Limiting total charge % - hidden feature?

[asthorman]

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

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!

 

[gps1539]

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

 

[asthorman]

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.

 

[vreihen]

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:

(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.....

 

[asthorman]

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!

 

[n1o2c3a4c5h6e7t]

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]

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.....

 

[asthorman]

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.

 

[jadnashuanh]

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.

 

[vreihen]

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.....

 

[asthorman]

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.

I get that, but research strongly suggests that keeping EV batteries at 100% state of charge will impact long term battery capacity/range. I am hoping to preserve my range as long as possible and if all I have to do it adjust a setting on the vehicle or the charger, it seems like a worthwhile extra step. Luckily my round trip daily commute is only about 52 miles, so leaving home with 80-90% charge isn't an issues, even with the AC cranking!!

Topic change:

Nashua, NH? I went to, and graduated from UNH a long time ago and have been spending time in the Lakes Region (Moultonborough) since I was a kid in the 80's and my grandparents retired there from Long Island, NY. It was only last summer that house was sold!

 

[gt1]

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.....

Your phone maybe at 85% capacity after 3 years and don't even notice it.

I have a 94AH model, I charge when the battery is below 50% and set EVSE timer to 2- 2.5 hours. This way I end up with 85-90% charge.

 

[jadnashuanh]

There are timers, even if your EVSE doesn't have logic built-in, that could turn the EVSE on/off. You'd want to probably turn it back on if you wanted to precondition and set a departure time, otherwise, you might suck a bunch of battery capacity out. It would take some calculations to keep things where you want, not worth it in my opinion, but hey, it's your car...

I've lived in various places around the world...NH has some nice perks: interesting terrain, real seaons, no income tax or sales taxes on general merchandise.

 

[Fisher99]

So which is actually worse for the longevity of the battery?

A. Charging every night but only to 80% of capacity.

B. Charging to 100% but only every couple of days?

Is reducing the number of charging cycles important? More important than reducing the charging percentage? I often hear of batteries being rated in "Number of charge cycles" so it would seem to be important to limit them? I can get by with charging less frequently if I charge the battery to 100% when I do charge.

 

[alohart]

So which is actually worse for the longevity of the battery?

A. Charging every night but only to 80% of capacity.

B. Charging to 100% but only every couple of days?

Li-ion battery cell electrochemistry degrades more slowly at lower charge levels, so "A" should statistically be preferable.

Is reducing the number of charging cycles important? More important than reducing the charging percentage? I often hear of batteries being rated in "Number of charge cycles" so it would seem to be important to limit them? I can get by with charging less frequently if I charge the battery to 100% when I do charge.

A full charge cycle is from 0% to 100% charge levels, so charging from 60% to 80% would be only 20% of a full charge cycle. So charging 5 times from 60% to 80% should be similar to charging once from 0% to 100%.

 

[n1o2c3a4c5h6e7t]

Would a WiFi controlled EVSE be able to stop charging at 80%? Is it possible to make a dumb EVSE "smart" with aftermarket technology? For example, with a WiFi controlled outlet, etc.

 

[Fisher99]

Good info alohart. Thanks!

 

[jadnashuanh]

Would a WiFi controlled EVSE be able to stop charging at 80%? Is it possible to make a dumb EVSE "smart" with aftermarket technology? For example, with a WiFi controlled outlet, etc.

If you use a smart outlet designed for the load of the EVSE, yes, you could set a timer. Now, most, but not all EVSE devices will reset properly when connected to a vehicle upon a power cycle. On some, you might find it will only connect properly if it is first turned on, then the plug is inserted into the car. Try yours first by either unplugging it, or turning it off with the circuit breaker while connected to the car.

But, there's no smart plug that I'm aware of that would interact with the car to identify when it was at 80%...you'd have to guess. That timing would change partly by the battery temperature and the value when it was plugged in.

As noted, charging 10x from 70-80% is the same as charging once from 0-100% in cycles and wear on the batteries.

Nissan, who doesn't have a great reputation for battery management (most don't have liquid cooling, so in hot climates, they can have issues) still finds that their batteries are holding up quite well long-term. BMW's choice on batteries, with their liquid cooling, IMHO, should be even better. IOW, I don't really worry about it. Leaving with 100% in the morning, and having it plugged in so I can precondition them and the cabin is worth it to me.