Can HX (battery internal resistance) be improved?

[BillyA]

Hello I have a 2 part question:
1) I'm considering purchasing a 2017 Leaf with 55K miles. I connected Leaf Spy lite and learned the Hx = 32.26%. The car has 8 out of 12 bars battery capacity. Would a deep discharge and slow charge help anything with the battery health? Can it help HX? Is there any way to increase HX without replacing or repairing the battery? (Leafspy image attached, feedback welcome)

2) Can I replace the 2017 30KWH with a healthier 24KWH battery from my rear ended 2015?

Thanks in advance for any input.

-Bill

 

[MikeinPA]

As far as I know, we do not have a verifiable description of what Hx is, nor how the car measures it. It is probably related to the internal resistance of the cell(s). My hunch is that the LBC is observing some part of the charge cycle, possibly voltage rise versus amps, and doing some calculations that would also include temperature to arrive at the Hx number. Then the car keeps track of the Hx values over time and then updates the reported value on some schedule.

Where has the car lived previously? How many bubbles of regen can you get?

 

[Drew21]

I think you could swap a 24 kWh battery in place of a 30 kWh battery, but you might not gain much in the process, especially once you account for costs of doing the work.

Even from Day 1, the 24 kWh battery had significantly lower capacity than a 30 kWh battery. So (just hand-waving, you should determine real numbers), it might take a 10 or 11 bar 24 kWh battery to exceed the usable capacity of your 8 bar 30 kWh battery.

 

[BillyA]

Thanks I appreciate the responses. My 24kWH battery has 10 bars so marginally better than the degraded 30kWh.

When I test drove the car I didnt pay attention to the regen bubbles, didnt look at leaf spy while driving, I should have. Also should have read the DTC error codes, seem to have forgot how to check out a used car.

The car lived in Oakland CA at least for first 18K miles which is where the Nissan national records stopped. Car did have the PC630 recall for the battery reprogram done at 18K miles.

 

[MikeinPA]

Billy, the questions you have about this pack are good ones. There will be hundreds of thousands of aging Leafs out there with really marginal batteries in the coming years. Each vehicle can potentially be kept alive and filling a specific niche for years--freeing up newer (and new) EVs for more demanding roles. But we really don't know that much about the various mileage and age related declines in these older Leafs.

 

[lorenfb]

As far as I know, we do not have a verifiable description of what Hx is, nor how the car measures it. It is probably related to the internal resistance of the cell(s). My hunch is that the LBC is observing some part of the charge cycle, possibly voltage rise versus amps, and doing some calculations that would also include temperature to arrive at the Hx number. Then the car keeps track of the Hx values over time and then updates the reported value on some schedule.

Where has the car lived previously? How many bubbles of regen can you get?

Do a search, this topic of Hx for Leaf1 has been discussed numerous times with referenced data. It's highly correlated with SOH (declines over time)
and as such, it's NOT resistance but battery conductance. Surprised as a member from 2015, that you missed this!

 

[MikeinPA]

" as a member from 2015" and lurking for two years previous!

There are a zillion "what is Hx?" threads out there on MNL, Reddit, Speak EV, etc. This one is pretty good: https://mynissanleaf.com/threads/what-is-hx.17482/ But I have not seen a verifiable description of exactly what the LBC is measuring and how it is doing the calculation. Which still surprises me. Collectively there is enough information out there to fully characterize the LBC blackbox--that is my opinion-- but this has not been done yet. Doesn't help that the firmware is changing over time.

 

[lorenfb]

Do

" as a member from 2015" and lurking for two years previous!

There are a zillion "what is Hx?" threads out there on MNL, Reddit, Speak EV, etc. This one is pretty good: https://mynissanleaf.com/threads/what-is-hx.17482/ But I have not seen a verifiable description of exactly what the LBC is measuring and how it is doing the calculation. Which still surprises me. Collectively there is enough information out there to fully characterize the LBC blackbox--that is my opinion-- but this has not been done yet. Doesn't help that the firmware is changing over time.

My '13 Leaf battery resistance over time:

11/20/14 -13,700 miles, 76 mohms per LeafDD, 20 Deg, 73% SOC
11/27 -13,800 miles, 67 mohms per LeafDD. 25 deg, 63% SOC
11/30 - 13,900 miles, 56 mohms per LeafDD, 27 deg, 71% SOC
12/2 - 14.100 miles, 55 mohms per LeafDD, 28 deg, 67% SOC
12/16 - 14,500 miles, 89 mohms per LeafDD, 15 deg, 93% SOC
12/27/14 - 14,800 miles, 103 mohms per LeafDD, 11 deg, 24% SOC
3/10/15 - 17,400 miles, 60 mohms per LeafDD, 30 deg, 73% SOC
3/14 - 17, 550 miles, 56 mohms per LeafDD, 32 deg, 47% SOC
4/14 - 19,100 miles, 59 mohms per LeafDD, 25 deg. 38% SOC
5/4 - 19,989 miles, 64 mohms per LeafDD, 24 deg. 48% SOC
5/15 - 20,400 miles, 73 mohms per LeafDD, 20 deg. 41% SOC
5/22 - 20,700 miles, 58 mohms per LeafDD, 28 deg. 50% SOC
12/10/15 - 28,000 miles, 90 mohms per LeafDD, 19 deg. 92% SOC
4/5/16 - 32,000 miles, 74 mohms per LeafDD, 24 deg, 55% SOC
5/16 - 33,700 miles,89 mohms per LeafDD, 22 deg, 47% SOC
5/16 - 33.700 miles, 58 mohms per LeafDD, 31 deg, 76% SOC
10/5 - 39,300 miles, 100 mohms per LeafDD, 22 deg, 50% SOC
10/6 - 39,400 miles, 61 mohms per LeafDD, 30 deg, 51% SOC
10/7 - 39,500 miles, 80 mohms per LeafDD, 25 deg, 56% SOC
10/15/16 - 40,000 miles, 71 mohms per LeafDD, 27 deg, 45% SOC

If you review the Leaf1 battery resistance (mohms) over time you'll see that it increases not like Hx which decreases over time like SOH.
This indicates that Hx is battery conductance (inverse of battery resistance) and NOT battery resistance! Where are your data?

 

[MikeinPA]

At no place have I said that a declining Hx means declining resistance; what I said was that Hx is related to resistance and is calculated from resistance (edit 3/21/24 ). Everyone knows that increasing resistance is the result of aging, that metrics like Hx are related to that, and that Hx will vary inversely with respect to resistance.

The questions are still out there--how is the LBC measuring resistance, and how is it calculating the metric Hx? If we know that, then we can start to make educated guesses on what Hx means in terms of future usability of that particular pack.

Cell resistance varies with temperature and state of charge, so if you are trying calculate a metric like "resistance at 25 deg C and 50% SOC" you are going to need some calculations:

 

[lorenfb]

At no place have I said that a declining Hx means declining resistance; what I said was that Hx is related to resistance and is calculated from resistance. Everyone knows that increasing resistance is the result of aging, that metrics like Hx are related to that, and that Hx will vary inversely with respect to resistance.

The questions are still out there--how is the LBC measuring resistance, and how is it calculating the metric Hx? If we know that, then we can start to make educated guesses on what Hx means in terms of future usability of that particular pack.

Cell resistance varies with temperature and state of charge, so if you are trying calculate a metric like "resistance at 25 deg C and 50% SOC" you are going to need some calculations:

Just like you do when testing any other battery technology, i.e. measure delta V and delta I, when the load changes - R = delta V/delta I.
It's just basic BSEE first year lab class. Yes, there might be some minor terms in the relationship, but for the most part it's insignificant.
Your graph is NOT the proper meaningful relationship, i.e. it's SOH & not SOC as the battery ages! It's about as meaningful as using
time of day as the independent variable, or tire pressure.

Read this; https://batteryuniversity.com/article/bu-902-how-to-measure-internal-resistance#google_vignette

Here's Gary Gid's (key Leaf contributor) work with his Tesla Model S on battery analysis under max load, i.e. indicates battery resistance;

 

[MikeinPA]

Sorry, I am just not getting any of what your are saying. Just point to your reference for how the LBC measures resistance, and the other reference for how the LBC then calculates Hx from that and temperature and SOC. Thank you.

 

[lorenfb]

Sorry, I am just not getting any of what your are saying. Just point to your reference for how the LBC measures resistance, and the other reference for how the LBC then calculates Hx from that and temperature and SOC. Thank you.

It's unfortunate, given your lack of any basic electrical/electronic knowledge. The references provided should've been insightful.

Here's a suggestion:
1. Take classes in "C" computer programming
2. Obtain the LBC processor memory binary file
3. Disassemble the file
4. Provide the corresponding "C" code
5. Provide the basic LBC math from the "C" code in an equation
6. Using your derived equation, present tabular data of expected battery resistance versus temperature
7. Relate the results of step 6 to a Hx equation versus temperature

Consider using the above results in an entry letter, i.e. a statement of purpose, to a PhD EE program at a major university.

 

[MikeinPA]

I love the internet.


The state of health calculation unit 7 includes a characteristic table showing a relation between the charge amount Q and the open-circuit voltage OCV for each state of health SOH classified into predetermined ranges. Details of the characteristic table is disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 2012-57956 filed by the present applicant.
The open-circuit voltage estimation value estimated by the state estimation unit 4 and the charge amount calculated by the charge amount calculation unit 5 are input to the state of health calculation unit 7. The state of health calculation unit 7 calculates to determine the range of the state of health SOH into which the open-circuit voltage estimation value and the charge amount are classified, and a corresponding state of health SOH is output.

The figure below is from the above link, also found here: https://patentimages.storage.googleapis.com/00/b0/dd/65922d06fe94cf/US10295607.pdf

 

[BillyA]

Getting back to my original question, I assume HX cannot be improved by conditioning the battery somehow like a deep discharge/slow recharge?

I did briefly drive the 2017 car again. With a 90% charged battery I could only get one regen bubble in the "B" mode. My 2015 gets 3. What does this indicate?

 

[MikeinPA]

one regen bubble in the "B" mode

Regen capability (amps displayed as bubbles) decreases as the battery ages. But regen capability will also be initially lower if the battery has been sitting for a while for my 2013s, if the battery temps are low, and absent at 100% charge of course. But if the car battery is at four or more temp bars, and been driven for about 10 miles, you should be seeing 4 bubbles on braking normally from about 20 mph or above. If you can't get more than one bubble, that is a big warning the battery is way off original spec.

Up until today I would have said fewer bubbles is also an indicator of increased internal resistance, but after looking at a few of the Caltronics patents...I genuinely do not know. BTW, I never departed from the "can the Hx be improved" question. I think it is important to know what Hx is before talking about can it be improved. However, Hx in my blue Leaf improved a few points after I replaced some cells and was able to fully cycle the battery from 100% down to 20%.

I am not deliberately ignoring the question of whether the 30 kwh chemistry can be conditioned through controlled cycling. There are so many unknowns in that question.

The question of placing a 24 kwh pack in a later model Leaf was a topic previously somewhere on this forum.

 

[Drew21]

As MikeinPA suggested, low temperatures also reduce available regen bubbles. Our 2014 is parked in an unheated garage. In the winter the battery temperature is often at 3 bars in the morning (especially if the car has been parked for >1 day), and in that state we'll only get 1 regen bubble. From our house our typical route takes us uphill for almost 2 miles, after which the battery temp increases to 4 bars and we have full regen.

 

[hornstudio]

We have a 2018 40kWh battery with only 60% HX but a cell difference of only 3-4mV and with 40000 miles on the odometer and it still has 35,2kWh left. It works more than great in any conditions.

 

[nlspace]

Some years ago i traced out the LBC schematic for the "conductance" measurement, aka internal resistance, and posted here:
https://www.diyelectriccar.com/thre...ry-controller-lbc-details.204369/post-1067783

The function is active when relay RLY1 is energized from IC1 to connect the Pack HV+ to HV- across a resistor divider circuit which has a divider-output measurement range of about 3.2 to 4.2 VDC for a Pack voltage of 300 to 400VDC.

The microcontroller IC1 has a timer which outputs to drive an RC network with time constant ~0.45s and create a saw-tooth sinusoidal which is summed with a low voltage DC and referenced with respect to the Pack low side HV- connection.

IC7 and IC8 had their part numbers etched off, so somebody wanted to hide what they are using.

The little white relay can be seen in the upper right quadrant along with the widely-spaced resistors in this photo:

 

[lorenfb]

Some years ago i traced out the LBC schematic for the "conductance" measurement, aka internal resistance, and posted here:
https://www.diyelectriccar.com/thre...ry-controller-lbc-details.204369/post-1067783

The function is active when relay RLY1 is energized to connect the Pack HV+ to HV- across a resistor divider circuit which has a divider-output measurement range of about 3.2 to 4.2 VDC.

The microcontroller IC1 has a timer which outputs to drive an RC network with time constant ~0.45s and create a saw-tooth sinusoidal injected at the HV- connection.

The little white relay can be seen in the upper right quadrant in the photo:

Thanks for your post. Based on your review of the LBC, one can conclude that by loading the HV battery with known resistor values and measuring
the voltage drop, the battery's internal resistance can be determined. Then the value of Hx (conductance) is determined by the inverse of the
measured internal resistance.

 

[MikeinPA]

Then the value of Hx (conductance) is determined by the inverse of the measured internal resistance.

And expressed as 0 to 100% conductance? How does one get 0% conductance? Infinite resistance? it just seems like such an odd way to express resistance.

I have skimmed about a dozen of the relevant Calsonic patents from 2006 to 2012 so far. The SOC and SOH estimation process is described clearly. There are candidates for what Hx could be; too soon for me to say, further reading needed. But consider, the engineers thought that this percent value is important enough to track and update alongside percent SOC & SOH. SOC is reported on the dash in a %0 to %100 fashion, and that is something we really need to know as operators; SOH is also prominently displayed, and also as %0 to %100, albeit as a step function, and this too is something we really want to know. So where does Hx, also expressed as a value from %0 to %100, fit into this paradigm? Would available power be a candidate?