eKrom
Posts: 12
Joined: Thu Jul 30, 2020 1:08 pm
Delivery Date: 29 Jul 2020
Leaf Number: 307821
Location: Bay Area, CA
Contact: Website

What values of Hx is worrisome, if any?

Mon Aug 03, 2020 11:47 am

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
'17 Leaf S, 15k, SOH=88% Hx=70%

LeftieBiker
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Re: What values of Hx is worrisome, if any?

Mon Aug 03, 2020 1:49 pm

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.
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goldbrick
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Re: What values of Hx is worrisome, if any?

Mon Aug 03, 2020 5:29 pm

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.

lorenfb
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Leaf Number: 416635
Location: SoCal

Re: What values of Hx is worrisome, if any?

Mon Aug 03, 2020 7:58 pm

LeftieBiker wrote:
Mon Aug 03, 2020 1:49 pm
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.
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.
#1 Leaf SL MY 9/13: 76K miles, 47 Ahrs, 5.0 miles/kWh (average), Hx=70, SOH=73, L2 - 100% > 1000, temp < 95F, (DOD) > 20 Ahrs
#2 Leaf SL MY 12/18: 10.3K miles, SOH 109Ahrs/115Ahrs, 5.2 miles/kWh (average), DOD > 20%, temp < 105F

eKrom
Posts: 12
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Leaf Number: 307821
Location: Bay Area, CA
Contact: Website

Re: What values of Hx is worrisome, if any?

Tue Aug 04, 2020 6:50 am

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?
'17 Leaf S, 15k, SOH=88% Hx=70%

eKrom
Posts: 12
Joined: Thu Jul 30, 2020 1:08 pm
Delivery Date: 29 Jul 2020
Leaf Number: 307821
Location: Bay Area, CA
Contact: Website

Re: What values of Hx is worrisome, if any?

Tue Aug 04, 2020 7:12 am

@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?
'17 Leaf S, 15k, SOH=88% Hx=70%

lorenfb
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Leaf Number: 416635
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Re: What values of Hx is worrisome, if any?

Tue Aug 04, 2020 9:47 am

eKrom wrote:
Tue Aug 04, 2020 7:12 am

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?
For Leaf 2 and basically meaningless
0% = Leaf non-start
eKrom wrote:
Tue Aug 04, 2020 7:12 am

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?
Correct
eKrom wrote:
Tue Aug 04, 2020 7:12 am
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?
Correct
#1 Leaf SL MY 9/13: 76K miles, 47 Ahrs, 5.0 miles/kWh (average), Hx=70, SOH=73, L2 - 100% > 1000, temp < 95F, (DOD) > 20 Ahrs
#2 Leaf SL MY 12/18: 10.3K miles, SOH 109Ahrs/115Ahrs, 5.2 miles/kWh (average), DOD > 20%, temp < 105F

cwerdna
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Location: SF Bay Area, CA

Re: What values of Hx is worrisome, if any?

Tue Aug 04, 2020 12:04 pm

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 viewtopic.php?f=9&t=25773&p=579357&hili ... al#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.

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SageBrush2
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Re: What values of Hx is worrisome, if any?

Tue Aug 04, 2020 1:53 pm

eKrom wrote:
Tue Aug 04, 2020 7:12 am
Although 30% lose of conductance (Hx=70%) would mean the 30% more energy is lost to heat
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
Last edited by SageBrush2 on Wed Aug 05, 2020 5:53 am, edited 9 times in total.

goldbrick
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Re: What values of Hx is worrisome, if any?

Tue Aug 04, 2020 3:29 pm

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.

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