BMS Update?

[jamesie]

It is indeed a poor show. It's a fact though, that lowering cell voltage to 4.16V will increase battery life.

Depends on the chemistry of the cell as I understand it.

Looks more to me that they wanted to reduce the voltage of the pack to avoid even more charge/discharge cycles for those that were recovering from the duff BMS (I have no evidence of this!!).

 

[Paulie68]

Depends on the chemistry of the cell as I understand it.

Looks more to me that they wanted to reduce the voltage of the pack to avoid even more charge/discharge cycles for those that were recovering from the duff BMS (I have no evidence of this!!).

It's a fact, whatever the chemistry, that lithium lasts much longer (exponentially so) the further away you can keep it from the top and bottom of it's voltage range. Whatever tweak of the lithium chemistry CATL are using, the original 4.22V per cell was pretty high for lithium.

 

[Coulomb]

At higher cell voltages, regardless of the chemistry (as long as it's lithium based), you get more lithium metal plating, and electrolyte breakdown. Both of these are irreversible, and both reduce life and increase cell internal resistance.

 

[ging353]

Would be very interested in the reply you get. I'm on the original BMS which appears to be fine but don't want to cause any "damage" by not moving to the latest revision. Problem is, I don't trust the MG dealership to do the job!

I am getting to be as wary as you. You never get told anything. I had to ask them to do the Comfort 2 update last year. Surely they should be contacting us about regular updates not the other way round. I love the MG ZS EV but the aftercare from MG is very sadly lacking and at best very poor. I am seriously thinking about a change the next time I'm looking for a car.

 

[jamesie]

At higher cell voltages, regardless of the chemistry (as long as it's lithium based), you get more lithium metal plating, and electrolyte breakdown. Both of these are irreversible, and both reduce life and increase cell internal resistance.

So would you suggest every owner should be insisting on the new BMS software?

 

[Lovemyev]

Surely they should be contacting us about regular updates not the other way round. I love the MG ZS EV but the aftercare from MG is very sadly lacking and at best very poor.

The dealers appear to be operating a “If they don’t request an update, then don’t offer it” type approach.
At the majority of dealerships, this is their first introduction EVER into the large world of EV’s.
That is why, in a lot of cases the owners are more knowledgeable than the people who are selling or working on our cars !.
Plain and simple, when it comes to EV dedicated problems, they are seen running for the hills !.
I have had a first hand experience of this when my car entered the workshop for its first service and the drivers door harness to be replaced ( service recall ) and the car refused to boot up after the work.
It was taking up space on a ramp for a couple of days until MG Tech came up with a fix.
I get a cold shiver down my back at the thought of having any work done, unless it is absolutely necessary !.
For many EV Tech’s that have no experience on EV’s before, the learning curve is massive !.
Remember, they are using our cars to learn their trade.
Dealerships that have experience on previous EV’s like Nissan Leak etc have to be a better option.
The Chorley group are the first people that spring to mind here.
My car will be going there for its next service THAT’S for sure.
Covid restriction prevented this from happening for its first service.
Applying software updates have to be done 100% correctly, otherwise you are entering a whole different world of pain with your car.
I can understand why people are reluctant to risk having them done.
It should NOT be that way, but we all know the risk of what happens when it all goes wrong.
If the update goes wrong, then the dealer is given a massive headache trying to sort out the problem remotely.
This causes all sorts of problems when it comes to workshop work load when you are working around a dead car.
If they don’t ask - don’t offer !.

 

[FCat53]

Well it's a poor effort if that's so. What about those that don't get their cars serviced by a main dealer?

I don't trust that they are making a change that is better than the original, tbh!!

They would just do a blanket recall if there was a real chance of warrantable degradation, that does not mean there will be none but that it will be lower than warranty levels. All batteries degrade, that's just how it is, but if it is 15 years from now that I have to upgrade the battery pack, that is to be expected.

 

[Coulomb]

would you suggest every owner should be insisting on the new BMS software?

Actually, yes. At least if you have the 455 V BMS. Obviously, definitely if you have the faulty BMS.

I'm a bit disappointed myself that my last full charge went to 452 V, much the same as before the update (I was slack at recording the voltages).

I'll also be attempting to limit most charges to 80% real SOC (displayed SOC while charging TBD), unless I'm planning a big trip soon after. If OVMS can do that automatically for me, that will likely tip the balance in favour of me purchasing and installing it.

 

[Kithmo]

It's a fact, whatever the chemistry, that lithium lasts much longer (exponentially so) the further away you can keep it from the top and bottom of it's voltage range. Whatever tweak of the lithium chemistry CATL are using, the original 4.22V per cell was pretty high for lithium.

I can't find any reference to what you're saying about 4.2v being damaging to the cells.
What I found was that a fully charged Li ion cell is 4.2 + or - 50mV so 4.15v to 4.25v.
Charging cut off is 4.4v.
I also found that the Ternary Li ion in our cars have a 0.4v higher base voltage than standard Li ion if that has any bearing on anything.
Do you have a link or reference I can read, as to why charging to 4.2v is more damaging that 4.16v ?
I'm not saying it isn't, I'm just interested to know why.

 

[JodyS21]

Let's be clear, we do not actually know the reason for MG lowering the top and bottom voltage, we are all guessing.

Yes it does seem to be advantageous; regen available quicker on "full" battery, DC charge slows down a bit later on. If you had the duff BMS, it is quicker for it to be fixed.

We do not fully know the battery chemistry details, battery tech secrets must be worth a fortune, so will never know what is "ideal" voltages/conditions etc.
I honestly don't think it's a simple case of saying maintaining lower voltage increases lifetime and that's why they've done it, otherwise surely if it's that obvious they'd have done it to start with!

MG (or CATL), must've figured something out in the last year that has made them decide to make this change.
Maybe the higher voltage has caused issues with other components; I doubt it but maybe it's related to the HV fuse blowing.

Maybe......it performed better in the WLTP test at the original voltages, so they're now trying to sneakily change it to this voltage without anyone finding out that it potentially has a worse WLTP.

From a previous message I posted, FYI:
"450V divided by 108 cells = 4.1667v
4.2V X 108 cells would give a total of 453.6V
So previous BMS with a total voltage of 459V would average 4.25V per cell."

 

[Coulomb]

Do you have a link or reference I can read, as to why charging to 4.2v is more damaging that 4.16v ?

See for example What is Lithium Plating? - News about Energy Storage, Batteries, Climate Change and the Environment

The last paragraph starts "The two simplest ways to avoid lithium plating is to prevent over voltage (above 4.2 volts per cell) during charging, and... "

It's a very short article. There are plenty of others, some very technical; search for "lithium plating".

Edit: see also BU-808: How to Prolong Lithium-based Batteries after table 3. They don't mention the specific mechanisms of cell degradation there. It's fairly readable.

 

[Coulomb]

Maybe......it performed better in the WLTP test at the original voltages, so they're now trying to sneakily change it to this voltage without anyone finding out that it potentially has a worse WLTP.

MG are supposed to have reduced the bottom buffer, to allow for about equal range.

 

[jamesie]

My car always fully charges and balances to give a reading of 456v. That works out at 4.22v per cell.

Is 0.02v over the stated 4.2v really an issue? I have read other articles that state maximum voltage can be 4.35v in certain cell types.

MG need to answer the simple question for owners that have the original BMS as to whether they should migrate to the new one.

 

[Paulie68]

My car always fully charges and balances to give a reading of 456v. That works out at 4.22v per cell.

Is 0.02v over the stated 4.2v really an issue? I have read other articles that state maximum voltage can be 4.35v in certain cell types.

MG need to answer the simple question for owners that have the original BMS as to whether they should migrate to the new one.

As said earlier, we don't know the actual chemistry of these cells, 4.22V is unlikely to be an issue over the short to medium term. What we do know is lithium likes to be kept away from the top and bottom of the charge range in general and leaving the battery fully charged or close to empty for any length of time will shorten its life.

It makes absolute sense to keep at least a
little bit away from the extremes and the decision by SAIC/MG to limit the top voltage will almost certainly be for purposes of longevity, there is no other valid reason.

If you're selfish and don't intend to keep the car long term, it really doesn't matter. Long term owners should absolutely get the latest update.

 

[Kithmo]

My car always fully charges and balances to give a reading of 456v. That works out at 4.22v per cell.

Is 0.02v over the stated 4.2v really an issue? I have read other articles that state maximum voltage can be 4.35v in certain cell types.

MG need to answer the simple question for owners that have the original BMS as to whether they should migrate to the new one.

On the app, mine shows a full charge of 456.25V. which I thought was an odd figure.
P.s. does having an extra 6-7v make my car faster than one with the new BMS ?

 

[RichardC]

I have just been reading this.

Update information

The MG5 recall is for the earlier activation of brake lights using Kers 3. The other item is the confirmation of 35 kg limit on the roof bars which requires an extra page being glued into the...

www.mgevownersclub.co.uk

Miles Roberts gives some useful information and there is a link for him speaking with Stuart Wright.

Apologies if it has been posted before

 

[jamesie]

As said earlier, we don't know the actual chemistry of these cells, 4.22V is unlikely to be an issue over the short to medium term. What we do know is lithium likes to be kept away from the top and bottom of the charge range in general and leaving the battery fully charged or close to empty for any length of time will shorten its life.

It makes absolute sense to keep at least a
little bit away from the extremes and the decision by SAIC/MG to limit the top voltage will almost certainly be for purposes of longevity, there is no other valid reason.

If you're selfish and don't intend to keep the car long term, it really doesn't matter. Long term owners should absolutely get the latest update.

I get what you are saying.

Selfishness doesn't come into it.

I haven't decided yet how long I will keep the vehicle. Regardless, I would like to keep it in as good a condition I can. For my own use and that of any future owners.

The problem is twofold for me.....

1. MG have not, to my knowledge, insisted that all ZS EV's are updated to the new BMS. If you have evidence, e.g. a service action, then I would like to see it.

2. If it is essential (i.e. insisted on by MG) then I will have it done. Done with trepidation as the MG dealerships are at best hit or miss with regard to software updates.

However, having read around the subject a bit, I'm not convinced that there is enough information available about the battery composition to suggest that this change is essential. Guessing why MG made the change is not good enough.

ps. Maybe ging353 will get a definitive message from MG.

 

[Paulie68]

On the app, mine shows a full charge of 456.25V. which I thought was an odd figure.
P.s. does having an extra 6-7v make my car faster than one with the new BMS ?

Yes it does! Well at least your battery will wear out faster than cars with the new BMS

 

[Paulie68]

I get what you are saying.

Selfishness doesn't come into it.

I haven't decided yet how long I will keep the vehicle. Regardless, I would like to keep it in as good a condition I can. For my own use and that of any future owners.

The problem is twofold for me.....

1. MG have not, to my knowledge, insisted that all ZS EV's are updated to the new BMS. If you have evidence, e.g. a service action, then I would like to see it.

2. If it is essential (i.e. insisted on by MG) then I will have it done. Done with trepidation as the MG dealerships are at best hit or miss with regard to software updates.

However, having read around the subject a bit, I'm not convinced that there is enough information available about the battery composition to suggest that this change is essential. Guessing why MG made the change is not good enough.

ps. Maybe ging353 will get a definitive message from MG.

My servicing dealer told me they have been advised by MG to apply the latest BMS update to all cars at time of service. Read into that what you may, I agree regarding the general incompetence of dealers.

It is a fact that a lithium battery, any lithium battery, has its lifespan increased the further away from minimum and maximum it is operated. By that logic, as long as the change doesn't allow the voltage to drop too low in compensation for keeping away from the top of the charge, and bearing in mind most people won't be running right down very often, or leaving the car battery depleted if they do, as opposed to a significant number who are in the habit of fully charging every day ready for tomorrow, it makes perfect sense. Whether or not your dealer can update your car without screwing it up is a different matter!!

 

[JodyS21]

MG are supposed to have reduced the bottom buffer, to allow for about equal range.

Exactly, "supposed to".
I have checked the new high & low voltage differences, but can't prove that the capacity is the same.