WhiteRexNJ
Posts: 6
Joined: Sat Mar 27, 2021 9:24 pm

Set a maximum charge limit

Sat Mar 27, 2021 9:27 pm

Its not in the default menu, is it possible to do it with the bimmercode app?

eNate
Posts: 755
Joined: Mon Sep 09, 2019 5:33 pm

Re: Set a maximum charge limit

Sat Mar 27, 2021 10:18 pm

Unfortunately, no. Any early cut-off has to be done externally.
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EvanstonI3
Posts: 64
Joined: Tue Nov 03, 2020 9:11 pm

Re: Set a maximum charge limit

Sun Mar 28, 2021 6:38 am

Not this again. This is not a Tesla. There is a Battery Management System that prevents us from "fully" charging or discharging the battery. About 10% of the capacity is held back as a buffer for this.
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eNate
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Re: Set a maximum charge limit

Sun Mar 28, 2021 9:08 am

That wasn't his question, and you're wrong.
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WhiteRexNJ
Posts: 6
Joined: Sat Mar 27, 2021 9:24 pm

Re: Set a maximum charge limit

Sun Mar 28, 2021 12:50 pm

EvanstonI3 wrote:
Sun Mar 28, 2021 6:38 am
Not this again. This is not a Tesla. There is a Battery Management System that prevents us from "fully" charging or discharging the battery. About 10% of the capacity is held back as a buffer for this.
Are you sure about that? I have read a bunch on this and it seems to be still widely debated. I haven't seen anything from BMW saying that they dont allow the battery to charge fully. I previously had a volt, and not only did chevy tell us that you cannot charge the car to 100%, but with the volt equivalent of bimmercode I could actually see (and edit) the buffer.

alohart
Posts: 2424
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: Set a maximum charge limit

Sun Mar 28, 2021 1:25 pm

WhiteRexNJ wrote:
Sun Mar 28, 2021 12:50 pm
I have read a bunch on this and it seems to be still widely debated. I haven't seen anything from BMW saying that they dont allow the battery to charge fully. I previously had a volt, and not only did chevy tell us that you cannot charge the car to 100%, but with the volt equivalent of bimmercode I could actually see (and edit) the buffer.
All BMW i3 battery packs have gross and usable capacities (e.g., the 60 Ah battery pack has a gross capacity of 21.6 kWh and a usable capacity of 18.8 kWh). The difference between gross and usable capacity is the unusable buffer capacity divided between low and high charge levels (i.e., no i3 battery pack can be charged to its absolute full capacity nor discharged fully). This among many other things is discussed in David Bricknell's excellent Electric Vehicles and the BMW i3 - 60, 94 and 120Ah.

Not all BMW system software is parameterized such that its behavior can be changed by changing the values of parameters (a.k.a., coding). The number of parameters that BimmerCode can access is large with most of them undocumented and many of them applicable to BMW models other than the i3. Changing the unusable buffer sizes might be possible with BimmerCode, but I'm not aware of anyone posting how this could be done.

The proprietary BMW ISTA+ service software can display current unusable buffer sizes but can't change them AFAIK. ISTA+ shows that these buffer sizes are dynamically changed over time by the battery management system (BMS). That makes determining whether a loss of actual range is due to battery cell degradation, the BMS increasing the unusable buffer sizes, or both. I'm surprised that the Volt's unusable buffer sizes can be changed by an owner because doing so could affect the battery cell degradation rate and thus could impact the battery capacity warranty.
Aloha,
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EvanstonI3
Posts: 64
Joined: Tue Nov 03, 2020 9:11 pm

Re: Set a maximum charge limit

Sun Mar 28, 2021 1:35 pm

eNate wrote:
Sun Mar 28, 2021 9:08 am
That wasn't his question, and you're wrong.
That is true about his question but I foresaw where he was going with it.
If I am wrong, what is it I am wrong about? Seriously.

On a 2017, the battery capacity is rated at 33kwh
Of that, BMW advertised that only 27.2 is "useable". That's about 82% of the capacity.
My observations are that when new it was probably more likely to be 30kwh based on the BATT.KAPA.MAX readout, which on my car with 20K miles still shows 29.5.

There is a buffer.
The BMS charges it to 100% of what it will allow leaving the buffer.
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WhiteRexNJ
Posts: 6
Joined: Sat Mar 27, 2021 9:24 pm

Re: Set a maximum charge limit

Sun Mar 28, 2021 9:27 pm

alohart wrote:
Sun Mar 28, 2021 1:25 pm
WhiteRexNJ wrote:
Sun Mar 28, 2021 12:50 pm
I have read a bunch on this and it seems to be still widely debated. I haven't seen anything from BMW saying that they dont allow the battery to charge fully. I previously had a volt, and not only did chevy tell us that you cannot charge the car to 100%, but with the volt equivalent of bimmercode I could actually see (and edit) the buffer.
All BMW i3 battery packs have gross and usable capacities (e.g., the 60 Ah battery pack has a gross capacity of 21.6 kWh and a usable capacity of 18.8 kWh). The difference between gross and usable capacity is the unusable buffer capacity divided between low and high charge levels (i.e., no i3 battery pack can be charged to its absolute full capacity nor discharged fully). This among many other things is discussed in David Bricknell's excellent Electric Vehicles and the BMW i3 - 60, 94 and 120Ah.

Not all BMW system software is parameterized such that its behavior can be changed by changing the values of parameters (a.k.a., coding). The number of parameters that BimmerCode can access is large with most of them undocumented and many of them applicable to BMW models other than the i3. Changing the unusable buffer sizes might be possible with BimmerCode, but I'm not aware of anyone posting how this could be done.

The proprietary BMW ISTA+ service software can display current unusable buffer sizes but can't change them AFAIK. ISTA+ shows that these buffer sizes are dynamically changed over time by the battery management system (BMS). That makes determining whether a loss of actual range is due to battery cell degradation, the BMS increasing the unusable buffer sizes, or both. I'm surprised that the Volt's unusable buffer sizes can be changed by an owner because doing so could affect the battery cell degradation rate and thus could impact the battery capacity warranty.

You can only edit the buffer with the volt if you use a weird 3rd party app, it also allows you to change when the engine kicks in, etc...

eNate
Posts: 755
Joined: Mon Sep 09, 2019 5:33 pm

Re: Set a maximum charge limit

Mon Mar 29, 2021 8:51 am

EvanstonI3 wrote:
Sun Mar 28, 2021 1:35 pm

That is true about his question but I foresaw where he was going with it.
If I am wrong, what is it I am wrong about? Seriously.
You're wrong to get so triggered when somebody asks this question. It's not just you. I see nearly violent reactions on Reddit and Facebook i3 groups as well. I don't get why somebody's desire to charge to 80% is so personally offensive. Just because the meme says "ABC" doesn't make it the rule.

You're wrong about the 10%. Yes, there's a top buffer, but it's closer to 5%, with a fatter buffer at the bottom where greater damage can be done. And 95% or even 90% is not 80%

You're wrong about the BMS. Not in that the i3 has BMS -- of course it does, as sure as my windows have panes of glass. You write "there is a battery management system..." as if other car's don't, or implying BMW's is somehow superior, leading it to my next point...

...being that there is much advice from major players to limit charging to 80% when the extra capacity is not needed. Tesla (who I expect has the most advanced BMS, and definitely has a better battery cooling system) suggests this, as do Kia and now VW. I'll give you that the 80% seems somewhat arbitrary with the lack of much hard data, so maybe on the cautious side, but that's the guessing game we're left playing.

I, as a possible i3 long-hauler but definitely somebody who wants to keep their battery in great shape, have no issue following what amounts to loosely agreed "industry best practices" even if BMW has opted to take the "don't worry your pretty lil' head" approach so as not to make EVs seem complicated. But I have the luxury of living within this self-imposed capacity / range reduction, L1 charging works for my daily needs, and without hesitation I would daily charge to 100% on L2 or even DC if that's what I needed to get around (though I wouldn't have picked this car).

So my questions to you are:
1. What do you find personally insulting if somebody wants to limit their charging to 80%?
2. What data do you have to be so certain the 80% recommendations are wrong and the "always be charging" mentality has no consequences, even if minimal? Hopefully more than a meme from
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EvanstonI3
Posts: 64
Joined: Tue Nov 03, 2020 9:11 pm

Re: Set a maximum charge limit

Mon Mar 29, 2021 9:20 am

eNate wrote:
Mon Mar 29, 2021 8:51 am
So my questions to you are:
1. What do you find personally insulting if somebody wants to limit their charging to 80%?
2. What data do you have to be so certain the 80% recommendations are wrong and the "always be charging" mentality has no consequences, even if minimal? Hopefully more than a meme from
Thanks for answering my question.

As for your questions:
1. I don't find it personally insulting so I'm not sure what you mean.
2. I've made no claims that 80% recommendations are wrong so I'm not sure how to answer that.
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