range predictor volatility

[peter downes]

yesterday morning I parked my 2015 i3 in my garage with 95 km range showing. At 3pm I turned it on and the range had dropped to 75. The air temperature and the heating/cooling settings were unchanged. Does anyone have any thoughts or comments ? cheers Peter

 

[EvanstonI3]

Your 12v battery may be dying. When it does, it self-discharges and the main battery comes on to boost it to keep it “alive”. I monitored mine doing this over 2 weeks with no external signs or warnings.

 

[GiantPeaches]

Ignoring the GOM range, did you check the HV battery state of charge?

 

[EvanstonI3]

Ignoring the GOM range, did you check the HV battery state of charge?

that is a good point. click the button on the end of the turn signal shaft until it displays the percentage of charge on your dash. Leave it this way and try to make a note of what the charge percentage is when you leave it overnight. When you come back, see if the percentage of charge has changed. The GOM range can change for a variety of reasons but if the percentage (SOC) of charge in the HV battery remains the same, it is not a problem.

 

[mojo]

IIRC, one other possible reason: If the car's default drive mode is "Comfort" but when you last drove it, you manually set the mode to "Eco Pro", the range when you parked up would be calculated on the basis of the latter. Next time you start to drive the car, the range will be recalculated on the assumption that you will be driving in "Comfort" mode.

 

[Timjohn]

It just did a renewed estimated that is done routinely after you parked. Maybe your previous driving was more aggressive. Don’t read too much into this. It could literally drive you crazy!

 

[peter downes]

thanks everyone. all good suggestions and I will check them all out. I had been driving in eco prop mode before parking in the morning, but usually that only makes a difference of a few k's compared to comfort mode, not 20. My i3 has done 85000 k's and I struggle to get more than 110k's out it in comfort mode. A couple on owners I know with the same year model and similar kilometers have told me that they regularly achieve 130k's, so maybe I have some bad charging habits. Any advice on long term battery preservation ? cheers

 

[mojo]

Any advice on long term battery preservation ?

At nine years old and 85,000 k's, it's probably a bit late to be asking?

Do you regularly charge to 100% or close? If not, you should do - cell balancing won't work if you don't. Do you regularly leave it in a high state of charge or a low state of charge? You should avoid that. Do you always rapid charge it? It's probably better to slow AC charge it more often than to always rapid charge.

 

[alohart]

Do you regularly charge to 100% or close? If not, you should do - cell balancing won't work if you don't. Do you regularly leave it in a high state of charge or a low state of charge? You should avoid that. Do you always rapid charge it? It's probably better to slow AC charge it more often than to always rapid charge.

If cell charge level balancing occurs only at very high charge levels, an i3 would need to be left at that high charge level for a considerable period of time because charge level balancing is a very slow process. That would conflict with your suggestion to not leave an i3 at a high charge level for a considerable period of time.

I have evidence over 9+ years of i3 ownership that cell charge level balancing occurs at charge levels significantly lower than 100%. I typically charge to 80%-90% and leave our i3 parked for several days between drives. Using the mi3 app, I have seen that the charge levels, capacities, and voltages of the all cells are almost identical, so the cell charge levels have remained well-balanced even though I rarely charge to 100%.

I agree with all of your suggestions except charging to 100% regularly. Only charge to 100% shortly before the full range might be needed. If one charges to 80%-90% instead, cell charge level balance should be maintained.

 

[mojo]

Agreed - there is something of a conflict about needing relatively high SOC charge for (passive) cell balancing to work, but it seems unavoidable.

So my solution is only to charge to 100% maybe once a month, and only when I know I'll be traveling more than 20 miles the next day. That way it can sit and cell balance in the intervening period.

As a counter-point, there are on some of the i3 related FB pages a group of people that adhere to the "ABC rule" (Always Be Charging when the car is not being driven), and quote cell balancing as one reason to justify their stance! I should add that I definitely don't recommend that approach.

 

[peter downes]

Hi all. I checked the battery charge level overnight as suggested and it remained unchanged at exactly 50%, so apparently no discharge while stationary. I mostly charge at home from a standard power point, and always to 100 %. The problem may be just the range software as I was recently driving with the AC set to 22 deg. I changed the temperature to 23 and the range instantly dropped from 88 to 77 k's, and when I changed back to 22 it stayed at 77. cheers

 

[alohart]

Hi all. I checked the battery charge level overnight as suggested and it remained unchanged at exactly 50%, so apparently no discharge while stationary.

When an i3 is off, not charging or preconditioning, and its HV system hasn't turned on due to the doors, frunk, or hatch being unlocked/locked or opened/closed, the contactor that connects the HV battery pack to the HV system is open preventing the battery pack from being discharged by external loads. Li ion battery cells do self-discharge, but only very slowly. When I have stored our i3's for several months, the battery pack charge level decreased by ~1% per month due to self-discharge which is hardly noticeable.

 

[robthebold]

I just pick the battery religion that suits my practice best, and like regular religon, I presume every other battery is going to hell. So far, so good, just like my plan to live forever .

 

[Simoni3]

120Ah, 5 yrs old, 75k miles, being charged to 100% 4-5 x a week
shows a battery capacity of 38.9 Kw at the moment - i dont see a problem

the bms does not allow 100% of all the actual tracton battery

 

[peter downes]

thanks for all the comments. I am going to stop thinking about this issue. cheers

 

[autobahndan]

thanks for all the comments. I am going to stop thinking about this issue. cheers

Right, good idea… My 2014 is a 22KWH battery that is showing Kappa of 15.3 and I’m perfectly happy.