I know that 100% battery and KERS is impossible, but...

I charged my pre-Facelift MG5 Exclusive, LR, overnight (last night) and this morning, when I disconnected it from my EVSE the charge level meter showed, as expected, 100%. (When the charge was first started the meter showed less than 20% battery remaining.)

In Eco mode and KERS3 I drove the car, literally 300 yards from my house and encountered yet another set of "roadworks" and traffic lights on a quite narrow road. I released the accelerator, fully expecting to have to immediately move to the break, but KERS kicked in and slowed the car. This was confirmed by the Power Consumption meter which registered almost the maximum battery input that the meter can show! And the battery level meter still showed 100%.

That would suggest that the battery level meter is "wrong" I think and the battery was not, actually, at 100%, even though charging had actually been stopped by the car some hours earlier and my ev.energy app seems to suggest that battery balancing had occurred. Or had it?

The GOM showed approx. 240 miles of range at "100%" so pretty much as expected.

I've attached below the "Statistics" page from my ev.energy app of this specific "charging event". I'm not sure whether it shows anything relevant, but I would like to hear the collective wisdom of forum users on this.

Thank you.

What probably happened is that the BMS did indeed do a battery balance at the end of the charge session. I see the same thing every so often and worried about it at first, seeming to drive for miles before the meter drops below 100%. Might be that a balance charge fills every cell including the "extra" hidden cells.

Thanks for that reply.

I agree the balancing almost certainly did take place; what intrigued me was why KERS was "active" even with 100% battery charge?

Interestingly, I've just been out in the car again. When we left home the battery was 98% and KERS did not operate.

Another of Life's MG Mysteries!

Regen is still present at 100% SOC but of course, it is reduced in its intensity.
There is a head / buffer at both the top and bottom of the pack, that can not be accessed, but still exists never the less.

As there were temporary traffic lights (presumably) in the road, could it have been the collision avoidance system applying the brakes?

5teep said:

What probably happened is that the BMS did indeed do a battery balance at the end of the charge session. I see the same thing every so often and worried about it at first, seeming to drive for miles before the meter drops below 100%. Might be that a balance charge fills every cell including the "extra" hidden cells.

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Not 100% if this also applies to the MG5 but usually in an EV charging stops once a cell reaches it’s upper limit as defined by the BMS, it is correct that there is additional capacity to go further but to extend battery life this upper buffer isn’t used (there is no ‘hidden’ cells)

The balancing function then compares all cell voltages and usually drains the high ones to match the lowest one as this is the easiest (cheapest) way to achieve equilibrium. The greater the imbalance the longer it takes for the process to complete.

To get back to the topic at hand, it’s technically possible to regen even with 100% SOC, but the BMS usually prevents this as you experienced @98% SOC, I gather you need to be below 95% for it to become active again, therefore you’re probably right ‘another MG mystery’

Of the 47kWh indicated by the wall charger about 90% go into the battery, let’s say 42kWh (80%) would translate into a total capacity of about 53kWh, which is probably OK given the current night time temperatures.

Lovemyev said:

Regen is still present at 100% SOC but of course, it is reduced in its intensity.

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Understood, but what completely surprised me was that the Power Consumption meter displayed, briefly, at its maximum negative level!

Verdigris said:

As there were temporary traffic lights (presumably) in the road, could it have been the collision avoidance system applying the brakes?

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I don't think so. Previous experience of that system in operation suggests it emits warning beeps and a message on the driver's screen. Neither occurred.

MickeySw said:

To get back to the topic at hand, it’s technically possible to regen even with 100% SOC, but the BMS usually prevents this as you experienced @98% SOC, I gather you need to be below 95% for it to become active again, therefore you’re probably right ‘another MG mystery’

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Agreed!

emmrecs said:

Understood, but what completely surprised me was that the Power Consumption meter displayed, briefly, at its maximum negative level!

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A question, just because the motor is regenning as per the meter does that necessarily mean that the energy is actually going to the battery ?

emmrecs said:

I've attached below the "Statistics" page from my ev.energy app of this specific "charging event". I'm not sure whether it shows anything relevant, but I would like to hear the collective wisdom of forum users on this.

View attachment 25418

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I use this app too and have decided that there is absolutely no indication of whether a balance has happened or not. If anything I would say it suggests it hasn't, although as mentioned I don't think it says anything at all.
In the last half an hour it has used just over 3kWh. On full blast as per the previous half hours it consumes 3.5 kWh so what does this tell us.....bugger all. Did it stop because it hit 100% or did it balance. Balancing usually consumes about 300 watts so it certainly wasn't balancing for that whole last half hour (0.15 kWh), maybe the last 2 or 3 mins but it's not possible to tell from that information.
This is my dilemma too, I have no idea whether my car balances or not and if so for how long. I don't have an IHD (In home device) and certainly wouldn't get up at 4am to monitor it if I did have one.

Gomev said:

A question, just because the motor is regenning as per the meter does that necessarily mean that the energy is actually going to the battery ?

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Good question! I have no idea!

Gomev said:

This is my dilemma too, I have no idea whether my car balances or not and if so for how long. I don't have an IHD (In home device) and certainly wouldn't get up at 4am to monitor it if I did have one.

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I do have an IHD but ditto to getting up at 4am!

Following on from your comment, I wonder whether there is any way to confirm, or otherwise, whether balancing has occurred? My available range has remained around the same (according to the GOM, weather-dependent, of course!).

I think I need to investigate more closely with my OBD2 dongle and Car Scanner Pro whether anything in its data would indicate balancing is happening, or not.

emmrecs said:

Good question! I have no idea!



I do have an IHD but ditto to getting up at 4am!

Following on from your comment, I wonder whether there is any way to confirm, or otherwise, whether balancing has occurred? My available range has remained around the same (according to the GOM, weather-dependent, of course!).

I think I need to investigate more closely with my OBD2 dongle and Car Scanner Pro whether anything in its data would indicate balancing is happening, or not.

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With an OBD you will be able to see the individual cell pack's voltages. If they are all the same, highest/lowest then they are balanced.

I wanted to try and catch our ZS EV ( Gen2 ) performing a balance cycle at 80% SOC - as some owners had said that their MG4 did balance below 100% mark.
So, I decided to charged our ZS LR to 70% SOC on the cheap off peak rate, then the following morning, I reset the charge level upto 80% and put the car back on charge.
I monitored the charging progress every couple of minutes, via our home energy meter.
The car continued to pull a full 7 kW right up until it hit the preset 90% SOC and then stopped charging.
It displayed no evidence that it had performed any balancing on this occasion.
Conclusion, either the ZS EV ( Gen 2 ) only performs a balance cycle when the the pack is 100% or no balancing was required ?.
My gut reaction is that the Gen2 LR follows the same pattern as the original Gen1 ZS EV with the NMC chemistry and only performs a balance after the pack has reached 100%.

I don't know about the balancing, but my understanding of the KERS is that level 3 is ineffective when you're 95% and above, as it has nowhere to go. What I find on mine is it feels like level 2 for the first 5%, then the level 3 kicks in after that. So you will always get some KERS effect, but not as much until it has somewhere to go.

rjb1970 said:

my understanding of the KERS is that level 3 is ineffective when you're 95% and above, as it has nowhere to go

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I agree, but that is exactly what did NOT happen in the situation of my original post.

I was on KERS 3, the Power Meter showed the battery was on 100% but KERS activated and the Power Consumption meter went as far negative as it its scale allows!

I was just watching a technical video on home batteries that may shed some light. When a battery, or stack of batteries, is charging, if just one cell reaches the maximum voltage cut-off value then charging will stop and the SOC will show as 100%, even though the SOC meter was showing, say, 94% just prior to the shut-off. That could possibly leave enough headroom for KERS to be operational, in the case of an EV battery.

Verdigris said:

I was just watching a technical video on home batteries that may shed some light. When a battery, or stack of batteries, is charging, if just one cell reaches the maximum voltage cut-off value then charging will stop and the SOC will show as 100%, even though the SOC meter was showing, say, 94% just prior to the shut-off. That could possibly leave enough headroom for KERS to be operational, in the case of an EV battery.

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Yes, that is generally how home storage batteries work, but not EVs.

I actually had an issue with my old EV where one cell was significantly higher than the rest and therefore stopped the charging process; as a result the battery never reached 100%.

It’s also very unlikely that the cell balancing is so far off to make such a significant difference.

It also makes most sense for the EV-ECU to use SoC to enable KERS