finman100
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Re: Regenerative braking - why have the option to NOT have this?

Wed Nov 18, 2015 10:41 am

Hmmm, excess regen generates heat you say? big ol resistor? i'd say we have another cold-weather package to sell! Take that heated resistor and force the hot air into the cab for all those in winter climates. Heck, even i'd like some of that for defog purposes up here in the PNW. Go fast, then brake to 'over-regenerate', thus creating defog/heat for the cab. win-win.
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pkulak
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Re: Regenerative braking - why have the option to NOT have this?

Wed Nov 18, 2015 10:52 am

LeftieBiker wrote:The best reason to not have full Regen all the time is loss of efficiency. Only about 40% of braking energy ends up back in the pack, so coasting is actually much more efficient than having Regen active on level ground when braking isn't needed. Sure, you can carefully modulate pedal pressure to cancel it, but that gets tedious fast. All EVs should have a strong Regen mode and a no or little Regen mode as well.


That's what I think Audi got right with their braking system. The default is pure coasting, but you can turn on strong regen if you'd like it. The tiny bit of regen to simulate an automatic transmission is the worst of both worlds, in my opinion. Give me all the regen on the accelerator pedal or none of it.

minispeed
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Re: Regenerative braking - why have the option to NOT have this?

Wed Nov 18, 2015 11:23 am

To a car engineer regen is also a lot more about brake pedal feel than just how it works with the accelerator and drive mode. It's interesting to note that 2 of the cars with the strongest right pedal only regen (tesla and i3) are both rwd. As you brake harder and the weight shifts to the front wheels you can't use the rear wheels to slow the car as much without risking traction loss. Possibly strong rwd right pedal regen is a way to get the energy back earlier and not cause the driver to hit the brakes harder and later and get into a situation where regen needs to be cut off because of the weight transfer. I've also read that Tesla in part chose to not integrate regen into the brake pedal to give a safer more traditional feel to the brakes. They also offer adjustable regen. I would assume part of this is acknowledging that it can be more efficient to coast for people who want to set the car up like that. There's too much that varies from car to car to say that they should have done it that way or this way. Anything we compare the leaf to is just an assumption.


To the OP you'll find that people have strong preference either way. I would hate it if the car started in B mode. I didn't like the strong regen of the i3 at all when I test drove it. On the tesla test drive I turned it up and would probably keep it that way only because it wasn't integrated with the brakes but in that case I would live with it and coast using my right foot. Also as far as I know there aren't any cars with brake lights triggered by regen (I may be wrong) but since ours doesn't do it I'd rather use a light pressure on the brake pedal which is all it takes to generate the same amount of regen as B mode without using the friction brakes at all. This has a second safety benefit other than the brake lights in that if you need to suddenly stop your foot is already on the pedal and your reaction times are better. Also if your wheels hit a bump and regen cuts out you are already on the brakes. The only time you should be driving with your foot not on a pedal is when the roads present a safe chance to coast, if you're going to be coming to a stop your foot should be on the brake. If you only need to slow down without coming to a stop the difference in using B mode vs D mode regen has nothing to do with how much energy goes back to the battery only in how long you would do it for.

I would agree with you that B mode is more like engine brakes in a manual transmission ice car if you're the type of driver to do it with high revs but I find D mode is more like it is in an automatic.
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jpadc
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Re: Regenerative braking - why have the option to NOT have this?

Wed Nov 18, 2015 5:27 pm

EVDRIVER wrote:Seems to work fine for Tesla. The LEAF has always had poor regen considering it is capable of 80kw.

Well I'm not sure what that statement is in reference to as even a DC fast charger (up to 500 VDC @ 125 A) is only providing 62.5kw to the battery and that is backed way off when the car is even close to an 100% charge. The battery can't handle that level of input without overheating.

But its not like the Tesla does anything different.

from the Tesla blog at: http://www.teslamotors.com/blog/magic-t ... ve-braking
Regenerative braking is necessarily limited when the batteries are fully charged. Because the additional charge from regenerative braking would cause the voltage of a full battery to rise above a safe level, our motor controller will limit regen torque in this case.

If your comment is in reference to my thoughts about Nissan wanting the LEAF driving experience to "feel" more like a regular car and Tesla being fine with a driving experience that is way different than a regular car, then I would say of course they would be. Who would want a $75k sports car to drive like a Camery? Nissan wants to move Honda and Toyota drivers to the LEAF. If I was paying that $75k for a car I sure would hope it would drive nothing like my Accord. But if had an Accord and wanted to see if an EV might be right for me, I'd likely be scared away if the driving experience was completely different. The Toyota Prius first broke into the top 20 cars sold in the USA once they started making it look and drive just like the Camery.

Tesla makes a great car, but its not the car that will move the general public from ICEs to EVs. Will they be leaders in developing the technology that will raise the bar for what an EV can be, likely true and thats great.
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EVDRIVER
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Re: Regenerative braking - why have the option to NOT have this?

Wed Nov 18, 2015 6:18 pm

Actually the superchargers are 120kw and may even go much higher soon. Tesla has much higher regen and it is not causing people to freak out, in fact the LEAF is designed more to Japanese standards then US with its over boosted steering and mild manners. The LEAF can draw 80kw form the pack and there is no reason it can't have much more regen, heat is not a fixed constant and is regulated just like the car regulates high SOC on a full pack and a Tesla will regulate output based on heat from high pack draw. The leaf has always been dumbed down for the masses. The LEAF has been a conservative design from the start and lacks some of the key fun factors EVs have because of this. Of course you won't do 80kw of off-pedal regen but boosting it significantly is not a safety issue or something that would scare people away since there are two modes available. Using the friction brakes vs higher regen is a bad implementation like the poor LEAF braking design.

Comparing the Tesla as a sports car is really is moot when it comes to regen and many EVs have stronger regen the LEAF. The Tesla is driving by most as a daily driver sedan, it is not an exotic quickly car with extreme enthusiast features. The buyer for the Tesla is all over the place and the car just happens to have lots of power which is not a penalty if it's not used unlike an ICE that must carry a bigger less efficient motor.

GRA
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Re: Regenerative braking - why have the option to NOT have this?

Wed Nov 18, 2015 7:04 pm

Personally, I'd want any EV I'd own to have variable regen. I'm used to driving a 5-speed stick, and there are situations (freeway cruising) where I want maximum coasting on liftoff, and others (steep downhills) where I want max. regen. Putting all regen on the accelerator pedal is a pain in the first case, as you have to find the sweet spot with your foot; it's much easier to know that if you take your foot off, you'll coast, and if you want to slow down, you can either select a higher level of regen (preferably via paddles rather than the gear selector lever) or use the brake. Chevy got this right with the new Volt, and other companies have also. Most of this is done via software, so it's no great extra expense to provide variable regen which can suit the taste of the widest possible group of customers. If you want it all on the accelerator peddle you can have it, or none, or some intermediate value.

At a minimum, I'd want at least three levels of regen, but preferably four or more; those in ( ) are optional:
5. Freewheeling, i.e. no or very little regen, equivalent to an overdrive top gear.
4. Mild regen, equivalent to 4th gear
(3). Moderate regen, say 3rd gear.
2. Strong regen, equivalent to 2nd gear.
(1). Very strong regen, equivalent to 1st gear.

Having ACC might shift my preference from level 4 to level 3, if I'm limited to only 3 choices. IIRR, VW gives you 4 levels on the e-Golf, albeit on the selector lever rather than via paddles. I forget how many levels the 2016 Volt has. The ideal would have your personal default level of regen keyed to the fob, seat memory position or what have you for multiple drivers, or at least have the default selectable, but manual selection on startup wouldn't be all that onerous. Still, that seems pretty ridiculous in this day and age, once an owner has taken possession of a car. I've got radio channel presets in electronic memory, so it's hardly any more trouble to do the same with my driving preferences, choices like normal/sport/eco modes, steering weight and feedback, regen, suspension settings etc.
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aarond12
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Re: Regenerative braking - why have the option to NOT have this?

Thu Nov 19, 2015 2:22 pm

Nubo wrote:It may be that the i-Miev "hides" more capacity from the user thus allowing a bit more overage from regen.

You may be correct: http://forums.aeva.asn.au/forums/forum_ ... tery#57814

This i-MiEV owner lives in a hill and if the battery is "full", his regen isn't strong enough to slow him down in the corners. I guess living in flat Texas made that pretty transparent to me. I do appreciate that the LEAF shows how much regen is available with the O O O(O)(O) outlined circles.
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jpadc
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Re: Regenerative braking - why have the option to NOT have this?

Thu Nov 19, 2015 3:22 pm

EVDRIVER wrote:Actually the superchargers are 120kw and may even go much higher soon. Tesla has much higher regen and it is not causing people to freak out, in fact the LEAF is designed more to Japanese standards then US with its over boosted steering and mild manners.

Tesla has an electronically-controlled liquid-cooled battery pack. Not something in the LEAF has, so controlling heat is a much greater problem.
EVDRIVER wrote:The leaf has always been dumbed down for the masses. The LEAF has been a conservative design from the start and lacks some of the key fun factors EVs have because of this.

You're just making my point for me. They want it to be a Camery/Accord. That is their target market. They are not trying to be a Mercedes-Benz, BMW Audi, or Acura.
EVDRIVER wrote:Comparing the Tesla as a sports car is really is moot ... The buyer for the Tesla is all over the place

You mean among 1%ers who can afford a $75k car.. right?

Agreed, the LEAF is dumed down for the masses. That makes it not right for you. We get that. But IF the goal is to get EVs to be accepted by the masses and Tesla wants to be in that market, they need to make a car more like a LEAF than an S. But I don't think they want to be in that market, and thats fine. BMW does not either.
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jpadc
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Re: Regenerative braking - why have the option to NOT have this?

Thu Nov 19, 2015 3:23 pm

jpadc wrote:
EVDRIVER wrote:Actually the superchargers are 120kw and may even go much higher soon. Tesla has much higher regen and it is not causing people to freak out, in fact the LEAF is designed more to Japanese standards then US with its over boosted steering and mild manners.

Tesla has an electronically-controlled liquid-cooled battery pack. Not something in the LEAF has, so controlling heat is a much greater problem.
EVDRIVER wrote:The leaf has always been dumbed down for the masses. The LEAF has been a conservative design from the start and lacks some of the key fun factors EVs have because of this.

You're just making my point for me. They want it to be a Camery/Accord. That is their target market. They are not trying to be a Mercedes-Benz, BMW Audi, or Acura.
EVDRIVER wrote:Comparing the Tesla as a sports car is really is moot ... The buyer for the Tesla is all over the place

You mean among 1/2%ers who can afford a $75k car.. right?

Agreed, the LEAF is dumed down for the masses. That makes it not right for you. We get that. But IF the goal is to get EVs to be accepted by the masses and Tesla wants to be in that market, they need to make a car more like a LEAF than an S. But I don't think they want to be in that market, and thats fine. BMW does not either.
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EVDRIVER
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Re: Regenerative braking - why have the option to NOT have this?

Thu Nov 19, 2015 5:54 pm

How the LEAF is cooled is not the point that is only a relative discussion not an exclusionary one. The point is Nissan chose to not allow it even though they could without penalty and it if they did it would not have to impact sales or freak people out, the is classic old EV FUD. Having any difference to an ice and impacting consumers is nonsense that has been debunked with every other poor Nissan design choice that was ignored before the car was released, and beaten to death by experienced EV drivers (invited to Japan) prior to final development. Examples included SOC , onboard charger, etc. Nissan still struggles to convey their own product at every level in the chain. Tesla EVs are not a good comparison to the LEAF, other then the fact that they are more clued in and get it. Nissan simply refused to listen and they were not alone. The car is not dumbed down to be like a Camary as that is not even the same, it was done for Asian markets and for over concern by a conservative Japanese company (risk avoidance) and really out of touch product developers. Speaking to any of them personally it becomes very apparent, they just did not get it and it took years of pounding by owners to finally get them to possibly wake up. The actually were terrified of having a percentage SOC meter. I have sat in meetings with executive level management of major auto makers on these topics and they all simply would not listen because they were stubborn, one major German company exec with production prototypes had never driven in an EV ever! There lies the issue when a very senior exec making EV decisions has never driven in an EV. Many years later they have gone 180 on all of their decisions. Guess what who they went to to fix those issues? The history of EV development is quite funny and unknown and if it were not for an NDA I would comment more.

I never said a LEAF was not for me, my LEAF vin was one of the first even produced and I am very familiar with the technical aspects of the car in great detail. Nissan needs to really change their product to win in the new landscape or even survive and I expect they will make an attempt but that is another discussion. Regen is one of the silliest and most misunderstood EV topics and remains as such.

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