Battery Electric Vehicle News / Enjoying the Transportation Revolution

JKenH

EricMears said:

JKenH said:

Counterintuitively, on an economy drive I like less regen as feel I can slow down by lifting off earlier without the round trip losses that come with more regen.

It's not counterintuitive !  With any knowledge of thermodynamics, car software writers would have realised that imposing regenerative braking is going to lead to the "round trip losses" that JKenH describes.  Tried & tested 'hypermiling' techniques eschew use of braking unless absolutely necessary.  Particularly galling when a so-called 'eco' button deliberately disables long held eco techniques !

Fair comment. Maybe, ‘counterintuitively’ wasn’t the best way to put it among a community of experienced EV users and engineers. What I was trying to say (not very well) was that with EVs marketed as being able to recharge their batteries by using regen when slowing down then, to someone who doesn’t think about it too deeply, it might seem more regeneration would always equate to more range. It does of course work like that when regen is used as a replacement for braking so in stop start traffic higher regen can be more economical. As you say, however, not the way to go for hypermiling. 

When I am trying to do an economy run to get the best mpk I can, I do find having the big economy dial selected on the Leaf dash lets me see more clearly that sweet spot where neither white nor blue bars are showing.

Out of interest, do you ever use Neutral when trying to eke out the miles? I did with my first Leaf but as yet I have not had range anxiety with the 40kwh to necessitate it. Do you know whether it would be detrimental to the transmission? 

Martyn1981

EricMears said:

JKenH said:

Counterintuitively, on an economy drive I like less regen as feel I can slow down by lifting off earlier without the round trip losses that come with more regen.

It's not counterintuitive !  With any knowledge of thermodynamics, car software writers would have realised that imposing regenerative braking is going to lead to the "round trip losses" that JKenH describes.  Tried & tested 'hypermiling' techniques eschew use of braking unless absolutely necessary.  Particularly galling when a so-called 'eco' button deliberately disables long held eco techniques !

I don't get what you are saying. If you want light regen then you just do this via the accelerator pedal by not lifting of as much as you would if you wanted full regen. The only difference between low and standard modes is that lifting off fully in standard mode will give you a higher amount of regen than lifting off fully in low mode. Hence why standard mode would give more regen and less friction braking than low mode, or the same amount of regen if a low user lifts off sooner. So it's not 'imposing' regenerative braking as you state, since you the driver get to choose the level via your foot on the GO pedal. 

This is just one pedal driving, as so many vehicles offer, just that the top level of regen lift off offers greater retardation if you want it. [Edit - In fact you go on to say that "hypermiling techniques eschew use of braking unless absolutely necessary" and higher regen will mean a greater chance of avoiding braking than low regen, especially if you are caught out suddenly by a change of traffic light etc.. M.]
Perhaps I'm missing something from what you posted?

Solarchaser

Yeah I always drive the leaf of eco and b.
So max regeneration.
If I don't want heavy regen, I leave my foot on the accelerator to balance demand

EricMears

Martyn1981 said:

I don't get what you are saying. If you want light regen then you just do this via the accelerator pedal by not lifting of as much as you would if you wanted full regen. 

 [Edit - In fact you go on to say that "hypermiling techniques eschew use of braking unless absolutely necessary" and higher regen will mean a greater chance of avoiding braking than low regen, especially if you are caught out suddenly by a change of traffic light etc.. M.]
Perhaps I'm missing something from what you posted?

Afraid you are.

'Retardation' is braking - albeit not friction braking.  Slowing down by regenerative braking reduces the kinetic energy of the vehicle by the not very efficient mechanism of charging the battery (admittedly more efficient than friction braking which doesn't even pretend to be efficient) and restoring the vehicles kinetic energy will require more energy than the amount 'saved'.  Slowing down by letting gravity & tyre-road friction do their stuff will not attempt that process.

Nobody should ever be 'caught out' by traffic lights changing !  But deliberately selecting 'B' for max regen remains an option.

I've seen all sorts of arguments in favour of adjusting accelerator to try and find a spot where regen is zero.  It's an awfully tiring procedure just to overcome an error in the car's software !

Solarchaser

You find using the accelerator in a car to modulate speed/acceleration / deceleration tiring?

EricMears

Solarchaser said:

You find using the accelerator in a car to modulate speed/acceleration / deceleration tiring?

Not so much the strain on ankle, but constant attention to a particular dial on the dashboard certainly is - not to mention the lack of attention to what else is happening around is downright dangerous.

Solarchaser

Weird, for me its a natural thing.
You can clearly feel when the car is pushing forward or pulling back, even the smallest amount, so keeping an "even keel" is not something I think about, I do it naturally. 

Martyn1981

EricMears said:

Martyn1981 said:

I don't get what you are saying. If you want light regen then you just do this via the accelerator pedal by not lifting of as much as you would if you wanted full regen. 

 [Edit - In fact you go on to say that "hypermiling techniques eschew use of braking unless absolutely necessary" and higher regen will mean a greater chance of avoiding braking than low regen, especially if you are caught out suddenly by a change of traffic light etc.. M.]
Perhaps I'm missing something from what you posted?

Afraid you are.

'Retardation' is braking - albeit not friction braking.  Slowing down by regenerative braking reduces the kinetic energy of the vehicle by the not very efficient mechanism of charging the battery (admittedly more efficient than friction braking which doesn't even pretend to be efficient) and restoring the vehicles kinetic energy will require more energy than the amount 'saved'.  Slowing down by letting gravity & tyre-road friction do their stuff will not attempt that process.

Ah, after reading this post I see I haven't misunderstood you at all, you seem to be completely confusing the issue.
You say that slowing down by rolling is more efficient than regen, and yes that's completely true, so your mistake in both posts is somehow to assume that driving the TM3 in standard regen rather than low regen means it uses regen unnecessarily ....... but of course that's entirely false, if you lift off the power you will have no regen, then low regen, then high regen, it won't regen for no reason, that's simply down to the one pedal driving technique.

Regarding attention to detail and dangerous driving, have you heard the phrase - "when you are in a hole stop digging"? If that was true then it would apply to all one pedal driving. The only way to remove this completely would be no regen, and then you get straight back to Tesla's position which is that you'll have to use the brake pedal more, which raises the possibility of friction braking. Note that for your claims we must be talking about the transition from no regen to low regen (high regen comes later with more lift off), so for this to be an 'issue' it applies to all levels of regen in all BEV's, unless you drive with zero regen (is that what you do?) so 'no to low' regen is where your claims of inefficiency come in, and has nothing to do with the higher levels of regen that only come later with greater lift off.

On to your claim that nobody should be caught out by traffic lights, and that's just silly. If you are obeying the law and driving at 20, 30 or 40mph and the lights change at just the right moment, then everyone will be 'caught out' and have to brake. High regen lift off will give you a slight edge over low/no regen before you hit the brake pedal and 'need' to modulate brake pressure just right, something that the high regen will do for you.

PS Regarding retardation. If you are going to comment on something I've posted, even if actually agreeing that what I said was correct, then you really shouldn't edit it out of your response. M.

EricMears

Martyn1981 said:

You say that slowing down by rolling is more efficient than regen, and yes that's completely true, so your mistake in both posts is somehow to assume that driving the TM3 in standard regen rather than low regen means it uses regen unnecessarily ....... but of course that's entirely false, if you lift off the power you will have no regen, then low regen, then high regen, it won't regen for no reason, that's simply down to the one pedal driving technique.

I'm afraid I know very little about Teslas.  My criticism of unwanted regen is based entirely on several years of Leaf ownership where there is no possibility of getting zero regen.  From the way the new Tesla regime was described here it sounded as though they would be aping the Nissan system.   Luckily,  there are better models to follow - e.g. in my VW e-Up!  the use of recuperative braking was completely under the drivers control : either none at all or 4 increasing levels were selectable.

Re your point about traffic lights :  it's very rare to find them just after a blind bend without a warning notice.  It would therefore be very easy to select an appropriate level of regen (but keep accelerating so that it isn't actually used) on approach to them when that might gain a fraction of a seconds advantage over starting to brake when they actually change.  That's a rather more advanced technique than driving along blindly with regen permanently selected.  But in most BEVs, gentle pressure on the brake pedal will trigger regen,  harder pressure is needed to activate friction braking  Hard braking is best reserved for real emergencies.

Martyn1981

EricMears said:

Martyn1981 said:

You say that slowing down by rolling is more efficient than regen, and yes that's completely true, so your mistake in both posts is somehow to assume that driving the TM3 in standard regen rather than low regen means it uses regen unnecessarily ....... but of course that's entirely false, if you lift off the power you will have no regen, then low regen, then high regen, it won't regen for no reason, that's simply down to the one pedal driving technique.

I'm afraid I know very little about Teslas.  My criticism of unwanted regen is based entirely on several years of Leaf ownership where there is no possibility of getting zero regen.  

Cool, I was wondering if you were trying to compare to a no regen setting. I just don't think that's fair as most BEV drivers would choose at least some regen most of the time. It's also completely irrelevant in this discussion as the TM3 is not going from from none to standard only, it's going for low to standard only, so a zero regen setting wasn't an option before.
So, regarding the TM3 choices of low and standard, think of your Leaf:- you have various levels of regen, from lowest to highest. If you select the highest it won't alter the amount of regen at the sweet spot between power - none (tricky (yes I agree)) - regen, it just gives you more regen if you lift off further, before switching to the brake pedal for more regen in low modes, or friction brakes if regen is maxed out.

Btw in case you are interested, the TM3 standard mode on full lift off will slow you down for even a last second light change, as the retardation levels are hard enough to push you into the seat belt thanks to the high regen levels that the Tesla can cope with pre-brake*, so you may not even need the brake pedal in that scenario, other than coming to a full stop if you are in 'creep' mode.

*Edit - Doh! So many side issues! Just to cover all angles, the level of regen can of course be reduced (by the car) if the battery is absolutely full, or too hot/cold when you first head off, to allow max regen. But this will be made clear by a notification on the screen.