dthwaite
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Regenerative braking - why have the option to NOT have this?

Tue Nov 17, 2015 12:41 pm

I think it would be simpler to always have maximum regenerative braking and just have the "eco" mode to dampen acceleration/limit aircon as it does. With "b mode" you get two levels of regen which is extra superfluous.

I find it tedious always to select "b mode" (its not the default) and I also find it disconcerting that the regen is significantly lessened when the battery is full, so my driving experience is materially altered for no good reason (hey, why's the car not slowing down? oh, battery full).

You can always reduce/control the regen braking effect by keeping your foot lightly on the accelerator. I also think the regen slowing is more similar to engine braking in cylinder cars .

The only reason I can think of having no (or less) regen is perhaps there being some regulatory requirement that lifting your foot of the accelerator pedal should not induce too much braking? Or maybe the brake lights don't go on in max regen mode? But I should think they would go on triggered by the rate of deceleration rather than by what means was used to slow the car.

What do others think?

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

Tue Nov 17, 2015 3:16 pm

Not sure what you mean by "no good reason". The battery being full, therefore having nowhere to put the energy transferred by the regen braking seems like a pretty good reason to me. ;)

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

Tue Nov 17, 2015 5:22 pm

dthwaite wrote:The only reason I can think of having no (or less) regen is perhaps there being some regulatory requirement that lifting your foot of the accelerator pedal should not induce too much braking? Or maybe the brake lights don't go on in max regen mode? But I should think they would go on triggered by the rate of deceleration rather than by what means was used to slow the car.

What do others think?


Well, its not going to help people move to an electric car if the driving experience is radically different than a traditional car so they try to make the transition as smooth as possible (including still having a pointless shifting knob that could be easily accomplished with simple buttons). Its no doubt also the very reason that you have to engage b-mode every time you drive so a new person in the car does not experience a very odd ride experience (although the car does "remember" the eco setting across startup, at least in the 2013 that I have). While brake lights that illuminate based on rate of deceleration would be a potential addition, regulatory requirements include that touching the brake peddle disable any cruise control feature and illuminate the lights in the back of the vehicle.

Just some thoughts back
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garsh
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Re: Regenerative braking - why have the option to NOT have this?

Tue Nov 17, 2015 5:25 pm

I've said before that I'd like to add a big-old resister. Whenever the battery is too full, shunt the regenerated power to the resistor. That way you always have full regenerative braking available, and the brake performance can always be the same, instead of having diminished regenerative braking when the battery is full.

But that's an extra expense, and you have to figure out how to safely dissipate the generated heat.
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Nubo
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Re: Regenerative braking - why have the option to NOT have this?

Tue Nov 17, 2015 5:43 pm

garsh wrote:I've said before that I'd like to add a big-old resister. Whenever the battery is too full, shunt the regenerated power to the resistor. That way you always have full regenerative braking available, and the brake performance can always be the same, instead of having diminished regenerative braking when the battery is full.

But that's an extra expense, and you have to figure out how to safely dissipate the generated heat.


These guys will hook you up. :lol:

http://www.mosebachresistors.com/resistors_rl.html

To OP, you can't just dump energy into the battery when it's full. That would result in disastrous overcharging of the cells. The alternative is as garsh suggested, a "big ol' resistor". That is what diesel-electric locomotives use. REALLY big ones. Converts the excess electricity into LOTS of heat.
I noticed you're still working with polymers.

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

Tue Nov 17, 2015 9:51 pm

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

Wed Nov 18, 2015 3:27 am

Nubo wrote:That is what diesel-electric locomotives use. REALLY big ones.
Yep. I worked for GE Transportation Systems back in the early 90's.

Heck, we could use that extra heat to heat up the coolant used for the heater, instead of using precious battery power to do the job. Probably not too useful in hot climates. ;)
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aarond12
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Re: Regenerative braking - why have the option to NOT have this?

Wed Nov 18, 2015 7:18 am

My Mitsubishi i-MiEV also had a "B" mode, which I used exclusively (as I do in my LEAF). The difference is, even on a full battery, the i-MiEV would give me full regenerative braking. My theory is that even if I got up to speed slowly and then used maximum regen, I would still have less power returned to the battery than it originally had. I wonder why Nissan has chosen a different route...
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EVDRIVER
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Re: Regenerative braking - why have the option to NOT have this?

Wed Nov 18, 2015 9:53 am

[/quote]

Well, its not going to help people move to an electric car if the driving experience is radically different than a traditional car so they try to make the transition as smooth as possible (including still having a pointless shifting knob that could be easily accomplished with simple buttons). Its no doubt also the very reason that you have to engage b-mode every time you drive so a new person in the car does not experience a very odd ride experience (although the car does "remember" the eco setting across startup, at least in the 2013 that I have). While brake lights that illuminate based on rate of deceleration would be a potential addition, regulatory requirements include that touching the brake peddle disable any cruise control feature and illuminate the lights in the back of the vehicle.

Just some thoughts back[/quote]


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

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

Wed Nov 18, 2015 10:05 am

aarond12 wrote:My Mitsubishi i-MiEV also had a "B" mode, which I used exclusively (as I do in my LEAF). The difference is, even on a full battery, the i-MiEV would give me full regenerative braking. My theory is that even if I got up to speed slowly and then used maximum regen, I would still have less power returned to the battery than it originally had. I wonder why Nissan has chosen a different route...


Keep in mind that concepts like "full battery" are not absolutes in practice. 100% is an engineering compromise taking into account safety, utility, and longevity. A manufacturer may say its cell is at 100% at, say, 3.7 volts. That doesn't mean the battery can't be charged to 3.8 volts or 4.0 volts, and therefore hold more energy. But the number of recharge cycles may be significantly less. At some point safety also becomes a concern. And battery-charging characteristics change depending on state of charge. This is why fast-chargers dial back the amps as the battery gets full. Heat increases near the top.

Also, the battery manufacturer's opinion of "100%" is not the same as what a car manufacturer presents to the driver as "100%".

So, "full" is an arbitrary construct, not an inherent property. It may be that the i-Miev "hides" more capacity from the user thus allowing a bit more overage from regen. Or Nissan may simply have chosen to be more conservative. I'd suspect though, that if you rode regen on a "full" i-MiEV on a long descent, that regen would eventually be cut back. Otherwise you'd be in great danger.
I noticed you're still working with polymers.

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