Is there a software update I can get to improve the range?

[Cocijo]

Yes - that makes good sense. Thank you.

 

[Stuart Wright]

That's great info to get a copy of that.

I wonder if @Stuart Wright could create a permanent post to which any official copies of letters such as this can be added to, to keep them all in one place?

Don't need to create a sticky, but if that letter could be scanned properly so it's decent quality and then posted in a thread, I can link to it from the resources page.

Useful MG EV information, articles and frequently asked questions index

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www.mgevs.com

 

[KasEV]

I wonder if @MilesperkWh could comment on this - this is the first time it has ever been mentioned that just leaving a car in Ready mode will rebalance the battery cell packs.

Obviously it is possible that it could do this, but I'd be surprised to be honest; as being in ready mode assumes the car is to be used and therefore you wouldn't expect the charging balancing process to run.


I was thinking the 1mV per hour, relates to each cell. So each of the cells within the 9 cell packs can have their min/max moved by 1mV per hour.
Remember there are 12 cells in each pack (12*9=108*4.2v=453.6)
So in theory you could move a maximum total of 108mV (0.108V) per hour.

In terms of the total voltage shown in the car, I believe it charges until the first cell reports it has hit "max" voltage, then it stops and kicks in balancing.
So it could potentially be one cell causing the charge to stop "early", so just fixing this worst one cell could kind of suddenly free up the others to be charged higher and then give a higher total voltage.

Well done @JodyS21 I personally do not have this charging / voltage problem and I truly feel for those that continue to have it and those that are just recovering from it. I thing we should be kind, patient and understanding when this issue is raised over and over again. Whatever MG got wrong seems rather difficult to understand it seems they infected the car with Covid and all the cars have gone on to develop full blown long Covid. Well just like the Covid variants each car seems to be a variant in it own right with characteristics that are worse than others

 

[AbuG]

It looks legit to me. MG is more of an authority than any dealer staff (where do you think the latter get their technical know how from?).
Well if some one with the residual effects of the withdrawn BMS firmware can try it and see if it makes a difference.
Best to use a good steering lock too.
And lock car from inside, via open driver window, then one-click pull to close the window.

 

[Mike]

I wonder if @MilesperkWh could comment on this - this is the first time it has ever been mentioned that just leaving a car in Ready mode will rebalance the battery cell packs.

@MilesperkWh has mentioned this for months on several of the podcasts and I also thought in posts as well!

 

[Cocijo]

@MilesperkWh has mentioned this for months on several of the podcasts and I also thought in posts as well!

I too must have completely missed those! This was news to me when i saw the MG service bulletin. I remember Miles discussing depleting to about 93% and then equalising rather than running lower, but nothing about just leaving in ready state to equalise. Do you have any details of the several podcasts where he mentions this please? ?

 

[Gomev]

@MilesperkWh has mentioned this for months on several of the podcasts and I also thought in posts as well!

I too must have completely missed those! This was news to me when i saw the MG service bulletin. I remember Miles discussing depleting to about 93% and then equalising rather than running lower, but nothing about just leaving in ready state to equalise. Do you have any details of the several podcasts where he mentions this please? ?

Sorry Mike, I have listened to all the podcasts but I too do not recall this being mentioned.
Leaving it to balance after charging obviously, but not just putting the car somewhere secure and 'switching it on'

My apologies in advance if it has been mentioned.

 

[Miles Roberts CG]

Sorry, I thought I had mentioned this before - Leaving the car in ready mode (or driving it) will do a negative cell balance down to 93%. So if you have access to a lockable garage etc then you can leave the car in ready mode overnight, then charge during the day (or vice versa). This is what Longbridge did to bring their batteries back into line a bit sooner than otherwise would be the case.

 

[JodyS21]

Sorry, I thought I had mentioned this before - Leaving the car in ready mode (or driving it) will do a negative cell balance down to 93%. So if you have access to a lockable garage etc then you can leave the car in ready mode overnight, then charge during the day (or vice versa). This is what Longbridge did to bring their batteries back into line a bit sooner than otherwise would be the case.

I didn't realise that either.
I misinterpreted that it just needed to be took to below 93% so that when plugged in it would cause it to do a rebalance.
Thanks for your confirmation Miles.
So once past/lower than 93% it won't help rebalance, so no point (unless obviously need to use the car!) in going lower than that before recharging/balancing in order to get the battery back to health asap.

 

[AbuG]

(Or driving it) ??
Don't think that was mentioned in the MG UK letter. I think it said everything needed to be otherwise off, heating, radio, auto lights, etc. Or have I misunderstood it?

Sorry, I thought I had mentioned this before - Leaving the car in ready mode (or driving it) will do a negative cell balance down to 93%.

 

[Cocijo]

What is a negative cell balance? Is this the same as an equalisation?

 

[JodyS21]

I've been thinking a little (as usual!)...

It would have to be doing the balancing differently if it's doing it on drain to 93% compared to when balancing after a full charge as it's drawing power in this situation still.

Thinking about it, balancing when driving sounds rather difficult to achieve, it needs the juice and can't be mucking around balancing at that time surely. Also, why would it only be able to do it down to 93%. To be clear I am not saying it can't be possible, but thinking about it, it doesn't sound right....

In my head, I'm assuming it uses different wired connections to the cells when it's balancing, I'm thinking it must have individual (small) wires to each cell to do things cell independently, but then uses a thick wire to drain usually which pulls from them all connecting in parallel/serial. Needs more investigation!

 

[Cocijo]

If you drive after a full charge, the balancing down to 93% will only last a few minutes anyway (15mins?), so not really that effective? How does regen operate when pack is balancing? This whole balancing thing intrigues me. So many questions! Has the recent bms that adjusted the top and bottom pack buffers also effected balancing? What are the parameters before a warning to balance pack is displayed? Why only 93% - why not lower? ?????

 

[John Arnold]

Just revisited this string after a few months. Had the latest BMS update done 2 weeks ago. Have been considering weather conditions and attributed my range problem to this. After the update did 2x50 mile trips. Both journeys used 100 miles of battery each way. I like others got approximately 160 from a full charge. All I can do is between 90 and 100.
Taking the car back tomorrow for another investigation. Any ideas would be helpful.

An update on my previous item. Dealer had the car for 2 days to rectify noise from sun roof and to fix range problem noted above. Car came back with rattle same as before. Another BMS was done. Not knowing if that would work, or not, I complained very loudly.
Giving my dealer his due he did understand and a very happy remedy was reached.
Pick up a 21 model next week at a great price.
Still very happy with the car hence accepting another car.
Great to know that members of the group share their collective experiences.
Thanks all for sharing.

 

[Coulomb]

It would have to be doing the balancing differently if it's doing it on drain to 93% compared to when balancing after a full charge as it's drawing power in this situation still.

I don't see why that would be the case.

Thinking about it, balancing when driving sounds rather difficult to achieve, it needs the juice and can't be mucking around balancing at that time surely.

Those are different computers doing driving and balancing Besides that, computers are pretty good at doing several things at once, using multiple tasks or threads.

But you are right that when driving, the cell voltages will be thrown to the winds by the large traction and even heavy regeneration currents. It's possible that the BMS can compensate for the effect of currents on the cell voltages, by using an estimate of the cell internal resistance, but that would be very approximate, and balancing is a relatively delicate process.

But when coasting or standing still, it might still be able to do some balancing when at a high stagte of charge.

Also, why would it only be able to do it down to 93%.

That's probably because you only want to equalise the state of charge when the cells are all nearly full. The capacity of individual cells always varies a little, and the difference between cells increases as the cells age. If you balance at the top (high SOC), then you will be ragged at the bottom (low SOC). Similarly, if you balanced at the bottom (or all the time), then you will be ragged at the top. If the car has an advanced BMS that can actually shuffle energy between cells, then it's good to balance all the time, because then you avoid unnecessary power reduction when just one or two cells get low, and avoid reduced regeneration because one or two cells are full. But my guess is that the balancing is just by "bleeding" resistors, which simply burn off energy from the highest voltage cells, allowing the others to catch up. With that system, it makes no sense to burn off energy in an attempt to equalise the cells; it will just heat up the BMS (and the cells slightly).

The Nissan Leaf is interesting in that it has very gentle balancing (≈10 mA), but balances all the time, even with the car off, 24/7. I'm guessing that the ZS uses more aggressive balancing (say 100 mA), but only when the car is in ready mode. In ready mode, the BMS computer is running (and consuming power). My understanding is that the Leaf balancing is done by the electronics in the BMS that runs all the time, so the power-hungry BMS computer doesn't have to be involved.

I'm still wondering if perhaps the ZS will balance at SOC higher than 93% even when not ready. There is no reason that the car has to have all the cells in series (that's what ready mode is) for balancing to take place. But it just depends on the BMS design. @MilesperkWh, do you happen to know if this is possible and it it actually happens?

In my head, I'm assuming it uses different wired connections to the cells when it's balancing, I'm thinking it must have individual (small) wires to each cell to do things cell independently, but then uses a thick wire to drain usually which pulls from them all connecting in parallel/serial.

Yes, that's right. The cells are usually connected to each other by straps of copper or aluminium, large enough to carry the hundreds of amps needed for full motor current. In addition to this, there are much thinner wires that connect each cell to the BMS. The BMS uses these thin wires to measure each cell's voltage, and also to carry the modest balancing current. For 108 cells, there has to be 109 of these thin wires. So this job is usually broken up into smaller blocks. Probably each module (there are 9 modules with 12 or 24 cells in each) will have a "mini BMS" that looks after that module, and communicates with the BMS computer (ECU? they have different names in different cars) for overall coordination.

 

[Kithmo]

Would the cells balance on their own if left with the car off, due to them all still being connected or would self balancing require them to be connected in parallel ?

 

[Gomev]

I don't see why that would be the case.


Those are different computers doing driving and balancing Besides that, computers are pretty good at doing several things at once, using multiple tasks or threads.

But you are right that when driving, the cell voltages will be thrown to the winds by the large traction and even heavy regeneration currents. It's possible that the BMS can compensate for the effect of currents on the cell voltages, by using an estimate of the cell internal resistance, but that would be very approximate, and balancing is a relatively delicate process.

But when coasting or standing still, it might still be able to do some balancing when at a high stagte of charge.

That's probably because you only want to equalise the state of charge when the cells are all nearly full. The capacity of individual cells always varies a little, and the difference between cells increases as the cells age. If you balance at the top (high SOC), then you will be ragged at the bottom (low SOC). Similarly, if you balanced at the bottom (or all the time), then you will be ragged at the top. If the car has an advanced BMS that can actually shuffle energy between cells, then it's good to balance all the time, because then you avoid unnecessary power reduction when just one or two cells get low, and avoid reduced regeneration because one or two cells are full. But my guess is that the balancing is just by "bleeding" resistors, which simply burn off energy from the highest voltage cells, allowing the others to catch up. With that system, it makes no sense to burn off energy in an attempt to equalise the cells; it will just heat up the BMS (and the cells slightly).

The Nissan Leaf is interesting in that it has very gentle balancing (≈10 mA), but balances all the time, even with the car off, 24/7. I'm guessing that the ZS uses more aggressive balancing (say 100 mA), but only when the car is in ready mode. In ready mode, the BMS computer is running (and consuming power). My understanding is that the Leaf balancing is done by the electronics in the BMS that runs all the time, so the power-hungry BMS computer doesn't have to be involved.

I'm still wondering if perhaps the ZS will balance at SOC higher than 93% even when not ready. There is no reason that the car has to have all the cells in series (that's what ready mode is) for balancing to take place. But it just depends on the BMS design. @MilesperkWh, do you happen to know if this is possible and it it actually happens?

Yes, that's right. The cells are usually connected to each other by straps of copper or aluminium, large enough to carry the hundreds of amps needed for full motor current. In addition to this, there are much thinner wires that connect each cell to the BMS. The BMS uses these thin wires to measure each cell's voltage, and also to carry the modest balancing current. For 108 cells, there has to be 109 of these thin wires. So this job is usually broken up into smaller blocks. Probably each module (there are 9 modules with 12 or 24 cells in each) will have a "mini BMS" that looks after that module, and communicates with the BMS computer (ECU? they have different names in different cars) for overall coordination.

I was under the impression it did the 'down' balancing when switched on but going nowhere, as in left in the dealers all night switched on, not when it was being driven.
Please correct if I am wrong

 

[Coulomb]

Would the cells balance on their own if left with the car off, due to them all still being connected or would self balancing require them to be connected in parallel ?

Connecting all 108 cells in parallel would be totally impractical. New cells that are yet to be installed into modules are sometimes connected in parallel though, e.g. with long bars of metal with holes for the screw terminals of the cells. Even this is not terribly successful, and doesn't tend to move charge from one end to the other, because of the resistance of the bars or wires. The equalisation can take days, too, so it's impractical for mass production, only for workshops doing conversions or battery cell replacements.

If I'm right about how the cells balance, i.e. each cell has a bleed resistor that can be placed across it, or not, under mini-BMS control, it doesn't matter how they are connected, so they can stay connected as they are. Each balancing resistor is independent of all the others.

 

[JodyS21]

I don't see why that would be the case.


Those are different computers doing driving and balancing Besides that, computers are pretty good at doing several things at once, using multiple tasks or threads.

But you are right that when driving, the cell voltages will be thrown to the winds by the large traction and even heavy regeneration currents. It's possible that the BMS can compensate for the effect of currents on the cell voltages, by using an estimate of the cell internal resistance, but that would be very approximate, and balancing is a relatively delicate process.

But when coasting or standing still, it might still be able to do some balancing when at a high stagte of charge.

That's probably because you only want to equalise the state of charge when the cells are all nearly full. The capacity of individual cells always varies a little, and the difference between cells increases as the cells age. If you balance at the top (high SOC), then you will be ragged at the bottom (low SOC). Similarly, if you balanced at the bottom (or all the time), then you will be ragged at the top. If the car has an advanced BMS that can actually shuffle energy between cells, then it's good to balance all the time, because then you avoid unnecessary power reduction when just one or two cells get low, and avoid reduced regeneration because one or two cells are full. But my guess is that the balancing is just by "bleeding" resistors, which simply burn off energy from the highest voltage cells, allowing the others to catch up. With that system, it makes no sense to burn off energy in an attempt to equalise the cells; it will just heat up the BMS (and the cells slightly).

The Nissan Leaf is interesting in that it has very gentle balancing (≈10 mA), but balances all the time, even with the car off, 24/7. I'm guessing that the ZS uses more aggressive balancing (say 100 mA), but only when the car is in ready mode. In ready mode, the BMS computer is running (and consuming power). My understanding is that the Leaf balancing is done by the electronics in the BMS that runs all the time, so the power-hungry BMS computer doesn't have to be involved.

I'm still wondering if perhaps the ZS will balance at SOC higher than 93% even when not ready. There is no reason that the car has to have all the cells in series (that's what ready mode is) for balancing to take place. But it just depends on the BMS design. @MilesperkWh, do you happen to know if this is possible and it it actually happens?

Yes, that's right. The cells are usually connected to each other by straps of copper or aluminium, large enough to carry the hundreds of amps needed for full motor current. In addition to this, there are much thinner wires that connect each cell to the BMS. The BMS uses these thin wires to measure each cell's voltage, and also to carry the modest balancing current. For 108 cells, there has to be 109 of these thin wires. So this job is usually broken up into smaller blocks. Probably each module (there are 9 modules with 12 or 24 cells in each) will have a "mini BMS" that looks after that module, and communicates with the BMS computer (ECU? they have different names in different cars) for overall coordination.

Very good info mate.

I'm pretty sure from my reading into different ways batteries can be balanced, it is just using the simple process of a resistor to waste away some power, this makes sense why it can only balance such a small amount each hour etc.

I can't see how it's realistically possible to do this whilst driving the car/draining the battery, as you say whilst "idle" coasting/standing still it could do it - although I guess realistically again it's just not worth doing it for brief periods of time.
Maybe after X minutes of not being under any load, it then kicks in balancing - this would then allow it to balancing when being left in Ready mode.

That makes sense why to only balance when at higher SOC.
There's no point really in balancing at a low SOC as after it is then charged up it could easily be out of balance again.

I'm going to guess that given the car won't even keep the 12V battery topped up when it's left in an off state, there's practically zero chance it's going to self balance when left "off".

Compared to the Leaf, I guess this is where experience comes into it, they've been building EVs for years, Chinese MG are new and that explains why their build is more basic.

 

[Johnberg51]

I was thinking the 1mV per hour, relates to each cell. So each of the cells within the 9 cell packs can have their min/max moved by 1mV per hour.
Remember there are 12 cells in each pack (12*9=108*4.2v=453.6)
So in theory you could move a maximum total of 108mV (0.108V) per hour.

I don’t understand the 9 CMU’s
I know that the MG battery is having 18 modules. (See screenshot Youtube)
Each module is having 6 blocks in serial connected.
Each block is having 6 cells in parallel, good for 110 Ah/4,2V
I guess these cells are the Catl cells, as far as I know prismatic cells which should be the basic component of the battery.
Another option could be is that the 110 Ah blocks are the basic Catl cells which contain 6 subcells in parallel.
Please correct me if you know more about this.
But why there are not 18 CMU’s just one for each module?
The only explanation I have is that each CMU is taking care of two modules.
Typical is that you see a gray and a black module, maybe this two together are forming one couple controlled by one CMU ( all guesses).

Also hard to understand for me is the fact that 100 mV unbalance is allowed. Always thought that for Lion batteries this should not exceed only 10 to 20 mV.
I know in an ebike battery it is not more then 1 to 2 mV.
These are much smaller, but in basic it is the same.