ztanos
Well-known member
Try sprinting around a track as fast as you can for a mile. Then try jogging around the track for a mile. It's definitely different efforts, but you are going the same distance.
Does fast acceleration cause battery degradation?
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DaveinOlyWA
Well-known member
ztanos said:
same distance but much different wind resistance.
LTLFTcomposite
Well-known member
How many bubbles constitute "fast acceleration"? More than 7 ?
FalconFour
Well-known member
Psh, I max out the bubbles every green light. :lol:
I'm still confused how weight affects mileage though. Weight should have no effect on mileage... it just makes the car heavier on its wheels which I wouldn't think has any effect on how much power it takes to keep rolling - which is 100% air resistance as far as I can understand! Wheels don't put that much resistance on it, do they?
Think of it this way... basically these are the forces in play:
1) starting off the car, taking this multi-thousand-pound mass and accelerating it to speed - takes a lot of energy.
2) stopping the car, taking that same multi-thousand-pound mass and stopping it - restores most of the same energy consumed in (1) back to the battery, provided the friction brakes never touch. ECO mode is great for this, as well as light braking that doesn't max out the 5 "bubbles".
3) moving at a constant "cruise" speed, just has to overcome air resistance, which is the act of pushing the air out of the way of the car at various rates. Faster consumes more power as the air gases are more quickly displaced at higher speeds - hence needing more power to keep going at higher speeds.
Basically, if I were to take a styrofoam mass of the shape of a LEAF and put it on my electric bike as I ride, it will consume the same amount of power as the LEAF going the same speed - maxing out around 17mph with a 450-watt motor, it might not reach 17mph as it maxes out due to air resistance force.
Where's (4)? No part of (3) involves weight of the car, and (1) and (2) nearly balance each other out (hence, leadfooting is OK in an EV). Only thing to add is that (1) and (2) are affected by current flow through the electronics, which, at higher currents, loses more energy to heat in the electronics due to the high load. That's it. I can't really see how weight affects it at all...
I'm still confused how weight affects mileage though. Weight should have no effect on mileage... it just makes the car heavier on its wheels which I wouldn't think has any effect on how much power it takes to keep rolling - which is 100% air resistance as far as I can understand! Wheels don't put that much resistance on it, do they?
Think of it this way... basically these are the forces in play:
1) starting off the car, taking this multi-thousand-pound mass and accelerating it to speed - takes a lot of energy.
2) stopping the car, taking that same multi-thousand-pound mass and stopping it - restores most of the same energy consumed in (1) back to the battery, provided the friction brakes never touch. ECO mode is great for this, as well as light braking that doesn't max out the 5 "bubbles".
3) moving at a constant "cruise" speed, just has to overcome air resistance, which is the act of pushing the air out of the way of the car at various rates. Faster consumes more power as the air gases are more quickly displaced at higher speeds - hence needing more power to keep going at higher speeds.
Basically, if I were to take a styrofoam mass of the shape of a LEAF and put it on my electric bike as I ride, it will consume the same amount of power as the LEAF going the same speed - maxing out around 17mph with a 450-watt motor, it might not reach 17mph as it maxes out due to air resistance force.
Where's (4)? No part of (3) involves weight of the car, and (1) and (2) nearly balance each other out (hence, leadfooting is OK in an EV). Only thing to add is that (1) and (2) are affected by current flow through the electronics, which, at higher currents, loses more energy to heat in the electronics due to the high load. That's it. I can't really see how weight affects it at all...
FalconFour said:
Rolling resistance is dominant at lower speeds, so yes they contribute quite a bit. There's also altitude changes - going uphill now takes more power, and you do not recover all of that on the way back down. Don't confuse "constant speed" with "constant power" - despite what the high school textbooks say, nobody actually drives on a perfectly flat and level road in a straight line.
=Smidge=
Herm
Well-known member
From the Tesla blog, rolling resistance is fairly level with speed, and goes up slowly with increasing weight.
two problems with fast acceleration:
1. Brake regen is nowhere close to 100% at recapturing the energy, assume 30% or so.. it is stupid to accelerate towards a red light. Anticipate what is ahead.
2. Higher accelerations require higher currents, thus higher IR losses everywhere.. this is just energy wasted as heat.
Hypermilers drive as if they had no brakes, momentum conservation is all important, even going around curves. If you dont have brakes obviusly you cant drive too fast since you are depending on air drag and tire friction to slow you down. A good hypermiler can probably get 175 miles out of a new Leaf in warm conditions.
two problems with fast acceleration:
1. Brake regen is nowhere close to 100% at recapturing the energy, assume 30% or so.. it is stupid to accelerate towards a red light. Anticipate what is ahead.
2. Higher accelerations require higher currents, thus higher IR losses everywhere.. this is just energy wasted as heat.
Hypermilers drive as if they had no brakes, momentum conservation is all important, even going around curves. If you dont have brakes obviusly you cant drive too fast since you are depending on air drag and tire friction to slow you down. A good hypermiler can probably get 175 miles out of a new Leaf in warm conditions.
FalconFour
Well-known member
I drove my whole 100-mile LEAF trip as if I had no brakes :lol:
But actually, regenerative braking does pretty much that... energy captured from momentum, or energy converted into momentum, either way - it has to go somewhere - into heat, or into motion. So unless regenerative losses are lost to heat somewhere, that percentage is wacky-off and it's a better guess to say it's identical to acceleration losses - more like 95% efficient. Double that - once onto each side - and an acceleration/regen cycle should be something like 90% efficient - nowheres near the ~25% deduced from those figures.
As proof to this hypothesis, watch the "energy usage" display. Accelerate at 4 "bubbles" for about 10 seconds, then within 2 seconds, begin decelerating with your foot barely on the brake to see 4 reverse "bubbles" - the energy usage/capture shown on the "energy usage" page should be about the same for each number of "bips" - AND it should take 9 seconds to come back to a near stop. Any fewer seconds to stop would reflect lost energy. 9 seconds takes into account the small amount of energy needed to coast at that speed, with a margin of error reflective of the varying power levels during transitions to the count of "bubbles".
To me, that experiment is quite clear: regenerating is FAR more efficient than a meager 30%, as long as the brake pads never touch the discs.
But actually, regenerative braking does pretty much that... energy captured from momentum, or energy converted into momentum, either way - it has to go somewhere - into heat, or into motion. So unless regenerative losses are lost to heat somewhere, that percentage is wacky-off and it's a better guess to say it's identical to acceleration losses - more like 95% efficient. Double that - once onto each side - and an acceleration/regen cycle should be something like 90% efficient - nowheres near the ~25% deduced from those figures.
As proof to this hypothesis, watch the "energy usage" display. Accelerate at 4 "bubbles" for about 10 seconds, then within 2 seconds, begin decelerating with your foot barely on the brake to see 4 reverse "bubbles" - the energy usage/capture shown on the "energy usage" page should be about the same for each number of "bips" - AND it should take 9 seconds to come back to a near stop. Any fewer seconds to stop would reflect lost energy. 9 seconds takes into account the small amount of energy needed to coast at that speed, with a margin of error reflective of the varying power levels during transitions to the count of "bubbles".
To me, that experiment is quite clear: regenerating is FAR more efficient than a meager 30%, as long as the brake pads never touch the discs.
planet4ever
Well-known member
I think Herm is being way too pessimistic, and that regen recovers much more than 30%, probably at least twice that much. Mountain runs that have been reported on this board seem to confirm that.
On the other hand, Falcon is being way too optimistic. I think that earlier discussions here have pretty much proven that there is a minimum of 10% loss in converting mechanical energy to AC electricity + AC electricity to DC electricity + DC electricity to chemical storage in the battery. There is another minimum of 10% loss in reversing those conversions. So the upper limit on possible regen efficiency is about 80%. (Well, OK, 81% if you want to be technical.)
The real world efficiency of LEAF regen is probably somewhere between 60% and 80%. And, yes, the extra energy ends up as heat. Note that the LEAF cooling system is cooling both the motor and the inverter during those energy transformations in both directions. (Perhaps somewhat surprisingly, it is the inverter, not the charger, which is used to convert AC to DC during regen. But if you think about it, the onboard charger maxes out at 3.3kW to the battery. The inverter may be pumping it up at more than ten times that rate!)
Ray
On the other hand, Falcon is being way too optimistic. I think that earlier discussions here have pretty much proven that there is a minimum of 10% loss in converting mechanical energy to AC electricity + AC electricity to DC electricity + DC electricity to chemical storage in the battery. There is another minimum of 10% loss in reversing those conversions. So the upper limit on possible regen efficiency is about 80%. (Well, OK, 81% if you want to be technical.)
The real world efficiency of LEAF regen is probably somewhere between 60% and 80%. And, yes, the extra energy ends up as heat. Note that the LEAF cooling system is cooling both the motor and the inverter during those energy transformations in both directions. (Perhaps somewhat surprisingly, it is the inverter, not the charger, which is used to convert AC to DC during regen. But if you think about it, the onboard charger maxes out at 3.3kW to the battery. The inverter may be pumping it up at more than ten times that rate!)
Ray
FalconFour
Well-known member
Which is why I always believed the term "inverter" was quite misleading when naming the device which is more properly known as a "motor controller". Its job isn't just to invert, but to fully monitor and control the motor in all parts of its operation... so why "inverter"? :lol:
That said, I agree... maybe a bit optimistic there, but definitely substantial in terms of reasoning to try to maximize regen to allow sprinty takeoffs :lol:
That said, I agree... maybe a bit optimistic there, but definitely substantial in terms of reasoning to try to maximize regen to allow sprinty takeoffs :lol:
DaveinOlyWA
Well-known member
Regen i also believe has efficiency of 65-85-% but then you have to remove friction losses, rolling resistance, air resistance, etc. by the time that is gone, you are down to probably 50%.
count it or not but fact of the matter is the only thing that matters is how far you can go, so we cannot ignore forces that apply every inch of the way.
at the same time; faster acceleration simply lowers your time to react to the constantly and quickly changing traffic situations. do we need to do that GEICO (or whoever it is) commercial "driving down the road in my car, another car cuts in front of me, what should i do? Beep, Beep!"
We are part of the car for a reason. the car is a tool. a tool that enables us to be "look good" reliable, punctual and all that stuff. like any tool, it has limitations.
dont take off 45 minutes before an appointment that is 35 miles away. you probably wont make it home without stopping to charge because you had to drive 70 to get there on time. take advantage of hills. if you are going down a hill and its steep enough, reduce your motor power usage to nothing or very little. try not to regen. its better to build a little speed instead. if possible, anticipate the elevation benefits. slow down a bit (avoiding regen) just before the hill so you can gain a bit of speed without getting a ticket or creating more wind resistance than you need to.
i find there is only a little you can do on the freeway but in town, especially heavily traffic controlled areas, playing the lights is a make or break opportunity.
if i see a light ahead that is red, i usually shift to neutral. this allows no power to be used and only a very slow reduction in speed (makes people behind me happier) hopefully, the light turns green and the intersection clears before i slow down too much so i dont have to expend a lot of power getting back up to my speed target.
yes, it can be a gamblers game. to regen or not to regen, that is the constant question. but generally avoid stopping. coasting slowly is much better
count it or not but fact of the matter is the only thing that matters is how far you can go, so we cannot ignore forces that apply every inch of the way.
at the same time; faster acceleration simply lowers your time to react to the constantly and quickly changing traffic situations. do we need to do that GEICO (or whoever it is) commercial "driving down the road in my car, another car cuts in front of me, what should i do? Beep, Beep!"
We are part of the car for a reason. the car is a tool. a tool that enables us to be "look good" reliable, punctual and all that stuff. like any tool, it has limitations.
dont take off 45 minutes before an appointment that is 35 miles away. you probably wont make it home without stopping to charge because you had to drive 70 to get there on time. take advantage of hills. if you are going down a hill and its steep enough, reduce your motor power usage to nothing or very little. try not to regen. its better to build a little speed instead. if possible, anticipate the elevation benefits. slow down a bit (avoiding regen) just before the hill so you can gain a bit of speed without getting a ticket or creating more wind resistance than you need to.
i find there is only a little you can do on the freeway but in town, especially heavily traffic controlled areas, playing the lights is a make or break opportunity.
if i see a light ahead that is red, i usually shift to neutral. this allows no power to be used and only a very slow reduction in speed (makes people behind me happier) hopefully, the light turns green and the intersection clears before i slow down too much so i dont have to expend a lot of power getting back up to my speed target.
yes, it can be a gamblers game. to regen or not to regen, that is the constant question. but generally avoid stopping. coasting slowly is much better
ztanos
Well-known member
FalconFour said:
Ask yourself this question... would you rather push an Escalade on a flat terrain in neutral or would you rather push a mini cooper?
Friction. It's what makes the tires and the road hot. The equation is [Gravitational Constant] X Mass X [Co-efficient of the Tires]. The losses are linear with mass and the co-efficient of the tires. Note these losses end up as heat and cannot be recaptured through regen.FalconFour said:
Performance tires are wide and soft and create more friction, which allows them to grip the road and makes going around corners easier. But all that friction kills efficiency. Low rolling resistance tires are narrow and hard, which decreases the frictional losses but doesn't help taking corners at high speed.
FalconFour
Well-known member
Only difference is how much effort it takes to get into motion... hence beefy motors needed to start and stop larger vehicles! I pushed my LEAF into a parking spot, it was no fun time to get started (or stopped!), but once it started rolling I could run along side it... :lol:ztanos said:
As for tires, they contribute some, but it can't possibly be that significant! Maybe 1-2% of the losses at most! Right...?
At lower speeds they're more like 35% - 50% of the losses. As you can see from the equation the losses are more or less constant, and, consequently, at higher speeds they make up a smaller percentage of the losses. Never as small as 1%-2% however. More like 10% - 20%.FalconFour said:
LEAFfan
Well-known member
Herm said:
Herm! You are right on! If I had had a new battery pack instead of a 10% loss, I could have driven 175 miles on my efficiency run. After 151 miles, I still had 4% left with 1.4% to Turtle.
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