Regenerative Braking Setting

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With recup on, let's say it would take 500m to decelerate to reach destination. The energy recovered in those final 500m is less than the energy you saved during that extra 1.5km you coasted in the first scenario. According to Porsche.

I mean that's obvious, because of thermodynamics. I thought the question was whether active brake pedal engagement or recuperation mode was more efficient, not vs. coasting. But... It seems that no one is on the same page what we're actually asking or talking about. The discussions in this thread that haven't been about efficiency have been interesting, though, those should keep going, the efficiency thing should probably be dropped.

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[W1NGE]

With respect, I don't understand how this makes sense. Maybe I'm misunderstanding what Porsche is saying here, or we are talking about a different question. But "the harder you brake, the more recuperation" does not matter when we are talking about the end result, i.e. the area under the curve.

(Also, I was talking about efficiency, you are now saying effectiveness, maybe that's the disconnect?)

It's quite simple really.

The more pressure you apply to the brake pedal the more retardation and therefore braking recuperation you generate - just watch the Power Meter light up green as you brake.

The auto / manual / off overrun recuperation is not driver variable and you end up with slow retardation (watch the Power Meter register a little).

Ergo, braking recuperation generates more energy back to the battery.

 

[magnitude]

Ergo, braking recuperation generates more energy back to the battery.

But we're talking about the end result, not about instantaneous rate. The area under the curve, i.e. the integral.

You're saying that as long as the power meter lights up to a higher green value once, more energy lands in the battery in total?

So, if I drive downhill 5 miles, you are saying that if I press the brake pedal hard for 1 second, so that the power meter goes fully green, at the end of the 5 miles more energy has been transferred to the battery than if I constantly braked such that the power meter is constantly half green for the entire 5 miles?

It's the area under the curve that matters, not the instantaneous rate at any given time.

It's like heating up water by applying 100W for a second vs. applying 10W for a week. Which water will be warmer/more evaporated?

As said, let's just drop this.

 

[W1NGE]

But we're talking about the end result, not about instantaneous rate. The area under the curve, i.e. the integral.

You're saying that as long as the power meter lights up to a higher green value once, more energy lands in the battery in total?

So, if I drive downhill 5 miles, you are saying that if I press the brake pedal hard for 1 second, so that the power meter goes fully green, at the end of the 5 miles more energy has been transferred to the battery than if I constantly braked such that the power meter is constantly half green for the entire 5 miles?

It's the area under the curve that matters, not the instantaneous rate at any given time.

It's like heating up water by applying 100W for a second vs. applying 10W for a week. Which water will be warmer/more evaporated?

As said, let's just drop this.

Yeah, let's drop but I think we are at cross-purposes and off point from the original context of the OP's query.

 

[tchavei]

I thought the question was whether active brake pedal engagement or recuperation mode was more efficient

If you manage to apply brakes so the car decelerates at the same rate as with recup on, the efficiency will be the same. No?

Or are you comparing efficiency between early recup and late breaking?

 

[magnitude]

If you manage to apply brakes so the car decelerates at the same rate as with recup on, the efficiency will be the same. No?

Ah, that is exactly the question, finally we are on the same page!

We don’t know. Because in theory at least, faster deceleration could have more heat losses than slow deceleration, or vice versa. For example, the battery might not be able to take up the energy more quickly, so more of it is wasted. Higher currents also cause higher heat loss through resistance (that’s why power lines are usually high voltage instead of high current), and it smells like faster recuperation incurs higher current to me

Or, again just as an example that may or may not be reality, recuperation goes through a mechanical path that has more or less friction than if you apply the brakes.

It’s definitely possible that it is the same though!

 

[tchavei]

I can't see how a 1 sec of 240kw regen can be the same as 10 sec 24kw recup (imaginary scenario). Maybe on paper but there are physical limits and many other variables I suppose. I'm not an engineer so can't answer that. Maybe someone else wants to speculate but let's look at this from another point of view:

Imagine the average speed of two Taycans is, let's say, 100km/h.

Both cars drive the same route. Taycan A has a standard deviation of the average speed of, let's say +/- 5km/h while Taycan B has a standard deviation of 10km/h

Regardless of what each one of the cars uses (recup vs regen), Taycan A will be more efficient energy wise, no?

So maybe the question isn't what is more efficient (recup or regen) but which driver is smoother with the tool they chose to use?

Edit: probably bad example. On a route with lots of uphill and downhill stages, the car with greater deviation might actually be more efficient by allowing the car to drop speed uphill and let the car overshoot downhill (That's why ice cars are less efficient while on cruise control than manual drive). I don't know. I confused myself now...

 

[daveo4EV]

and you can blow ALL of that recuperation away in less than 10 seconds flooring it at a stop light gone green

i love my taycan!

 

[WasserGKuehlt]

Alright, that clears up every question then. By my reading:

• Recuperation may turn the light from .7㎨ on, but definitely will above 1.3㎨.

I tried auto-recup on the way home yesterday, with the g-force thing on. The 'auto' deceleration never exceeded .2g - at least not in the situations I felt comfortable trying it (~40mph approach speed to standing traffic, hovering over brake pedal and no-one behind me). The regen braking easily would go past .3g.

I'd surmise that the auto recup does not trigger the brake lights. (And I doubt I'll ever try the feature again.)

 

[WuffvonTrips]

I tried auto-recup on the way home yesterday, with the g-force thing on. The 'auto' deceleration never exceeded .2g - at least not in the situations I felt comfortable trying it (~40mph approach speed to standing traffic, hovering over brake pedal and no-one behind me). The regen braking easily would go past .3g.

I'd surmise that the auto recup does not trigger the brake lights. (And I doubt I'll ever try the feature again.)

But according to the UN regs., the brake lights should come on from anywhere between 0.07 - 0.13g.

 

[magnitude]

(And I doubt I'll ever try the feature again.)

As said, maybe one last time, try it for what I think it was made for (and not interesting but uncharacteristic experiment). On a highway or country road with low to moderate traffic for example. See how much it saves you from actuating the brake pedal at all when approaching other cars, or when they swerve into the lane.

That's not saying I only turn it on in those situations, but that's where it's actually beneficial for me (it's on all the time).

Still subjective preference, of course.

 

[magnitude]

But according to the UN regs., the brake lights should come on from anywhere between 0.07 - 0.13g.

It sounds so bad if you put it that way. Like our cars are violating UN conventions. Next thing you know they bring us to Den Hague!

But I think in this case we might be able to avoid being hit by a UN resolution:

≤ 0.7 m/s² The signal shall not be generated
> 0.7 m/s² and ≤ 1.3 m/s² The signal may be generated
> 1.3 m/s² The signal shall be generated In all cases the signal shall be de-activated at the latest when the deceleration has fallen below 0.7 m/s²
5.2.23. When a vehicle is equipped with the means to indic

So it's 0.7m/s^2 at which they turn on the earliest, not 0.07m/s^2. (And m/s^2 instead of g, this time you fell into that trap, it's such an easy one. ?)

 

[WasserGKuehlt]

But according to the UN regs., the brake lights should come on from anywhere between 0.07 - 0.13g.

I think the wording was "[signal] MAY be displayed"; it was "SHALL be displayed" above. Still, I couldn't quite reconcile the NHTSA regulation (which says >.35g) with the EU one you quoted - .35g is quite vigorous braking!

Incidentally, I was following an old pick-up truck, who came to a rather abrupt stop due to someone turning left ahead of them. The pick-up's lights never lit up once ? - goes to show how academic these regulations might be. (Or maybe it says something about the nonchalant attitude of the US wrt road worthiness - no MOT/TUEV over here..)

As said, maybe one last time, try it for what I think it was made for (and not interesting but uncharacteristic experiment). On a highway or country road with low to moderate traffic for example. See how much it saves you from actuating the brake pedal at all when approaching other cars, or when they swerve into the lane.

Still subjective preference, of course.

Sorry, I didn't mean it as a knock - as I mentioned in my first post, I don't consider the feature to be flawed, just not for me - perhaps it is its non-linearity that rubs me the wrong way. Absolutely no contest that the same may rub someone else in the opposite direction ?. When in "attack mode" I don't mind using the brake pedal as late as possible and with maximum effect; in cruising mode, the coasting was annoying in traffic but the plain recup (not auto) works perfectly fine for me.

Happy driving to all - looks like winter's finally gone in my neck of the woods, and I'm looking forward to some weekend drives.

 

[WuffvonTrips]

But I think in this case we might be able to avoid being hit by a UN resolution:
...
So it's 0.7m/s^2 at which they turn on the earliest, not 0.07m/s^2. (And m/s^2 instead of g, this time you fell into that trap, it's such an easy one. ?)

You had me worried for a second while I checked...no, my 0.07g is correct, and is the equivalent of 0.7m/s^2 (approximately. 1g = 9.81 m/s^2 rounded to 2 decimal places).
I was using g's for units in response to @WasserGKuehlt reporting that he observed up to 0.2g (which is 2m/s^2, so well above the threshold that should trigger the brake lights).
The perils of switching between units of measurement!

 

[magnitude]

You had me worried for a second while I checked...no, my 0.07g is correct, and is the equivalent of 0.7m/s^2 (approximately. 1g = 9.81 m/s^2 rounded to 2 decimal places).
I was using g's for units in response to @WasserGKuehlt reporting that he observed up to 0.2g (which is 2m/s^2, so well above the threshold that should trigger the brake lights).
The perils of switching between units of measurement!

Ah. I stand corrected, again, and it is me who really should work on reading those units with attention.

In this case I’m curious as well.

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