Battery charge limit

[Blue20]

I'm a yet-to-be i3 owner.

Can i3 set a charge limit like in Tesla? I understand that Tesla recommends charging battery up to 80% for normal use to slow down battery degradation.

B Class ED's "optional range package" seems to do the same thing.

 

[jadnashuanh]

You can adjust the charging rate, but I've not noticed a level menu choice. I think it all depends on the charging technique and battery technology along with the temperature management. The i3 has both battery heating and cooling capabilities - the Tesla may or may not...I do not know. Batteries do not temperature extremes, andf if you can manage them well, they should last longer.

 

[mindmachine]

I'm a yet-to-be i3 owner.

Can i3 set a charge limit like in Tesla? I understand that Tesla recommends charging battery up to 80% for normal use to slow down battery degradation.

B Class ED's "optional range package" seems to do the same thing.

I believe there was a discussion about that in 2 or 3 places on this site, do a search. If I remember correctly BMW has it set up to prohibit charging the battery to 100%, they reserve space at both ends, I think only using 85% of the battery capacity.

 

[jadnashuanh]

I know they limit how far you can discharge the battery, but had not read about limiting the maximum charge level. I know that it slows down the charge rate as it approaches whatever it deems max, and adjusts based on the temperature of the battery pack. This is one reason why on DC fast charging, they only get to 80% before it slows down significantly...to limit heat and preserve battery life.

 

[fdl1409]

Unfortunately you can`t. I would like to be able to limit SOC to for example 90%. Charging efficiency deteriorates as SOC approaches 100%.

There are a number of reasons why drivers would want to limit the charge:
- efficiency
- better regenerative braking from the start ( reduced when battery is full )
- owners of solar systems on a cloudy day, when PV power is less than charging rate will only want to charge what is needed and wait for a sunnier tomorrow for a full charge
- drivers who have an opportunity to get free power at work or other places. If you need for example 60% of a full charge one way you will charge to 65-70% at home and charge to 100% at work

This is something which I would like to have fixed in a software update.

Frank

 

[RJSATLBA]

Hi, hadn't spotted all the issues around this, in particular the loss of energy recovery from regen if the battery is always charged to 100%, which would affect me as I live within half a mile of a one mile slope with a drop of around 400 feet, so on short local journeys I'd stand to have heavy battery usage on the climb but little or no regen on the descent when leaving home with a full charge.

However, because I have recently installed PV's I was thinking of setting an 'off-peak' charge time at the low charge rate to coincide with my peak generation period, which is mid morning as my PVs face 120. Then I could adjust the length of the charge period through the seasons so my charge is roughly equal to my average daily mileage. This should mean that on average my SOC will have a daily range of about 35% which would fall towards say 15-50 after higher than average usage or rise towars 55-90 after lower than average usage. It should certainly mean that I'm normally not charging to 100% of the level that the battery management allows. Obviously, when I do more miles so my low point is getting too low I'll need to use 'charge now' to recover, just as I'll need to use it if I've been away from home at my set charge time or to get 100% before a longer trip.

I don't have any technical knowledge of battery management other than what I've learned from the forum since Jan and would appreciate any comments on this approach. It may not be as good as having a max SOC setting but it should be a crude surrogate.

 

[lturcotte]

The maximum charge level is 18.8 kWh but the battery capacity is 22 kWh
this mean that the maximum charge level is 85% of the pack

Laurent

 

[Gonville]

The maximum charge level is 18.8 kWh but the battery capacity is 22 kWh
this mean that the maximum charge level is 85% of the pack

Laurent

....or.....it means the battery charge limit is 100% and you can't discharge the bottom 15%? It's a possibility.

I think BMW designed it so that we don't have to have these concerns and that is expressed in a 10 year warranty. From what I am reading we are applying knowledge of existing lithium cells or other EV battery management techniques to a system that we don't know they apply too. Let's hope some clarity comes from manufacturer explanations in due course.

 

[ultraturtle]

The maximum charge level is 18.8 kWh but the battery capacity is 22 kWh
this mean that the maximum charge level is 85% of the pack.

Several sources quote a capacity of 21.6 kWh, making the useable capacity 87% of the total capacity. Perhaps BMW rounds the number, since their spec states "22" rather than "22.0" kWh.