Battery balancing

[EVready]

Thanks @Vince31 & @Alb, that’s very useful … and reassuring.

 

[Deleted member 6309]

Balancing the battery's 90 (Trophy LR) or so cell modules ensures they are all equalised at 100% charge, this will ensure that each single cell is protected from being overcharged at 100% or below min volts when the pack is very low. Sort of resets everything to make sure all the cells stay within limits.
In your case, if you routinely set the max charge to 80% and never charge to 100% then you'll probably never overcharge any of the cells anyway. Then if you don't let the pack drop below 10% then you'll also probably not drain any one cell too low either. But, again in your case, NEVER try to charge to 100% on a DC Rapid charger as your cells are not balanced and the risk of overcharging one/two out of balance cells is now greater, this can cause pernament damage to those cells. If you ever need to charge to 100% then always do it (or the last 20% anyway) on AC fast or granny charger, and if you can then let it balance as well.

You can watch (&hear) DC rapids being throttled back by the car to avoid this issue?

AC fast & grannies charge the battery with DC anyway?

 

[peterseddon]

I've had my car for a year now and have balanced only once albeit I do fit into that 20-80 mould.
SOH is still 100%.

How can you get at your SOH reading? Is this at the dealers on servicing or is there an app with an OBD dongle?

 

[Alb]

I used the Car Scanner App.

 

[Vince31]

You can watch (&hear) DC rapids being throttled back by the car to avoid this issue?

AC fast & grannies charge the battery with DC anyway?

DC Rapids can't balance your battery, they can't measure each cell's voltage, they only know the overall pack voltage; so they can't protect a single cell from over charging.

AC Fast and Granny Chargers supply the car with AC, the car's inbuilt charger converts it to DC. So its only the cars inbuilt charger and BMS that knows each cell's voltage and only they can look after the cells.

 

[Lovemyev]

Balancing the battery's 90 (Trophy LR) or so cell modules ensures they are all equalised at 100% charge, this will ensure that each single cell is protected from being overcharged at 100% or below min volts when the pack is very low. Sort of resets everything to make sure all the cells stay within limits.
In your case, if you routinely set the max charge to 80% and never charge to 100% then you'll probably never overcharge any of the cells anyway. Then if you don't let the pack drop below 10% then you'll also probably not drain any one cell too low either. But, again in your case, NEVER try to charge to 100% on a DC Rapid charger as your cells are not balanced and the risk of overcharging one/two out of balance cells is now greater, this can cause pernament damage to those cells. If you ever need to charge to 100% then always do it (or the last 20% anyway) on AC fast or granny charger, and if you can then let it balance as well.

Good advice !.
If @EVready you intend to charge your LR in that nice sweet spot window, between a low of around 25% and then up back up to 80% SOC, that should be fine.
You are not stressing the pack in anyway.
I know I lot of people will say, that you have all that range and you are not using it !.
But it's not that, you charge to suit your likely usage requirements.
Why charge and balance to 100% if your usage over the next week is local based stuff ?.
When you need to take on that larger trip, then you have the capacity in the pack and then charge accordingly to the 100% mark if needed.
Avoid letting the SOC drop WAY to low on a regular basis, then charging it close to 100% ( without balancing ) on a regular basis, this is not really good practice on a regular basis.
Also charging to 100% and then letting the car sit at that high SOC is not kind to your pack either.
We collected our LR in mid March, we have now covered over 3,000 miles.
I find charging from around 30% SOC back up to 80% SOC will satisfy our usage, for majority of the time.
Remembering that when charging a Gen 2 LR to 80% you are still getting around 210 miles of predicted range, this time of the year.
I have charged to 90% once, in order to make a longer trip.
So, NO - I have not performed a balance cycle yet in the three months and 3,000 miles !.
Am I concerned - NO !.
This was a regular thing on our Gen 1 ZS EV and I could never get it to complete a balance cycle in less than about 3 hours.
Even though it was conducted very frequently.
Longer balance cycles are common on Gen 1 cars who had the BMS update done.
Factory software cars, regularly about 45 mins ( ish ) to about 1.30 max.

 

[Deleted member 6309]

DC Rapids can't balance your battery, they can't measure each cell's voltage, they only know the overall pack voltage; so they can't protect a single cell from over charging.

AC Fast and Granny Chargers supply the car with AC, the car's inbuilt charger converts it to DC. So its only the cars inbuilt charger and BMS that knows each cell's voltage and only they can look after the cells.

I think I'd need to read something official to backup your understanding before I'm going to accept that.

 

[Coulomb]

DC Rapids can't balance your battery, they can't measure each cell's voltage, they only know the overall pack voltage; so they can't protect a single cell from over charging.

They don't need to. A DC rapid charge is orchestrated by the car's BMS. The car's BMS should throttle the charge current back near the end of the charge, so it can detect a single cell heading for over-voltage well in time.

My understanding is that some balancing happens any time that the battery is over about 93% SoC average. So if you occasionally rapid charge to say 95% SoC, then the battery should stay reasonably balanced.

If going to 100% SoC, then AC charging is best, since it takes about 300W to keep the cells at balancing voltage, and a rapid charger likely doesn't want to deal with paltry rates like 0.3kW. Plus, it's a waste of a valuable resource unless no one happens to be waiting. But if you don't need 100%, then balancing might take the SoC from 95% to 94% overnight, but you don't care. Balancing is a slightly lossy process by its nature. I don't believe that rapid charging to high SoC will be dangerous to the battery, just really slow compared to most rapid charging.

 

[Kithmo]

Since this thread has been resurrected, I’m going to take the opportunity to ask a question that’s been bothering me. I am waiting on a facelift LR Trophy ZS but know that I am not going to be able to balance regularly. I live in a third floor flat with no private parking, so just park on the street and there aren’t any nearby public 7kW fast chargers that I’m likely to be able to stop at long enough to charge and balance. I may manage it every few months or so.

My question is whether failure to regularly balance the battery can have a permanent negative impact on the battery health, or would the impact be temporary and fixed next time the battery is fully balanced (appreciating that fully balancing the battery may take longer if not done regularly as per the this thread).

Thanks for any advice on this point!

I don't know about the Gen 2 but the Gen 1 gives you a warning on the dash if the battery needs balancing.

 

[Alb]

As does the MG5 although I don't know of anyone that's ever seen it!

 

[profdraper]

Being an LFP battery on the short range MG ZS EV facelift, surely this does not need balancing at all? (as per recommendations for other LFP EVs, eg, the Atto 3 or the shorter range Teslas). Seems to be differning opions about this, plus whether on not is is recemmended to regularly charge to 100% or not (again, as per convention for other LFP Evs).

 

[Coulomb]

Being an LFP battery on the short range MG ZS EV facelift, surely this does not need balancing at all?

No, LFP cells differ slightly in capacity just like any other chemistry, and require balancing. LFP also has the property that between about 20% and 80-90% SoC the cell voltage changes very little with SoC, so it's usually only possible to balance when nearly empty or nearly full. [ Edit: Unless the imbalance is severe. ]

So it is still important to charge them to 100% once a month or so. Since LFP cells have lower voltage when full, degradation when full is considerably lower than when an NMC cell is full.

I know others will say it's good for the battery to be full all the time, but I still claim that by limiting the time it spends at 100% SoC, it will improve battery life. Whether that extra longevity turns out to be significant or not remains to be seen.

 

[Godard]

If a heater or anything else draws from the 12v battary or the main battery makes no difference to your range. The main battery will charge the 12v battery of it is not full. The seat heating just uses less kw than the AC.