hmmm - my lovely Taycan is limited to 220 miles range - [Edit] I think it's the tires…

[daveo4EV]

Regen is also on display when going down a medium to long downhill grade - it’s quite expensive to move this car’s “a$$” up hill - but it’s zero cost to some recovery on the other side - I routinely recover 2-4% battery from the top of Hwy 17 in california down (either direcction) lowering the average cost of the segment to being not much more expensive than similar distance on flat terrain - with out regen and only coasting this would not be possible…

Regen has a dramatic effect on most any EV’s overall efficiency and elongates the time between required charges…just go drive up/down the grape-vine in Southern California if you don’t believe me…

Sponsored

 

[Vercingetorix]

https://www.caranddriver.com/features/a37419238/pikes-peak-mountain-2021-porsche-taycan-4s/

 

[JimBob]

I’m not sure that’s the right way to think about it. The values are fairly arbitrary.

I would just look at the kinetic energy of the car and then consider that if the deceleration rate doesn’t exceed the max braking recup, then decreases in kinetic energy are recovered (with losses).

There are other braking forces as well, like rolling resistance and air drag, but you can see how low these are compared to typical pedal braking by allowing the car to coast.

More generally, I like to imagine a graph of the power and then consider the energy integration. I think that gives the best illustration.

@madeyong is right about both it being cumulative as well as the energy expended for acceleration taking place regardless. While the acceleration will have an affect if looking at overall battery charge, it has no bearing when considering the magnitude of benefit of recup on it’s own.



There are really several reasons. Energy recovery is only one of them.

See this post:

https://www.taycanforum.com/forum/threads/recuperation-modes.5718/#post-79271

We actually said the same thing but differently. Where we may differ is on the magnitude of the effect.

Yes my values are arbitrary. Increase the braking time to 5 seconds at 265 kw and you increase the energy supplied to the battery to .37 kWh from .15 kWh. Or pick whatever other number you feel is appropriate.

What you are calling kinetic energy I am quantifying in kWh. Your integration is the area under the charging curve. For a straight line , it's a rectangle which is the energy input in kW x the time applied. The simple formula I used. For a more complex charging curve you will need a different method to calculate the area under the line. Unfortunately, Porsche supplies nothing in the way of metrics to do these calculations.

If I were to ask you this question.

If you accelerate hard to 100 mph then brake hard to 0 mph, what fraction of the energy expended on accelerating the car was recovered on braking and returned to the battery?

And for fun, if you accelerate slowly to 100 mph and brake hard to 0 mph. Do you recover the same fraction of energy as the previous, or more or less?

If we knew how much energy from the battery is required to accelerate a Taycan to 100 mph or other speed then we could make a good stab at it.

 

[SteveDC]

My car just sat in my garage for 23 hours and 55 minutes without losing a single battery percentage. Not plugged in.

Try 3 weeks! I was on vacation and left it home. Same battery %, about 54% (I was trying to be close to the 50% storage percentage recommended in the manual).

 

[f1eng]

On my plug-in hybrid I gain about 9 miles of range on the A5 through Snowdonia on the way down to the coast.
Having energy that can be used later recovered during slowing down rather than wasting the energy heating up brakes and producing dust is obviously better however little it may be.

 

[Kingske]

Try 3 weeks! I was on vacation and left it home. Same battery %, about 54% (I was trying to be close to the 50% storage percentage recommended in the manual).

Typical SoC loss through vampire drain is about 1% per month (with internal monitoring set to off).

 

[Jhenson29]

We actually said the same thing but differently.

I don’t think we did. At least not beyond agreeing that recup puts energy back into the battery. But less than that would be a very poor starting point, indeed, so I’m not sure how much credit we should give ourselves.

What I was trying to suggest was to just take a more relative approach to it and to just think in terms of energy.

Like, look at this here:

Or pick whatever other number you feel is appropriate.

It’s not about picking a number we think is appropriate. We can think about it without considering specific numbers much at all.

If you accelerate hard to 100 mph then brake hard to 0 mph, what fraction of the energy expended on accelerating the car was recovered on braking and returned to the battery?

If you don’t exceed the max braking recup, then it’s the same energy minus losses. There are losses on acceleration and losses in recup. But I feel like I basically already said this:

I would just look at the kinetic energy of the car and then consider that if the deceleration rate doesn’t exceed the max braking recup, then decreases in kinetic energy are recovered (with losses).

But, ok, let’s look at it for a minute.

Accelerate to 100mph. My first thought is…how much kinetic energy does the car have at 100mph?

energy (j) = 1/2 * mass (kg) * velocity (m/s) ^ 2

I’ll use 5k lbs for the car for the purpose of this post.

We’ll also assume flat ground.

So, at 100 mph, the 5000 lb car has 0.63 kWh of energy. Where did that energy come from? The battery. How much energy did it take? 0.63 kWh + losses. Losses in energy transport and conversion as well as losses to overcome resistive forces (rolling resistance and air drag). Call these losses a.

How much does it recup when you brake hard to 0 mph? Well…are you exceeding the recup limit? If so, it will be a lot less. But I don’t think that’s what we’re interested in here, so let’s assume you don’t exceed the braking recup.

Then you have 0.63 kWh of energy to dissipate to get to zero. The recup amount will be 0.63 kWh minus losses. Same types of losses as before. Rolling resistance, air drag, and energy transport/conversion. We’ll call those losses b.

So, what fraction of the acceleration energy is recuperated?

(0.63 - b ) / ( 0.63 + a )

I don’t know the values of the losses. We could look up some data and make some good guesses at it and be within some margin of error, but I’m not doing that right now.

We could also take measurements with the car for rolling resistance and air drag by measuring coasting deceleration rates at different speeds. I’ve done this some with a dragy to estimate overrun recup power before I realized it appears to vary by speed and slope, so it would have taken many additional tests to flesh out and Porsche may still have other variables I haven’t noticed yet.

And for fun, if you accelerate slowly to 100 mph and brake hard to 0 mph. Do you recover the same fraction of energy as the previous, or more or less?

Same formula:

(0.63 - b ) / ( 0.63 + a )

And the value of b is the same, but I don’t know if a is higher or lower. The resistive forces are applied for a longer time, which will increase a. But the current is lower so less losses on energy transport (and it’s not linear, it’s by the square of the current).

So…I don’t know. Could be more, could be less.

Note that the 100mph was arbitrary and not needed for these considerations.

We could just say the kinetic energy is x and the recup fraction relative to acceleration is:

(x - b ) / ( x + a )

But even this is only considering accelerating. That’s why I said typically think of the power curve and energy integration in general. Acceleration, constant speed, delectation, up/down hills.

Then, the for range that’s added, look at the average consumption for the car. My car is at 3.4 miles per kWH. So, every kWh that is recup’ed, it adds approximately 3.4 miles of range.

And remember, it’s additive. Maybe each individual recup is small. But they all add up also.

Think of Porsche options. Many small options can add up to tens of thousands of dollars on single car. We should all understand that fairly well…

 

[daveo4EV]

and right on cue…

https://www.yahoo.com/autos/charging-porsche-taycan-4s-using-143000016.html

regen isn’t BS…

”We got it right, and all that regeneration meant we'd barely pinched the discs on the way down. So, when we arrived at Glen Cove at 11,440 feet for a mandatory brake-temperature check, we had a surprise in store for a park ranger and his infrared thermometer. He said he's seen front-rotor temps exceed 900 degrees. The Taycan's registered a comfortable 67 degrees—an unofficial Pikes Peak record.”

Between the summit and the entrance gate, we were able to charge the battery to 17 percent and convert our range anxiety into 48 miles of optimism. Our range once we reached downtown Colorado Springs was over 100 miles, thanks to the grade of Highway 24 that pours back into the city. We didn't have to plug-in again until later that night when we returned to the hotel.

 

[daveo4EV]

turns out I have mounds of data…

the porsche connect app has complete history of “trips” and if you scroll back far enough you can find all your “efficiency” data from your deep dark past

my Taycan was clearing a 2.8-3.2 mile/kWh consumption rate in april/may - then I swapped tires in June/July (all seasons were at wear bars) - and after that point my trip data clearly indicates a drop of new ratings in the 2.2 - 2.7 mile/kWh range - making the Taycan a 220 mile vehicle…

turns out with summer tires on the car the EPA range estimate isn’t too far off the mark - the Taycan still does better than the official 201 range estimate - but with OEM Factory All Season the vehicle routinely did 260-290 miles vs. the 210-220 range I’m seeing with the Goodyears…

I’m ditching the summer tires as soon as I can find some Factory OEM all seasons EV tires in stock - for street driving I want the range more than I want the marginal increase in grip vs. all seasons.

 

[daveo4EV]

Before the tire change with Factory OEM All Season Tires (contenential) - 3.2 mil/kwh - max range = about 265 miles (easy to accomplish)

after tire change - Goodyear F1 summer tires installed by Porsche Dealer…max range = 207 miles maximum range - 210 - 220 possible - hmmm pretty much in line with EPA estimates of 201 - hmmmmm - seems the all season factory tires save Porsche’s butt in terms of real world experiences.

 

[daveo4EV]

and right on cue…

https://www.yahoo.com/autos/charging-porsche-taycan-4s-using-143000016.html

regen isn’t BS…

hmmm - so the brake rotors were 67F - I’d love to know the battery temp at the top of the hill vs. the bottom

 

[JimBob]

I don’t think we did. At least not beyond agreeing that recup puts energy back into the battery. But less than that would be a very poor starting point, indeed, so I’m not sure how much credit we should give ourselves.

What I was trying to suggest was to just take a more relative approach to it and to just think in terms of energy.

Like, look at this here:

It’s not about picking a number we think is appropriate. We can think about it without considering specific numbers much at all.


If you don’t exceed the max braking recup, then it’s the same energy minus losses. There are losses on acceleration and losses in recup. But I feel like I basically already said this:


But, ok, let’s look at it for a minute.

Accelerate to 100mph. My first thought is…how much kinetic energy does the car have at 100mph?

energy (j) = 1/2 * mass (kg) * velocity (m/s) ^ 2

I’ll use 5k lbs for the car for the purpose of this post.

We’ll also assume flat ground.

So, at 100 mph, the 5000 lb car has 0.63 kWh of energy. Where did that energy come from? The battery. How much energy did it take? 0.63 kWh + losses. Losses in energy transport and conversion as well as losses to overcome resistive forces (rolling resistance and air drag). Call these losses a.

How much does it recup when you brake hard to 0 mph? Well…are you exceeding the recup limit? If so, it will be a lot less. But I don’t think that’s what we’re interested in here, so let’s assume you don’t exceed the braking recup.

Then you have 0.63 kWh of energy to dissipate to get to zero. The recup amount will be 0.63 kWh minus losses. Same types of losses as before. Rolling resistance, air drag, and energy transport/conversion. We’ll call those losses b.

So, what fraction of the acceleration energy is recuperated?

(0.63 - b ) / ( 0.63 + a )

I don’t know the values of the losses. We could look up some data and make some good guesses at it and be within some margin of error, but I’m not doing that right now.

We could also take measurements with the car for rolling resistance and air drag by measuring coasting deceleration rates at different speeds. I’ve done this some with a dragy to estimate overrun recup power before I realized it appears to vary by speed and slope, so it would have taken many additional tests to flesh out and Porsche may still have other variables I haven’t noticed yet.



Same formula:

(0.63 - b ) / ( 0.63 + a )

And the value of b is the same, but I don’t know if a is higher or lower. The resistive forces are applied for a longer time, which will increase a. But the current is lower so less losses on energy transport (and it’s not linear, it’s by the square of the current).

So…I don’t know. Could be more, could be less.

Note that the 100mph was arbitrary and not needed for these considerations.

We could just say the kinetic energy is x and the recup fraction relative to acceleration is:

(x - b ) / ( x + a )

But even this is only considering accelerating. That’s why I said typically think of the power curve and energy integration in general. Acceleration, constant speed, delectation, up/down hills.

Then, the for range that’s added, look at the average consumption for the car. My car is at 3.4 miles per kWH. So, every kWh that is recup’ed, it adds approximately 3.4 miles of range.

And remember, it’s additive. Maybe each individual recup is small. But they all add up also.

Think of Porsche options. Many small options can add up to tens of thousands of dollars on single car. We should all understand that fairly well…

The a in your formula is the difficult number, because it is a variable dependent on a bunch of other factors. This is my case.

With respect to accelerating slowly and braking hard, and what fraction of energy is recovered. You will recover a greater fraction of the energy under this case. Hard acceleration requires a larger amount of current then slower acceleration, so more heating and efficiency drops. The difference between a heavy foot and a light foot.

The point I am trying to make is that I think that the amount of power input into the battery from braking is smaller than you think it is. There are just a ton of variables, and the headline number of 265 kW serves to obscure what is really going on as most braking is much less than this number.

Your paragraph “Then, the for range that’s added, look at the average consumption for the car. My car is at 3.4 miles per kWH. So, every kWh that is recup’ed, it adds approximately 3.4 miles of range.” is the 64,000-dollar question. But you don’t know how much is recup’ed. Cruising on the highway not much at all, on the track all the gains are swamped by hard acceleration. City driving? You need lots of braking to get the recup and have more light accelerations. Maybe the best case?

You could do a simple model in a spread sheet assuming x number of braking periods that generate y kWh in output per period and see how many it takes to make an impact on range using your historical data.

And downhill is another case all together. The system is no longer closed as gravity potential is converted to electrical energy. Not much different than plugging into a charger.

 

[JimBob]

turns out I have mounds of data…

the porsche connect app has complete history of “trips” and if you scroll back far enough you can find all your “efficiency” data from your deep dark past

my Taycan was clearing a 2.8-3.2 mile/kWh consumption rate in april/may - then I swapped tires in June/July (all seasons were at wear bars) - and after that point my trip data clearly indicates a drop of new ratings in the 2.2 - 2.7 mile/kWh range - making the Taycan a 220 mile vehicle…

turns out with summer tires on the car the EPA range estimate isn’t too far off the mark - the Taycan still does better than the official 201 range estimate - but with OEM Factory All Season the vehicle routinely did 260-290 miles vs. the 210-220 range I’m seeing with the Goodyears…

I’m ditching the summer tires as soon as I can find some Factory OEM all seasons EV tires in stock - for street driving I want the range more than I want the marginal increase in grip vs. all seasons.

You are right on getting tires designed for EV 's. Not too much talk about this but they can add a lot of range from what I can see for little or no extra cost. But would be at the cost of some handling. The options can only get better as more EV's are on the roads.

This from Continental https://www.continental-tires.com/car/tire-knowledge/tire-basics/electric-vehicle-tires

 

[Jhenson29]

With respect to accelerating slowly and braking hard, and what fraction of energy is recovered. You will recover a greater fraction of the energy under this case. Hard acceleration requires a larger amount of current then slower acceleration, so more heating and efficiency drops. The difference between a heavy foot and a light foot.

I can easily show that statement is false with a simple thought experiment.

First, the absolute amount of energy recovered is the same in either case, so what the argument amounts to is which acceleration consumes less energy: slow or fast.

If I start at 100% SoC and accelerate to 100mph as fast at possible, I will get to 100mph. The amount of energy used has an upper bound of the battery capacity (else I couldn’t get there).

If I start at 100% SoC and accelerate at 0.5mph/h, I will never reach 100mph, because it would take 10,000 miles to get there. I would deplete the battery long before that. The amount of energy used has a lower bound greater than the battery capacity (else I could get there).

Therefore, it certainly can take less energy to accelerate faster.

Also note that I don’t have to know how much energy either one actually took.

You are likely confusing absolute energy consumption with range efficiency. They are not the same.

The point I am trying to make is that I think that the amount of power input into the battery from braking is smaller than you think it is.

How can that possibly be your point if I’ve never said how much I think it is?

My point has been that you are approaching the problem wrong.

There are just a ton of variables, and the headline number of 265 kW serves to obscure what is really going on as most braking is much less than this number.

It’s good if braking is less than that. That means less losses to the friction brakes. So, as long as you stay under that max recup rate, the only thing that matters is the losses on the recup. Geez, how many times have I said that now? I apologize; I don’t know how else to explain it. I’ll try to think of a good analogy sometime.

And the 265kW isn’t obscuring anything for me. I haven’t been referencing it at all. You’re the one that has been mentioning it.

 

[daveo4EV]

the C&D article shows pretty clearly what happens if you stay off the friction brakes…

Sponsored