asthorman
Posts: 5
Joined: Fri May 31, 2019 12:36 pm

Limiting total charge % - hidden feature?

Thu Jun 13, 2019 9:58 am

I haven't seen this discussed before, so I thought that I would mention it.

When I set both the 120v and 240v charging to their lowest setting, my i3 automatically stops charging at 85% or 87% capacity. Like others, I've been somewhat disappointed by the inability to avoid charging to a full 100%. However, I seem to have accidentally stumbled onto a hidden feature, either that, or my i3 is not working properly :D :D

Since I live in Phoenix, and my garage is regularly over 100 degrees this time of year, I like being able to leave the i3 plugged in all night to keep the battery cooling system active. This seemingly hidden feature allows me to check both boxes, keeping the battery cool, and not charging to a full 100%.

Thanks!
Andrew in Phoenix, AZ
2017 BEV

gps1539
Posts: 52
Joined: Tue Jul 03, 2018 3:08 pm

Re: Limiting total charge % - hidden feature?

Thu Jun 13, 2019 1:18 pm

Does it charge to 100% if you set the higher charging rates?

asthorman
Posts: 5
Joined: Fri May 31, 2019 12:36 pm

Re: Limiting total charge % - hidden feature?

Thu Jun 13, 2019 1:54 pm

gps1539 wrote:
Thu Jun 13, 2019 1:18 pm
Does it charge to 100% if you set the higher charging rates?
Yes, when I change the settings back to 'Maximum', it will charge up to 100% like normal. The first time I noticed this, was after receiving a message on the Juicenet app saying 'Energy limit reached' or something along those lines.
Andrew in Phoenix, AZ
2017 BEV

vreihen
Posts: 303
Joined: Tue Apr 30, 2019 4:55 pm
Location: Orange County, NY (FN21vm)

Re: Limiting total charge % - hidden feature?

Thu Jun 13, 2019 2:26 pm

I wonder if the reason for this happening is because BMW's charge-tapering function is clashing with J1772's minimum Level 2 supply current of 6 amps at the car's lowest charge settings?

The right side of this graph shows my i3 charging at 16 amps, and you can see the taper-down as it approaches full:

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(The left two traces on the graph are my DW's new Kia Niro EV, which does not appear to have a graceful taper-down in its charging system judging by the vertical line when it completes.)

Anyway, this may explain the "energy limit reached" message from the EVSE if it happened as the car's demand dropped below 6 amps.....
2015 BMW i3 BEV, Giga World, Tech and Driving Assistant packages, 15K miles

asthorman
Posts: 5
Joined: Fri May 31, 2019 12:36 pm

Re: Limiting total charge % - hidden feature?

Tue Jun 18, 2019 3:01 pm

More investigation is required. My i3 is back to charging to 100%, despite the charge settings adjusted to the lowest possible for 120 and 240v. I am somewhat disappointed as I liked being able to keep the vehicle plugged in all night to allow the batteries to self-cool in my hot garage, while simultaneously not letting the vehicle sit at 100% for hours and hours. I will update this thread if anything changes!
Andrew in Phoenix, AZ
2017 BEV

n1o2c3a4c5h6e7t
Posts: 23
Joined: Wed May 01, 2019 12:35 pm

Re: Limiting total charge % - hidden feature?

Wed Jun 26, 2019 6:43 am

What is the point of running the battery cooling for hours a day when you're not using it? How much energy does that use? Are you suggesting that this increases the battery's longevity?

I also doubt that a closed garage can get to 100 degrees overnight, and perhaps not during the day either. Shade can take 20 degrees off the ambient temperature in the desert.

vreihen
Posts: 303
Joined: Tue Apr 30, 2019 4:55 pm
Location: Orange County, NY (FN21vm)

Re: Limiting total charge % - hidden feature?

Wed Jun 26, 2019 9:27 am

I believe that the rationale is based on the experiences of older Nissan Leaf drivers from the Arizona area, where the heat radiated from the pavement caused premature battery issues.

As for the temperature of a garage at night, I was on the ground floor of an open parking garage in Las Vegas back in 1996 and measured a temperature of 99F...at MIDNIGHT...in early May. I'd hate to have to live there in the actual summer! The concrete just doesn't let go of the heat very fast.....
2015 BMW i3 BEV, Giga World, Tech and Driving Assistant packages, 15K miles

asthorman
Posts: 5
Joined: Fri May 31, 2019 12:36 pm

Re: Limiting total charge % - hidden feature?

Wed Jun 26, 2019 9:41 am

n1o2c3a4c5h6e7t wrote:
Wed Jun 26, 2019 6:43 am
What is the point of running the battery cooling for hours a day when you're not using it? How much energy does that use? Are you suggesting that this increases the battery's longevity?

I also doubt that a closed garage can get to 100 degrees overnight, and perhaps not during the day either. Shade can take 20 degrees off the ambient temperature in the desert.
Thank you for the reply. I am hoping to find the best balance of keeping the battery cool vs. keeping it at a full state of charge too long. I may be overthinking it a bit, as the BMW engineers surely considered all this when designing the car! :)

I keep a thermometer in the garage, it is totally closed up overnight, no vents .... definitely stays at 100 + some nights! Our other garage, has high and low vents to the outside and it stays a bit cooler, but still super hot this time of year.

I think that I may have figured what is going on, but I am still trying to verify. On my Juicenet App, one of the screens asks for the range when plugged in, so if I enter 81, and the Juicenet App says my max range is 114, it seems to automatically turn off after adding 33 miles of range. The challenge is that my Guess o Meter will go as high as 151, therefore my overall charge % will be under 100%. More experiments is required, and I will report back.
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Andrew in Phoenix, AZ
2017 BEV

jadnashuanh
Posts: 5196
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Limiting total charge % - hidden feature?

Wed Jun 26, 2019 8:15 pm

You do realize that even when physically connected, the car does disconnect the acv input once it thinks it's fully charged? It's not like most cell phones or computer batteries. IOW, the batteries are not always sitting with a charging voltage applied to them.
Jim DeBruycker
2014 i3 BEV, 2021 X5 45e
(The i3 will be sold soon, <17K-miles, interested?)

vreihen
Posts: 303
Joined: Tue Apr 30, 2019 4:55 pm
Location: Orange County, NY (FN21vm)

Re: Limiting total charge % - hidden feature?

Thu Jun 27, 2019 4:11 am

Show me a recent cell phone or computer that doesn't also have an intelligent charge-management circuit in it. All of mine sit on the chargers 24/7 when not in use, and the batteries are still fine after several years.....
2015 BMW i3 BEV, Giga World, Tech and Driving Assistant packages, 15K miles

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