Regenerative braking best practices

I use it like you would an engine braking adjustment. I leave it on level 1 for around-town and highway cruising since it most closely mimicks a normal car such as I've driven for hundreds of thousands of miles; level 2 for mildly twisty roads, and level 3 for very twisty or very sporty driving with lots of aggressive throttle and braking. I live on a mountain and drive down a twisty canyon road to get pretty much anywhere, so my commute starts on level 2, goes up to 3 for a brief very twisty section, then back down to level 1 when I hit town. The reverse going home.

 

For whatever reason, your testing proof link will not open (may be my end, may be your end).

 

I think I found it; http://techno-fandom.org/~hobbit/cars/ev/regen.html

 

Just like to follow up on something; this week I had opportunity to do some fair bit of highway driving in addition to my typical commute, and decided to set regen to 0 (still ECO mode) and try my hand (foot?) at optimizing efficiency.

After about 150 miles I can say that my "spring conditions" range (no heat, no AC, clear if not sunny weather and cool but not cold temps) is not significantly impacted by regen level; about 4.8 to 5.0 mi/kwh. It could be that I'm so used to diving in Lv3 that I just easily find the "sweet spot" for cruising and braking, and thus negate any benefits of either setting, or it could be that there's really no intrinsic benefit to either setting.

My opinion so far is that regen and driving efficiency is much like a diet - there are different philosophies, but ultimately the best strategy for you is the one you're going to stick to and be consistent with.

 

This explanation of regen and the general operation of this car is an excellent, informative, and amusing read and well-worth time to read.

 

Yes, thank you for getting that in, I sometimes drop parts of those URLs for some reason, when just typing in rather
than c&p-ing from a page. Downside of reading these forums and trying to type on a tablet...

_H*

 

I agree, a very informative and well written article. But it has my head spinning as to just exactly what the best practice is to obtain maximum range. I have been leaving the regen setting at Level 3, and using the left paddle to bring the Kona to a stop. Have become quite skilled in lifting my foot just the right amount to decelerate smoothly and hardly ever using the brake pedal. However, now I am thinking of the effects of momentum and letting the Kona collect kinetic energy while going downhill. Then, I learned that the action of putting pressure on the brake pedal also engages the regeneration process. This was new and surprising to me. So is there really a best practice, or do these different regen setting and use of momentum or not, wind up being all the same anyway?

 

I honestly think that paddles, brakes, or throttle regen are all about as efficient for regen. What's matters most is not abruptly slow enough to engage the wheel brakes except to stop at the end. It's really just personal choice. I use ECO regen level 3 because for me I like controlling my speed, up and down, with just the throttle pedal.

 

Well, that's what the entire thread is about. The short, concise answer is that it's all going to be about the same and that other driving conditions such as road speed and grade are far more influential to economy.

Otherwise you'd have to ask yourself where else does the energy go while slowing down if it isn't going into heating the brake disks?

 

Regen is regen. It doesn't matter if regen is activated by the brake pedal, the paddle, or by regen mode when you lift off the throttle. I guess the only difference would be that the paddle offers only one level of regen whereas the other two can be modulated by foot pressure? The friction brakes don't kick in until the very end, and if you use the paddle it doesn't apply the friction brakes at all which to me is kinda freaky. I suppose you can argue that the paddle can potentially "waste" a little bit of energy because it's keeping the motor powered while at a full stop.

It seems to me that however you control it, it's all about your driving habits. Someone who drives carefully, with gentle acceleration and focusing on steady speed, will get better efficiency than someone who thrashes about. That's true of literally *any* vehicle, though.

One philosophy is to keep regen set to 0 and coast as much as possible, which is a classic hypermiling strategy. If you have good foot control, you can achieve this by finding the neutral position of the throttle for whatever speed you're going, including downhill! Having tried both, regen level 0 is definitely easier to manage coasting, and you can still take full advantage of regen through the brake or paddle controls. The automatic regen at levels > 0 is really nice, though, for that one-pedal-driving feel...

I used to be in the "ECO mode Level 3" camp but I think I'm getting used to "ECO mode Level 0." The biggest difference is that if I use the brake pedal to slow down a little bit, the brake lights actually come on. If you're using regen level > 0 then the brake lights don't come on until you completely release the throttle, which means you can be slowing down quite a bit at level 3 and banking on anyone behind you paying attention. Nothing to do with efficiency, but that's a potential safety thing.

 

I got really good at foot control to hold various coasting modes in the Prius, notably "warp stealth",
and it was a pain in the *** especially when the SoC started to drift down. I very much like the
ability to take my foot off the pedals completely in the Kona and just roll. It also lets me cover the
brake instead of having to micromanage the go-pedal for miles.

_H*

 

Made an observation today that seems relevant to this thread;

If you use cruise control, the car will use regenerative braking if you lower the set speed using the SET- switch, even if you have the regen level set to 0.

Obviously this doesn't happen if you cancel cruise control with the CRUISE button or by tapping the brakes - in either of those cases it will obey the regen level setting.

 

Another observation, purely by chance as I happened to pull up the energy usage screen that tells you how much power the motor/climate control/etc are using: Even with regen set to level 0, the car still reports 2kw worth of regen going into the battery when "coasting."

I guess it's simply not possible to be in motion with the motor completely de-energized? I wonder if there's a technical reason for it or if it's just a quirk of the software... or if it's even real at all tbh.

 

It's always been like that. I have no idea exactly why but from a technical perspective the back EMF from the motor needs to be kept under control so that the generated open-circuit voltages at the field windings don't exceed the ratings of the driver semiconductors that they are always connected to. It's the same reason why towing with the front wheels on the ground is not recommended.

 

I have a similar suspicion as well - though you could handle back EMF in other ways, you'll still be losing energy in the process, so maybe it makes the most sense to put as much of that energy back into the battery as you can rather than let it make your motor and inverter hot.

 

You'll have trouble distinguishing the amount of drag from regen-0 coasting vs. neutral
coasting. The amount of energy going back into the battery is in the noise, and the
"miles recovered" counter doesn't even come on until you do some real regen slowing.

_H*