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TonyWilliams
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Re: Regen question

Fri Sep 02, 2011 11:26 pm

I'd like a lever that is along side the gear selector, that I can pull back to provide drag (regen).

The lever to the left of the #1 engine thrust lever, label "SPD BRK" (Speed Brake):


Image

Volusiano
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Re: Regen question

Fri Sep 02, 2011 11:37 pm

Is it safe to assume that as long as the regen indicator doesn't hit the 30KW max that you never use the mechanical brake?

I must say that the few times I exceed 30KW regen, I can't really tell at all whether the system started activating the mechanical brakes or not. It's indistinguishable to me.

You know, like how on a hybrid you can tell when the enginer turns on or shuts off, even ever so slightly? Well, on the other hand, the switch from regen to mechanical braking can't be detected at all.

And as I continue to apply pressure and the car slows down further, the regen bars retract away from 30KW back down to 20KW or 10KW before coming to a complete stop. I wonder if the mechanical brakes, once activated after 30KW, stay on until the car reaches a complete stop or not? Or whether there is truly regen going on when the indicator goes back down from 30KW to 0 KW.

If the brakes get deactivated and regen takes over again on the way back down from 30KW to 20 to 10 to 0, I sure as hell can't tell. I'd also think it can't be that kind of switching back and forth between mechanical and regen that quickly and seamlessly. So I gotta assume that once the mechanical braking takes over, it stays on until the car stops. Unless you release the brakes before that happens, like riding downhill. In which case regen kicks right back in.

Then, at a complete stop, I must assume that the mechanical brakes stay on to keep the car in place, right? Surely, you can't rely on regen to keep a car stationary in place.

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DaveEV
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Re: Regen question

Fri Sep 02, 2011 11:45 pm

Volusiano wrote:Is it safe to assume that as long as the regen indicator doesn't hit the 30KW max that you never use the mechanical brake?
No. Depending on conditions friction brakes may engage at any time. There's a lot of things which may cause friction brakes to kick in under 30 kW. Primary culprits that I've noticed.

1. Battery over 80% full.
2. Quick application of the brakes.
3. Hard braking.
4. Bumpy road.
5. Low vehicle speed.

There's probably a few more.
Volusiano wrote:I must say that the few times I exceed 30KW regen, I can't really tell at all whether the system started activating the mechanical brakes or not. It's indistinguishable to me.
It's not always easy to tell when the friction brakes engage. Sometimes you can hear/feel them.

ERG4ALL
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Re: Regen question

Sat Sep 03, 2011 7:16 am

One way to tell how well you are using regen is to look for brake pad dust on the front wheels when you wash the car. I washed ours yesterday and found very little and the car only gets washed about once every other month.
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TomT
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Re: Regen question

Sat Sep 03, 2011 7:43 am

That's not necessarily an accurate indicator. Our Acura never produces any brake pad dust on the wheels even after months of not being washed...
ERG4ALL wrote:One way to tell how well you are using regen is to look for brake pad dust on the front wheels when you wash the car. I washed ours yesterday and found very little and the car only gets washed about once every other month.
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Herm
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Re: Regen question

Sat Sep 03, 2011 9:12 am

You could rig up an indicator if you monitor the hydraulic pressure in the brake lines.

Its just easier to drive like you had no brakes at all.

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abasile
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Re: Regen question

Sat Sep 03, 2011 12:35 pm

Volusiano wrote:Then, at a complete stop, I must assume that the mechanical brakes stay on to keep the car in place, right? Surely, you can't rely on regen to keep a car stationary in place.
This is correct. The friction brakes are needed to bring the car to a complete stop and hold it there.
Herm wrote:You could rig up an indicator if you monitor the hydraulic pressure in the brake lines.
There are two approaches that I use to determine whether the friction brakes are being applied or not:
1. Monitor the Energy Info screen. If you increase pressure on the brake pedal and the amount of regen (kW) doesn't increase (go further below zero on the circular, graphical gauge), then you know that the additional braking is being done by friction.
2. Look at the efficiency meter above the tree growing area. The indicated efficiency will drop whenever the friction brakes are applied. Of course, that's not the only thing that affects the indicated efficiency.
planet4ever wrote:Nissan seems to be concerned about doing too much QC, so the regen level might also be about as high as they feel comfortable having it. Of course most people don't regen for 30 minutes straight, but if you're dropping 5000' feet like abasile does routinely ...
For most of this descent, we are doing in the range of 10-20 kW of regen. I believe I remember reading that QC can do 0%-80% (usable) SOC in 26 minutes, and that it maxes out at 50 kW, with a taper as the SOC approaches 80%. So I don't think we are hitting the battery quite as hard as QC.

It seems to me that Nissan is more conservative with continuous regenerative braking than with quick charges, probably because the former could potentially be done with much greater frequency. Even when the car has a little under nine bars of charge, we notice that it starts to limit continuous regen to ~ 10 kW after we've descended a few thousand feet. At 10 bars after a few thousand feet of descending, we might only have ~ 3-5 KW of regen. This is why we like to start our descents with 7-8 bars of charge or less. We've been making that 5000 foot descent once or twice per week on average.
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planet4ever
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Re: Regen question

Sat Sep 03, 2011 3:11 pm

abasile wrote:
planet4ever wrote:Nissan seems to be concerned about doing too much QC, so the regen level might also be about as high as they feel comfortable having it. Of course most people don't regen for 30 minutes straight, but if you're dropping 5000' feet like abasile does routinely ...
For most of this descent, we are doing in the range of 10-20 kW of regen. I believe I remember reading that QC can do 0%-80% (usable) SOC in 26 minutes, and that it maxes out at 50 kW, with a taper as the SOC approaches 80%. So I don't think we are hitting the battery quite as hard as QC.
Yeah, I kinda guessed you wouldn't be using 30 kW regen all the way down, which is why I cheated by not finishing the sentence. ;)

On the QC charge, page CH-6 of the Owner's Manual shows "approximately 0.5 hours," so, yes, the time could be 26 minutes, but I expect it is really variable. More significantly, the chart shows the half hour QC time as being from Low Battery warning to 80%. Tony's chart shows bar 1 disappearing at 17% SOC and has a footnote that LBW can be before or after that. My experience is that LBW comes quite a while before the last bar disappears, so I thought I was being generous by calling it 15%. It might be more like 20%. Next, I don't remember seeing any figures on taper below 80%, and assumed that only happened above 80%, but I could be wrong. To back up my calculation, I do remember seeing reports that actual QC draw was running at about 30kW even though theoretically it could go up to 50kW.

Ray
End of April 2013: Traded my 2011 SL for a 2013 S with charge pkg.

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TonyWilliams
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Re: Regen question

Sat Sep 03, 2011 4:22 pm

Tony's chart shows bar 1 disappearing at 17% SOC and has a footnote that LBW can be before or after that. My experience is that LBW comes quite a while before the last bar disappears, so I thought I was being generous by calling it 15%. It might be more like 20%.

I think the note says that LBW may happen before Bar 1 disappears. The 17% (48 of 281 raw data) is when LBW comes on, regardless of Bar 1. The chart is not clear as to when Bar 1 will disappear, since the range planning would be based on LBW from that moment on.

I actually don't know when the number 1 Bar is supposed to disappear (by SOC data). It's not important to range.

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surfingslovak
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Re: Regen question

Sat Sep 03, 2011 5:22 pm

planet4ever wrote:So our 30kW regen is already hitting the battery about as hard as QC does.
I'm with Ray on this, in fact that was my first thought when I saw the requests for more regen. I believe that this video has been posted on the forum before, but it's worth watching is you haven't seen it yet. It's in Dutch with English subtitles ;-)

Image
Click to play video
Last edited by surfingslovak on Sun Sep 04, 2011 9:10 am, edited 1 time in total.

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