Is this SoH OK?

[wattmatters]

The MG owners manual isn't written for people to easily understand this process

It's not written for technical people either. It's full of translated information that is sometimes inconsistent.

It says that in our MG manuals (for the ZS page 9)

The MG4 manual is pretty ambiguous about the need for a (near) full discharge prior to an equalisation charge.

It just says a "full slow charge" is required, which can simply mean charging the car to full.

Further in it gives expected charge duration for slow charging which includes an equalisation charge at the end, but again it does not explicitly state that prior deep discharge is required for equalisation to occur.

 

[Data]

Yes, the ZS manual is similar although does mention iirc taking the soc down to just below the low battery warning to do a full & proper equalisation. On my NMC 72.6KWH battery that usually happens at 20% soc. Anyway for clarification I went to my dealer & MG technical who told me to get the low battery warning then charge slowly non stop & let the BMS control the charge all the way to 100%. And don't interrupt it or it won't fully equalise.

 

[Everest]

My point being that very few people actually get issues with batteries. It is clear "it works ok" might be a better way of putting it. We know active balancing is better, but not really needed.

Agree - passive balancing works OK. And is probably safer in a (relatively) hostile environment like an EV. Active balancer can, and do, fail. When that failure happens due to poor connections and under-reading of a cell's voltage they can pump too much energy into a cell and cause over-voltage / bloating issues. The mode of failure is not possible with a passive balancer.

 

[MickeySw]

View attachment 44699

First of all thanks for sharing 'real life data', am I correct in assuming you used a granny EVSE with the aim to balance the cells? Did you by any chance check the result min/max cell voltages aferwards?

I would be grateful if some of the 'gurus' can help me understand what I'm seeing:

- for starters let's assume that there are no losses and all the energy goes into the HV battery (400DC @100%SoC, 200Ah cell capacity).

• as long as SoC is below 100% the current into the battery is about 3.75A
• however after being 'fully charged' 3.75A is still 'flowing' for another 35min (2.2Ah)
• the current then sharply drops to about 0.6A afterwards for approx 25min (0.25Ah)
• the remaining 2.5h (balancing?) are averaging around 125mA (0.3Ah)

What triggers the initial current reduction:
a) the highest reported voltage cell is reaching cut-off voltage
b) the highest reported voltage cell is getting close to reaching cut-off voltage
c)?

At what stage are the parallel bleeding resistors (post #127) activated?
a) after SoC 100%
b) after 1st current drop
c) during the 2.5h (balancing) section
d)?

Assuming that to increase the cell voltage by 1mV, approx 150mAh of energy is required, there doesn't seem to be any scope to significantly 'lift' low reading cells during the balancing phase?