Is Regenerative Braking Real? Does it work as we thought?

[bestclimb]

Coast to a stop best, regen next best and brakes bad. Any system that converts your motion into energy will not be 100% but will be better than converting motion to heat and loosing it.

[jamesqf]

Practical example with an Insight (since I don't have an EV): start by climbing up to Carson Pass (westbound) on Calif. 88, which is about 8500 ft. This will definitely drain the battery pack. Keep going west until you reach the valley floor, about 60 miles. You will have used very little gas - my trip mpg shows its 150 mpg max - and your batteries will be fully charged.

It's not a perfect test, since there are several upgrades where I need to use engine + assist, but I will repeatedly drain the pack on those upgrades, and recharge on the next downhill. So how does this happen, if regen doesn't work?

[vpoppv]

I've really enjoyed all this debate, because even if it ends up being a hoax, it stirs up thought. While most people just jump on the bandwagon and say "well the ONLY explanation is your data is wrong and/or you tested wrong" (because conventional wisdom is that regenerative braking works), a few people have given ideas as to why it might NOT work. If you just sit back and think "how would it be possible for regen NOT to work" it's kind of a fun brain exercise. The way I see it is that maybe we can come up with a way of using regenerative braking more efficiently.
I know I'm in the minority here, and my reasoning will be quickly dismissed by some more technically minded than me, but when I was working on my adapter plates, I used my cordless drill A LOT. Well, obviously I would drain the battery A LOT. But what I noticed was that my best use of it was always at the beginning of the day: if I tried to put it back on the charger between uses, it just didn't work as long as that first use. It appeared pretty significant. Granted, apples and oranges, and it's a NIMH battery vs LiFePO4, but I wonder if perhaps it might just be possible that charging/discharging/charging/discharging might very well lead to reduced total amp hours a battery can give out than if you just discharged all the way? Jack has already dismissed that hypothesis, as well as at least two others, but I am still not convinced.....

[Nevyn]

Sounds like the whole P&G vs. P&DFCO thing, except in this case it's P&R(egen).

So basically, my thought to him is this:

EVs - You're doing it wrong.

[NeilBlanchard]

I'm thinking that it very possible that Jack Rickard did not change his driving style when changing the ways that regen was set up; and when you do not take advantage of coasting (or if the cars he drove do not coast very well?), then that would not improve things.

With a lot of regen, then you have to use a lot of accelerator, and since regen is less than 100% efficient, you are bound to use more. Coasting is always better, since you can use less throttle and if you underestimate, just add a little more throttle. It is too easy to overestimate, especially if the regen is on the throttle and set too strong, so you over accelerate and then over brake, then you can easily waste energy.

[dcb]

well the edison 2 folks have a pretty picture, looks like ~22% return in an EPA drive cycle here in a VHC (Very Heavy Car) with next to nothing in a light car

[Frank Lee]

...and yet I wonder if regen on even the lightest bicycle EV would have merit in a place like steep hilly California...

[dcb]

Yah, that would be the best scenario for regen, something where you would have to ride the brakes a lot to prevent overspeed anyway.

[NeilBlanchard]

The energy from regen is proportional to weight (just like braking and acceleration) so the weight doesn't affect the proportion of energy you can get from regeneration.

[Patrick]

Neil, Edison2 doesn't seem to think so:

"Other conclusions that can be drawn are that there is less energy available to regenerate in a light car because less has been spent accelerating it, and that as weight shrinks the benefit of regenerative braking becomes vanishingly small."

Edison2 | Facebook