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

Re: 12V battery

Sat Dec 14, 2019 5:27 am

For the archives...Programmed departure times will disable themselves after a few missed departures.....
2015 BMW i3 BEV, Giga World, Tech and Driving Assistant packages, 15K miles

frictioncircle
Posts: 173
Joined: Fri Nov 25, 2016 11:23 pm
Location: USA West Coast

Re: 12V battery

Sun Dec 15, 2019 10:53 pm

alohart –

I used to use a different style of quick disconnect on an ICE car years ago. It had an aggressive idle draw which would kill its full-size battery in about a week and a half.

After I sold that car I thought about installing the quick-disconnect on the replacement ICE car but decided against it. I was concerned about the potential for corrosion at the connections and any resistance increases that might subsequently occur.

MarkH
Posts: 77
Joined: Mon Jun 10, 2019 1:17 pm

Re: 12V battery

Thu Dec 26, 2019 1:02 am

From the manual:
For idle phases that last several weeks, park
the vehicle with a fully charged battery if possible.
Do not park the vehicle for longer than 14 days
if the electric range is less than 6 mls, approx.
10 km.
With storage times of up to three months, if
possible plug the vehicle into a suitable power
source or park it in a nearly fully charged state.
Note
The service center can advise you on what to
consider when storing the vehicle for longer
than three months.
Given that the HV disconnect switch on my i3 is not the same as that displayed in any online instructions that I have seen (and which appears to be a prerequisite for disconnecting the 12V battery, to prevent it going flat, my intention, at this stage is to leave the HV battery fully charged; leave the frunk and doors unlocked. Maybe, with the doors unlocked, the HV battery will charge the 12V battery as needed.
I, also, am reluctant to leave the car plugged into the mains while I am away for 2 months.
This seems a nightmare and a major design oversight by BMW. Why not have the system turn itself on once a month and recharge the 12V: there's plenty of HV capacity?

alohart
Posts: 2450
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: 12V battery

Thu Dec 26, 2019 1:43 pm

frictioncircle wrote:
Sun Dec 15, 2019 10:53 pm
I used to use a different style of quick disconnect on an ICE car years ago. It had an aggressive idle draw which would kill its full-size battery in about a week and a half.

After I sold that car I thought about installing the quick-disconnect on the replacement ICE car but decided against it. I was concerned about the potential for corrosion at the connections and any resistance increases that might subsequently occur.
After searching the Web for auto battery disconnect switches that would be easy to install on the negative battery terminal, I am not impressed with their quality based on reviews. It would just add a potential point of failure. I don't disconnect the 12 V battery more than once per year, so I'll just disconnect the negative cable which is quite easy to do, even without removing the frunk box.
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

alohart
Posts: 2450
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: 12V battery

Thu Dec 26, 2019 2:40 pm

MarkH wrote:
Thu Dec 26, 2019 1:02 am
Given that the HV disconnect switch on my i3 is not the same as that displayed in any online instructions that I have seen (and which appears to be a prerequisite for disconnecting the 12V battery, to prevent it going flat, my intention, at this stage is to leave the HV battery fully charged; leave the frunk and doors unlocked. Maybe, with the doors unlocked, the HV battery will charge the 12V battery as needed.
The design of the high-voltage disconnect must have changed over the model years. However, it's basically just a plug and socket that connect/disconnect a 12 V line, so there's no high-voltage risk. On early i3's, the plug cannot be separated fully from the socket and can be slid only about ½" to unplug it from the socket. A tab on the plug must be pushed in to move the plug. The plug is embossed with "ON" and "OFF" to indicate its state. Your high-voltage disconnect must operate similarly although it apparently looks different.

If you decide to take another look, be sure that the high-voltage system is off when disconnecting the disconnect. This is indicated by the Start/Stop button lighting being off. If it's a pulsing orange light or steady blue light, the high-voltage system is on.

There's no strong evidence that the HV battery pack will charge the 12 V battery as needed. In fact, it's just the opposite.
MarkH wrote:
Thu Dec 26, 2019 1:02 am
This seems a nightmare and a major design oversight by BMW.
I wouldn't describe merely disconnecting the 12 V battery as a nightmare. This would be necessary for any ICE vehicle as well. No modern vehicle can be parked for an extensive period without its 12 V battery being discharged.
MarkH wrote:
Thu Dec 26, 2019 1:02 am
Why not have the system turn itself on once a month and recharge the 12V: there's plenty of HV capacity?
That would have been a nice feature. However, without it, disconnecting the 12 V battery is the best way to prevent the 12 V battery from discharging. Leaving an EVSE powered and plugged in for weeks at a time doesn't absolutely prevent the 12 V battery from discharging. However, it's slightly easier to do than disconnecting the 12 V battery, so BMW seems to be recommending the easiest but less certain method.

Why does BMW recommend against charging with an EVSE for more than 3 months of parking? Might BMW recognize that leaving the HV battery pack at a high charge level for more than 3 months could lead to enough battery cell degradation to increase the number of battery packs replaced under warranty? That's another reason why I have always stored our i3 with its charge level at 40% - 60% without our EVSE plugged in and with the 12 V battery disconnected.
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

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

Re: 12V battery

Thu Dec 26, 2019 4:29 pm

THe i3 waits until the HV batteries have discharged a couple of percent prior to re-engaging the EVSE. That process can take weeks in between. So, the EVSE, even though it's connected, isn't doing much of anything the vast majority of the time. There's a constant, but normally low, level of discharge on the 12vdc battery that maintains the alarm, the cellular connection (even if periodic), and the sensing, if you have comfort access. The internal clocks are still running, at least some of them. I haven't measured the current draw on the i3 when sitting idle, but would guess it's in the 10's of milliamps.

People have mentioned 'transport mode'. Don't know what that is, or how to activate or exit it, but it might provide some relief WRT battery SOC if someone were to figure that out. Anyone know what the characteristics of that mode are and how to enter/exit it?
Jim DeBruycker
2014 i3 BEV, 2021 X5 45e
(The i3 will be sold soon, <17K-miles, interested?)

leocelli
Posts: 5
Joined: Thu Dec 01, 2016 6:01 pm
Location: Brazil
Contact: Website

Re: 12V battery

Fri Dec 27, 2019 4:17 am

Here in Brazil I did like this. I3 Rex with 85.000 km and 3.5 years.

* portuguese

https://youtu.be/VX5AqfhLdtk

MarkH
Posts: 77
Joined: Mon Jun 10, 2019 1:17 pm

Re: 12V battery

Sun Dec 29, 2019 8:05 pm

Thanks for all the replies.

Art, I described disconnecting the battery in an i3 as a "nightmare" only because in an ICE there are no issues whereas with an i3 there are multiple warnings of dire consequences should you miss a step or do something wrong.

One of the references given in the posts, above, states that if charging the 12V battery then:
"If the integration level in the vehicle is 14-03-505 or more recent, then it is not necessary to deactivate the high-voltage system."
I have found in my i3 profile download a line that reads <i-step> I001-16-07-503 </i-step>

Can I safely assume, then, that, if I want to charge the 12V battery, I do not have to isolate it from the HV system?

It seems to me, from what I have read, that it may be satisfactory for me to do the following:
1. Permanently wire an Anderson socket into the 12V connections on the motor under the boot of the i3.
2. Purchase a small (10W - 20W?) solar panel with a PWM controller, terminated with an Anderson plug.
3. Whenever leaving the car unused for any length of time, put the car in "sleep" mode and connect the solar panel.
4. Leave a "safety notice" on the Start/Stop switch to remind me to disconnect upon my return - before starting it.

Can anyone see any "gotcha's" with this?

AndySwan
Posts: 2
Joined: Sun Jun 04, 2017 9:13 am
Location: Scotland

Re: 12V battery

Thu Jan 02, 2020 10:23 am

I left my 2015 REX (I001-16-11-502) for 3-4 months a few times just parked in the garage without plugging it in or disconnecting the battery, at different levels of SOC (about 60-90%), it has always started as usual afterward.

I'm not saying everyone should follow my lead, just my 50¢.

MarkH
Posts: 77
Joined: Mon Jun 10, 2019 1:17 pm

Re: 12V battery

Thu Jan 02, 2020 12:35 pm

Yeah, I think I may have been scared into taking unnecessary precautions.

Reading back through the advice in the manual, it seems that it is aimed at ensuring the HV battery comes through a period of storage unscathed.
If the DC-DC charger (of 12V battery) never activates unless the car is turned on, then either leaving the HV system fully charged or leaving the car plugged in does nothing at all for the 12V system.

As it happens, however, I have installed a 10W solar panel on the roof of the garage and today will connect it to a PWM solar controller. This can be plugged in to a socket that I have installed in the car, connected to the 12V charging terminals on the motor.

The system will be completed today and will, at least, give me peace of mind whenever I have to leave the car unused for several weeks/months.

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