What values of Hx is worrisome, if any?

Hi,

I am new to EV and Leaf. Few questions about battery state.

Leaf 2017 (30kWh) used in Bay Area:
15K miles
SOH=88%
Hx=70%
below 20mV cell voltage difference (varies 4mV-20mV)
120 QCs 190 L1/L2

Questions:

1) It appears that the Hx is lower than what others see? I cannot find any definition nor correlation with SOC. Is the meaning explained somewhere (some handwriting about some measure of "ability to accept charge" and or "battery resistance")?

2) Is the SOC of 88% w/ on 15k/3yr low or a ok?

3) Seems that statistically it was charged every 3-4 days in 3yr, hence possibly to full?

4) Seems to loose range quicker at the top of the charge (on a 30mile mixed freeway/highway drive went from 95m to 50m range) than below 50% starts to slow down (return trip was 50->20 estimated so closer to driven miles).

5) Is driving at 65mph usually consuming much more energy than at 55? (Energy Efficiency shows ~3m/kWh at 65)? Normal?


Thanks,

Michal

Hx on the Gen I cars seems to represent battery resistance. It goes up and down, but usually very roughly tracks the SOH. I would focus on the SOH. Have you read about the 30kwh Leafs in my buying guide? If not I'll link the guide later.

Don't bother with the estimated range. That is called the GOM (guess-o-meter) and it simply projects your expected range based on the last few (?) miles of driving. Going up a hill makes it drop, going down a hill increases it, etc. It is quite useless.

If you scroll through the menus you should be able to display the % of charge left in the battery. This is much better gauge of how much juice is left in your battery. You can use that to estimate range based on % lost per mile, etc.

Driving at 65mph will take substantially more power than 55mph. That said, 3.0 m/kWh is pretty low in experience. I'd expect at least 4.0 m/kWh but I live in CO where the air is thin and I drive conservatively, so YMMV. Keep in mind that road conditions, wind, hills, battery temperature etc will also make a difference.

LeftieBiker said:

Hx on the Gen I cars seems to represent battery resistance. It goes up and down, but usually very roughly tracks the SOH. I would focus on the SOH. Have you read about the 30kwh Leafs in my buying guide? If not I'll link the guide later.

Click to expand...

It's (Hx) conductance, the inverse of resistance, since that parameter (Hx) decreases as SOH decreases where as resistance increases as SOH decreases.
With Leaf 2, it's become meaningless.

Thanks for the reply. I have read the about the 30kWh version deteriorating faster than the previous version, presumably due to higher internal heating.

If the Hx is some representation of "internal resistance" of the battery, it would mean that more energy goes to heat, both during driving and charging. I suppose this would be noticeable with range decrease and charging temp increase and efficiency? But alas I would think the SOH represents the "usable energy storing capability" and hence also include the loses due to internal resistance?

@lorenrf

Hx - a % of some reference conductance chosen by Nissan (possibly statistically)? (i have seen the values bigger then 100% reported?). I'd suppose 0% would mean an open circuit but who knows?

Hx = 100% * Gmeasured / Greference

Although 30% lose of conductance (Hx=70%) would mean the 30% more energy is lost to heat which should be proportionally noticeable in the driving range?

Is the mile/kWh meter measuring energy consumed by the electric motor or energy depleted from battery (estimated by voltage drop)? That is is it representing driver-train efficiency or whole system efficiency?

eKrom said:

Hx - a % of some reference conductance chosen by Nissan (possibly statistically)? (i have seen the values bigger then 100% reported?). I'd suppose 0% would mean an open circuit but who knows?

Click to expand...

For Leaf 2 and basically meaningless
0% = Leaf non-start

eKrom said:

Hx = 100% * Gmeasured / Greference

Although 30% lose of conductance (Hx=70%) would mean the 30% more energy is lost to heat which should be proportionally noticeable in the driving range?

Click to expand...

Correct

eKrom said:

Is the mile/kWh meter measuring energy consumed by the electric motor or energy depleted from battery (estimated by voltage drop)? That is is it representing driver-train efficiency or whole system efficiency?

Click to expand...

Correct

We don't really know the true meanings of SOH, Hx or many other things rendered in Leaf Spy other than obvious ones like VIN, tire pressure, temps and a few others that can be confirmed/we can work backwards from.

I've made comments about SOH and Hx along w/their history at https://mynissanleaf.com/viewtopic.php?f=9&t=25773&p=579357&hilit=soh+hx+historical#p579357. We can certainly compare notes and track them but Nissan may never release docs or comment on their true meaning, precision, hysteresis, necessary conditions needed for them to be accurate, etc.

eKrom said:

Although 30% lose of conductance (Hx=70%) would mean the 30% more energy is lost to heat

Click to expand...

R = 1/0.7 in the battery. And those heat losses are proportional to I^2*R where I is current, itself proportional to power

But for most typical driving battery losses are only a small fraction of energy use. Somewhere along the line in the life of the LEAF an owner might decide to only fast charge if no L2 option, and perhaps not stomp the accelerator to the floor at every opportunity. If that is your behavior anyway then the low(er) Hx has little daily effect on energy consumption. Someone who runs up and down the hills of San Francisco might say otherwise.

I think the arithmetic goes like this, but I'll rely on loren to correct any errors:
Say a new cell is 50 milliOhm
The pack is 192 cells arranged as 96S2P. The 2P parallelism reduces the resistance of the pack by 50% compared to a 96S pack.
We'll presume a 360 volt pack
Using I = W/V, If you are driving at 3*10*360 watts then the pack is pushing 30 Amps. That would be city driving at ~ 50 kph
Using I^2*R and taking account of the parallelism, Battery power losses are then 1/2 of 30*30*0.05 = 22 watts

Now say internal resistance has increased 50%. Losses in the battery will increase from 22 to 33 watts, and overall energy consumption will increase from 30*360 to 30*360+11.
Call it 0.1% more energy losses as the Hx drops.

---
That is easy city driving. Now let's look at DC fast charging at 120 Amps
The new pack heat generation will be 0.5*120*120*0.05 = 16*22.5 = 360 watts,
And a pack with 50% greater internal battery resistance will be 540 watts

Addendum: small edits for clarity

What concerns me is the extra heat generated by the increased R, since I'm constantly trying to keep my battery temp as low as possible. Or maybe I'm not paying attention and it's trivial ?

Anyway, welcome back.

goldbrick said:

What concerns me is the extra heat generated by the increased R, since I'm constantly trying to keep my battery temp as low as possible. Or maybe I'm not paying attention and it's trivial ?

Click to expand...

You and me both. Nowadays I do the following:
If the car says 5 temp bars or less -- I'm good since it means the battery pack is under 80F
Over 5 bars I pull out LeafSpy. If the pack is over 90F I start doing only_with_a_LEAF things to cool it down.

Oh, and my days of DC fast charging just for fun are over. One silver lining of the Covid-19 epidemic -- the LEAF has not exceeded 5 bars this summer in Albuquerque. It can handle the ~ 20 miles a week or so it gets used, and the remainder of the time she sits under a tree on relatively cool ground, as befits a prima donna.

@SageBrush2
duh! me a dummy! Yes, the actual losses depend on absolute value of conductivity (1/resistance) so my statement should read: "my leaf has 30% more loses in battery resistance than a nominal one" and not "30% more absolute loss of energy/range"

Thannks!

Alas, since I am very new here - I have ignored the fact that LeafSpy reports most of the cells as "red". There a few blue ones (about 8) which have the highest voltage of the pack. I would expect these blue ones are the one being "shunt" to equalize (unless my BLM lost its marbles ). So perhaps the bits reported from BLM are now inverse?

SageBrush2 said:

eKrom said:

Although 30% lose of conductance (Hx=70%) would mean the 30% more energy is lost to heat

Click to expand...

R = 1/0.7 in the battery. And those heat losses are proportional to I^2*R where I is current, itself proportional to power

But for most typical driving battery losses are only a small fraction of energy use. Somewhere along the line in the life of the LEAF an owner might decide to only fast charge if no L2 option, and perhaps not stomp the accelerator to the floor at every opportunity. If that is your behavior anyway then the low(er) Hx has little daily effect on energy consumption. Someone who runs up and down the hills of San Francisco might say otherwise.

I think the arithmetic goes like this, but I'll rely on loren to correct any errors:
Say a new cell is 50 milliOhm
The pack is 192 cells arranged as 96S2P
We'll presume a 360 volt pack
If you are driving at 3*10*360 watts then the pack is pushing 30 Amps. That would be city driving at ~ 50 kph
Battery power losses is then 1/2 of 30*30*0.05 = 22 watts

Now say internal resistance has increased 50%. Losses will increase from 22 to 33 watts, so 11 more than the 30*360 when new. Call it 0.1% more energy losses as the Hx drops.

---
That is easy city driving. Now let's look at DC fast charging at 120 Amps
The new pack heat generation will be 0.5*120*120*0.05 = 16*22 = 352 watts,
And a pack with 50% greater internal battery resistance will be 528 watts

Click to expand...

Very good!
As it turns out, though, using the step function test (Resistance = (V1 - V2)/I) for measuring internal battery resistance neglects entropy changes.
So the resultant battery losses can be typically 3X the value determined using the step function resistance test.

Read here for more insight; https://mynissanleaf.com/viewtopic.php?f=34&t=27600&hilit=MUX&start=390#p585497

Thanks, I did realize that absolute loses in internal battery resistance are negligible in normally operating battery.

However, I still wonder what does Hx=70% mean? That is if the Hx=100% represents "nominal conductance" and Hx=0% represents open circuit (conductance G=0) then the lower the Hx is the more its change is significant?

Assuming the nominal Rn=50mOhm so conductance Gn = 1/50mOhm = 20 Simens
so at
Hx=70% the G=0.7*20=14 S --> R = 1/G = 0.07 Ohm
Hx=50% ... R=0.1 Ohm 2x nominal
Hx=30% ... R=0.16 Ohm
Hx=10% ... R=0.5 Ohm
(which is 10x more than the nominal - the resistance grows in hyperbolic fashion with falling Hx)

With Hx: 100%-->10% we go from 20W to 200W lost power ...significant but not critical (except it all turns in the heat in the battery). Likely the battery goes dead before this happens?

eKrom said:

Thanks, I did realize that absolute loses in internal battery resistance are negligible in normally operating battery.

However, I still wonder what does Hx=70% mean?

Click to expand...

I've taken it as follows, but again, take with a grain of salt until blessed by loren:

If new cell resistance is 50 mOhm, then 100% Hx = 50 mOhm
Since R = 1/Hx

If Hx = 2/3 then R = 50*3/2 mOhm

And more generally, a decrease of conductance to a lower Hx = 1/Hx rise in resistance

Long time lurker, etc. This seems like the closest on-point discussion for me, & couldn't quite find info on this.

Been driving the 2016 30kwh for several months (& basically very happy!). Recently had two substantial (hypermiling to avoid turtle) "range underperformance" experiences and am trying to chase down why using LeafSpy logs. It seems that Hx might be a suspect. Really want to chase it down to have an idea of how to account for it. (Less range is one thing, but unexplained significant underperformance is a special kind of bad.)

SOH 77-78
Hx 50-51

The greater-than-expected loss of GIDs seems to happen on fairly long net-climb segments. An example of two runs over the same leg:

Conditions:
Same driver
Same time of day, similar temp
Similar load (700? lbs including driver)
Windless (less than 1mph according to weather station history)
Minimal (115W avg) & no A/C
Similar tire pressures (41-43 PSI at this stage)
Similarly balanced pack at this stage, dV ca 15mV
Similarly hot pack after 2 QCs (121-123 F max, 115-117 min)

20 miles, 1150ft net climb, not much up & down

average speeds of 45.5. and 46.5mph. Fairly low variation (rural highway with bends etc.)

Range chart says ~53 GIDs for mileage at 4.7 mi/kwh (50mph flat) & 22 GIDs for net climb at 1.5kwh/1000ft. Actual use:

91 and 99 GIDs, or 16-25% over. On slightly lower speeds to boot. I know GIDs are at best a BMS-interpreted value, but if all the modeling error is in the speed it's like 65mph instead of 45; if it's all in the elevation gain it's 2.4kwh/1000ft instead of 1.5.

Is it possible one culprit is fairly high internal resistance? I.e. the longer-term greater power demand of hill climbing leads to disproportionately high energy loss due to internal resistance? Or should I be looking at the transmission fluid or some other drivetrain gremlin? (Alignment? but how does the alignment know you're going up hill?)

Or is this mostly down to GIDs are a convenient fiction and just have to assume that sometimes (in the 30-50% range?) they're just...low energy?

Thanks everybody

Read the section of my used Leaf buying guide on the 30kwh Leaf. You have either a bad pack that is covered under warranty, or the car needs a software update for the Battery Management System, or BMS.

https://www.mynissanleaf.com/viewtopic.php?f=27&t=26662&p=538030

Thanks! I did read the guide, and this car turns out to be an early-build 2016 (January, Oct 16 in-service so battery warranty is until 2024) according to the carfax anyway. Live & learn, apparently.

Has had the BMS update (according to firmware versions in LeafSpy) & much of the time meets expectations for range/performance vs capacity. Bought CPO with 11 bars (now 10). Spent its first years in Bay Area it looks like. Specifically chose a 16 30KWH in order to get the longer battery warranty. And at the time had neither need nor expectation of roadtrips much outside the city.

Don't suppose you have any info/experience on warranteeing the battery (bad cell/module?) without being below 9 bars? Of course a 40KWH pack under warranty would be nice but I have a little allergy to expecting good things at the dealership. And like I said most of the time it seems to act as expected.

Thanks again for the info

If I understand the question correctly, you are asking if batteries get replaced under the defect warranty as well as the capacity warranty? They do indeed, although Nissan has the option of replacing bad cells instead of the whole pack. We are still in new territory with the 40kwh replacements, so I don't know how likely it is to get a 40kwh battery if you have, say, one bad cell.