Elevated HVB Module Variation - What's yours? (Solved post 26)

[bmwhitetx]

In March 2024, I got the Service Vehicle Soon along with reduced power and charging constraints. Long story short, it was a bad cell in module 6. Lots of us got this. I had been using Car Scanner and taking screenshots each month. Two parameters were of interest now: "HVB SOC module variation (%)" and "HVB Voltage module variation (V)"

Back in 2024 my variation jumped from less than 1% to over 4% when the module "failed". Now, two years later, I am seeing a increase even greater than what triggered the Service Error. I wonder if Ford changed the threshold for the error?

Here is my history graph:

Here are my current readings. Anyone else seeing numbers above 1%? I have no relevant DTC's.

EDIT: I customized the title of the sensors in the screenshots above. Here are the actual Sensor names:
HVB Voltage Variation Battery Modules (units =V)
HVB SOC Variation Battery Modules (units=%) My historical graph above used this value.

EDIT: See post 26 for resolution. Bad battery module.

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[digitaldad]

FYI Bruce, getting "not found" errors on your attachment.

EDIT: NM, it changed/removed.

 

[Heliian]

Charge it to 100%, check again, drive down to 50%, check again.

 

[bmwhitetx]

Charge it to 100%, check again, drive down to 50%, check again.

I've been thinking of doing that since I have heard it can reset/calibrate the SOH parameter and balance cells. But concerned it came on so suddenly.

Some info on the truck. It is 3.4 years old, has only 15K miles. Typically charge to 85%. Only charged to 100% about 10 times, last time was 10 months ago. With low miles, I average 10 days between charging (35-85%).

 

[Heliian]

average 10 days between charging (35-85%)

How's the weather?

 

[bmwhitetx]

How's the weather?

Typical Texas weather but it stays garaged so not exposed to temps below 40.

 

[Oafboy182]

Isn't it better to keep the truck plugged in even if it doesn't need to charge. You apparently don't drive much, lucky you, but I wonder if keeping it plugged in all the time would be better. My truck is always plugged in whether it needs to charge or not.

 

[digitaldad]

@bmwhitetx - Was this a custom dashboard for you? I found what I think are the default/dashboard values.

From the "all sensors"

I did not click into the variation modules (from sensors) to see if it matched the 0.003.

EDIT: spelling/tag Bruce

 

[Zprime29]

Mine went to 99% a couple days ago at free the work charger. I think I was around 2kWh shy of last time I hit 100%. I popped in the OBD reader and checked my module variation. Didn't screenshot it but it was 0.01V, 0.46% (I think).

I don't check it regularly, the few times I have it's always been in that ballpark. I agree the suggestion to charge to 100% and let the BMS try to top balance.

 

[bmwhitetx]

@bmwhitetx - Was this a custom dashboard for you? I found what I think are the default/dashboard values.

From the "all sensors"

I did not click into the variation modules (from sensors) to see if it matched the 0.003.

EDIT: spelling/tag Bruce

Yes, sorry, I have indeed customized the dashboards over the years to try and organize the pages better and shorten the name.

The actual sensors that I'm using are named
HVB Voltage Variation Battery Modules (the units will be V)
HVB SOC Variation Battery Modules (unit will be %)

So, the ones you listed are correct. I meant to clarify that. I'll edit my first post. Thanks!

 

[bmwhitetx]

Isn't it better to keep the truck plugged in even if it doesn't need to charge. You apparently don't drive much, lucky you, but I wonder if keeping it plugged in all the time would be better. My truck is always plugged in whether it needs to charge or not.

Good question. I'm not sure anyone here really knows and I don't want to turn this into a "how to charge post" There are already plenty of those .

I do agree with @Heliian that maybe an occasional charge to 100% might be beneficial. We have heard anecdotally that the the onboard charger does a lot of extra work between 99% and 100% that may indeed be balancing the pack.

I mainly want to know if others are seeing an elevated level - a level that 2 years ago would have been flagged as a module replacement.

 

[Firn]

Good question. I'm not sure anyone here really knows and I don't want to turn this into a "how to charge post" There are already plenty of those .

I do agree with @Heliian that maybe an occasional charge to 100% might be beneficial. We have heard anecdotally that the the onboard charger does a lot of extra work between 99% and 100% that may indeed be balancing the pack.

I mainly want to know if others are seeing an elevated level - a level that 2 years ago would have been flagged as a module replacement.

Fwiw it appears that as the truck nears 100% it starts to split the input current to various cells to balance them, giving a fairly high balancing current.

Alternately the pack does balance by itself over time, which is pretty typical for a BMS on a multi-cell NMC. My dashboard thread shows variation by idle time.

I expect the current available for balancing is higher when it's off the L2 and thus it balances faster.

 

[ZSC100]

So, your graph of SoH means nothing without noting the reference to previous charging details and SoC.

For instance, if you charge to 90% each night on a L2 at home, then you'd take the SoH measurement @90% SoC after each charge i.e. each morning before you leave. Your driving habits are certainly rare compared to 90%+ of people charge their EV every night.

The Lightning BMS does passive balancing only, and will only balance at the top end of a charge once the first cell reaches maximum SoC. Basically resistors are switched on to waste the charge power as cells reach maximum SoC, in this way all cells can be raised to the same maximum level (balancing).

So, if you have 8% variation and you don't charge past 92% SoC then you haven't balanced anything. This is why you should charge to 100% occasionally, to fully balance everything. Yes, I do fully believe FMC has relaxed the threshold of detection of bad modules to ease the pain of module replacements, but will they ever disclose this: NO. Just like they will not disclose any of the BMS algorithms for balancing, power limiting, or pre-conditioning. They only view disclosure of tech details as increasing their liability. I have tested this after 2 module replacements, one at 50kmi and one at 90kmi. I now have 140kmi, I charge every night to 90%, if I go over a month without charging to 100% I have seen over 6% module variation, soon as I charge to 100% it's back down to less than 0.2%. It's the rate at which the cells become unbalanced that is a problem. If you charge to 100% and get to less than 1% variation, then drive one battery and get more than a few % that's a problem. If you get 6% in a month charging to 90% or less, that's not a problem.

 

[bmwhitetx]

Tried to charge to 100% last night and the app says it went to 100% but when I start the truck, the SOC dropped to 84. I think this is just an error with the fact I have my home set as a charge location with 85%. I moved the override slider to 100% but I think it's not taking. I believe others have reported this with the most recent OTA. The app also way over reported the amount of kWh ingested - no where close to what my EVSE reported it saw.

I'll try again tonight. I have deleted all charging locations and confirmed neither the app or truck now shows a charging location. And for good measure I did a 12V disconnect for an hour.

 

[ZSC100]

Tried to charge to 100% last night and the app says it went to 100% but when I start the truck, the SOC dropped to 84. I think this is just an error with the fact I have my home set as a charge location with 85%. I moved the override slider to 100% but I think it's not taking. I believe others have reported this with the most recent OTA. The app also way over reported the amount of kWh ingested - no where close to what my EVSE reported it saw.

I'll try again tonight. I have deleted all charging locations and confirmed neither the app or truck now shows a charging location. And for good measure I did a 12V disconnect for an hour.

While you are charging, open the app and verify it is actively charging at a stable rate.

Use the app to slide to 100%, it will specifically ask you "this charge session only"?

This is how I charge to 100% once a month, it always works for me.

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