Everything you need to know about BMS & voltage balancing

Orcadian said:
I picked up my ZS EV on 21.10.20. I have just done 1000 miles from new. My battery at 85% voltage reads 438. Can you tell me if I have the correct BMS? I know the car was ready for pick up a week before I got it.
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It is about time when I got mines. So BMS is "old" but stable. With voltage when fully charged 456/457 V. When your battery is nearly full, connect your granny charger to balance. Shouldn't take to long....
 
JodyS21 said:
Maybe the july version wasn't quite out when you had the comfort pack 2 update?
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Going by the spreadsheet provided in the earlier comment there were at least 2 updates since my one in November 2019 by July. They didn't say they would update the BMS updates at the time they were applying the comfort pack but I did expect them to apply the latest one with the service today. Especially as they said part of the service is to apply the latest updates
 
I think all cars are going to get the latest BMS update when owners take cars in for service.
 
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rbpasapera said:
I heard on a podcast with Miles Roberts from Chorley MG that the latest BMS update would be installed when cars get serviced.
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Unfortunately (or maybe fortunately if you have the "original" stable BMS) this doesn't appear to be the case.

Someone on the Facebook group suggested that BMS will not be updated at the moment until MG are certain the new BMS is stable. Don't know where they get their information from but could make sense (given previous releases!).
 
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My zs ev is only just over a week old, and I gave it a full charge on 7kw home charge till the light went out. It only shows 456v with a range of 139 miles.
I would have thought that it would have the latest update that everyone is talking about
 

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The range is reduced as you have something running in the car. The display shows 3A (HVAC?). Turn everything off to get the max range (guess) in each driving mode (Normal, Eco, Sport).

As for the BMS.....who knows? Is the car brand new?
 
jamesie said:
The range is reduced as you have something running in the car. The display shows 3A (HVAC?). Turn everything off to get the max range (guess) in each driving mode (Normal, Eco, Sport).

As for the BMS.....who knows? Is the car brand new?
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got the car on 1st march brand new. The only thing running when i took pic was dash cam, would that reduce it that much
 
BigAl46 said:
got the car on 1st march brand new. The only thing running when i took pic was dash cam, would that reduce it that much
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TBH....I'm no expert. But 3A seems rather a lot for a dash cam.

I think the BMS largely depends on the dealership. The new BMS was available in January (and there appears to be a further update in February). However, whether cars come from the factory with either of those updates....who knows! Appears that some owners are having services done and no BMS update at service so MG may be holding back on the new BMS being applied to all vehicles.
 
BigAl46 said:
My zs ev is only just over a week old, and I gave it a full charge on 7kw home charge till the light went out. It only shows 456v with a range of 139 miles.
I would have thought that it would have the latest update that everyone is talking about
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Turn the car on, by pressing the start button WITHOUT the brake pedal pressed. The HV battery will not be on then and will be under no load.
If you want a range figure to compare to others, you must also reset the Accumulated Trip, as that will reset the GOM calculation.

You got the car brand new 1/3:
If the car left the factory after July 2020, it should've have the (455v) 07/20 slight bug BMS on it.
If the car left the factory between October-ish & Late December-ish 2020, it should've have the (455v) 24/10/20 Big bug BMS on it.
If the car left the factory after mid-January 2021, it should've have the fixed 15/1/21 (450v) BMS on it.

It is possible the dealers aren't updating the BMS at the moment for some reason, BUT if the car had the 24/10/20 Big bug BMS on it - I would very strongly suggest refusing to take the car until it has been updated.
 
jamesie said:
TBH....I'm no expert. But 3A seems rather a lot for a dash cam.

I think the BMS largely depends on the dealership. The new BMS was available in January (and there appears to be a further update in February). However, whether cars come from the factory with either of those updates....who knows! Appears that some owners are having services done and no BMS update at service so MG may be holding back on the new BMS being applied to all vehicles.
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BigAl46 said:
got the car on 1st march brand new. The only thing running when i took pic was dash cam, would that reduce it that much
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It can't be the dash cam as such, as it's running from the 12v battery system.
The HV battery could be charging the 12v battery of course.
 
JodyS21 said:
Turn the car on, by pressing the start button WITHOUT the brake pedal pressed. The HV battery will not be on then and will be under no load.
If you want a range figure to compare to others, you must also reset the Accumulated Trip, as that will reset the GOM calculation.

You got the car brand new 1/3:
If the car left the factory after July 2020, it should've have the (455v) 07/20 slight bug BMS on it.
If the car left the factory between October-ish & Late December-ish 2020, it should've have the (455v) 24/10/20 Big bug BMS on it.
If the car left the factory after mid-January 2021, it should've have the fixed 15/1/21 (450v) BMS on it.

It is possible the dealers aren't updating the BMS at the moment for some reason, BUT if the car had the 24/10/20 Big bug BMS on it - I would very strongly suggest refusing to take the car until it has been updated.
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Great info...

1. How can you tell the date of manufacture?
2. Is there a way to tell the BMS version without purchasing an OBD2 and using an app?
 
Stuart Wright said:
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
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Why is it that some MG ZS EVs received the compromised update and others didn't?
 
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