More Regenerative Braking Results. It gets worse...

[Right Lane Cruiser]

With MORE regen, it appeared it was actually LESS efficient????

Jack Rickard - BLOGSPOT - July 11, 2010

An interesting dilemma... What could cause this unexpected result? --Ed.

In our first initial drives with the Mini, we were getting apparent ranges that matched my calculations for range initially without regen. We had assumed we would get some extension in range from having our first car with regenerative braking.

After just a few drives, it became apparent to me that with 100AH pack, and just under 1 AH per mile, that our range would be limited to about 100 miles - really quite similar to the BMW MIni-E. We had a larger pack, but also a larger car as we used the Clubman. But I was assuming we would get something from regenerative braking.

The question was of course what? Most comparisons indicate AH consumed and AH recovered and the Toyota RAV-4 even has a little indicator showing you your efficiency gains from regen based on this. I rather suspected that a real world comparison didn't yield the 21-25% gains that this measurement routinely provided. But I assumed 6-8% would be "real."

In the case of the Mini, it didn't look like we were getting much.

But we were busy completing the Speedster build and we have already heard from a number of people who want to purchase it from Special Editions Inc as a finished car when they can produce it. They can't produce it until we send them the prototype and... [Read More]

[Butterfly Mage]

Wow! That is really screwed up! Fortunately the regen on my Insight works better than that. If I ride the brakes slightly on a long downhill grade, the regen will dutifully charge the battery indicator to 100%. It sounds like Mini needs to go back to the drawing board.

[Right Lane Cruiser]

Hi, BM -- there is no question of the regen doing its job of shoving charge back into the battery. It seems however that the car is capable of driving further without doing any regen at all. Even when still braking.

We don't have a choice in a non-plugin hybrid... we have to get that battery charged somehow and regen is the only option. In an electric car however, things are a bit different. Jack's results indicate that in spite of returning charge to the battery through recovery of some small part of kinetic energy... it is somehow less efficient than not capturing any of it. That's the headscratcher...

I'd like to see a controlled test on a closed circuit without any other traffic. Run it like a timed rally effort such that the speeds at particular points on the route are specified and braking is orchestrated to be at identical rates, over identical distances, and at identical speeds. Have that course traveled with all 3 sets of regen configurations and then see what the difference is.

[volton]

I didn't read the whole post, but if the regen is aggressive meaning it slows the car down as soon as you lift off on the accelerator, then yes I can see it would be less efficient as you are throwing away momentum. Downhill gliding is always more efficienent than any energy gains you would get through regen. I have heard of some BEV cars that will use this agressive regen, that is bad news for hypermilers.

If its not agressive, meaning it only uses regen if the brake pedal is pushed then it should be more efficient.

[Right Lane Cruiser]

I agree, Volton -- yet his data shows that the best range is to be had with zero regen of any sort.

[TheForce]

When I get back from Hybridfest I want to do an ABA test in my Prius. The only issue would be disabling regen. The only way to do it is to put the car in neutral.

[Chuck]

Side topic: places with a very steep grade like I70 just west of Denver downhill....I dream of the excess regen transmitted to a local power plant.

[EVuser]

As a owner of a AC induction drive vehicle with throttle modulated regen (and 33000 miles) I think Jack's basic conclusion is incorrect. Regen is beneficial but the gains aren't always huge and they definitely need to be applied in the right condition.

When I'm hypermiling my Force there are some basic rules. Disobey any one of them and the amount of power used can change from an average AH per mile of <0.9 to >1.3 plus in just one stop/start. In other words it is extremely extremely hard to repeat a given drive result right down to the the 6-10% accuracy. I can be nailing at 20 mile 0.9 AH drive and one need for a extra use of power blows it. But I can recover power with regen. I can't recover power with the use of anything else in the vehicle. But I get my maximum range coasting. Pretty much a no brainer.

Coast-regen-brakes is the required order for getting the vehicle to come to a rest. Towards the end of Jack's post he also points out this. Another unmentioned point in his article is that it is in fact very hard to duplicate an exact SOC (state of charge) on a EV battery pack. So this could have a bearing on results. It is a chemical change not a specific amount of "fuel" being added or taken away.

With practice and an adjustment in driving style regen is a positive. It is certainly more beneficial in a stop and go city drive where the driver is required to do forced stops. The nice thing is it comes "free" with a AC induction drive system and makes DWB really possible. Obviously regen will not extend the range of a vehicle driven at a steady pace. And if you use it when coasting is possible it isn't as good for range as coasting. But it really beats turning energy into brake dust.

Regen is Good! But not as good as some other range extending options.

[ItsNotAboutTheMoney]

+ Charge from Regen
- Cost of Regen (Cost of applying the regneration system)
- Regen Process Effect (Side-effect of charging by regen on the battery)
- Regen Momentum Grab (Cost of undesired lost momentum)
- Inactive Regen System (Cost of having the regeneration system available for use but inactive)

Those are the negatives I can think of.

[EVuser]

Originally Posted by ItsNotAboutTheMoney

+ Charge from Regen
- Cost of Regen (Cost of applying the regneration system)
- Regen Process Effect (Side-effect of charging by regen on the battery)
- Regen Momentum Grab (Cost of undesired lost momentum)
- Inactive Regen System (Cost of having the regeneration system available for use but inactive)

Those are the negatives I can think of.

Regen costs virtually nothing in a AC induction system it is there if you decide to use it. And it doesn't add weight. Deciding not to use it also requires some active engineering.

There is a potential for battery harm if unregulated but voltage regulation is also built into the controller by default and there is a greater potential for it to be beneficial.

Unintended regen isn't anymore likely than unintended braking or anything else the driver does to increase fuel use.

As there was virtually no cost in having it, so turning it off isn't costly either.

It also greatly saves brake linings and after a few miles of using it it makes you wish all vehicles had it.

But how well it is implemented for driver use in the vehicle is going to be very important as to how well it is liked or disliked. Trying to make the vehicle behave too much like a ICE vehicle could result in misapplication.

A simple DC conversion is cheaper than a AC conversion and often some equate some of this cost to regen braking ability but that just isn't true. New production BEV's will certainly have regen capability along with efficient motors and controllers.