Regen question

[abasile]

In any case, I imagine someone will offer aftermarket regen boosting for LEAF owners.

That would be great, because on my mountain descents, I'm tired of regen tapering off at higher speeds. There is no reason that I should be able to get 10 kW of regen at 30 mph and barely anything at 55 mph; I should still be able to get 10 kW at 55 mph. Perhaps the new 'B' mode in the 2013 model will address this.

 

[DaveinOlyWA]

a full regen mode in ECO might break my "neutral" driving habit. I love one pedal driving and its become a challenge to complete trips with minimal brake pedal of any kind.

a great article "somewhat" related on heat, brakes and regen benefits

http://www.pluginrecharge.com/2013/01/thermography-shows-efficiency-of-nissan.html" onclick="window.open(this.href);return false;

 

[thankyouOB]

a full regen mode in ECO might break my "neutral" driving habit. I love one pedal driving and its become a challenge to complete trips with minimal brake pedal of any kind.

a great article "somewhat" related on heat, brakes and regen benefits

http://www.pluginrecharge.com/2013/01/thermography-shows-efficiency-of-nissan.html" onclick="window.open(this.href);return false;

nice site, overall.

 

[RegGuheert]

That would be great, because on my mountain descents, I'm tired of regen tapering off at higher speeds. There is no reason that I should be able to get 10 kW of regen at 30 mph and barely anything at 55 mph; I should still be able to get 10 kW at 55 mph.

I'm not sure the limit you are seeing is based on speed. The local mountain I cross in the LEAF is pretty steep in one direction and the speed limit is 55 MPH. The LEAF is the only vehicle I have ever driven which can hold its speed going down this hill without physical brakes. Our Honda Civic Hybrid is capable of 14kW of regen (I think) and it cannot hold speed, so I think the LEAF is regenerating at ~20kW. I'll check the exact value next time I go across.

I suspect your issue is that you are also at a relatively high SOC (like 75% or more) when you need to have the regeneration. Perhaps the way the regen is designed it limits the amount of *energy* that can be put into the battery at higher SOCs before it limits it.

If that's not it, then I agree you should be able to get as much power for regen at 55 MPH as at 30 MPH.

 

[abasile]

If that's not it, then I agree you should be able to get as much power for regen at 55 MPH as at 30 MPH.

Having a higher SOC (60% and higher) is definitely a factor, along with my battery being cold (four temperature bars), but for some reason the car also reduces regen at higher speeds. On our ~5000' descent, when I slow down, the available regen power increases. When I speed up, I sometimes lose almost all regen, until I slow down again. If no one is behind me, I'll sometimes maintain 25-30 mph just to keep regen up.

 

[DaveEV]

That's really weird - I can't say I've seen that behavior myself, but I don't live on a mountain, either. Do you see that behavior all the time? In my experience the faster I am going, the more regen I get when letting off the pedal up to about 25 kW at freeway speeds in Eco mode. I rarely drive in Drive mode so don't have much regen experience there except that it's too little all the time!

I personally wish for either 1 of 2 things:

1. Maximum regen always when off the accelerator (like Tesla).
2. No friction braking at all until regen is at maximum level when pressing on the brake pedal.

 

[surfingslovak]

The ActiveE inherited some of this legacy from the MINI-E, which had a powertrain from AC Propulsion. It took me a while to transition from the LEAF, but I would not want to miss the strong regen now. It truly makes an EV stand out, and relegates conventional cars to the 20th century.

I certainly hope the brake lights come on at some level of regen!

Yes. The photo below links to a relevant discussion about that in our Facebook group.

Click to open

Very instructional also, that I could study the brake light behaviour in real world situations... I would prefer a little more sensitive brake light threshold, at times I thought it came on a tad late. I don't mind looking like a novice riding the brakes downhill, since this is an EV.

 

[surfingslovak]

That would be great, because on my mountain descents, I'm tired of regen tapering off at higher speeds. There is no reason that I should be able to get 10 kW of regen at 30 mph and barely anything at 55 mph; I should still be able to get 10 kW at 55 mph.

I'm not sure the limit you are seeing is based on speed.

I wouldn't know what abasile is seeing exactly, but I have experienced limited regen like that before. The last regen bubble or two would be missing, and they become available once the vehicle slows down. I believe there might have been other reports of this type of behavior.

 

[RegGuheert]

I wouldn't know what abasile is seeing exactly, but I have experienced limited regen like that before. The last regen bubble or two would be missing, and they become available once the vehicle slows down. I believe there might have been other reports of this type of behavior.

What I have seen with the bubbles is sometimes I will have all the regen bubbles, but ONLY when not braking. If I push the brake pedal, one regen bubble immediately disappears.

In any case, I don't think losing one, or even two, regen bubbles is related to abasile's issue, as he is reporting almost NO regen at 55 MPH.

Edit: Fixed quote.

 

[edatoakrun]

I'm not sure the limit you are seeing is based on speed.

...he is reporting almost NO regen at 55 MPH.

abasile:

...Having a higher SOC (60% and higher) is definitely a factor, along with my battery being cold (four temperature bars), but for some reason the car also reduces regen at higher speeds...

Abasile is describing the LEAFs regen behavior correctly, but IMO it may be ambient temperature dependent rather than battery temperature dependent and regen limitation seems to be stepped rather than on a continuum with speed.

I also begin almost every daily drive with a large descent, but in colder conditions I seem to see my available regen dropping off in steps at specific speeds, ~38 and ~48m mph, IIRC, and available regen is almost negligible, above that ~48 mph speed.

So I try to use regen to slow before I hit the steepest grades, to what I believe will be a sufficiently low speed that I will not lose regen due to excessive speed, after I accelerate even with maximum regen along the grade. This often allows me to avoid using to use the brake pedal.

I have never noticed this regen behavior not occurring at lower SOC, as abasile reports, but my driving needs make this a very rare occurrence. I'll try to look for it next chance I get.

The only likely explanation I ever came up for this LEAF design feature was safety.

Perhaps Nissan thought thought drivers might find the driving experience of frequent loss of traction or traction control initiation on a cold and wet or icy road surface without using the bake pedal, either unsafe or disconcerting?

But this would make no sense if this cold-weather regen limitation can be "overridden" by lower SOC, as abasile reports.

 

[RegGuheert]

Abasile is describing the LEAFs regen behavior correctly, but IMO it may be ambient temperature dependent rather than battery temperature dependent and regen limitation seems to be stepped rather than on a continuum with speed.

How cold are you talking about? I see the ~20kW regen at 55 MPH at ~30F. There are four battery temperature bars and about four battery charge bars when I see this.

If I drove up there just to test this, I could probably do it with as many as 9 charge bars. Maybe I'll try that one of these days.

 

[edatoakrun]

Abasile is describing the LEAFs regen behavior correctly, but IMO it may be ambient temperature dependent rather than battery temperature dependent and regen limitation seems to be stepped rather than on a continuum with speed.

RegGuheert:
How cold are you talking about?...

I believe I've seen the regen limited by temperature virtually every day in the Winter, more like the minimum temperature is somewhere above ~40 F ambient, IIRC. My battery temp varies during Winter from ~25F to ~45F, always 4 bars on the dash.

The trick for me to observe this, is that I usually charge to ~11 bars in the Winter.

I often need over "80%" in cold weather, to make the ~55 mile minimum trip without hitting the LBW (my preferred minimum SOC) before I get back home.

And if I charge above 80% at home, I also will lose regen due to high SOC on the initial ~ 2000 ft (~1700 net) descent in my first ~7 miles of driving.

Now that the subject has come up, I'll try to observe and report back what happens with a cold battery and higher ambient temps.

 

[DaveEV]

In 55F weather I lose a regen bubble on a 80% charge and am limited to about 20 kW regen. Even after the bubble stays on and dropping a couple charge bars, I still notice that regen doesn't hit 30kW. Even down to 6-7 charge bars and 45F weather it's still hard to get 30 kW regen.

Still, abasaile's completely disappearing regen at higher speeds is weird and sounds like a bug. It could be a bug, or perhaps somehow temp related.

 

[RegGuheert]

The trick for me to observe this, is that I usually charge to ~11 bars in the Winter.

I cannot make it to that point with 11 bars to be able to test this unless I stopped at a friend's house nearby and recharged.

In any case, I will be making the trip both tomorrow and Thursday, but the temperature both days should be over 40F and my bars will be much lower than 11. In any case, I will drive at 55 MPH (56 MPH indicated) and I will report back how much regen I see.

Is there any possibility we have different firmware? Our LEAF is completely updated, but I'm not even sure which systems are involved and whether they have even received any updates. EV battery system (EVB)? EV Control System (EVC)?

 

[DaveinOlyWA]

My regen bubbles ceased to make sense about the time i posted the pix of a fully charged battery with regen available. Since that time, i have taken notice oftheir comings and goings and i can no longer make any statement that would alwaysbe true.
I used tothink that i had to be down to 11 bars to have all regen circles but have seen times when i was at 6 bars and only had 3 of 5 lit up and heat was highly unlikely to have been a factor

 

[abasile]

The regen behavior that I described above is something I see almost daily, i.e., every time I drive down the mountain. Lesser descents aren't really enough to bring this bug to light; normally I have to do at least a few hundred feet of descending, with regen, before it becomes an issue. Yes, I consider it a bug, because I don't see why speed should have anything to do with available regen kW.

Again, to maximize available regen power on big descents in the cold or at somewhat high SOC, I have to keep my speed way down. To be clear, this is independent of the fact that more energy is lost to wind drag at higher speeds; I am talking about the amount of regen that the car's firmware allows.

Also, it's clear to me that the relevant temperature is that of the battery pack, not the ambient temperature. On occasion, our LEAF makes two round trips to the Valley within one day. This heats the pack quite noticeably. On the second descent, substantially more regen is available, even if the ambient temperature hasn't risen much.

 

[RegGuheert]

The regen behavior that I described above is something I see almost daily, i.e., every time I drive down the mountain. Lesser descents aren't really enough to bring this bug to light; normally I have to do at least a few hundred feet of descending, with regen, before it becomes an issue.

O.K. That implies that they are further limiting regen after a certain amount of energy has entered the battery, as previously suggested:

I suspect your issue is that you are also at a relatively high SOC (like 75% or more) when you need to have the regeneration. Perhaps the way the regen is designed it limits the amount of *energy* that can be put into the battery at higher SOCs before it limits it.

Another similar possibility is that the SOC of the battery simply is increased to a point where further limiting would normally be done.

BTW, it makes more sense to do this limiting based on energy or SOC instead of temperature since the thermal time constant of the battery is probably fairly long and the temperature sensors are mounted on the outside of the cases. As such, there could exists a very high temperature situation inside the cells before the temperature at the sensor would rise enough to trigger the system to limit regeneration. Of course, regeneration is also limited based on battery temperature, but at lower temperatures it probably goes in the opposite direction from what would protect the batteries during a long mountain decent.

Yes, I consider it a bug, because I don't see why speed should have anything to do with available regen kW.

Agreed, but perhaps the correct behavior is what you see at 55 MPH and the bug is in the behavior at 30 MPH.

 

[edatoakrun]

...I consider it a bug, because I don't see why speed should have anything to do with available regen kW...

Also, it's clear to me that the relevant temperature is that of the battery pack, not the ambient temperature...

If you have been able to confirm that battery temp is controlling, I can think of no possible benefit for this regen limitation, and it must just be a "bug".

BTW yesterday I watched for this carefully, and at 10 bars capacity with a 4 bars battery temp, with a ~35 F battery and ~50 F ambient I saw my regen limited (when not using the brake pedal) to an indicated ~10 kW under ~40 mph, about~5 kW at ~50 mph, and I still had a 1 or 2 kW(?) sliver or regen indicated at my max speed, 63 mph by the speedometer.

On the return trip I only have one short low speed grade I can test on, and at ~60 F ambient, and with perhaps a ~45 F battery (since I was about 20 miles, 35 minutes, and ~7 kW of driving prior to when my battery first indicated 5 bars temperature) I could get ~15 kW regen maximum at ~40 mph.

 

[RegGuheert]

I just drove over the mountain in the direction which is not too steep when going downhill. When I reached the summit I had 10 charge bars and 5 temperature bars and ambient temperature was 49F. Speed was 56 indicated. Regen went to 18kW and gradually decreased as the slope decreased down the 400-ft drop in altitude. Speed held steady, so it seemed to have all the regen it needed.

On the way home, I have two steeper inclines and total drop is about 650 ft, but there is a rise between the two, I will report the power levels going that way.

Edit: On the return trip, I had 3 charge bars and 5 temperature bars and ambient temperature was close to 50F. Regen went to 20kW and held there during the first drop of perhaps 400 ft. Speed held steady at 56 MPH indicated, so I guess that is what is needed on this incline. During the second drop, regen went to 23kW and stayed there, but the LEAF did NOT hold speed. It drifted up to 59 MPH indicated, so I guess 23 kW is the limit for our LEAF's regen under these conditions.

In any case, it must not have been cold enough and/or a long enough downhill for me to see what you guys are seeing. I'll give it a try some day when it is 20F or something to see if it can happen here.

 

[abasile]

Yes, I consider it a bug, because I don't see why speed should have anything to do with available regen kW.

Agreed, but perhaps the correct behavior is what you see at 55 MPH and the bug is in the behavior at 30 MPH.

According to my gid meter's "power" readout, when my LEAF's regen reaches zero or close to it, the car is actually drawing power from the battery pack. At the same time, I'm going downhill and having to use the friction brakes. Running the heater at full blast doesn't seem to help in this case (other than by slowly reducing SOC); it simply draws more power from the battery. This makes no practical sense.

In general, my expectation is that, for a given set of battery conditions, available regen should be equal to the allowed Quick Charge power, or perhaps somewhat less so as to treat the battery more conservatively. Only when "user SOC" approaches 100% does QC taper all the way down to zero.

I'm hoping the 2013 LEAF's 'B' mode regen will be a bit more generous...