Set a maximum charge limit

[alohart]

On a Chech forum they wrote that the max. voltage of the 60 Ah battery is 392 V while the 120 Ah battery is 402 V. The 60 Ah i3 software didn't accept the higher voltage of the replacement battery (120 Ah) as such.

The maximum battery pack voltage on BMW's TIS Website:
60 Ah: 395 V
94 Ah: 398 V
120 Ah: 403 V

No EV manufacturer would allow its battery pack to charge to its absolute maximum voltage unless it supports limiting the top charge level when charging (e.g., Tesla). To do so would result in cell degradation that would make warranty replacement of many battery packs likely. The BMS limits the top charge level on all i3 battery packs.

 

[Arm]

You can limit the charge to 80% via the app but it'll have to be done manually. Rule of thumb...every 1% battery charge takes around 2.8 minutes on a 7.2 kWh charge rate for the 94aH pack.

Where can you set a charge limit of 80%?

Do you have a screenshot?

No you don't set it. You check the charge state via the app as you're charging and stop the charging from changing from "charge immediately" to "set departure time" and make sure you set the start time to a time where you'll unplug your car before it begins to charge again.

 

[Star63]

The BMS limits the top charge level on all i3 battery packs.

But more so on 60 Ah packs? (Compared to 120 Ah)

 

[Hacky]

No EV manufacturer would allow its battery pack to charge to its absolute maximum voltage unless it supports limiting the top charge level when charging (e.g., Tesla). To do so would result in cell degradation that would make warranty replacement of many battery packs likely. The BMS limits the top charge level on all i3 battery packs.

Of course there must be a maximum voltage limit and it depends on the chemistry. The question here was, if the i3 also leaves some buffer at the top. As you can see from the discussion, the i3 charges the batteries up to the maximum voltage given in the battery specs from Samsung SDI. So they are not overcharged but for me it means, there is also no buffer left on the top end of the voltage range. This is stress for the battery and especially when it is left in this state over longer periods, this is not good for LiIon cells. The whole "buffer" seems to be left only at the lower end of the voltage range.

So this means, the strategy to charge only up to 80% or 90% (as long as you do not plan a longer trip) will be more gentle and it is a pity that BMW never added a feature to set this as the charging target, although their hardware provides all what would be required.

 

[websterize]

So this means, the strategy to charge only up to 80% or 90% (as long as you do not plan a longer trip) will be more gentle and it is a pity that BMW never added a feature to set this as the charging target, although their hardware provides all what would be required.

Interestingly, BMW has enabled a charging target — and specific guidance on extending the service life — of the high-voltage pack of its new flagship electric vehicle, the iX.

From the back of its U.S. owner's manual (highlight mine):

 

[eNate]

Interestingly, BMW has enabled a charging target — and specific guidance on extending the service life — of the high-voltage pack of its new flagship electric vehicle, the iX.

Not only that, they have provided the owner the means to set the charging current as well (not just Max / Reduced / Min). So, for instance, I could opt to charge at a leisurely 16A or 24A while plugged in to my 40A EVSE, a feature which is available through some "smart" EVSEs, but not via the i3 directly.

 

[Darlouis]

BMW might recommend charging the iX to 80% but do we know how the battery chemistry compares and how it balances the cells vs the i3? The i3 only balances cells at a high state of charge and when plugged in I think, so charging to to only 80% I don't think will allow that process to complete fully.

Slightly off topic, has anyone tried the Electrified app with a 120AH i3? Mine is showing a max capacity of 123.5AH and 3% battery degradation(SOH 97%) which I think is actually +3%, as there's a 2.9% difference between 120 and 123.5 . Interestingly the car through the Unlock menu shows a usable capacity of 38.8 too (isn't this supposed to be 37.9?).
I'm assuming 120AH is the equivalent of 42.3 rather than the usable capacity.

 

[alohart]

The i3 only balances cells at a high state of charge and when plugged in I think, so charging to to only 80% I don't think will allow that process to complete fully

Since 2014, I've routinely charged to a displayed 80% - 90% except when I might need full range. The mi3 app shows that the charge level balance among the 96 battery cells is excellent as indicated by the tiny difference between the minimum and maximum cell voltages at full charge of only 0.003 - 0.004 V. The BMS implements passive cell balancing that occurs whenever no power is flowing into or out of the battery pack, so it doesn't occur when charging is active and doesn't require an EVSE to be plugged in.

 

[Darlouis]

Since 2014, I've routinely charged to a displayed 80% - 90% except when I might need full range. The mi3 app shows that the charge level balance among the 96 battery cells is excellent as indicated by the tiny difference between the minimum and maximum cell voltages at full charge of only 0.003 - 0.004 V. The BMS implements passive cell balancing that occurs whenever no power is flowing into or out of the battery pack, so it doesn't occur when charging is active and doesn't require an EVSE to be plugged in.

Thanks for the info. It's difficult to find the correct detail rather than opinions although I might have misunderstood some info found elsewhere. Good to see a long term owner. I'm planning to keep mine a long time too so might change my charging habits to only charge to 100% when a fully charged battery might be required. I have a smart charger but only used it in dumb mode so far.