Set a maximum charge limit

[WhiteRexNJ]

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

 

[eNate]

Unfortunately, no. Any early cut-off has to be done externally.

 

[EvanstonI3]

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.

 

[eNate]

That wasn't his question, and you're wrong.

 

[WhiteRexNJ]

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]

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.

 

[EvanstonI3]

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.

 

[WhiteRexNJ]

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]

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

 

[EvanstonI3]

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.

 

[gt6k]

Although I think the 80% charging is the EV equivalent of a fad diet I will suggest a way to achieve it as it is the OPs right to do what he wants with his car.

The answer is that if you have a sufficiently smart charger such as the OHME one then you can set the charge level on that. It even allows you to set a charge % against individual schedule items.

 

[eNate]

Another option is a spring wound mechanical timer. There are outlet box-mountable versions of these rated at 20A so would work at L1 charging. I installed one in my garage and connected it to the 120v receptacle I plug in to, but so rarely charge at home that I just don't use it. But given that at 16A I recoup 5% of my battery it's pretty simple to figure out how many hours I want to charge. The niftier thing about these timers is they have two switched terminals, one normally on and one normally off. So it can be wired to a split duplex receptacle so that (for instance) the top receptacle will remain OFF for 4-hours while the timer is counting down, the turn ON, but the bottom receptacle will remain ON for 4 hours while counting down then switch OFF.

 

[jadnashuanh]

If the vehicle is fully charged, with the latest software, it should unlock the charging plug from the socket. If the vehicle is locked while it's charging, and with older software, you can't remove the plug unless you unlock the i3 first. But, normally, when you want, just press the release button and pull the plug out. Pressing the release button opens a switch, which causes the ACV to be shut off so you don't get a spark when you then break the connection by pulling out the plug.

The last 5-10% of charge tends to be much slower than the first 90%. If the batteries are super cold or hot, the first charge can slow until things are brought more into the optimum temperature. They can be heated or cooled, depending on what's needed.

Power = volts * amps. It's likely your level two EVSE can source more amps, but even if it couldn't, having twice the inlet voltage would mean twice as much power going into the i3 per time.

 

[Hacky]

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.

Dispite many other statements, the i3 does not hold back a buffer at the higher end of the cell voltage range. The buffer only prevents exhaustive discharge.

You can see, that it charges the cells up to 4.20 V when reading out data from the OBD2 connector. See also: https://www.goingelectric.de/forum/viewtopic.php?p=1454473#p1454473

I have seen this for the 94Ah and 120Ah models and I assume the same strategy for the 60Ah models.

 

[alohart]

Dispite many other statements, the i3 does not hold back a buffer at the higher end of the cell voltage range. The buffer only prevents exhaustive discharge.

You are basing your assertion on the output of the Electrified app that indicates a battery pack voltage of 402 V, and then you assume that this is the maximum possible voltage for a pack of 96 120 Ah cells. Pack voltage is temperature-dependent, so did you correct this voltage for the cell temperature?

In one of the screen shots in the forum that you referenced, the Electrified app displays a battery health of 99%. It also displays a charge level range from 12.0% to 96.3%. You state that no high charge level unusable buffer exists yet the Electrified app shows a 3.7% buffer. The fact that you believe the pack voltage but not the maximum allowed charge level of 96.3% reduces the credibility of your assertion.

Electric Vehicles and the BMW i3 (60, 94, & 120 Ah) by David Bricknell includes charts from testing labs that clearly show low and high charge level unusable buffers. His description of the battery management system clearly states that unusable buffers exist at both low and high charge levels. The difference between BMW's published gross and net battery pack capacity can't be explained by the existence of only a low charge level unusable buffer unless one assumes an unreasonably large low charge level unusable buffer. BMW's TIS Website describes the SME as controlling the charge level range of the battery pack without specifying buffer sizes which vary by battery cell capacity.

There's overwhelming evidence from credible sources disputing your assertion that no high charge level unusable buffer exists.

 

[SuperPoly]

There is less regen braking above 90%, right? For that reason alone I would like to set a lower charge limit for my daily use. I use between 0-10% of the battery most days.

 

[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.

 

[Hacky]

You are basing your assertion on the output of the Electrified app that indicates a battery pack voltage of 402 V, and then you assume that this is the maximum possible voltage for a pack of 96 120 Ah cells. Pack voltage is temperature-dependent, so did you correct this voltage for the cell temperature?

On the lower left corner of the screenshots you see the (max.) voltage on cell level and beside that with smaller numbers the range between lowest and highest cell voltage measurement across all cells. Both examples show 4.19V as highest cell voltage (cell levels ranging from 4.18V to 4.19V). So I do not talk about pack voltage here. The first example shows a battery temperature of 10.7 °C, so also nothing special that should be taken into account.

As you may know, most Lithium Ion cells have maximum charge voltage of 4.20 V as long as these are not special LiIon HV cells (which can be charged up to 4.35V). But those HV cells will not be found in normal automobiles due to lower cycle life times.

The 94Ah cells from Samsung SDI are specified for maximum charge voltage of 4.15V per cell and even those are charged up to 4.20 V on the i3.

So I see no indication for a buffer at the "top" end.

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?

 

[Star63]

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.

This would mean that the cell voltages are about 4.08 V vs. 4.19 V. ? And that the 120 Ah battery has a smaller buffer (if any)?

 

[Hacky]

Yes, I also found this post from "Havrla", who is well known in Europe for his 60Ah -> 120AH battery upgrade skills.

As I said already, I did not yet see OBD2 read outs for the 60 AH i3 and I have not yet seen the specs for the Samsung 60 Ah SDI cells. May be that for this one, there is some upper buffer.

EDIT:
Looks like a module (12 cells) of the 60Ah SDI batteries is specified for a maximum voltage of 49.2V (see here: https://secondlifestorage.com/index.php?threads/bmw-i3-60ah-specifications.10971/) which means 4.1 V per cell. So if the i3 60 Ah charges the whole battery up to 392V, that means 4.0833 V/cell and also in this case almost no top buffer.