Battery balancing and battery life - fast or slow charging?

[Data]

@Data, I do not think this thread is in the ZS Forum but rather it appears to me to be in the General Chat Forum. I note that the Similar Threads list at the bottom of the page does have a majority of ZS links.

I am confused by the first sentence of your second paragraph. Are you referring to my car's battery, or is it a typo that implies it and you are just making a statement about LFP batteries in general?

Lastly, could you please tell me how, other than seeing the the low battery warning message, that the car has been fully equalised? I will try in September when I'm due to travel over 50 miles in one go.

I thought my profile shows me driving an MG4 with Trophy Mk1 added to my location. Is that not what you see?

@siteguru, the images I posted are not from my car but from posts to the MG4 forum.

Hello Martin, yes I'm sorry. It is of course the General Chat Forum & not the dedicated ZS forum. My bad.

I did actually assume you had the MG4 with the LFP battery pack. Many long range MG's with LFP's have adjustable battery health levels on the infotainment screen, like the MG5. I didn't know they even did an MG4 with an NMC. So I've learned something.

The best way to be sure the car is properly equalising is to watch the car wall charger screen (if you have a screen on yours) to see how the wall charger ends the charge. Or watch the charging app for your wall charger so you can see the amount of power being delivered at 100% soc. It's best to turn off any smart charging you might be using & let your wall charger control everything. That way the smart aspect of your charging won't interrupt the charge. If the battery is equalising the charge should slowly step down bit by bit at 100% until it reaches a level of charge around 0.3kwh, 0.2kwh, holding that charge level for anywhere from 10mins to even an hour or two. If the battery is very unbalanced it might go on for several hours. A friends car balanced for 3hrs when he did his first balance. He realised he'd never done a proper full charge one before, relying on just the little balance that occasionally occured at 80%. The good news was that the car gained an extra 28-30 miles of average range after the equalisation was complete. At least that's what he had calculated.

Your profile doesn't show you have an MG4, just the Trophy trim level. Hope this might help.

 

[siteguru]

@siteguru, the images I posted are not from my car but from posts to the MG4 forum.

Fair point. But your signature says you have an MG4 Trophy - so my NMC comment still stands.

 

[Data]

Fair point. But your signature says you have an MG4 Trophy - so my NMC comment still stands.

Siteguru, where does it say in his profile he has an MG4. I don't see that. It just says he has a MK1 Trophy.

 

[siteguru]

Siteguru, where does it say in his profile he has an MG4. I don't see that. It just says he has a MK1 Trophy.

And his signature under every one of his posts shows:

Are we talking about the same forum member?

 

[Martinonline]

I see that there are 2 ways to access a poster's details, via the header of the post and via the avatar to the left of the post. (Note that with mobile phones this avatar is only visible with the phone in landscape mode.)

I will amend my location details to make them similar to @siteguru's who include their full car details on their location.

I think we have exhausted this discussion but @Data you may like to view the battery discussions on the MG4 forum, particularly by @T1 Terry.

 

[Data]

Ok that explains it. I'm on my phone doing this most of the time in my workshop. Thanks everyone.

 

[decrep]

well that seems to be some of the confusion cleared up, TGFT

 

[Data]

I see that there are 2 ways to access a poster's details, via the header of the post and via the avatar to the left of the post. (Note that with mobile phones this avatar is only visible with the phone in landscape mode.)

I will amend my location details to make them similar to @siteguru's who include their full car details on their location.

I think we have exhausted this discussion but @Data you may like to view the battery discussions on the MG4 forum, particularly by @T1 Terry.

Yes, I see battery discussions are all over the forum. Seems to be quite some confusion in some quarters, especially about battery equalisation. I think this forum is doing a pretty good job of helping to point folks in the right direction.

 

[Corindikev]

There was a discussion on the MG4 forum a year or so back on battery balancing. My MG4 has a 64kWh NMC battery.

At the time a number of posters were adamant that balancing ONLY occurred at 100% charge. The thing is that I'd seen the screen telling me it was balancing at 80% so I decide to experiment & found it balanced at 60%, 70%, 80%, 90% & 100%. In each case when the charge reached the set % the iSmart app showed the battery continuing to charge with the finish time as the current time.

The infotainment screen in the car showed balancing & on that screen & the iSmart app the charge rate continued for a short while at 6.6 kWh then dropped to around 4 kWh & eventually dropped to a trickle which was displayed as 0.0 kWh.

If you just charge to 60% or 80% etc the battery cells will be balanced to that level. As others and experts have pointed out the only way to get a FULL battery cell balance is to charge to 100% & wait till the balancing process is complete.

 

[aleks57]

There was a discussion on the MG4 forum a year or so back on battery balancing. My MG4 has a 64kWh NMC battery.

You have a single-phase power supply installed in your MG4, 6.6 kW is 30A AC. A drop in power consumption to 4 kW, AC current 18 A, shows that the battery charge has exceeded 90%. The higher the voltage on the battery cells, the lower the power consumption. When the maximum voltage of the cells is reached, scanning of the middle points in the groups begins, and the power consumption drops to 0.4 kW. This is how the imbalance of pairs of cells is checked, and balancing begins with a current of 350 - 400 mA, a higher value is not allowed. kWh or Ah is the battery capacity characteristic, and kW or W is the power consumption, these are different electrical parameters. If you want to see the real picture of the battery, install the Car Scanner application, it does not cost much money.

 

[Corindikev]

The single phase inverter/charger in the car will supply a maximum of 6.6 kW DC to the battery. My ZJBeny EVSE reports delivering usually between 29 & 32 Amps to the car depending on the voltage which fluctuates based on the amount of supply and usage from the grid. The legal variation allowed is +10% to -6% of the standard 230 volts meaning it can vary between 216.2 volts to 253 volts.

The drop to 4 kW does not occur before the battery percentage displayed on the infotainment screen or the iSmart app reaches 100% and as I stated the battery continues to receive up to 6.6 kW for a short time after it reaches the set charge limit.

It is only when using fast DC chargers that the BMS slows the current for the last 20% of the battery, that is after getting to the 80% charge point.

The 64 kWh battery can charge at up to 140 kW DC & I have seen 144kW displayed on a 350 kW DC charge point. At one of these chargers if the battery is around 20% it takes less than 20 minutes to top up to 80%.

 

[Martinonline]

And so the discussion continues. If only there were an MG authority posting here. In the absence we must look at what recorded evidence there is and to separate BMS activities, managing charging power leading up to balancing and the balancing activity itself.

@akeks57, please see the two images I posted on page 2. The infotainment screen shows battery balancing at 80% with a power of 4.2kW. (It is an assumption that the car was charging higher than this to begin with as there are no earlier images. I have seen, but not recorded the reduction to ~4kW from ~7kW at the start of balancing at the 80% level.) This change with balancing is below the 90% limit you posted but your statement is probably correct if you are charging the car to 100%. (A few images would be useful showing battery level versus charging power.)

 

[Data]

And so the discussion continues. If only there were an MG authority posting here. In the absence we must look at what recorded evidence there is and to separate BMS activities, managing charging power leading up to balancing and the balancing activity itself.

@akeks57, please see the two images I posted on page 2. The infotainment screen shows battery balancing at 80% with a power of 4.2kW. (It is an assumption that the car was charging higher than this to begin with as there are no earlier images. I have seen, but not recorded the reduction to ~4kW from ~7kW at the start of balancing at the 80% level.) This change with balancing is below the 90% limit you posted but your statement is probably correct if you are charging the car to 100%. (A few images would be useful showing battery level versus charging power.)

To be honest Martin, I don't think we need an MG authority on this as we already have one called 'The manual'. It's very clear on how to do a full & proper equalisation & calibration. It's simple & needs doing. Everything else we have all been chatting about is fairly incidental stuff. But very interesting none the less. I've also learned some stuff too. This is all great stuff.

 

[Martinonline]

I do not disagree with your statement about doing a full equalisation is what is recommended in the manual. And that it leads to the most accurate battery capacity and range prediction.

However in my MG4 manual the word 'calibration' never appears in relation to the HV battery only the word 'equalisation'. The word 'balancing' does not appear in the manual either but only on the infotainment display preceded by the word 'battery'.

Thus we are dealing with semantics here. I propose the following definitions:

Balancing: The BMS activity that seeks to ensure the battery groups are all at the same voltage specified by a battery percentage level.

Calibration: The BMS activity that seeks to record the battery level range and shape of discharge so as to translate that to percentage battery capacity and predicted mileage

Equalisation: The BMS activity starting from a low battery voltage level to a maximum voltage level to ensure the most accurate battery capacity and range prediction. This involves balancing and calibration. It is essential for those cars only DC charged where no balancing occurs.

Thus 'balancing' is not 'equalisation' and thus cannot give the most accurate range and battery level estimates.

 

[Data]

You are right Martin. But I think as you say it's all semantics but to be clear equalisation & balancing are pretty much the same thing. It's only the terminology that's different. You seek to "equalise" the voltage levels of each individual cell. Or, you seek to "balance" the voltage of each individual cell so they are matching. These appear to be the same thing entirely from what I've learned. Going to 100% allows full equalisation of the battery & allows the BMS to know exactly where 'full' is & so it can calibrate much more exactly your predicted range. But actually none of that matters to most of us. We just need to do what it says in the manual from time to time.. Or not...if someone doesn't want to!

We have four electric cars in our family & two of them are over 5yrs old. None of the family pays much attention to their battery packs & everything seems fine. However, my young niece did an equalisation charge on her Kia a couple of months ago for the first time, after which the car did give her quite a bit of extra range. How much exactly I don't know but she was pleased with it. That was on a 5yr old Kia E Niro. Anyway, again it's all very interesting.

 

[Data]

Oh & by the way, the Mk2 MG ZS EV is way ahead of the Kia E-Niro, although slightly less efficient. The MG still gives better range overall. MG more comfortable & better inside too.

 

[Martinonline]

I entered this discussion again to provide evidence to support @Corindikev's post that the reduction in power to ~4 kW was after the set battery level was reached and the battery was balancing and it was not due to the battery level exceeding 90% as @aleks57 posted. And not to continue a balancing vs equalisation debate. I tried to resolve the issue by providing words to describe different aspects of charging but it looks like it will continue. And without me.