Balance Charging - a few questions

[2Sheds]

A few EV noob questions

I have had my phase 2 Trophy for about 2.5 months now, and as it is owned not leased, I am keen to keep the battery in as good a state of health as I can. With that in mind I have been cycling it between around 20-80% as per recommended practice. The thing is that we aren't doing a lot of mileage, particularly after the first couple of weeks of getting the car, and I've been waiting for a long while now for a charge cycle to fall just before a long run to do a balance charge, so the car doesn't sit around at 100%. Just isn't happening though! As a consequence I haven't yet done a balance charge ?. (It was at 100% when we picked it up though). So far the car has done about 1400 miles, been exclusively charged at home, averaging about once every ten days or so (using Ohme charger, not granny lead) with the exception of one 25% top up at a 50kW rapid. So...I have a few questions:

1) The recommendation is to perform a balance charge once a month. So is this requirement purely a time based thing, or is that just based on an average usage? In other words, is it ok to do it less often if the car is used infrequently/does light mileage?

2). Does it matter what SoC the battery starts off at when doing a balance charge, ie is it ok to do it from 80%, 60%, whatever, or should it be a from low SoC? (I think I read somewhere that the battery should be occasionally charged 10-100%). I ask this so that if we do a longer trip in-between the normal 20-80% routine, I could balance it then, eg if it was at 60%.

3). Am I overthinking this? I am worrying too much about it?!

Thanks in advance.

 

[zAndy1]

So on intelligent octopus how do you schedule these balance charges exactly? Say the battery is on 70% so I have a schedule active to add 30% and plug in, will it just get to 100% and stop and not do the balancing? If so how do you get around that, with an ohme home pro charger? Ta

 

[Jomarkh]

So on intelligent octopus how do you schedule these balance charges exactly? Say the battery is on 70% so I have a schedule active to add 30% and plug in, will it just get to 100% and stop and not do the balancing? If so how do you get around that, with an ohme home pro charger? Ta

Put the percentage to add to 80% that should do it.

 

[MGFour]

Yeah if you set your charge to more than required the car will get to 100% and then start to balance as long as power is supplied, so like above request far more in the ohme app to ensure it gives it time to do its magic

 

[EVentropy]

Greetings,
First post on purchase of MG4 LFP.
Really am having fun with the car after 50yrs+ of ICE's.
I went LFP as was familar. I DIY installed 6KWh of LiFePO4 in my boat, for house bank,4S2P
with 2x bms's a couple of years ago and caught the bug. Audible alerts only-KIS.
Dismayed that the MG4 doesnt have readily available parameter checks as does my cheap
JBD bms's. Such as individual cell monitoring with deltas etc. Ismart is very mundane imo.
i can see why, but a basic info system like Leafspy would be nice. Funny how the Nissan dealerships go vague when you ask permission to scan NZ new vehicles! Definitely cagey on their API, as much as trying to keep it secret it didn't work.

As for charging, I stay at crest of "knee" (90%), and will do a balance (100%) periodically until I learn to contrary.

Does the SAIC API open source provide info at a cellular level in real time? Not keen on HA just for this. Bit much to implement for this luddite. Car scanner pro just gave me mostly garbage. OVMS doesn't do MG4. Woe, I need to know! Maybe not need, just want.

 

[Corindikev]

LFP batteries can be charged to 100% all the time. When you set the parameter in iSmart or on the car to charge to a specific % then the car will perform a balance charge when it reaches that level. Depending on when the last one was done it can take from 10 to 40 minutes (on the 64kWh NMC) to complete the balance. This is with a slow EVSE charger. Power input at the beginning of the balance can still be 7.4kW AC (6.6kW after DC conversion) for a short period then input drops eventually to almost zero once balancing is almost complete.

Given there are over 400 cells to monitor MG do not provide individual cell data either in the car or on the app. You may be able to extract this if you have an OBD2 scanner

 

[EVentropy]

AFAIK,
There are studies of % max charge Vs number of cycles to "X"% SOH degradation that prove you get more cycles if you keep out of the "knee" as much as possible. The knee is where lithium plating starts to occur. Exactly where and to what level has not been explored.
Of course you can charge to 100% all the time, but be aware of the loss of cycles.
You really buy your vehicles capacity and chemistry to suit the use. Max 80-90% suits our use.

As LiFePO4 lose cycles/capacity siting at 100% not being used, we switch alternator off on motor to marina to avoid this and leave loads on (fridge- ever cold beer) to avoid leaving at high SOC for extended periods. WRT balance charge, after the "knee" we do not charge past 0.02C tail current. I acknowledge power output for stationary battery less is much less with probably <1% duty cycle at >1kW. Still we pamper them as much as poss.
I'm not overly paranoid , I just prefer to get the most out of my purchase.
I guess horses for courses.
Interesting the balance power input you noted as I haven't done one yet.
I thought the MG4 was 104S 1P. So There must be 4 cells in each "module" hence 104S?

TBH, I am used to BMS printout and the CALB 3.2V nominal cells. I need to do some cycles
with total HV at 100% , HV rested at 100% and HV at 10% to get a handle on the EV. Also do a capacity test. I'm guessing cell voltage will be ~3.4x V rested. (100%)

 

[Corindikev]

CATL have considerable faith in their batteries. When the MG4 was released with a 7 year unlimited km battery warranty the company was asked what did they think the expected life would be. Their response was probably around 1 million km.

Just a few weeks ago SAIC have announced a 1 million km warranty on all MG 4s produced in Thailand and this warranty extends to all the previous vehicles sold before the announcement. This warranty has apparently been in place in the Chinese domestic market for a while. It is believed this will extend to other markets as well. We will just have to wait and see. As far as I know it covers both NMC & LFP batteries

This shows the confidence they and CATL have in their batteries and management software. I imagine the warranty has plenty of conditions like ensuring balancing is done regularly etc

The Tesla high mileage club has shown that even older EVs with earlier technology can get phenomenal mileage out of one battery some doing over 1 million miles (1.6 million km).

A bloke in Australia had 666,666 km on his 2018 Tesla model X and got a message on the screen to say the battery had lost x amount of capacity. Whether it had or not didn't matter. He got on to Tesla & they swapped it for a new one under warranty. He'd never bothered about slow charging or battery balancing using a lot of super chargers as well as his home AC EVSE with no regime at all. The Everything Electric show has a video with the interview on Youtube.

The takeaway from this is that while it is probably a good idea to use battery management techniques it doesn't seem to matter much if you don't.

 

[barry7153]

I am about to change to an EDF off peak EV tariff and therefore intend charging my MG Trophy whilst I am in bed. What I would like to know is, is there is any simple way of finding out post charge, whether the battery achieved balance/equalization or when it last took place? I did read above that the car will display a message when it needs to be done, but wonder what that is based on and whether that can be reliably used to decide when to do a monitored slow charge (80/100% - still confused on that) to see the process displayed in the car so to be certain, as all current info suggests this is necessary to prolong battery health.

 

[Corindikev]

If the only charging you do is on DC fast or super chargers then the battery cells never get balanced. When the cell voltage variance gets to a specific level then you will get the message to balance the battery. This can only be done using AC slow chargers i.e 11kW 3 phase or 7.4 kW single phase input or less.

If you set the battery charge level to a maximum of 80% as soon as the battery reaches 80% it will go into balance (or equalisation) mode. If you are monitoring charging via the iSmart app, the display will show the battery 80% charged and the finish time is the current time. For a short period the DC input to the battery will remain at around 6.6 kW (assuming you have a single phase EVSE capable of delivering 32 amps at 230 volts, 7.36 kW). Then the delivery current will slow eventually to only a few watts before the battery balance (battery equalisation) is complete.

During the balancing process the battery display on the car infotainment screen will say "Balancing". Prior to that it displays "Charging".

So whenever you use your home AC EVSE or granny charger and set the maximum charge to 80% or 90% or 100% the battery will be balanced automatically every time unless you interrupt it and finish charging manually.. It may actually balance the battery at lower settings but I have not checked that.

So there is no way post charging to find out if balancing has been carried out as it is done automatically. If you have a histogram of the delivery power from you EVSE or an OBD2 data collection device providing this information in some digital or graphical format, then that can be displayed later.

 

[Coulomb]

If you set the battery charge level to a maximum of 80% as soon as the battery reaches 80% it will go into balance (or equalisation) mode.

I'm not sure that's true. I have heard that on my ZS Mark 1, balancing only happens at 93% SoC or above.

After all, that's why you are supposed to charge to 100% every 4-6 weeks, if you have an NMC battery.

 

[PeteC]

I'm not sure that's true. I have heard that on my ZS Mark 1, balancing only happens at 93% SoC or above.

After all, that's why you are supposed to charge to 100% every 4-6 weeks, if you have an NMC battery.

My Trophy certainly behaves as if it's balancing at 80%. The charging continues once 80% is reached and drops to a very low, but not zero, input. It also keeps updating the finish time to the current time and then it eventually stops charging. So it behaves just as it does balancing at 100%. But I have no idea what sort of a balance it can do at 80%.

 

[Martinonline]

@GrayCat reported at post#81 on page 5 of the thread MG4 Balancing/Equalisation a photo of the screen showing balancing at 90%.

 

[wattmatters]

Does the SAIC API open source provide info at a cellular level in real time?

With the SAIC API you will get pack voltage. With an OBD you will get min, max (and hence cell voltage delta). There is no individual cell data provided. And that's fair enough given the nature of the battery pack. It's just not consumer level data.

Sample of some of the data from the SAIC API in Home Assistant:

The API data is not real time - it is taking periodic snapshot of status, the frequency of snapshots varies depending on what the car is doing. When driving it's about every minute, when parked/off then after a while it stops polling. When charging it's up to the HA software integration to decide on polling interval (it varies depending on charge rate).

OBD does provide real time data, although I probably needed to leave it connected for a bit longer to populate all the fields:

I don't use it much, been months since I plugged it in to have a look.

If you set the battery charge level to a maximum of 80% as soon as the battery reaches 80% it will go into balance (or equalisation) mode.

I think that's an NMC only thing as the balancing logic for NMC is different than for LFP. It's to do with the significantly different charge curves (voltage v SOC) for NMC and LFP. In any case the LFP models do not provide the ability to set a SOC limit on charging.

NMC has a near linear charge curve while LFP is very flat (very little voltage rise between 10% to 90% SOC). LFP cell voltages don't rise quickly until above 95+% SOC.

As a result LFP cell voltage differences are not really apparent until you are at a high SOC. With NMC they are still apparent at lower SOC levels and so NMC balancing can be done at lower SOCs such as at 80%.

With LFP (good) balance logic waits until cell voltages are above ~3.45 V or more before balancing. "Balancing" at too low a SOC (e.g. 80%) with LFP can actually result in cell imbalances at higher SOC. In an EV application it shouldn't matter all that much as the cells should be very well matched, but it may become more of an issue as the pack ages.

 

[wattmatters]

I am about to change to an EDF off peak EV tariff and therefore intend charging my MG Trophy whilst I am in bed. What I would like to know is, is there is any simple way of finding out post charge, whether the battery achieved balance/equalization or when it last took place?

The only way to know is by monitoring the power draw of your charger. It will drop from the normal charge rate (which depends on your charger, might be anywhere from 1.3 kW to 6.6 kW or even 11 kW for the 3-phase model) to a very low level around 50-100W for a while (perhaps 5-10 minutes) before ceasing charge altogether.

Here's when I last charged mine to 100% SOC (mine is 64 kWh NMC battery):

Can see right before 100% SOC was reached the charge rate slowed down for a few minutes then dropped right down to hover between ~30 W and ~140 W for about 7-8 minutes before ceasing entirely.

For reference up to the above full charge it had been 74 days since my car had last received a 100% charge.

If the car absolutely needs a balance/recalibration it will tell you and you'll need to charge up using an AC charger. It would be unusual for that to happen unless it is never charged to 100% (for LFP) and/or most charging is done with DC fast chargers.

 

[EVentropy]

Excellent- Thanks WM.
I get the consumer level thing, but my exposure to LFP has been DIY with A grade cells and deciding to what level BMS polling and comms, all easily configurable via BT and RS485 I wanted for stationary battery led me to expect it would be possible with the MG4 with a bit of research.

I realise the difference between 4S 2P and 104S 1P, but the wires are there for cell balancing so should it not just take the right PID to access via API with something like Car Scanner? Leafspy has cracked the Nissan API, to this level, on a supposed 96S 1P. I nearly went Nissan but baulked on NMC uncooled and my average use of climbing 1200' then back down 2x every trip.

I used an LELink OBD and carscanner on MG4 but readings were mostly nonsense. Perhaps I should try with the OBDLink mx+, but I think I'm clutchin at $300 straws here.

Balancing at above the "knee" and shy of HVD (high voltage disconnect ) is pretty fundamental to LFP chemistry, as you and other have pointed out.
Could someone give me the pack voltage of the 51 kWh at 100%, unrested and rested please?
Nothing like real world numbers!
Perhaps I should go read the manual. Haha!

 

[wattmatters]

I get the consumer level thing, but my exposure to LFP has been DIY with A grade cells and deciding to what level BMS polling and comms, all easily configurable via BT and RS485 I wanted for stationary battery led me to expect it would be possible with the MG4 with a bit of research.

It might be but you would be one of a very few interested in such application.

The cycling of an EV battery is different to a stationary battery. Not many EV batteries are cycled between a low and high SOC on a regular daily basis and the charge rate is typically lower (~0.1 C or lower, except for occasional DC fast charging) while stationary applications tend to cycle much more and settle on ~0.2 C for charging, although some drive them harder up to 0.5 C.

The battery pack will outlast the car.

I thought about doing a DIY LFP pack for home but the server rack units I use were already cheap enough. I can view the 16S cell voltage data on their displays while my Home Assistant tracks min, max and cell delta for each unit, e.g.:

Could someone give me the pack voltage of the 51Kwh at 100%, unrested and rested please?
Nothing like real world numbers!

It would be interesting to know how the LFP pack voltage responds to charging to 100%. Can at least see what average cell voltage they are using. Should be something in the range of 3.6 V/cell I'd expect.

My NMC pack peaked at 441 V the other day when charged to 100%.
441/104 = 4.24 V/cell.

4.20-4.25 V is the typical upper charge voltage for NMC depending on cell brand.

MG4 pack details:

 

[Coulomb]

My Trophy certainly behaves as if it's balancing at 80%. The charging continues once 80% is reached and drops to a very low, but not zero, input. It also keeps updating the finish time to the current time and then it eventually stops charging. So it behaves just as it does balancing at 100%.

I sit corrected! ?

But I have no idea what sort of a balance it can do at 80%.

NMC has a pretty wide voltage range, with no really flat spots. So balancing at 80% would be pretty effective, I think. So the recommendation to charge to 100% every 4-6 weeks must be for fine tuning at the top end, and/or evaluating state of health.

Interesting, thanks!

I'm guessing that my Mark 1 ZS EV can't do this because it doesn't have a charge-to-80% option at all. I'd be open to a firmware/software update that did this. But I'm sure that SAIC aren't interested in such a non-trivial update for such an old (in EV terms!) model.

 

[EVentropy]

Sterling stuff! Probably migrate to NMC 64kWh in future. Wet the feet with the 51kWh.
Thankyou again! Starting to become familiar. 379.6/104= 3.65V which is the HVD default
in BMS's for boat LFP. Low end 260/104=2.5V.........My LVD is set at 3V/cell so I don't go lower
than 12V. (3V x 4S). ($10k of electronics at stake) One day I will install the DC-DC to protect them and set it lower ~2.8V)
More important things to fix atm- as in coffee machine thermal switch!

 

[Corindikev]

My 64 kWh NMC battery balances every time it gets to the 80% limit I set & at 90% or 100%. I can set the charging stop % in 10% increments & set it recently to 50% as it was low at about 20% & I just wanted it to charge while I had free power. It was at 50% & had stopped charging when I disconnected the charger. I don't know whether any balancing was done & at that level there is not much point in doing so but I'd like to find out what the lowest SOC set level balancing is carried out.

I'll experiment a bit & advise.

 

[barry7153]

The only way to know is by monitoring the power draw of your charger. It will drop from the normal charge rate (which depends on your charger, might be anywhere from 1.3 kW to 6.6 kW or even 11 kW for the 3-phase model) to a very low level around 50-100W for a while (perhaps 5-10 minutes) before ceasing charge altogether.

Here's when I last charged mine to 100% SOC (mine is 64 kWh NMC battery):

View attachment 28163

Can see right before 100% SOC was reached the charge rate slowed down for a few minutes then dropped right down to hover between ~30 W and ~140 W for about 7-8 minutes before ceasing entirely.

For reference up to the above full charge it had been 74 days since my car had last received a 100% charge.

If the car absolutely needs a balance/recalibration it will tell you and you'll need to charge up using an AC charger. It would be unusual for that to happen unless it is never charged to 100% (for LFP) and/or most charging is done with DC fast chargers.

Thanks for that. I have scheduled a charge between 0002 and 0458 this morning and wonder if that information will still be available 4 hours later when I get up to check.