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      08-06-2019, 09:53 PM   #1
PK1
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How does the F8x charge the battery?

Looking at the "EfficientDynamics" screen in the iDrive, it shows that the battery is only charged when the car is in gear and under engine compression/slowing down (2018 M3 6MT). While accelerating, driving or idling the battery isn't being charged - at least according to iDrive.

I'm assuming the car is programmed to charge the battery when the engine is running if the battery is below a certain charge level, and then switch to efficient charging once it reaches a certain charge level, but this is just a guess basis what seems logical.

I was experimenting with this to assess how quickly the car would charge the battery during short drives: after a couple of days of sitting in the garage I measured the battery voltage at around 13.3V, then took the car for a 20 or so min drive and deliberately using engine compression to charge the battery, the voltage then raised to about 13.5V. I'm not sure what the voltage would have been if I had driven normally and not deliberately slowing down while in gear frequently to attempt to charge the battery faster. I then used a CTEK LiFePO4 charger until step 7 (full charge), and measured the voltage at just under 14.3 - close to a nominal full charge of 14.4V for a 4-cell battery.

Does anyone know what the charge algorithm for the car is? Given how expensive these batteries are, and also considering that I travel a lot (car sits a few days relatively frequently) I was hoping that it would charge the battery at all times when the engine was running until it reaches full charge or close to a full charge, not only when slowing down while in gear. I know it's programmed like this for efficiency purposes, but this doesn't help maintain the battery as well if driving distances are relatively short, especially If the car sits a few days at a time in between.
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      08-07-2019, 11:03 AM   #2
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It'd be interesting to know...

I drive my car probably.... 1-2 miles / day... maybe once every other day. I had some battery issue with my old Porsche Panamera Turbo...
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      08-07-2019, 11:05 AM   #3
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I believe you are on the right track. The battery is certainly being charged under engine coasting or braking scenarios, and it is also being charged when needed while driving normally.

My car sits for over a week at a time due to travel, the longest was 12 or 13 days and the car started without any issues at all. I would not worry one bit about the car sitting for a few days. LiFePO4 batteries can take a lot more 'abuse' than the old lead acid batteries they replace.
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      08-07-2019, 11:51 AM   #4
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Quote:
Originally Posted by PK1 View Post
Looking at the "EfficientDynamics" screen in the iDrive, it shows that the battery is only charged when the car is in gear and under engine compression/slowing down (2018 M3 6MT). While accelerating, driving or idling the battery isn't being charged - at least according to iDrive.

I'm assuming the car is programmed to charge the battery when the engine is running if the battery is below a certain charge level, and then switch to efficient charging once it reaches a certain charge level, but this is just a guess basis what seems logical.

I was experimenting with this to assess how quickly the car would charge the battery during short drives: after a couple of days of sitting in the garage I measured the battery voltage at around 13.3V, then took the car for a 20 or so min drive and deliberately using engine compression to charge the battery, the voltage then raised to about 13.5V. I'm not sure what the voltage would have been if I had driven normally and not deliberately slowing down while in gear frequently to attempt to charge the battery faster. I then used a CTEK LiFePO4 charger until step 7 (full charge), and measured the voltage at just under 14.3 - close to a nominal full charge of 14.4V for a 4-cell battery.

Does anyone know what the charge algorithm for the car is? Given how expensive these batteries are, and also considering that I travel a lot (car sits a few days relatively frequently) I was hoping that it would charge the battery at all times when the engine was running until it reaches full charge or close to a full charge, not only when slowing down while in gear. I know it's programmed like this for efficiency purposes, but this doesn't help maintain the battery as well if driving distances are relatively short, especially If the car sits a few days at a time in between.
It's definitely not showing the charge from the alternator.

The "efficiency" portion is to show you that you are coasting without using gas and that you are charging the battery from the compression as well.

If the battery only charged from coasting in gear, pretty sure most 6MTs would need an external battery charge every week.
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      08-07-2019, 01:31 PM   #5
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      08-07-2019, 01:38 PM   #6
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My dash cam eats up the battery even though I set a minimum voltage at which point the dash cam shuts off. When I get in the car it says the battery was being drained. How bad is this for the battery if it charges up after I drive? I guess prolonged use of a dash cam in parking mode is a bad idea.
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      08-07-2019, 02:21 PM   #7
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Are you asking how an alternator works?
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      08-07-2019, 03:57 PM   #8
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      08-07-2019, 04:31 PM   #9
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At one point this push for efficiency lead to insufficient charging. And there really was little to no charging except when decelerating in gear. And in the US, so many drivers dont lift and coast. Its gas/brake/gas/brake/complain about poor MPG/gas/brake. lol.

Anyhooo, batteries were not lasting very long so there was a service change where at every oil change they would also swap the battery. And you think, this should be a trivial software update to force the system to charge more, but there was an excuse I recall hearing: it was "related to braking logic and would require the full round of crash/saftey testing/blah"

I would also like to know the actual charge state/logic on newer/current cars.
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      08-07-2019, 05:03 PM   #10
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Be carful with charging your Lithium-ion battery. Everything over 13.6V will kill you battery long term. You can charge your battery with a regular charger but need to limit the output to Max. 13.6V.
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      08-07-2019, 06:52 PM   #11
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By the wag - you can change the setting so the section under your RPM shows your driving modes as opposed to the silly/useless charging screen
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      08-07-2019, 07:01 PM   #12
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I don't have an answer for you but my car routinely sits for 3-4 days at a time and has sat 10 days or more on multiple occasions. Never had an issue and I wouldn't worry about it unless you plan on it sitting a couple of months.
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      08-07-2019, 08:40 PM   #13
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Quote:
Originally Posted by agentrnge View Post
... there was an excuse I recall hearing: it was "related to braking logic and would require the full round of crash/saftey testing/blah"
...
What I'd heard was it had to do with the fuel efficiency ratings it got. Since the Efficient Dynamics charging settings were done to improve fuel economy BMW would have had to recertify the cars with the EPA. This would have resulted in new lower official MPG numbers which would have opened them to a huge class-action lawsuit from owners.

The problem wasn't so much that people only braked vs coasting to a stop, it was that people spent too much time cruising. BMW hadn't counted on just how long drivers on US highways could spend at a steady speed.
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      08-07-2019, 10:42 PM   #14
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Thanks all. I'm not really worried about the battery life per se, but became curious about charging algorithms when playing with iDrive screens and got to the EfficientDynamics screen.

I'd still be interested to know how the car charges the battery if someone here actually knows. Just for giggles, I measured the battery charge tonight after taking the car to work in the morning and back tonight (7 miles of highway driving each way). The voltage was 13.3V, exactly what it was when I measured it after a couple of days of sitting!
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      08-07-2019, 10:47 PM   #15
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Quote:
Originally Posted by LOW4LYF View Post
Be carful with charging your Lithium-ion battery. Everything over 13.6V will kill you battery long term. You can charge your battery with a regular charger but need to limit the output to Max. 13.6V.
You may be conflating Li-Ion with LiFePO4, the latter being the chemistry of the battery in our cars. The voltage per cell is higher in Li-Ion than it is in LiFePO4, so if a car used Li-Ion (less safe), then it would need to be a three-cell pack and not four as it would be with LiFe. Unless my understanding is wrong, a four-cell LiFe battery can safely be charged to 14-14.2V.
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      08-08-2019, 08:57 AM   #16
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The BMW Intelligent Charging System constantly charges the battery at a rate commensurate with the age of the battery - it increases as the battery ages. It's the same in all BMWs, and that's why you have to "register" a new battery when it's replaced so it own't be overcharged. The "efficiency" indicator has no bearing on whether or not the battery is being charged and is more of an indicator of how "efficient" the powertrain is at any given moment with regard to throttle position, engine load, etc.
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      08-08-2019, 01:21 PM   #17
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As part of EfficientDynamics technology, BMW has an Intelligent Alternator Control (IAC): "The battery is charged to only about 80% of its capacity whenever the engine is pulling the vehicle, always maintaining an adequate reserve for the consumption of energy at a standstill and for starting the vehicle. A higher charge level is generated only when the vehicle is in overrun or upon application of the brakes, that is in phases with a better energy balance."
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      08-08-2019, 02:18 PM   #18
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Section 6 of the technical training manual is well worth a read if not already

http://f80.bimmerpost.com/forums/att...5&d=1406475520

Loads of interesting info on the expensive box and its contents that BMW made look like a conventional battery with Li-Ion on the sticker on it !
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      08-08-2019, 05:31 PM   #19
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Very helpful! Thanks all, especially the link to the training manual.
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      08-10-2019, 02:55 AM   #20
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I've been watching my voltage trough radar detector since I've got the car. I know some will say it's not accurate way but it's been within 0.2V compared to Voltmeter or voltage read out from test screen in cluster.

Hopefully this won't look confusing, it's pretty much the same as explained above.

Example, hwy cruising with outside temp above 20C reads 12.8V - 13.00V most of the time. Occasionally jumps to 13.3V. and it happens after long periods without coasting or using brakes.

In winter time and temp around and bellow 0C voltage doesn't drop bellow 13.4 with engine running and it goes as high as 13.8V, not affected by full throttle which is the case in summer/hot weather when voltage drops even to 12.6V under hard acceleration.

Car off 13.2V after starting and holding brake pedal for few seconds brings it up to 13.6-13.8, without holding the brake it stays at 13.2V. This sounds like if you wanna charge up battery, there's no need for driving the car. Just hold the brake pedal for 5 seconds to activate charging and keep idling.

Majority of charging happens when brake pedal is used and vehicle is stationary. Highest voltage I've seen was coasting downhill without using accelerator nor brakes (engine braking) it goes up to 14.4V, short downhills usually 14.2V.

In the end charging maps for every car could be slightly different, depending mostly on the condition of the battery and outside temperature.
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      08-13-2019, 07:35 AM   #21
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Quote:
Originally Posted by agentrnge View Post
And in the US, so many drivers dont lift and coast. Its gas/brake/gas/brake/complain about poor MPG/gas/brake. lol.
It's because Americans are such opportunistic people. Even when staring into a wall of brake lights and stopped traffic ahead, each one still inherently believes that he alone will break through and succeed unencumbered in getting to his destination. Even still after slamming on his brakes and cursing over his selection of either mumble rap or Rush Limbaugh, his resilience is so strong that he immediately casts aside the lessons of the past 10 seconds, 10 minutes, or 10 years and proceeds to manifest destiny all over again.
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      08-14-2019, 02:13 PM   #22
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Originally Posted by ellipsis212 View Post
It's because Americans are such opportunistic people. Even when staring into a wall of brake lights and stopped traffic ahead, each one still inherently believes that he alone will break through and succeed unencumbered in getting to his destination. Even still after slamming on his brakes and cursing over his selection of either mumble rap or Rush Limbaugh, his resilience is so strong that he immediately casts aside the lessons of the past 10 seconds, 10 minutes, or 10 years and proceeds to manifest destiny all over again.
This made my day.
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