What to ask the HV tech if your car plotted this.......

[EVentropy]

If you not into how 100+ cells are managed, don't read as somewhat OCD.

I discovered this some months ago but the car performed fine and I was too busy at work to pursue.
I recreated as I didn't save and I have booked my first service, this is as good a time as any to ask the experts.

Last night charged to "100%", balanced per usual, didn't drive for 15hrs.
Did our standard "blow off the top" tonight , by driving on flat for 1km, up the hill ~150m (vert), back down and a couple of km's on flat. Plotted V vs time.
In addition, I've established previously, via OBD & car scanner, that charging terminates with highest voltage cell at 3.66V, and balancing begins. Delta at this point is ~360mV. I have what this in detail . (real time roll over) Reducing SOC by driving to 98% gives ~10mV delta. El cheapo balancing by inherent characteristics of LiFePO4?
7kW charging power diminishes reasonably quickly approaching end of charge/start balance, as would be expected, to 3.6kW at termination to balancing. 3.6kW/350V=~10A which = 0.07C (for 51kWh ) using 350V as nominal. This conforms to std charging practice for LiFe. Shunt based termination is common on higher end stuff.
At termination of balancing, highest cell to lowest ~130mV.
Start of drive SoC still 100%, Delta 108mV. (22mV blown off resting after balancing)


Plot of highest cell voltage and lowest cell voltage vs time.

Expanded time axis for rapid acceleration hill climb​

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* Is cutting off charging with first high cell hitting ~3.65V, the way SAIC have designed this?​

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* Is cutting of balancing at a delta of ~130mV normal for MG4 LiFePO4. Why not 10mv, or zero, or until next highest is 10mv?​

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* Is a voltage sag to 2.9V under load of lowest cell within the parameters for a supposed close to 100% SOC'd cell acceptable? It seems to me that​

that the lowest cell here is no where near fully charged and the high cell is not lowered enough. So balancing is not functioning correctly. (Tip hat to T1-terry.)​

* Is there any proprietry software that can monitor individual cell voltage in real time via VDI , SIPS etc, as being able to detect highest & lowest?​

Current plot would suggest that individually they are monitored as opposed to per module.​

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* The above suggest that "100%" SOC is governed by how far you bring down the high cell(s) so you can continue to bring up the mean pack voltage without​

retripping the HV cutoff. So it is wholey up to the balancing parameters and sophistication.​

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*Recent Capacity test from 100% steep climb from sea level to 500m , descend to sealevel, drive mild hilly route for 115km. Repeat in reverse. 230km total with 28% left,so ~300km per charge.​

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* Second plot 39:20 has 70mV delta. At 39:28 with lowest charged cell max sag, delta is 120mV. I'm going to repeat this at 20% SOC and see where the sag gets to​

and what happens to delta; and min V, within safety spec or lower? I assume there is no bottom balancing facility as car is rarely used there.​

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Any input welcome!​

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[hojnikb]

It's pretty normal for LFP cells to go "out of balance" when you top charge them at ~3.6V. The difference in capacity between 3.45V and 3.65V is very small and even a % of difference between cells will cause lots of voltage fluctuations.

As for balancing voltages; i would suggest updating the BMS to the latest version and trying again. There were some updates and they might have changed that.

 

[EVentropy]

Can the MG service technicians change the parameters of the bms(s)? Do they?
My diy install ( in my boat) only uses the 3.65V cutoff as a battery protection device in the event the programming fails. It also is user configurable. Hence my dismay when I observed this occurring.
Cell Voltage sensing triggers balancing, end of charge, etc to parameters user configures.
Max voltage is a separate identity. (Safety)

My thinking atm, possibilities :
My bms is faulty.
It is configured incorrectly.
It is not very sophisticated , and owing to the forgiving chemistry of LiFePO4 and a max voltage cutoff, it works but is not optimal.

“There were some updates and they might have changed that.”
These will be via sips right?
Do you have a revision number?
Thanks!

 

[hojnikb]

Can the MG service technicians change the parameters of the bms(s)? Do they?
My diy install ( in my boat) only uses the 3.65V cutoff as a battery protection device in the event the programming fails. It also is user configurable. Hence my dismay when I observed this occurring.
Cell Voltage sensing triggers balancing, end of charge, etc to parameters user configures.
Max voltage is a separate identity. (Safety)

My thinking atm, possibilities :
My bms is faulty.
It is configured incorrectly.
It is not very sophisticated , and owing to the forgiving chemistry of LiFePO4 and a max voltage cutoff, it works but is not optimal.

“There were some updates and they might have changed that.”
These will be via sips right?
Do you have a revision number?
Thanks!

Yes, you need to update the BMS via SIPS. Don't have the revisions unfortunally. I've updated my whole car and didn't really bother checking that.

I'd still say what you're seeing is normal. I highly doubt anything serious is wrong or configured poorly. SAIC likely woulndn't give you 8 year warranty and mess up such basic settings so badly.

I would worry much more, if high inbalance would occur at the lower states of charge (like 50%). That could be an indicatior of poor cells.


And there's also one more thing. I'm guessing you're pulling this data from OBD. There might be a change this data isn't even accurate.

 

[EVentropy]

For any that are interested, complements of AI
“Horses mouth.”

AI Overview
can the parameters of the bms be updated in sips for mg4 in terms of charging termination, balance start and stop and delta of highest and lowest cell voltage by servicing dealerships


Yes, the parameters of the Battery Management System (BMS) in an MG4 can be updated by a servicing dealership, including settings for charging termination, balance start and stop, and cell voltage delta, though access and availability depend on manufacturer procedures and software versions, and may be limited to updates addressing specific issues rather than routine parameter changes. Servicing dealerships have the tools and software to access and potentially modify these parameters, but updates are often applied to resolve problems or as part of broader system upgrades, not for customer-requested modifications to basic settings like charging behavior.

How it works

• Dealership Access:
  MG servicing dealerships are equipped with specialized software and hardware to connect to the vehicle's BMS and make adjustments.
  
  
• Parameter Control:
  The BMS has parameters that determine how it operates, such as the voltage thresholds for charging termination, when to start cell balancing, and the acceptable voltage difference between cells.
  
  
• Software Updates:
  Parameter settings are managed through software, and while dealers can modify them, this is usually done in conjunction with official software updates from MG to address performance or safety issues.

Limitations

• Not for Routine Changes:
  Dealerships are unlikely to change basic operational parameters like the default charging termination voltage or balance start/stop settings on customer request, as these are part of the battery's protective design.
• Milk
• Problem-Driven Updates:
  Software updates are typically released by MG to fix known problems or improve functionality, and may only be performed if the vehicle exhibits a specific issue that the update addresses.
• Manufacturer Control:
  The ability to adjust these specific parameters is ultimately controlled by MG through their diagnostic tools and software, not something a user can modify directly.

In summary, while a dealership can technically update BMS parameters for your MG4, it is not a common service for routine adjustments and is primarily done for technical reasons or to resolve faults with manufacturer-approved software and updates.

 

[EVentropy]

I’m going to do identical tests at 50% and 20% to confirm the trend of potentially non-linear increase in delta under hi load with decrease in SOC. To establish a DOD that I will not drive the car hard at and push the low cell in to degradation zone. < 2.7V
With this tabulated I will consult with the tech guy next week and hopefully confirm I don’t have bad cell(s) and or bms ithat is either faulty or badly configured.
And it’s is not a way lesser elegant system than what I cobbled together for my boat. ( for comparative pennies)

Thankyou hojnikb for your input.

If any body is curious about results of next tests I will post them and the response of the dealership tech.

 

[hojnikb]

For any that are interested, complements of AI
“Horses mouth.”

AI Overview
can the parameters of the bms be updated in sips for mg4 in terms of charging termination, balance start and stop and delta of highest and lowest cell voltage by servicing dealerships


Yes, the parameters of the Battery Management System (BMS) in an MG4 can be updated by a servicing dealership, including settings for charging termination, balance start and stop, and cell voltage delta, though access and availability depend on manufacturer procedures and software versions, and may be limited to updates addressing specific issues rather than routine parameter changes. Servicing dealerships have the tools and software to access and potentially modify these parameters, but updates are often applied to resolve problems or as part of broader system upgrades, not for customer-requested modifications to basic settings like charging behavior.

How it works

• Dealership Access:
  MG servicing dealerships are equipped with specialized software and hardware to connect to the vehicle's BMS and make adjustments.
  
  
• Parameter Control:
  The BMS has parameters that determine how it operates, such as the voltage thresholds for charging termination, when to start cell balancing, and the acceptable voltage difference between cells.
  
  
• Software Updates:
  Parameter settings are managed through software, and while dealers can modify them, this is usually done in conjunction with official software updates from MG to address performance or safety issues.

Limitations

• Not for Routine Changes:
  Dealerships are unlikely to change basic operational parameters like the default charging termination voltage or balance start/stop settings on customer request, as these are part of the battery's protective design.
• Milk
• Problem-Driven Updates:
  Software updates are typically released by MG to fix known problems or improve functionality, and may only be performed if the vehicle exhibits a specific issue that the update addresses.
• Manufacturer Control:
  The ability to adjust these specific parameters is ultimately controlled by MG through their diagnostic tools and software, not something a user can modify directly.

In summary, while a dealership can technically update BMS parameters for your MG4, it is not a common service for routine adjustments and is primarily done for technical reasons or to resolve faults with manufacturer-approved software and updates.

i dont see any settings you can change in the bms, at least not in sips or vds.

So as always, AI is telling bull

 

[Geekice]

i dont see any settings you can change in the bms, at least not in sips or vds.

So as always, AI is telling bull

Yes, I updated my bms via Sips, but you can only install software update from saic not change manually the parameters.

 

[hojnikb]

Yes, I updated my bms via Sips, but you can only install software update from saic not change manually the parameters.

And they don't expose these things to service tools for good reason.

There's no reason why 3rd parties or servicing shops would have to change these parameters. Factory likely tested everything beforehand and how it acts in the wild. Just modifying some crucial values could have adverse effects if not tested correctly.

At the end of the day, a car isn't a basic home ESS where you can more freely play around with the bms settings.

 

[EVentropy]

Yes, I updated my bms via Sips, but you can only install software update from saic not change manually the parameters.

And the bms update didn’t divulge what the upgrade “fixes” were? I wonder if the service dealership gets that information in terms of bulletin thru some dealer only part of portal.
Like “secret screens” etc but via sips and Saic.
I am surprised Saic has left the door ajar wrt to access to downloads by other than bonafide dealers. Is that a bottom end Chinese compromise to OTA automatic?
Unless even this dealer access contains zero on proprietary design and access by business rego is just an 0mmision that didnt “need” fixing. Like keep everyone in the dark.

I have serviced my own cars from the first, 60yrs ago and are not comfortable with this change yet. I was attracted by the simplicity of moving parts, optimisations and the eco sustainability (In long term) of going electric.
Beside having tested the water with diy install
Of my own.