in road cars have little effect on the overall kinetic energy in the whole system.

 

[Bellow]

The Newton cradle is a good example of conservation of energy.

Conservation of energy is what delivers good fuel efficiency in our driving....

File:Newton’s_cradle_slo_mo.webm

....but with a bit less of the 'crashing'.

 

[HappytalkAgain]

How would this be explained then?

Brim the tank of your car, any car. Drive it like it’s stolen until the tank is empty. Record the mileage.

Repeat the process then drive exactly the same route and roads but driving like ya typical 80 year old grandma until the tank is empty. Record the mileage.

I’m expecting the gran would have to double back on herself along some of the same roads.

 

[HappytalkAgain]

An accompanying sentence on 'husbanding momentum' would go along way to aid an understanding that the problem with braking is that fuel consuming acceleration is required immediately after it…..

Add the fact that the later you brake, the longer you’re on the throttle beforehand- the more fuel you use. Hence the F1 term ‘lift & coast’.

 

[Mactech]

How would this be explained then?

Brim the tank of your car, any car. Drive it like it’s stolen until the tank is empty. Record the mileage.

Repeat the process then drive exactly the same route and roads but driving like ya typical 80 year old grandma until the tank is empty. Record the mileage.

I’m expecting the gran would have to double back on herself along some of the same roads.

Simple! If gran tootled along at around 40mph, she would have to use the brakes far less that the 'thief' who was heavy on both throttle and brakes.
...and remember, the kinetic energy in the car is proportional to the square of the speed, that's a massive amount of energy to dissipate if you travel quickly.
One of my quotes after the Bentley Le Mans win in 2003 was:

The 2000 litre tank of oil to heat a house was not dissimilar to the amount of fuel we put in the car for the race.

 

[HappytalkAgain]

Simple! If gran tootled along at around 40mph, she would have to use the brakes far less that the 'thief' who was heavy on both throttle and brakes.
...and remember, the kinetic energy in the car is proportional to the square of the speed, that's a massive amount of energy to dissipate if you travel quickly.
One of my quotes after the Bentley Le Mans win in 2003 was:
View attachment 145599
The 2000 litre tank of oil to heat a house was not dissimilar to the amount of fuel we put in the car for the race.

Understood 100%.

But the fact remains the grans driving style would be rewarded with much better fuel economy and/or EV range. But she’d be much later to the party than the common tea leaf!

 

[markjay]

EVs turn stored electric energy into kinetic energy, then turns the kinetic energy back to stored electric energy when braking.

The energy loss is from kinetic and electric energy turning into heat. The heat is dissipatedvat from the tyres as result of friction with the road, from the car's exterior as result of wind resistance, from the electrical motors, and from the battery cooling system. This accounts for the energy losses when driving on level ground.

When driving uphill, some if the stored electric energy is converted to potential energy. When driving downhill, the potential energy is turned back into stored electric energy, again with losses resulting from heat dissipation.

Overall, an EV as a car is much more energy-efficient than a comparable ICE car, because there are far less losses resulting from heat dissipation.

However, the issue with the energy efficiency of EVs is in fact not with the car itself, but with the overall process of converting fuel to energy. The EV will see many losses even before the electricity reaches the battery. The higher efficiency of the car itself does not compensate fully for the losses between the power plant and the home or public charger.

In any event, EVs do not use the brake discs for braking, instead they brake using the resistance of the electromagnetic field inside the motor, which is a frictionless process (hence the greater efficiency).

 

[Mactech]

Understood 100%.

But the fact remains the grans driving style would be rewarded with much better fuel economy and/or EV range. But she’d be much later to the party than the common tea leaf!

That's where you had to have many years Gp C racing knowledge wining races on restricted amount of fuel...