What happened to my Regen?

[Reddy]

I wonder if regen is not just a function of battery temps and SOC, but also "age" or "health" of the battery. Several have pondered what the %HX is. Could it be a complex measure of resistance in the packs and as the battery ages, the resistance goes up and regen dumps more heat into the cells. Perhaps the engineers, included %HX (or some other resistance measure) into the regen calculations and we are experiencing reduced regen because of pack age. If true, unfortunately, it means things will only get worse at 5, 6 and 7 yrs.

Do folks with a 2011 and a new battery experience the same reduced regen?

Here's anecdotal evidence that the new batteries are better (at least in a new car). I do remember when new, I only got 1 regen bubble at 100%, but don't remember the KWs, maybe 5 KW below 25 mph.
http://www.mynissanleaf.com/viewtopic.php?f=55&t=17820&start=10#p407869

 

[RegGuheert]

I wonder if regen is not just a function of battery temps and SOC, but also "age" or "health" of the battery. Several have pondered what the %HX is. Could it be a complex measure of resistance in the packs and as the battery ages, the resistance goes up and regen dumps more heat into the cells. Perhaps the engineers, included %HX (or some other resistance measure) into the regen calculations and we are experiencing reduced regen because of pack age. If true, unfortunately, it means things will only get worse at 5, 6 and 7 yrs.

I think that is precisely what it is. (And I believe %HX is %CapacityRemaining times %AdmittanceRemaining.) But I had always imagined the concern was primarily local heating of the cells. But I'm starting to think that maintaining overall cell balance may be a bigger concern.

I suppose we will never know for sure.

 

[TickTock]

Also, it just dons on me that the reason regen reduces in the winter may be because of the use of the heater. This results in an additional drain on the battery and battery drain = available regen reduction.

That seems backward to me. Wouldn't an increasing load allow for more regen "space"? The heater could be partially fueled by regen, with less needing to be put in the battery.

Regardless, the regen drops with cold even when the heater isn't used and I can't recall any difference in regen levels — at a given battery temperature — with the heater on or off. Easy to test though.

I did a quick test tonight. Put the Leaf into cruise on a long level stretch. While holding constant speed, I saw no change in the available regen when I turned on the heater. Different speeds did result in different, constant, amounts of available regen - independent of the power coming from the battery. Looks like it really is speed and not power from the battery that is the primary modulator (along with SOC and temperature as secondary influencers). So much for my theory on the non-intuitive behavior. Really scratching my head now. Agree, the battery shouldn't care about speed.

 

[DaveEV]

I did a quick test tonight. Put the Leaf into cruise on a long level stretch. While holding constant speed, I saw no change in the available regen when I turned on the heater. Different speeds did result in different, constant, amounts of available regen - independent of the power coming from the battery. Looks like it really is speed and not power from the battery that is the primary modulator (along with SOC and temperature as secondary influencers). So much for my theory on the non-intuitive behavior. Really scratching my head now. Agree, the battery shouldn't care about speed.

Your test results are exactly what I've observed happening in my car for ages.

I wonder if regen is not just a function of battery temps and SOC, but also "age" or "health" of the battery. Several have pondered what the %HX is. Could it be a complex measure of resistance in the packs and as the battery ages, the resistance goes up and regen dumps more heat into the cells. Perhaps the engineers, included %HX (or some other resistance measure) into the regen calculations and we are experiencing reduced regen because of pack age. If true, unfortunately, it means things will only get worse at 5, 6 and 7 yrs.

Yes, that is quite likely, and something I proposed a while ago. The P3227 update results in a significantly lower %Hx value - this is easily seen before/after the update as the %Hx value updates quite rapidly - unlike the AHr reading.

The typical method for programming car parameters is to use 2 or 3-dimensional maps. If %Hx is used to approximate overall internal resistance of the pack and thus used to determine maximum allowed regenerative braking, a lower %Hx reading would result in less regen being available.

It's pretty clear that the amount of regenerative braking allowed is a combination of these factors: SOC, speed of vehicle, battery temperature and %Hx.

 

[TickTock]

But why speed?

 

[DaveEV]

But why speed?

My guess is that they tried to keep the rate of deceleration constant. So at higher speeds with more air resistance they decrease regen.

But who knows, could be anything...

 

[TimLee]

But in any case the 2011 and 2012 regeneration is poor compared to the 2013 forward LEAFs and Nissan appears unable or unwilling to do anything about :shock: :?

Of course if it is all degrading Hx, and someone has a 2013 or later with Hx below 70 and their regeneration is fading fast, then maybe all LEAFs have deteriorated regeneration as the battery gets old.

Kind of like human age caused deterioration :shock: :?

 

[dgpcolorado]

I did a quick test tonight. Put the Leaf into cruise on a long level stretch. While holding constant speed, I saw no change in the available regen when I turned on the heater. Different speeds did result in different, constant, amounts of available regen - independent of the power coming from the battery. Looks like it really is speed and not power from the battery that is the primary modulator (along with SOC and temperature as secondary influencers). So much for my theory on the non-intuitive behavior. Really scratching my head now. Agree, the battery shouldn't care about speed.

Thank you for doing that test. It is much harder for me to do here as there are no roads that are level where I can hold a constant speed around here.

But why speed?

My guess is that they tried to keep the rate of deceleration constant. So at higher speeds with more air resistance they decrease regen.

But who knows, could be anything...

That's an interesting hypothesis. It might explain why abasile and I find the reduction in regen at higher speeds so annoying: less drag from being at higher altitude — I live at 7670 feet — and needing higher regen to help with descending steep hills. I'll have to ponder that one.

Regardless, it is something that needs to be fixed. Full allowed regen should be available at all speeds save, perhaps, for very low speeds when approaching a full stop. I can modulate it just fine with the accelerator pedal.

 

[dgpcolorado]

...Of course if it is all degrading Hx, and someone has a 2013 or later with Hx below 70 and their regeneration is fading fast, then maybe all LEAFs have deteriorated regeneration as the battery gets old...

If this is so, the question then becomes "is it really necessary to protect the battery?" I am skeptical.

Are batteries without P3227 being damaged by the higher regen? Because of localized heating due to resistance? Again, I am skeptical.

 

[mwalsh]

Again, I am skeptical.

Oh hell, me too! Does P3227 really do anything but help Nissan avoid warranty claims? I certainly have my suspicions.

 

[TimLee]

... Does P3227 really do anything but help Nissan avoid warranty claims? ...

If so, kind of like shooting your toe off to fix an in grown toe nail :shock:
Do we really think Nissan is that dumb :?: :?:

 

[abasile]

But why speed?
My guess is that they tried to keep the rate of deceleration constant. So at higher speeds with more air resistance they decrease regen.

But who knows, could be anything...

That's an interesting hypothesis. It might explain why abasile and I find the reduction in regen at higher speeds so annoying: less drag from being at higher altitude — I live at 7670 feet — and needing higher regen to help with descending steep hills. I'll have to ponder that one.

Regardless, it is something that needs to be fixed. Full allowed regen should be available at all speeds save, perhaps, for very low speeds when approaching a full stop. I can modulate it just fine with the accelerator pedal.

If the goal is to keep the rate of deceleration constant, this could be achieved by varying the amount of regen on the accelerator pedal. But I can think of no functional reason to limit regen, as a function of speed, on the brake pedal. (I'd prefer much more regen on the A-pedal, maybe Tesla-style, but that's not the point here.)

I also consider it a serious bug that available regen doesn't increase with the use of climate control and other accessories. Again, this has nothing to do with protecting the battery pack.

 

[mwalsh]

No unwelcome negative change in my regen post-P3227. Dare I say a bit (marginally?) better even?

 

[RegGuheert]

No unwelcome negative change in my regen post-P3227. Dare I say a bit (marginally?) better even?

Like others, I felt that I had more range to go along with the capacity spike that accompanied P3227. I'm not sure about regen, though. It is DEFINITELY much worse now that it is cold and the LEAF is eight months past P3227, but during the summer when it was first done, it seemed O.K.

OTOH, some of us think regen is related to the Hx parameter and my Hx dropped immediately and quickly following the P3227 update. Has yours done the same.

 

[mwalsh]

OTOH, some of us think regen is related to the Hx parameter and my Hx dropped immediately and quickly following the P3227 update. Has yours done the same.

Dropped, but not significantly...yet.

 

[RegGuheert]

For reference, here is a plot showing %Hx along with %Capacity:

You can see that %Hx tracked just below %Capacity until the P3227 update. After the reprogram, the %Hx dropped off very quickly.

 

[TimLee]

You can see that %Hx tracked just below %Capacity until the P3227 update. After the reprogram, the %Hx dropped off very quickly.

Thanks.
I had missed that.
But my Hx is already at 72.3% at close to 24,000 miles and lost second capacity bar just a few days back.

Hard to predict what P3227 would do, but regeneration is already degrading without it.
If Hx fell off the cliff like yours did, I cannot imagine how bad it would be :shock:

LEAF Advisory Board never received any comment from Nissan other than "We will look into it", Right :?:

 

[RegGuheert]

But my Hx is already at 72.3% at close to 24,000 miles and lost second capacity bar just a few days back.

Wow! You have lost two bars already and still have Hx of 72.3%?

One question: Do you quick charge often? I'm starting to believe that quick charging helps reduce the resistance of the cells. But we did not have access to any QCs until last spring. I'm convinced that every time we quick charge the battery is helped just a bit.

Who knows? Maybe it's just wishful thinking...

LEAF Advisory Board never received any comment from Nissan other than "We will look into it", Right :?:

That's right. That's as much as the old LEAF Advisory Board got. But I do think this topic is on the new board's agenda. Maybe drees will comment on this...

 

[TimLee]

...
One question: Do you quick charge often? ...

143 DCQC to date in a bit less than 24,000 miles.

 

[RegGuheert]

...
One question: Do you quick charge often? ...

143 DCQC to date in a bit less than 24,000 miles.

Four times total here. The first time was less than one week after P3227 was applied at the end of May, 2014.