Regen Braking Question

[Norbu72]

I just watched this recently posted YouTube video and it brought up a question in my mind about regen braking. See: https://www.caradvice.com.au/883187/2020-mini-electric-review-233km-driving-range-tested/

I think this guy gets multiple things wrong but one of his major points is that the power from the regen braking is a big factor in the SE getting the 233 km range in town. I currently own a hybrid and a plug-in hybrid and the brake regen doesn’t seem to provide a whole lot of additional battery power.

So my question for those of you who are much more into the tech than I am, does the brake regen on the SE really make that much difference in the range?



Sent from my iPhone using Inside EVs

 

[F14Scott]

There is no such thing as a perpetual motion machine.

Regen helps recapture lost energy, but a car is going to burn Watts at some rate for any given condition (speed, wind, altitude rain, load, tire inflation, etc.) The best condition (in an airplane we call it Rmax for maximum range) in a car is in top gear, at the speed where the engine efficiency and wind and other resistance curves cross, probably around 45 MPH.

I don't know what Rmax is in the SE, but I suspect it is less, around 25 or 30, since there is no gearing*. Slower is better, until you start figuring in the "hotel load" (the AC, the radio, etc.), which, if you drove slowly enough, would eat a proportionally higher percentage of your power.

Driving the SE as close to its Rmax is what gets you more range. Regen helps if you must brake. But, overall, it would be better to drive Rmax constantly than it would to drive Rmax and brake and then accelerate back to Rmax.

*at least, I don’t believe there is gearing that changes while driving. There may be a reduction gear in the drive train, somewhere.

 

[Toi]

There is no such thing as a perpetual motion machine.

Regen helps recapture lost energy, but a car is going to burn Watts at some rate for any given condition (speed, wind, altitude rain, load, tire inflation, etc.) The best condition (in an airplane we call it Rmax for maximum range) in a car is in top gear, at the speed where the engine efficiency and wind and other resistance curves cross, probably around 45 MPH.

I don't know what Rmax is in the SE, but I suspect it is less, around 25 or 30, since there is no gearing*. Slower is better, until you start figuring in the "hotel load" (the AC, the radio, etc.), which, if you drove slowly enough, would eat a proportionally higher percentage of your power.

Driving the SE as close to its Rmax is what gets you more range. Regen helps if you must brake. But, overall, it would be better to drive Rmax constantly than it would to drive Rmax and brake and then accelerate back to Rmax.

*at least, I don’t believe there is gearing that changes while driving. There may be a reduction gear in the drive train, somewhere.

There is a single reduction gear in the drivetrain, but it doesn't change at any point.

 

[Norbu72]

Thanks F14Scott! That’s what I was looking for. It didn’t pass the smell test and you provided all the details I was looking for.


Sent from my iPhone using Inside EVs

 

[F14Scott]

Thanks F14Scott! That’s what I was looking for. It didn’t pass the smell test and you provided all the details I was looking for.

One thing I could have clarified is that an SE doing city acceleration/regen cycles around 30 MPH may very well use less energy per distance than an SE cruising steady state at, say, 65 MPH. That has nothing to do with regen "adding" energy, only that regen reduces the city car's braking losses, and the net effect is that a cycling city car (averaging near Rmax) may beat a steady state highway car (averaging well above Rmax).

 

[Toi]

This thread reminds me of when I was studying for my PPL-H and had to be able to describe the difference between max range and max endurance

 

[F14Scott]

This thread reminds me of when I was studying for my PPL-H and had to be able to describe the difference between max range and max endurance

Totally where I learned it, too: US Navy basic aerodynamics class, 1991.