Everything you need to know about BMS & voltage balancing

Orcadian · Mar 11, 2021

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.

Davemac278 · Mar 11, 2021

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

Davemac278 · Mar 11, 2021

On full charge after balance and nothing switched on the new BMS should show 449v.

If you had earlier BMS update it would be 455v. If your range is ok at the moment your car will be given new BMS at next service.

If you have poor range I would contact your dealer and they will confirm if your car needs to come in quickly for the new BMS update released by MG after 16th January 21.

Useful video on BMS here

Orcadian · Mar 11, 2021

Davemac278 said:
On full charge after balance and nothing switched on the new BMS should show 449v.

If you had earlier BMS update it would be 455v. If your range is ok at the moment your car will be given new BMS at next service.

If you have poor range I would contact your dealer and they will confirm if your car needs to come in quickly for the new BMS update released by MG after 16th January 21.

Useful video on BMS here

Thanks for the reply. As you can see due to lock down I have done very little mileage. Range seems to be OK, I rapid charge mostly (no home charger) but I have a neighbour willing to let me balance the battery now and then.

JodyS21 · Mar 11, 2021

Orcadian said:
Thanks for the reply. As you can see due to lock down I have done very little mileage. Range seems to be OK, I rapid charge mostly (no home charger) but I have a neighbour willing to let me balance the battery now and then.

You have the granny charger that came with the car? Just plug that it and let it fully charge and balance, then check your voltage

Gomev · Mar 12, 2021

Davemac278 said:
On full charge after balance and nothing switched on the new BMS should show 449v.

If you had earlier BMS update it would be 455v. If your range is ok at the moment your car will be given new BMS at next service.

If you have poor range I would contact your dealer and they will confirm if your car needs to come in quickly for the new BMS update released by MG after 16th January 21.

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.

Just to add, if your voltage fully charged and balanced is not 455 or 449/450 and going by the date you picked yours up I would guess you may have the buggy BMS.

Stuart Wright · Mar 12, 2021

Gomev said:
balanced is not 455 or 449/450

give or take, when it's fully charged with no load.

Conradu · Mar 12, 2021

Need some advice. I have just paid for and picked my car up after 1st years service. I checked my BMS Update version beforehand which was 1125600R15, this would have been from when I first bought the car in March 2020. I just checked what the new version is, in case I got the dodgy one and found its exactly the same??!! I can see the latest one is supposed to be 1230621A01. Has anyone any idea why it wouldn't have been updated? The Dealership is shut till Monday and I can see me having to go back to them, which is a nightmare journey

JodyS21 · Mar 12, 2021

Conradu said:
Need some advice. I have just paid for and picked my car up after 1st years service. I checked my BMS Update version beforehand which was 1125600R15, this would have been from when I first bought the car in March 2020. I just checked what the new version is, in case I got the dodgy one and found its exactly the same??!! I can see the latest one is supposed to be 1230621A01. Has anyone any idea why it wouldn't have been updated? The Dealership is shut till Monday and I can see me having to go back to them, which is a nightmare journey

Unfortunately there doesn’t seem to be a consistent approach to these things from MG.
I’d imagine if you paid for/had the comfort pack 2 update they’d update it then, I’m assuming you’ve not got that - it’s well worth paying a few quid for the improvements.

Cocijo · Mar 12, 2021

Aren’t all cars regardless getting the 449v update ?

Chrisb · Mar 12, 2021

Mines been for service and still on the same one.

Dr Dave · Mar 12, 2021

Conradu said:
Need some advice. I have just paid for and picked my car up after 1st years service. I checked my BMS Update version beforehand which was 1125600R15, this would have been from when I first bought the car in March 2020. I just checked what the new version is, in case I got the dodgy one and found its exactly the same??!! I can see the latest one is supposed to be 1230621A01. Has anyone any idea why it wouldn't have been updated? The Dealership is shut till Monday and I can see me having to go back to them, which is a nightmare journey

Is the very latest BMS update mid 2/2021 version 0210622EU1?

Conradu · Mar 12, 2021

JodyS21 said:
Unfortunately there doesn’t seem to be a consistent approach to these things from MG.
I’d imagine if you paid for/had the comfort pack 2 update they’d update it then, I’m assuming you’ve not got that - it’s well worth paying a few quid for the improvements.

Thanks for the reply. I did actually pay for the comfort pack 2 around July, they didn't do a bms update then

Kithmo · Mar 12, 2021

Cocijo said:
Aren’t all cars regardless getting the 449v update ?

I hope not actually, mine's fine as it is at 455v, if it ain't broke, don't fix it.

Conradu · Mar 12, 2021

Chrisb said:
Mines been for service and still on the same one.

I asked a week before service what they will do for the price. They stated they apply the latest update, so will be on the phone to them on Monday

Cocijo · Mar 12, 2021

Kithmo said:
I hope not actually, mine's fine as it is at 455v, if it ain't broke, don't fix it.

I know what you mean but it is supposed to further protect your battery and maximise its useful life.

Kithmo · Mar 12, 2021

Cocijo said:
I know what you mean but it is supposed to further protect your battery and maximise its useful life.

I agree, but I'm not one for keeping cars a long time, the 5 year old 2016 Prius I just traded for SWMBO's 5 is the longest I've kept the same car for some years. I'll probably change the ZS when a longer range facelift one comes out in the next couple of years.

Conradu · Mar 12, 2021

Dr Dave said:
Is the very latest BMS update mid 2/2021 version 0210622EU1?

The one I quoted was end of January, didn't know 0210622EU1 came out Feb 21

JodyS21 · Mar 12, 2021

Dr Dave said:
Is the very latest BMS update mid 2/2021 version 0210622EU1?

Yes.

ECU Module version spreadsheet

I'll update this top post as more data is provided. In an attempt to figure out what the different versions of all the software do/cause, we are putting together a list of peoples car ecu versions. If you have the OBD2 device (currently being looked at in another post) or OVMS, please post your...

www.mgevs.com

Why there's a feb version to replace the jan version, we don't know.

JodyS21 · Mar 12, 2021

Conradu said:
Thanks for the reply. I did actually pay for the comfort pack 2 around July, they didn't do a bms update then

Maybe the july version wasn't quite out when you had the comfort pack 2 update?

Everything you need to know about BMS & voltage balancing

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