Skids wrote

Web search (forums etc.) to get an understanding of the charging system has raised a few questions .. so hoping that a reasonable explanation can be offered by a forum member.

BMW says that charging (both batteries 12 & 48) occurs during breaking, coasting etc., but doesn't specifically say that 'a normal alternator' recharges whenever the motor is running.

The last iDrive update was paused due to low voltage / charge and my current understanding is that a 12v charger also charges the 48v battery .. which must be via an inverter.

Is this correct ?

BTW I've not experienced any problems other than noticing that indeed the charger sensed a low charge .. but is that only for the 12 or also associated with the 48 ?

I'd appreciate anybody's take or understanding of the system generally.

jad03060

GREENPUS wrote

On the Pre LCI, where is the 12v connected into the system. It's like it's missing lol

Skids wrote

"Battery tender/charger for 2021 M340i with 48 volt system" - seems to be one of the better threads and after 16 pages, frankly, the subject is not well understood (collectively).

Does a 20A + charger replenish the 48v battery (hood open)?

Did BMW design the car (s) with a hybrid system that is designed for stop / go conditions (whereas being semi-rural I have little breaking / coasting)?

Also to mention that almost nothing is detailed in the BMW manual ... but thanks, I appreciated the responses.

Skids wrote

Did BMW design the car (s) with a hybrid system that is designed for stop / go conditions (whereas being semi-rural I have little breaking / coasting)?

jad03060 wrote

If your commute is stop and go in the city, all batteries will likely be sufficiently charged. It's when it may sit unused for long periods of time or you're on a major highway that is flowing freely where you're not slowing and accelerating to stay with traffic where it could be an issue.

Most people don't live where the roads are billiard table flat, so even little undulations in the road will have some charging opportunities.

But, again, IF the battery charger has at least 20A output, the 48VDC battery will also get charged...it won't if your hood is closed or it's smaller than that.

M a r t y wrote

Wait, if you use a charger capable of 20+amps, how will it charge the 48v battery if the hood is open? Because when you open the hood, it disconnects the 48v battery, at least that is what I've always thought.

GREENPUS wrote

When I had my MY21 X6 I drove 5 miles to work and 5 miles home. That was essentially my use of the car. I was always concerned about the batteries 12v and 48v not getting fully charged. So my thought process lead me to monitor the 48v battery charge on my iDrive and coast a lot during that drive. The LED segments on my 48v battery had 5 segments and I kept it up to 4 segments at all time. From my Internet web searching that was most likely as much as this system will charge the 48v lithium battery ( ~80% ). The 48v battery would also keep my 12v fully charged. Even with that short distance of driving in the 3 years I owned the car, I never had battery issues and the 12v was always fully charged.

TurtleBoy wrote

It doesn't disconnect the the 48v from the power distribution system it just shuts down the connection from it outward. In other words, the charge from the terminals can be routed to the 48v battery.

woodlecj wrote

Where are you seeing battery status? In iDrive?

M a r t y wrote

Ya know, just when you think you understand it.. .. this happens

Ok, its actually the opposite than what I thought.. so, opening the hood tells the charging system that you are charging the batteries (both of them) and they are now connected via the internal system circuitry) even though you are only supplying 12v, the DC/DC converter then jumps into action for the 48v battery, if needed.

When the hood is closed and the car is turned off, the system disconnects the 48v battery from the engine compartment charging terminals. This disconnection prevents the 48v battery from discharging during periods of non use/storage.

How's that, is this correct?

woodlecj wrote

Where are you seeing battery status? In iDrive?

M a r t y wrote

I believe he's referring to the Eco Mode display where it shows a graphical representation of the energy flowing out of and into the battery as you drive. I'm going from memory but try driving in Eco Mode, then on the LCD screen poke around till you see it, I forget the exact name of the display.

Found this pic online, looks like its called Energy Flow.

.