Turning off regen and power limiting for increased range

[mxnym]

Never heard of that and certainly not my experience driving two EV for aprox 200k miles total and comparing it to the 4 ICE vehicles I owned.

Admittedly, I have no source on that, but I have seen headlines about special tires being developed to combat that particular issue. Moreover, it stands to reason that braking will cause more tire wear than coasting, and regen is a form of braking. Beyond that, experience really doesn't necessarily mean squat here because so many other factors can also affect tire life.

...I don't disagree but that has nothing to do with the situation where you try to start coasting on a freeway a mile before the off ramp to be able to come to a stop without regen.

To be clear, I don't do this, and I have specifically recommended against extreme hypermiling in this thread due to safety concerns. That doesn't change the fact that such a theoretical scenario would be more efficient.

...Same with trying to coast to a stop sign or red light.

We'll have to agree to disagree here. As far as I'm concerned, suggesting that one should keep going full speed toward a red traffic light is about the same as suggesting that one should accelerate and brake hard for each vehicle that goes at a stop sign (that is what "normal traffic" does). At intersections with stop signs, I find a speed where that I can maintain while the gap ahead of me grows and shrinks as I approach the stop sign behind a line of traffic. At intersections with traffic lights, if a light turns red and it isn't far enough away to turn green before I get to it, my foot comes off (or at least lets up on) the accelerator, period. Sometimes, I kinda hope it pisses people off while it saves them fractions of a cent or more, because the stop lights piss me off. Why? Because when traffic lights are involved, it seems like I'm always either spending massive amounts of time stopped at lights while no one is around or stuck dealing with blocked intersections due to inattentive drivers (who don't realize they'll be blocking the intersection until too late) or impatient drivers (who can't wait for the next traffic light cycle). Beyond that, traffic lights are almost always less efficient in terms of traffic control than four way stops for competent drivers (my experience in multiple trips through inner Chicago has been that I get through four way stops with long lines of traffic much faster than I get through traffic lights with similar lines of traffic), and as far as I'm concerned, traffic lights shouldn't be used the way they currently are unless there are at least four lanes on at least three branches of an intersection (although traffic lights might make more sense at other intersections if they switched to flashing red and yellow except during the busiest hours). In addition to the time wasted by traffic lights, they undoubtedly have an environmental impact, because the extra harsh braking (in vehicles that wouldn't make it through before red) leads to extra tire and brake pad particles in the air and that is then compounded by the longer idling times ([number of vehicles times seconds at still idle] vs stop signs) in ICE vehicles that lead to increased emissions.

 

[flar]

The presence of an immediate uphill right after the downhill also complicates things because not only do you spend the added speed immediately into a buffer against gravity, but it also reduces the amount of time you spend on the uphill.

Most of your post I agree with, and in fact, I pointed out in an earlier post that regen doesn't know/care/target that sweet spot you mention regarding wind resistance vs coasting on a long downhill. Regarding the quoted section, though, I must point out that efficiency is measured in kWh/Mi. The "less time" on the uphill is actually a good thing, as it is more Mi at a lower kWh. This is especially true if climate control or accessories are active, because they draw at a steady state, so when you aren't expending energy to gain speed or sacrificing it to maintain speed, the higher speed actually reduces the cost per Mi of your accessories.

Yes, that is the detail behind what I meant by it "complicates things". I was referring to those things complicating my otherwise simplified focus on a comparison of kinetic storage to battery storage, but didn't want to get into the specifics in that post. The momentum-to-momentum storage/spending and the added speed mean that it isn't just a simple "which form of energy makes the best storage" discussion.

But, having gone there now with details, I'd point out that these same considerations are also an argument for *applying* energy on the downhill. In other words, if these effects are important and a net benefit for added speed then zero electrical output may still not be the answer there, potentially positive energy output could be warranted. And, on flats before a hill, potentially increasing energy output might help...? Has anyone every tried that or found it to be true? (Searching online for bicycle advice on climbing hills they don't recommend increasing speed before a hill, but I'll admit that I've done that because it feels better to my novice muscles. Perhaps I'd feel differently if I was as highly trained as a tour cyclist?)

But, does any of this fall on the side of gaining speed (and inviting more air resistance)? I'd like to see math and/or experiments before I take it as a foregone conclusion, but it is a more complicated bit of math than simply looking at steady state downhills or long flat sections.

And how much speed will you gain and how quickly will it dissipate? If the hill is long enough to reach a steady state then you lost some energy you could have saved with regen. Do we then calculate how much speed is optimal and how far from the end of the downhill to end the regen so we can gain exactly that much speed? And for what % of the total drive time on a given trip does that calculation matter?

In the end, though, while we are discussing if and how often coasting is a useful tool, I'd still point out that regen is often an optimal answer as well and so eliminating regen (OP point) isn't the best control configuration either. And if coasting is a good answer a lot of the time, is there a more natural way to achieve it by looking ahead and using good observation and situational awareness and rules of thumb about what you see on the road than there is by having the accelerator end at the coasting state? Would having "foot off pedal == coasting" provide the driver with a crutch that will make them want to use that tool more often than it is the best answer?

 

[mxnym]

Yes, that is the detail behind what I meant by it "complicates things". I was referring to those things complicating my otherwise simplified focus on a comparison of kinetic storage to battery storage, but didn't want to get into the specifics in that post. The momentum-to-momentum storage/spending and the added speed mean that it isn't just a simple "which form of energy makes the best storage" discussion.

But, having gone there now with details, I'd point out that these same considerations are also an argument for *applying* energy on the downhill. In other words, if these effects are important and a net benefit for added speed then zero electrical output may still not be the answer there, potentially positive energy output could be warranted. And, on flats before a hill, potentially increasing energy output might help...? Has anyone every tried that or found it to be true? (Searching online for bicycle advice on climbing hills they don't recommend increasing speed before a hill, but I'll admit that I've done that because it feels better to my novice muscles. Perhaps I'd feel differently if I was as highly trained as a tour cyclist?)

But, does any of this fall on the side of gaining speed (and inviting more air resistance)? I'd like to see math and/or experiments before I take it as a foregone conclusion, but it is a more complicated bit of math than simply looking at steady state downhills or long flat sections.

And how much speed will you gain and how quickly will it dissipate? If the hill is long enough to reach a steady state then you lost some energy you could have saved with regen. Do we then calculate how much speed is optimal and how far from the end of the downhill to end the regen so we can gain exactly that much speed? And for what % of the total drive time on a given trip does that calculation matter?

In the end, though, while we are discussing if and how often coasting is a useful tool, I'd still point out that regen is often an optimal answer as well and so eliminating regen (OP point) isn't the best control configuration either. And if coasting is a good answer a lot of the time, is there a more natural way to achieve it by looking ahead and using good observation and situational awareness and rules of thumb about what you see on the road than there is by having the accelerator end at the coasting state? Would having "foot off pedal == coasting" provide the driver with a crutch that will make them want to use that tool more often than it is the best answer?

At least you admit there is a lot of information that we don't have. I agree those are all very good questions, and for lack of information, I haven't argued about whether regen is better than plowing into the wind while speed doesn't increase further. There has been a lot of talk about "you could be using regen instead of fighting wind" and that argument may be accurate, but it seems counter-intuitive to me. I don't understand how one could gain from regen while also rolling at a speed where wind-resistance prevents further speed gain, because gravity is a constant, so either regen will reduce speed (because it is additional resistance against the same gravitational constant) or wind won't prevent speed gain (allowing regen to absorb the remaining gravitational pull, but you could gain speed instead). However, I don't have data, and it is certainly complicated, so I'm not arguing.

Speaking of data, my very first post on these forums was a link to a video of the energy chart doing something that doesn't make sense to me, and it was never responded to. What the energy chart is doing may well be accurate, but I believe that what I capture in the video implies something is incorrect that may or may not be covered in these three possibilities:
1) The "average" line is labeled wrong (it isn't an average, but some other function).
2) The "average" line and historical graph come from different time samples (possibly of the same length, but not covering the same start and end points).
3) The vertical axis for the chart is not consistent with vertical axis for the average (the numbers or units of measurement actually differ even though one set isn't displayed).

It is also possible that the chart is wrong, in which case the data could be wrong elsewhere as well, and that might even make certain testing moot.

Now, regarding the pedal off equals coasting discussion. The OP request (regen disabled) is not an option I personally would expect to ever use, but that doesn't mean it shouldn't exist (I say for user preference, but technically, it might be justifiable even if solely because even low regen could be dangerous in some weather).

 

[Peteski]

A lot of over-thinking going on here! Low and standard regen settings are fine. Low feels much like a conventional ICE car on lift off, standard obviously more toward 1 pedal. In low setting I can't imagine you would lose a significant amount of energy when cruising at more or less constant speed on the highway compared to having no regen at all. That's probably why they don't offer zero regen as an option. That and it would put a lot of stress on the brakes if people started using it all the time. It's basically quite a dangerous option in the wrong hands!

 

[flar]

At least you admit there is a lot of information that we don't have. I agree those are all very good questions, and for lack of information, I haven't argued about whether regen is better than plowing into the wind while speed doesn't increase further. There has been a lot of talk about "you could be using regen instead of fighting wind" and that argument may be accurate, but it seems counter-intuitive to me. I don't understand how one could gain from regen while also rolling at a speed where wind-resistance prevents further speed gain

Not "while", but "instead of". If a hill is long enough to reach a terminal coasting velocity, then doing so is fairly obviously a bad tactic because you've put a limit on how much energy you can recapture from gravity.

At terminal velocity, there is no net gain of energy by the car. The remainder of gravity's force is being delivered to the air particles that are resisting your speed gain. By holding it from reaching that terminal velocity instead, regen can recover energy into the battery fairly indefinitely.

because gravity is a constant, so either regen will reduce speed (because it is additional resistance against the same gravitational constant) or wind won't prevent speed gain (allowing regen to absorb the remaining gravitational pull, but you could gain speed instead). However, I don't have data, and it is certainly complicated, so I'm not arguing.

Absolutely, regen would be used to *prevent* speed gain. That's the tactic. Unless the battery is already at 100%, regen recovers energy for as long as the hill lasts, but gaining speed only gains a fixed amount until you reach terminal velocity.

Now, regarding the pedal off equals coasting discussion. The OP request (regen disabled) is not an option I personally would expect to ever use, but that doesn't mean it shouldn't exist (I say for user preference, but technically, it might be justifiable even if solely because even low regen could be dangerous in some weather).

I think preferences are fine.

 

[mxnym]

Not "while", but "instead of". If a hill is long enough to reach a terminal coasting velocity, then doing so is fairly obviously a bad tactic because you've put a limit on how much energy you can recapture from gravity.

At terminal velocity, there is no net gain of energy by the car. The remainder of gravity's force is being delivered to the air particles that are resisting your speed gain. By holding it from reaching that terminal velocity instead, regen can recover energy into the battery fairly indefinitely.

This I agree with, but we can't know the speed at which regen would be more efficient than speed gain (beyond knowing that it is [probably significantly] below 120MPH [assuming I am correctly remembering terminal velocity in open air]). Perhaps the car could calculate it and provide an optimum coasting mode, but like you said further in your post, preferences are fine.

 

[mxnym]

A lot of over-thinking going on here! Low and standard regen settings are fine. Low feels much like a conventional ICE car on lift off, standard obviously more toward 1 pedal. In low setting I can't imagine you would lose a significant amount of energy when cruising at more or less constant speed on the highway compared to having no regen at all. That's probably why they don't offer zero regen as an option. That and it would put a lot of stress on the brakes if people started using it all the time. It's basically quite a dangerous option in the wrong hands!

Of my last two automatic two wheel drive ICE vehicles, one coasted the same as throwing most vehicles into neutral when I let off the accelerator and the other coasted the same as a manual transmission when I let off the accelerator. Put another way, there is no "conventional ICE car" to compare to, because some people drive vehicles in the Toyota and GM families that coast like a dream (several years ago, I read that Science Channel's "How It's Made" had an episode where they mentioned a coasting gear in an episode covering automatic transmissions and that said transmission had a GM stamp in it) while other people drive Nissan and other families that don't. Also, because regen doesn't do anything when battery is 100% and because regen could fail and would need redundancy, I find it difficult to believe that relying solely on the brakes could be dangerous, as such a design would be a huge liability for Tesla.