Braking with the Pedal safer?
Discussion
TheDeuce said:
Bizarre thread!
It's not even an EV thing, loads of ICE cars have automatic braking and some use a little regen too.
All that's happened as a result is brake lights are more accurately linked to deceleration rates than before, it's a good thing.
I'm going to rate this a 0/10 effort in terms of trying to find new ways to take a dig at EV's
To be fair to the OP, if you don't know, you don't know.It's not even an EV thing, loads of ICE cars have automatic braking and some use a little regen too.
All that's happened as a result is brake lights are more accurately linked to deceleration rates than before, it's a good thing.
I'm going to rate this a 0/10 effort in terms of trying to find new ways to take a dig at EV's
I wasn't aware of EV brake lights illuminating under regen until a few weeks after ownership of my Tesla.
blueacid said:
georgeyboy12345 said:
Nope. Coasting is still much more efficient than regen, even around town.
Yes, it is. But in congested driving conditions, there isn't as much opportunity to coast to a halt; quite often you'll be required to brake more often. Storing this energy to reuse is better than the (unavoidable) braking.There's a reason loads of taxi drivers in cities use the Prius.
Of course where possible, coasting is indeed better - but those opportunities are limited when you're in heavy traffic, or have lots of traffic lights on your route.
NDA said:
TheDeuce said:
Bizarre thread!
It's not even an EV thing, loads of ICE cars have automatic braking and some use a little regen too.
All that's happened as a result is brake lights are more accurately linked to deceleration rates than before, it's a good thing.
I'm going to rate this a 0/10 effort in terms of trying to find new ways to take a dig at EV's
To be fair to the OP, if you don't know, you don't know.It's not even an EV thing, loads of ICE cars have automatic braking and some use a little regen too.
All that's happened as a result is brake lights are more accurately linked to deceleration rates than before, it's a good thing.
I'm going to rate this a 0/10 effort in terms of trying to find new ways to take a dig at EV's
I wasn't aware of EV brake lights illuminating under regen until a few weeks after ownership of my Tesla.
Apologies to the OP if I'm wrong about it being a lightly disguised snipe at EV's..
First 'electric vehicle' I drove was a fork lift in about 1982.
It had three pedals, FWD, Reverse and Brake.
People tended to drive using the Reverse pedal to slow down when going forwards and V/V, great for complex shuffling in tight spaces, but not so good when you mess up, screech to a halt, then shoot backwards nearly hitting the boss's Merc. The sharp deceleration/reverse acceleration available from the motor throws your weight onto the pedal....
Happy Daze.
(no apologies for thread drift)
It had three pedals, FWD, Reverse and Brake.
People tended to drive using the Reverse pedal to slow down when going forwards and V/V, great for complex shuffling in tight spaces, but not so good when you mess up, screech to a halt, then shoot backwards nearly hitting the boss's Merc. The sharp deceleration/reverse acceleration available from the motor throws your weight onto the pedal....
Happy Daze.
(no apologies for thread drift)
andy43 said:
Coasting is more efficient but if anybody else is using the road it’s not an option unless you want to be ‘that person’.
I disagree, it’s absolutely possible to coast on city streets with the tiniest bit of looking up the road and forward planning. In traffic too, you can be on 10% accelerator for a second or so, then let off and it’ll coast for ages, without holding anyone up. A quick Google gives values for idle consumption, that is what you are doing when coasting right, of 0.6 - 0.8l/h. Petrol has an energy density of 9.6kWh/l so call it 6kWh
That is what, 24-30 miles around town in an EV, at least?
When you coast on the flat you are losing kinetic energy to drag as you slow down, as EVs are not 100% efficient that is going to be a bit less than the energy it would take just maintain speed, fair enough. Accepted regen isn't perfect, 60-70% is a figure I found quickly, however coasting recovers no energy.
I'm not going to say if coasting is better or worse, but I suspect it is highly sensitive to driving style and road conditions.
That is what, 24-30 miles around town in an EV, at least?
When you coast on the flat you are losing kinetic energy to drag as you slow down, as EVs are not 100% efficient that is going to be a bit less than the energy it would take just maintain speed, fair enough. Accepted regen isn't perfect, 60-70% is a figure I found quickly, however coasting recovers no energy.
I'm not going to say if coasting is better or worse, but I suspect it is highly sensitive to driving style and road conditions.
georgeyboy12345 said:
Coasting is definitely better - I'm telling you from experience, not theory.
It depends on conditions really, if you just take it as variation between the same max and minimum speeds then coasting will mean your average speed is lower, therefore it makes sense that this will use less energy. On the other hand if you want to make the journey in the same amount of time using coasting means you need to attain higher peak speeds. You will use more energy to reach and maintain higher speeds. It is really going to depend on the ratio of the time you spend at a steady cruise and the time you spend coasting.
I looked at the difference between coasting down from 28.3mph to 20mph, picked as the KE has a ratio of near enough 2, and braking for 25% of the time instead. For the same average speed of 24mph you would start at approx 24.8mph or about 77% of the KE at 28.3mph.
That means the worst case is both cars had just reached their top speeds just before the coaster needed to slow down again. The coaster of course has to use quite a bit more energy to reach 28.3mph, none of which they get back.
Accelerating slowly will just make it worse as the coaster will need reach much higher peak speeds to attain the same average speed.
It’s all about the conservation of energy. Therefore coasting, and using regen only when actually needing to slow down is the most efficient.
Coasting consumes no battery energy, with drag being the only loss of useful energy over the distance travelled. During regen, drag and approx 30% of the useful energy is lost over the distance travelled because regen is only about 70% efficient at recapturing that useful energy.
Coasting consumes no battery energy, with drag being the only loss of useful energy over the distance travelled. During regen, drag and approx 30% of the useful energy is lost over the distance travelled because regen is only about 70% efficient at recapturing that useful energy.
dvs_dave said:
It’s all about the conservation of energy. Therefore coasting, and using regen only when actually needing to slow down is the most efficient.
Coasting consumes no battery energy, with drag being the only loss of useful energy over the distance travelled. During regen, drag and approx 30% of the useful energy is lost over the distance travelled because regen is only about 70% efficient at recapturing that useful energy.
This is what I am getting at. Coasting consumes no battery energy, with drag being the only loss of useful energy over the distance travelled. During regen, drag and approx 30% of the useful energy is lost over the distance travelled because regen is only about 70% efficient at recapturing that useful energy.
To me at least it seems slightly counter-intuitive but it does work. When I first got the e-up I drove everywhere using level 3 or max regen. Now I tend to use level 1 or 2, coast further and only use max for the final coming to a stop and I'm definitely getting better range. Current average over the last 10 journeys is >6.8mi/kw (with a/c on, and never use eco+ mode).
georgeyboy12345 said:
100%. I have an EV and can confirm this is true.
The regen process is not 100% efficient, converting kinetic energy back to chemical energy in the battery via electrical energy, with associated losses through friction, heat and sound overall consumes more energy than just utilising the kinetic energy you already have while moving. It’s the first law of thermodynamics.
Regen is only useful under braking.
But braking is quite useful and regen is better than heating up brake disks.The regen process is not 100% efficient, converting kinetic energy back to chemical energy in the battery via electrical energy, with associated losses through friction, heat and sound overall consumes more energy than just utilising the kinetic energy you already have while moving. It’s the first law of thermodynamics.
Regen is only useful under braking.
I full analysis would need to consider the balance of coasting and braking.
That way you could explain why all the engineers implementing it have made a mistake.
Consider how many drivers do lots of coasting, so the impact on the whole fleet is in the analysis.
BTW, some people do like coasting for fuel saving, but if everybody did it what would the impact on traffic and safety?
doesthiswork said:
To me at least it seems slightly counter-intuitive but it does work. When I first got the e-up I drove everywhere using level 3 or max regen. Now I tend to use level 1 or 2, coast further and only use max for the final coming to a stop and I'm definitely getting better range. Current average over the last 10 journeys is >6.8mi/kw (with a/c on, and never use eco+ mode).
While achieving a lower mean speed, no doubt. This uses less energy on its own, so the delta cannot reliably be attributed to coasting.That long coast to a halt means a big space in front, which spreads traffic out. What's the impact in town driving in congested conditions?
911hope said:
doesthiswork said:
To me at least it seems slightly counter-intuitive but it does work. When I first got the e-up I drove everywhere using level 3 or max regen. Now I tend to use level 1 or 2, coast further and only use max for the final coming to a stop and I'm definitely getting better range. Current average over the last 10 journeys is >6.8mi/kw (with a/c on, and never use eco+ mode).
While achieving a lower mean speed, no doubt. This uses less energy on its own, so the delta cannot reliably be attributed to coasting.That long coast to a halt means a big space in front, which spreads traffic out. What's the impact in town driving in congested conditions?
Every EV we've had I've always set regen to max if it's adjustable in any way as I think it replicates ICE driving closest, plus it bungs more back into the battery on a hill or when coping with "other drivers".
Squirt-and-coast is used in all the super economy runs where weird shaped single seaters get 2000 mpg so that's definitely the most efficient when you're using a fuel that can't be fed back into the tank when you're travelling downhill, but for an EV I'd guess it's not as clear cut.
911hope said:
georgeyboy12345 said:
100%. I have an EV and can confirm this is true.
The regen process is not 100% efficient, converting kinetic energy back to chemical energy in the battery via electrical energy, with associated losses through friction, heat and sound overall consumes more energy than just utilising the kinetic energy you already have while moving. It’s the first law of thermodynamics.
Regen is only useful under braking.
But braking is quite useful and regen is better than heating up brake disks.The regen process is not 100% efficient, converting kinetic energy back to chemical energy in the battery via electrical energy, with associated losses through friction, heat and sound overall consumes more energy than just utilising the kinetic energy you already have while moving. It’s the first law of thermodynamics.
Regen is only useful under braking.
I full analysis would need to consider the balance of coasting and braking.
That way you could explain why all the engineers implementing it have made a mistake.
Consider how many drivers do lots of coasting, so the impact on the whole fleet is in the analysis.
BTW, some people do like coasting for fuel saving, but if everybody did it what would the impact on traffic and safety?
Engineers haven’t made a mistake, it’s a very easy bit of tech to implement and people like it, doesn’t mean it’s the most efficient way of driving.
There is no impact on safety associated with coasting in an EV.
Yep, I think if you start with the situation of "I am travelling at 30mph and will need to stop at the 'STOP' sign that I can see in the distance".
The most efficient way to do this would be to know when to start coasting, so that you coast to a halt at precisely the stop line. If you're in an ICE, leave it in gear and then burn no fuel for that time. If you're in something with regen, don't (and therefore use only the kinetic energy already present in the vehicle to travel the rest of that distance).
The next most efficient, if you need to be quicker, would be to keep cruising at 30 until later, then slow down with regen. You used more energy to stay at 30 for longer, but then you'll have recouped some of that with the regenerative braking.
The worst is to keep driving, then apply the friction brakes. With this you use more fuel to stay at 30mph for longer, and then the kinetic energy you might have used just gets turned pointlessly to heat. Granted, you will arrive at the stop sign quicker, but at the cost of more energy.
..right?
The most efficient way to do this would be to know when to start coasting, so that you coast to a halt at precisely the stop line. If you're in an ICE, leave it in gear and then burn no fuel for that time. If you're in something with regen, don't (and therefore use only the kinetic energy already present in the vehicle to travel the rest of that distance).
The next most efficient, if you need to be quicker, would be to keep cruising at 30 until later, then slow down with regen. You used more energy to stay at 30 for longer, but then you'll have recouped some of that with the regenerative braking.
The worst is to keep driving, then apply the friction brakes. With this you use more fuel to stay at 30mph for longer, and then the kinetic energy you might have used just gets turned pointlessly to heat. Granted, you will arrive at the stop sign quicker, but at the cost of more energy.
..right?
The way I understand it for a given mean speed the lower the standard deviation in speed the more efficient the drive.
That has its own spherical chickens though, level ground, no wind and a motor that is equally efficient at all loads.
As KE and drag are proportional to the second power lower peak speed means lower energy. If you start to lower the peak speed of the coasting drive, reducing the mean speed, at some point it will use less energy than low SD drive.
That has its own spherical chickens though, level ground, no wind and a motor that is equally efficient at all loads.
As KE and drag are proportional to the second power lower peak speed means lower energy. If you start to lower the peak speed of the coasting drive, reducing the mean speed, at some point it will use less energy than low SD drive.
I think there’s some unawareness of how regen is implemented on various EV’s which is confusing the conversation. Some (eg VAG products) default to coasting with selectable lift-off regen level, all the way up to “one pedal driving”. But upon pressing the brake pedal, it starts off with regen, until you max that out, then it starts to blend in the friction brakes on top as needed.
Some cars like Tesla don’t have brake blending. The brake pedal only operates the friction brakes. So on a Tesla pressing the brake pedal is definitely wasting energy, but on others, it depends how hard you’re pressing the brake pedal.
Some cars like Tesla don’t have brake blending. The brake pedal only operates the friction brakes. So on a Tesla pressing the brake pedal is definitely wasting energy, but on others, it depends how hard you’re pressing the brake pedal.
dvs_dave said:
I think there’s some unawareness of how regen is implemented on various EV’s which is confusing the conversation. Some (eg VAG products) default to coasting with selectable lift-off regen level, all the way up to “one pedal driving”. But upon pressing the brake pedal, it starts off with regen, until you max that out, then it starts to blend in the friction brakes on top as needed.
Some cars like Tesla don’t have brake blending. The brake pedal only operates the friction brakes. So on a Tesla pressing the brake pedal is definitely wasting energy, but on others, it depends how hard you’re pressing the brake pedal.
This!Some cars like Tesla don’t have brake blending. The brake pedal only operates the friction brakes. So on a Tesla pressing the brake pedal is definitely wasting energy, but on others, it depends how hard you’re pressing the brake pedal.
Low level regen on most EVs does not necessarily mean less regen - it just means the regen is more controlled more by the brake pedal, as when you touch the brakes it is regen NOT friction that slows you down in most cases. Of course you can achieve exactly the same - less braking / more coasting - with regen set to max simply by feathering the throttle.
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