Timed charging of my I3

[Isandula]

I have a level 2 charger and want to be able to do a timed charge of my i3 when the electric rates are lowest. In my NC area from 1 AM to 6 AM is the lowest rate. So I set the charger time to begin at 1 AM and to end at 3 AM for instance. Everytime the car charges until it is maxed out with the charge and so the timer does not work. Help. I had a 2018 and could not get this to work, and now I have a 2021 and still cannot I have contacted BMW genius several and even took my i3 to the dealer with no success.

 

[alohart]

Unfortunately, iDrive in the i3 doesn't support guaranteed start and end times for charging. Installing an EVSE that supports such functionality would be one way to accomplish your goal.

 

[eNate]

Just to add on to what Art wrote, if you browse your owner's manual, you'll see that BMW for some inexplicable reason tied timed charging to a departure time, and seemed to bend over backwards to give us owners no convenient way to cut the charge off either at a set state of charge or a set time. The system will even violate the low rate window that the owner sets up, in order to ensure a 100% charge by the user-set departure time. It's super frustrating to somebody like me who is perfectly keeping the battery below 80%, but it seems with this car BMW focused on making charging "simple" and thoughtless (unlike on their current fleet which provides user-settable SOC cut-offs and even L2 charge current limiting!).

 

[jeeringtowser]

I am a very new owner who was disappointed that the charging percentage cannot be set to below 100%.
I have used a simple 24hr timer that charges for the times required but always shows an error message!
I expect someone with more knowledge than me will say this method should not be used!
This is the only way I can see to use cheap rate electricity and not charge to 100%.
Any advice gratefully received.

 

[eNate]

I use a EVSE by Zencar that features a delayed start timer, but nothing to shut it off early. I agree with you, an oversight by be in my view. But it seems BMW was aiming for the KISS principle, and many of not most owners are happy to follow their advice and charge to 100% (which is not true 100% but it's also not 80%).

Some more advanced "connected" EVSEs feature start stop controls and timers.

 

[alohart]

I have used a simple 24hr timer that charges for the times required but always shows an error message!
I expect someone with more knowledge than me will say this method should not be used!

There's an on-off switch on our EV charging circuit just upstream of our EVSE. If I turn this switch off while charging is active, an error message is displayed. I think it's displayed so the i3 owner would understand why charging stopped prematurely. I don't think there's any harm caused as a result. An EVSE and the i3's on-board chargers have to be able to deal with a sudden loss of electric grid power without any damage resulting.

An EVSE with a built-in charge level limitation almost certainly signals to the i3's on-board chargers that it can no longer provide the current that the chargers have requested resulting in an orderly shutdown that doesn't result in an error message.

 

[Neil]

I went through this issue almost 9 years ago with BMW, back and forth, for my 2014. I gave up trying to get this to work the way I wanted it to, and installed a electric water heater timer to power up my EVSE (which didn't have a timer) when the rates dropped. The car was set to immediate charging and all was well from then on.

 

[frictioncircle]

Isandula –

Welcome to the forum!

Do a web search for "EVSE with timer".

 

[MarkH]

I have been doing a timed charge for over a year, now.

My first method was just to use an electro/mechanical timer, Whenever the charge got down to less than 30%, (every 2-3 days) I'd use the timer to give it ,say, 9 hours of charge - or whatever I felt was needed to take it back up to around 80%. That worked fine.

Recently I have got an electricity supply agreement that gives me free electricity between 9pm and midnight. I installed a WiFi switching device (Shelly 1PM) into the charging electricity socket. Every evening I plug the car in and I control how many hours of charge it gets each night through my phone. It varies between 1 and 3 hours, depending on how much I have used the car.

 

[Derek2]

I am a very new owner who was disappointed that the charging percentage cannot be set to below 100%.
I have used a simple 24hr timer that charges for the times required but always shows an error message!
I expect someone with more knowledge than me will say this method should not be used!
This is the only way I can see to use cheap rate electricity and not charge to 100%.
Any advice gratefully received.

I'm on Intelligent Octopus Energy. It allows you to set 80% charge, and it determines when to charge your car at the low cost rate. Mine always seems to charge 11:30pm - 5:30am, the off-peak times.

edit to add: This is in the UK

 

[jeeringtowser]

I too have signed up to Intelligent Octopus, which has solved my previous issue

 

[Ciprico1]

I got around this issue by moving the departure date to "yesterday", so Idrive calculates there are enough 4 hour cheap rate windows to fully charge the car before it thinks you want to leave.

Annoyingly if you forget and departure date becomes the next day it will fully charge to 100% and ignore the cheap rate window.

It is a daft system.

All I want is to simply charge the car for 4 hours every night regardless of soc and regardless of departure date.

 

[LittleBear]

Can you code this to work as we want using an OBD program like Bimmercode?

 

[Marscar]

Some possibly useful notes arising from one year of using the BMW app:

Here in the UK at present we have cheap rate from Midnight to 7am.

Apart from a couple of motorway stops we have, in the last year, only ever charged from a 3 pin domestic socket (on its own circuit, with its own circuit breaker at the main board) during these cheap rate hours.

We almost always let the car charge to "100%" because:

A)
Afaik this is not 100% anyway, being subject to the buffer set by BMW.
(You know, the one that a main dealer will change (allegedly) when you take it in for a warranty check of battery degradation, only to discover it has a higher than 70% capacity!)

B)
Our understanding is that the last stage of this "100%" charge is "managed", at least in part, to help with balancing all the cells.

C)
Kind of tied in with that is the assumption that owners want to benefit from the "conditioning" of the battery that arises from the charging of it, (mainly through raising its temperature in winter months?) and therefore want to complete charging shortly before setting off.

So ... If I set the app to charge in the cheap rate time slot, but set a departure time that would not allow for a "100%" charge, the app will start charging before the cheap rate period.
The way I now get round this is to simply set the departure as several hours into the next day so that the app starts at the appointed time but then continues on into the next morning ... at which point all I have to do is throw the main board circuit breaker when the weather is bad, or unlock the car and remove the charging cable.
OK so it tells me charging has been interrupted and that I should check the supply etc etc, but when I then go to use the car having re-locked it, there's no issue.

Our "Kappa Max" has INCREASED in the year that we have charged in this way ... I know the read out will vary with external temp, but we have always checked when the battery has just been charged to "100%" and whereas initially the read out varied between 28.9 and 28.6, it now varies between 29.7 and 29.0.
That's covering 10,000 miles (16,000km)

I guess my point is that if you have enough cheap rate hours to charge slowly from say no less than "30%" to "100%" then going to that "100%" clearly isn't an issue.

I started out with this charging plan having read a couple of articles about studies that fly in the face of the conventional wisdom that V2G full charge and almost full discharge will shorten the battery life.

In summary, I think it is far more important to not fully discharge the battery than it is to not "fully" charge it

 

[eNate]

We almost always let the car charge to "100%" because:

I try not to take a hard stand against this because 100% / "ABC" is what BMW recommends for the i3. So with that in mind, here are my rebuttals to your justifications -- and again, I'm trying not being judgmental, just presenting what I consider logical counterpoints.

a) almost all EVs have a top (and bottom FWIW) buffer. 100% is almost never 100%, with (I think) a few select Tesla models. So there's nothing unique going on with our i3s.

b) the whole charge is managed, same with any other EV. It's the same reason fast charges slow as they approach 100%. And the fact of the matter is battery management systems have only been getting better since 2014, and yet EVs being introduced today with state of the art BMS (including the new crop of BMWs) advise limiting charge to 80% and provide the tools to do so. BMW even now gives owners the ability to limit not just state of charge, but rate of charge.

b2) the i3's balancing is passive and only occurs after the charge has stopped and the battery has returned to "resting voltage." A balanced battery may give the user a more accurate state of charge estimate, but it won't dramatically allow for an increase in the stored energy content of the battery unless the battery is way out of balance and charged to 100% then allowed to balance and finally once again charged to 100%.

c) the battery is going to get "preconditioned" no mater what level it's charged to, the difference of course being that if it's taken to 100% it will be charging for a longer period of time and therefore given more time to build heat. But this has more to do with the rate of charge and a DC session will get the battery warmer than a 40A charge which in turn will be warmer than a 10A charge.

Personally, I stick with 80% because I can do so without any great sacrifice (I'm not waking up at 2am to unplug my car), and because I feel like this is an unresolved battery care issue. I want this car and battery to last me for a good long while and feel like this rises above the level of "myth" mainly because the main industry players continue to preach the 80% suggestion. I have no qualms charging this car or my VW to 100% when the need arises.

 

[alohart]

I couldn't have expressed my beliefs any better.

b2) the i3's balancing is passive and only occurs after the charge has stopped and the battery has returned to "resting voltage." A balanced battery may give the user a more accurate state of charge estimate, but it won't dramatically allow for an increase in the stored energy content of the battery unless the battery is way out of balance and charged to 100% then allowed to balance and finally once again charged to 100%.

For those concerned that not always fully charging might prevent passive cell charge level balancing from working well, no need to be. The mi3 (iOS) and electrified (Android) apps display the minimum and maximum cell voltages among all 96 cells. The cell voltage is directly measurable and is what the cell charge level balancing logic uses to balance the cell charge levels. To check on how well the charge levels are balanced, I periodically drive until the charge level is a displayed 0.0% and the available power begins to decrease as indicated on the power gauge. I then save screen grabs of the mi3 app paying attention to the minimum and maximum cell voltages. I then fully charge and save another set of screen grabs. I did this last week and was happy to learn that the difference between minimum and maximum cell voltages was only 0.04 V at the lowest absolute charge level that the BMS allows in our 2019 i3, 11.4%, and only 0.07 V at the highest BMS absolute charge level, 93.6%. Not only are the cell charge levels well-balanced at both minimum and maximum allowed charge levels but the cell capacities must all be very similar or the voltages differences would be much greater at the minimum charge level because balancing occurs at high charge levels.

 

[Marscar]

I try not to take a hard stand against this because 100% / "ABC" is what BMW recommends for the i3. So with that in mind, here are my rebuttals to your justifications -- and again, I'm trying not being judgmental, just presenting what I consider logical counterpoints.

a) almost all EVs have a top (and bottom FWIW) buffer. 100% is almost never 100%, with (I think) a few select Tesla models. So there's nothing unique going on with our i3s.

b) the whole charge is managed, same with any other EV. It's the same reason fast charges slow as they approach 100%. And the fact of the matter is battery management systems have only been getting better since 2014, and yet EVs being introduced today with state of the art BMS (including the new crop of BMWs) advise limiting charge to 80% and provide the tools to do so. BMW even now gives owners the ability to limit not just state of charge, but rate of charge.

b2) the i3's balancing is passive and only occurs after the charge has stopped and the battery has returned to "resting voltage." A balanced battery may give the user a more accurate state of charge estimate, but it won't dramatically allow for an increase in the stored energy content of the battery unless the battery is way out of balance and charged to 100% then allowed to balance and finally once again charged to 100%.

c) the battery is going to get "preconditioned" no mater what level it's charged to, the difference of course being that if it's taken to 100% it will be charging for a longer period of time and therefore given more time to build heat. But this has more to do with the rate of charge and a DC session will get the battery warmer than a 40A charge which in turn will be warmer than a 10A charge.

Personally, I stick with 80% because I can do so without any great sacrifice (I'm not waking up at 2am to unplug my car), and because I feel like this is an unresolved battery care issue. I want this car and battery to last me for a good long while and feel like this rises above the level of "myth" mainly because the main industry players continue to preach the 80% suggestion. I have no qualms charging this car or my VW to 100% when the need arises.

Who are you rebutting?
I was giving my reasons for not worrying about charging to "100%".

I know 100% isn't really 100% hence the inverted commas ... The buffer against what we used to call "boiling" the battery to 100 is built in.
Ours is a 33kwh unit.
It's considered full at 30kwh ... so we know that charging to "full" is really more like 90% anyway.

I know that charging slows towards the end of a "full" charge.
We charge at 2.4kw here, for up to seven hours overnight so, as you point out, relatively little conditioning.
It seems best then to take it right through to "full" as "expected" by the system.

I have NEVER unplugged at 2am!
Very VERY occasionally we need to depart somewhere around 8 for a 130 mile trip and we're not up to full charge so out comes the cable and off we go.

I'm not sure what you're saying in "B2" but do you have your doubts about the Kappa Max readings?
Sorry if that's not right but, I've only ever checked Kappa Max after having charged to "100%".
This isn't immediately after, as that's reached before 7 am, but usually within an hour / hour and a half.
I made a point of keeping this as consistent as possible because I've heard that it's not an absolute number, with variables affecting it.
The Kappa Max figures definitely started to climb after about four months.
I'm not expecting this to continue obviously!
More likely that there'll be a plateau before the inevitable decline ... but I have NO idea how long that will take.

Finally, since we've been forced to use the car much more for "long" distance trips this last year, and that situatuon has now come to an end, it will be imteresting (to me at least) to see whether anything changes.

 

[alohart]

Batt. Kappa. max varied ±2 kWh in our former 2014 i3 over a period of a few weeks, so I don't consider it to be very meaningful. I didn't attempt to read Batt. Kappa. max under similar conditions which might have affected its readings. For several months, it was an unrealistically high 20+ kWh for a battery pack whose new nominal usable capacity was 18.8 kWh. It is a calculated estimate of the maximum usable capacity, but we don't know how this calculation is made and what affects the calculation.

The capacity of a battery cell depends on the charging or discharging power under which the capacity was measured, the cell's temperature, and maybe other factors, so there's not a single correct usable capacity.

 

[eNate]

Batt. Kappa. max varied ±2 kWh

That's one more reason to believe the i3's BMS isn't "all that." I'm not calling it primitive, but technology has advanced.

The NXP battery management system that VW uses monitors each of the 288 cells (pouches) individually and these can each be read for energy content / voltage on an OBD scanner.

That system also uses passive balancing, but can take a pack right to to 100% all while monitoring for an overcharge on any particular cell. Works the same at the bottom end to ensure no cell is overly-discharged.

And even with all that and healthy top and bottom buffers, VW still recommends 80% for fault use and not letting the car sit around if it's charged to 100. And one more reason I'm skeptical of talking my i3 to 100 regularly.

 

[alohart]

That's one more reason to believe the i3's BMS isn't "all that." I'm not calling it primitive, but technology has advanced.

Good point! I've not read that the i3's BMS hardware was ever updated since the first i3 was built in 2013. So improvements must have occurred over the past decade.

The NXP battery management system that VW uses monitors each of the 288 cells (pouches) individually and these can each be read for energy content / voltage on an OBD scanner.

The i3's BMS monitors each of the 96 prismatic battery cells in the battery pack. However, the mi3 and electrified apps report only minimum and maximum cell voltages, energy content, temperature, etc. I don't know whether BMW's ISTA maintenance software can read data for each cell.

That system also uses passive balancing, but can take a pack right to to 100% all while monitoring for an overcharge on any particular cell. Works the same at the bottom end to ensure no cell is overly-discharged.

The i3's BMS works similarly. It stops charging when the voltage of any cell exceeds a certain limit and stops discharging when the voltage of any cell decreases below a certain limit which protects all cells against accelerated degradation due to being overcharged or over discharged. Good cell charge level balancing is important to be able to use as much of the capacity of the battery pack as possible.