Everything you need to know about BMS & voltage balancing

[Stuart Wright]

Later today, @MilesperkWh and I are making a video to explain what BMS is and to address the concerns of ZS EV owners regarding potentially unbalanced batteries.
I will ask Miles a series of questions to answer, the purpose being to create a definitive video on the subject which addresses all the questions and concerns that people might have.
This is the list of questions:

1. What does BMS stand for?
2. What is BMS generally and why is it important?
3. Can MG ZS EV owners see the battery health?
4. What should the voltage display read?
5. What if the voltage display reads something else?
6. What is battery balancing?
7. Why have some ZS EV owners got an imbalanced battery?
8. How can a ZS EV owner identify whether their car has the particular software version?
9. What impact will an imbalanced battery have?
10. Will having an imbalanced battery damage the battery or car?
11. What should an owner who believes they have an imbalanced battery do?
12. What is the procedure for re-balancing the ZS EV battery?
13. Why does balancing a battery take so long? Is there any way to speed it up?
14. Do MG5 owners need to rebalance their battery?

Can you suggest any questions to be added to this list?
Please reply. Thanks

 

[Chvarvind]

Later today, @MilesperkWh and I are making a video to explain what BMS is and to address the concerns of ZS EV owners regarding potentially unbalanced batteries.
I will ask Miles a series of questions to answer, the purpose being to create a definitive video on the subject which addresses all the questions and concerns that people might have.
This is the list of questions:

1. What does BMS stand for?
2. What is BMS generally and why is it important?
3. Can MG ZS EV owners see the battery health?
4. What should the voltage display read?
5. What if the voltage display reads something else?
6. What is battery balancing?
7. Why have some ZS EV owners got an imbalanced battery?
8. How can a ZS EV owner identify whether their car has the particular software version?
9. What impact will an imbalanced battery have?
10. Will having an imbalanced battery damage the battery or car?
11. What should an owner who believes they have an imbalanced battery do?
12. What is the procedure for re-balancing the ZS EV battery?
13. Why does balancing a battery take so long? Is there any way to speed it up?
14. Do MG5 owners need to rebalance their battery?

Can you suggest any questions to be added to this list?
Please reply. Thanks

I did not have the faulty BMS. I had the January BMS installed at the time of my car service on 22nd January. Battery voltage changed from 455 to 449. Current Max Volt is 4.16 and min is 4.14. Why is the balancing still taking between 3 to 4 hours in spite of having balanced cells? How long does it take for balancing time reduced to less than an hour?

 

[Cocijo]

Why do EV’s need a BMS?
how is the BMS linked to other areas of the car? For example some say comfort2 update has changed their BMS?
for example is timed charging and charging unlocked part of the BMS or something else?
Does rapid charging create more of an imbalance than fast charging?
how does the BMS control rapid charging?
what are the top and bottom voltages for the latest BMS software - the usable range of the pack?
what is the purpose of displaying voltage to the user? How should it be used?
what are the key signs to look for on a faulty BMS?
for those that have had battery packs severely out of balance caused by the faulty BMS update will this impact the longevity of the battery pack?
what about owners who are not aware they have a faulty BMS? Has there been an official recall and have they all been contacted?
how often should owners just leave their battery on charge to fully equalise - is it only needed when a warning message is displayed or after faulty BMS?

 

[mystreet]

If you have the 'bad' BMS should you balance your battery or will it make it worse.

How many ZS are on the list that MG circulated to dealers and what should the dealer be doing to contact the owners to rectify the issue

 

[Lovemyev]

If you have the 'bad' BMS should you balance your battery or will it make it worse.

If you have the “Buggy” BMS update installed, there is no point trying to balance your pack really, there is no benefit.
Update to the latest 15th Jan 2021 - then start charging / balancing would be my advice.

 

[Lovemyev]

Hi Stuart, can you please ask @Miles to clarify these two points please.
I am sure more than a few owners will be interested to hear the responce to these two questions.

1. Are cars now leaving the factory with the new BMS latest update applied that will reduce the full pack voltage down to 448 - 450 volts when fully charged, to help protect longevity of the pack, and if not - why not ?.

2. Are cars leaving the dealerships now, having the BMS update applied as part of the PDI inspection and will all cars currently in circulation have the 15th Jan 2021 BMS upgraded applied when the car is submitted to the dealer for service or any other type of work required long term.
E.g. - In an attempt to standardised the software on all ZS EV cars ?.

Thank you.

 

[Tango130]

1. What does BMS stand for?
2. What is BMS generally and why is it important?

Can Miles elaborate on previous 'BMS' updates that have included updating the EVCC - Electric Vehicle Charge Controller (delayed charging) & OBC - On Board Charger (unlocked charging).

Also what does IPK stand for, this module was updated as part of a BMS/HV Battery update.

 

[Kithmo]

If you have the early BMS, 455v fully charged, is it best to fully charge and balance the battery before having the latest (450v) BMS update installed ?
Does having the BMS update put the battery more out of balance ?
Is it best to run the battery right down before charging back up to full, after the BMS update to get better balance ?

 

[Stuart Wright]

Can Miles elaborate on previous 'BMS' updates that have included updating the EVCC - Electric Vehicle Charge Controller (delayed charging) & OBC - On Board Charger (unlocked charging).

Also what does IPK stand for, this module was updated as part of a BMS/HV Battery update.

We're going to focus on the voltage problems with the BMS update rather than any other elements of car updates.
I've searched for IPK and I can't find out what it stands for.
[Edit]: IPK is instrument pack. Unrelated to the BMS or software.

 

[Lovemyev]

When do you estimate that you will be in a position to post the video Stu ?.
I realise it is not made yet of course !.
O.B.T.W. - I think what you are doing is a great idea.
Miles in the firing line once again though !.
Good luck with the video ?.

 

[Stuart Wright]

When do you estimate that you will be in a position to post the video Stu ?.
I realise it is not made yet of course !.
O.B.T.W. - I think what you are doing is a great idea.
Miles in the firing line once again though !.
Good luck with the video ?.

I hope Miles isn't in the firing line because he's working here for the benefit of MG owners and MG themselves.
It will probably take about a day to edit the video. I hope to publish over the weekend some time.

Here is the revised list of questions. They are organised so that they first explain the basics and then go deeper with the answer to each question leading into the next question.

In December 2020, a small number of MG ZS EVs had a software version installed which contained a bug which caused the batteries of the cars to become imbalanced. In this interview, Miles Roberts, Innovations Development Manager at Chorley Group answers the questions that MG ZS EV owners have about this software update, the effect it has, and what they should do about it.

1. About the car’s software
   1. How is the software in electric cars different to the software in internal combustion engine cars?
   2. Do electric cars have more frequent software updates than ICE cars?
   3. How are software updates to MG electric cars installed?
   4. What changes to the ZS EV have been made with the various updates?
   5. How can a ZS EV owner identify what version of the software they have?
2. About the BMS and cell voltage
   1. What does BMS stand for?
   2. What is BMS generally and why is it important?
   3. Can MG ZS EV owners see the battery health?
   4. What is the max and min voltage on the display and why is it there?
   5. What should the max and min voltage display read for the ZS EV?
   6. What if the voltage display reads something else?
3. About battery cell voltage balancing
   1. What is battery cell voltage balancing?
   2. Does cell voltage balancing happen on all electric cars?
   3. What causes an imbalanced battery?
   4. When will ZS EVs usually need to have their battery balanced?
   5. Is battery balancing an automatic process?
   6. Does rapid charging create more of an imbalance than fast charging?
   7. Which particular ZS EV software update caused imbalanced batteries?
   8. Does this software update affect other MG models?
4. Dealing with an imbalanced battery
   1. What impact will an imbalanced battery have on the car?
   2. Will having an imbalanced battery damage the battery or car?
   3. What should an owner who believes they have an imbalanced battery do?
   4. Have ZS EV owners with the particular software version been contacted to update it?
   5. What is the procedure for re-balancing the ZS EV battery?
   6. Why does balancing a battery take so long? Is there any way to speed it up?
5. Current situation
   1. What is the latest version of the ZS EV software and when was it released?

 

[Gomev]

@Stuart Wright - Perhaps you could ask for the definitive BMS update version that is the newest as at least 2 of us that have used the same dealer seem to have a different version to everyone else after having the update for the buggy software.

 

[Lovemyev]

he's working here for the benefit of MG owners and MG themselves.

I don’t think anybody on the forum would argue with that Stu !.
With out his help and input we would be up shit creek without a paddle that’s for sure !.
His kind offer to help to us owners is to be commended, my statement was not offered or intended to invite criticism of his good work.
I look forward to watching the video and hearing his views on this on going subject. Hopefully it will reassure owners that this situation will be rectified to every bodies satisfaction.
It maybe wrong to start pointing the finger at the dealerships here, it is not there fault they where given corrupted software to apply.
But it certainly is NOT the owners fault that’s for sure !.
Just on the receiving end of a bad deal.

 

[micky]

I don’t think anybody on the forum would argue with that Stu !.
With out his help and input we would be up sh*t creek without a paddle that’s for sure !.
His kind offer to help to us owners is to be commended, my statement was not offered or intended to invite criticism of his good work.
I look forward to watching the video and hearing his views on this on going subject. Hopefully it will reassure owners that this situation will be rectified to every bodies satisfaction.
It maybe wrong to start pointing the finger at the dealerships here, it is not there fault they where given corrupted software to apply.
But it certainly is NOT the owners fault that’s for sure !.
Just on the receiving end of a bad deal.

we are so lucky to have a great forum like we have and thank you to all the people who input to make it even better, for myself i have learned so much from every ones input.

 

[Lambo51]

Question 1
How is a software update containing a bug allowed to get Anywhere near your customers car?
Question 2
Will further updates with bugs get near Your customers Cars?

 

[Cocijo]

Far from it for me to stand up for MG - but software errors happen all the time - they are a fact of life and will never be completely eliminated. Apple do it - Microsoft do it. The real test is how they are dealt with, how customers are looked after and what preventative and quality measures are put in place to minimise reoccurrences

 

[JodyS21]

@Stuart Wright
I think there's a very important new development hopefully Miles can shed some light on - There's another new version of the BMS that has just appeared in the last week or 2!!!

 

[Lambo51]

Far from it for me to stand up for MG - but software errors happen all the time - they are a fact of life and will never be completely eliminated. Apple do it - Microsoft do it. The real test is how they are dealt with, how customers are looked after and what preventative and quality measures are put in place to minimise reoccurrences

Fair point . I’m guessing they don’t realise there are errors when It’s being released to customers

 

[Cocijo]

Yes - I think there may be a degree of incompetence particularly in testing but no malice.

 

[Jaygee]

Far from it for me to stand up for MG - but software errors happen all the time - they are a fact of life and will never be completely eliminated. Apple do it - Microsoft do it. The real test is how they are dealt with, how customers are looked after and what preventative and quality measures are put in place to minimise reoccurrences

True. However, the dodgy BMS can potentially damage the batteries....
We all know how manufacturers like to honour their warranties.