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BMW F10 520d -Battery or alternator ?

  • 13-02-2022 11:51am
    #1
    Registered Users, Registered Users 2 Posts: 10,153 ✭✭✭✭


    Hi folks,

    I've had an intermittent BATTERY NOT CHARGING mesage on idrive screen. Car driving fine - no other warning lights. Checked voltage this morning at battery terminals. 11.5v when off. Same when running. I'd expect if the alternator was functional I'd get over 14v at the terminal ? Just don't want to fork out for a battery if the alternator is the root cause. In cars of old, i'd have just whipped of one of the battery terminals when running and if it died, then it was a good indicator that the alternator was toast but I'd wager that this exercise would be unwise with the complexity of current auto electronics !



Comments

  • Registered Users, Registered Users 2 Posts: 1,242 ✭✭✭BlakeS94


    If the alternator was bad the car would keep dying while its driving because its not giving enough of a charge to the battery.

    I would say your battery is toast and is refusing to hold a charge. 11.5volts is a fully discharged battery.

    An alternator is designed to maintain a battery's voltage, not to recharge a dead battery, but I think the alternator is just about keeping the battery going for now.

    A working battery will hold a charge between 13.5v and 14.5v while the engine is running.

    Try stress testing the alternator by turning on all the accessories while engine is running, lights, A/C, radio, demister then check the voltage at the battery with all that stuff on, the voltage shouldn't drop.

    The old remove a terminal while engine is running is not recommended with all the modern electronics in cars



  • Posts: 468 ✭✭ [Deleted User]


    Easy times is over. Now is smart alternators and these can be much harder to diagnose. You need oscilloscope to see what is going on single communication wire. On that car it should be linbus (if I am not wrong). Some "smart" alternator can work if the communication wire is disconnected. Not so efficient as computer controlled but it can show to you the problem...network/module.

    I am sure we all agree 11.5V the alternator should work over time, smart or not.

    Start from battery terminals. If there is not good connection, no any alternator can charge that battery. Clean the terminals if necessary. Do not over torque the terminals. Soon as you can not wiggle the terminal anymore, it is tight enough. Manufacturers ask typically only around 8Nm torque +/- something.... I do not go deeper rabbit hole, you need to start from somewhere and tell to us the progress



  • Registered Users, Registered Users 2 Posts: 10,153 ✭✭✭✭dodzy


    Thanks lads,


    Blakes, exactly my thinking....battery just about holding on by a thread. I'll take the plunge and grab one from halfords (€150). 110ah as opposed to the stock 105ah should be fine ? Will recoding be required do you guys think ? I have Ista to reg the battery anyway but not sure if recoding is required because difference in amp hour? Hmmm, bimmercode might work



  • Posts: 468 ✭✭ [Deleted User]


    It is recommended to program the right values by computer. Sure, car can learn it over the time but it can cook the battery before that time. To avoiding "big explosion" program it and remember to connect the ventilation hose too.



  • Registered Users, Registered Users 2 Posts: 3,623 ✭✭✭John.G


    Even if a battery is fully discharged and knackered (not holding charge) a working alternator will certainly register more than 11.5V, as a matter of fact a knackered battery will often "fully" charge in a matter of minutes even with a trickle charger as it may only have a capacity of a few AHs.

    I would get the alternator checked out first.



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  • Registered Users, Registered Users 2 Posts: 839 ✭✭✭mk7r


    It will be the alternator not the battery



  • Registered Users, Registered Users 2 Posts: 10,153 ✭✭✭✭dodzy


    So folks, based on above and only registering 11.5v at battery terminals when running, the alternator is the likely culprit ? I should be getting c.14v when running at the terminals even if the battery is knackered ?



  • Registered Users, Registered Users 2 Posts: 3,623 ✭✭✭John.G


    Yes, definitely, without doubt, the battery may well recover if it has only been deep discharged only once or so.

    Obviously you have checked all connections secure.



  • Posts: 468 ✭✭ [Deleted User]


    How you make that conclusion? The smart alternator does not start charging the weak battery. If BMS changes that battery registration value almost to 0Ah, then that type of battery does not need any charging.... First test everything!



  • Registered Users, Registered Users 2 Posts: 3,623 ✭✭✭John.G


    A battery with a terminal voltage of 11.5V still has approx 10% to 12% SOC, you can have a brand new battery that has been discharged to this low level, a new say 100AH battery will still have ~ 10AH so will require 90AH to return it to its original SOC, A 10 or 12 year old 100AH battery may only have 20AH when fully charged so will only require 18AH to return it to its 100% SOC. In either case a healthy alternator, smart or otherwise, will return either to its 100% SOC. (either 100AH or 20AH)

    Not quite in the same league as smart alternators but most smart trickle chargers will only refuse to charge if the terminal volts are down around 8V or so.

    Also bear in mind that we are merely suggesting that a new battery shouldn't just be thrown at the above problem and obviously some testing has to be carried out.



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  • Registered Users, Registered Users 2 Posts: 9,619 ✭✭✭CoBo55


    Jaysus you must have bought the Ladybird book of smart charging!! You hadn't a clue about it a few days ago.

    @Op Your alternator is a gonner, without a doubt.



  • Posts: 468 ✭✭ [Deleted User]


    So, you claim BMS does not measure anything? May be for you the BMS is only another expensive useless toy.

    It is very important part on modern cars and battery charging base on BMS. Of course you did not know that, because you are another "40 years of experience guy".



  • Registered Users, Registered Users 2 Posts: 9,619 ✭✭✭CoBo55




  • Registered Users, Registered Users 2 Posts: 9,619 ✭✭✭CoBo55




  • Posts: 468 ✭✭ [Deleted User]




  • Registered Users, Registered Users 2 Posts: 3,623 ✭✭✭John.G


    A BMS system, will inhibit or turn off non essential items like stop/start, air con, HRS, etc while monitoring the battery voltage, with a healthy battery and alternator then, yes, it does control the alternator output, in mine, it limits the charging voltage to ~ 12.8/13.0V while driving and sets it as high as 15.0V on car overrun, it's called regenerative charging.



  • Registered Users, Registered Users 2 Posts: 9,619 ✭✭✭CoBo55


    But you'd never see a voltage as low as 11.5V with the engine running. Looks like the alternator has packed in. One of those cigarette lighter digital voltmeters would tell the story.



  • Registered Users, Registered Users 2 Posts: 3,623 ✭✭✭John.G


    Yes, definitely looks like the Alternator, is been 4 days now so expect to get some feedback shortly.



  • Registered Users, Registered Users 2 Posts: 10,153 ✭✭✭✭dodzy


    Sorry guys, update has arrived. Knocked off early on Monday and whipped off the engine bay cover and AF housing to expose alternator terminal. Metered out running at 14.4v. Checked at battery and while running, it was showing 12.5(ish) fluctuating slightly. Again, still 14.4 at the alternator. When I turned engine off message on dash, not idrive, sated that battery was “discharging” when not running.

    headed to local motor factors for a 105ah AGM. None local so headed for green hills at 4pm. Dreaded m50. Battery is a monster: 40cms long and a heavy mother. €280 and 1 hr later, I’m back at the house. 10 mins later, new battery was in and registered with bimmerlink. Fast forward 4 days, and all is good.

    Using the nifty hidden menu on the dashboard (accessed by holding down trip meter reset) and selecting unlock in conjunction with your chassis number, there is a VOLTAGE display that’s quite slick. While driving, display fluctuates between 12.7 when engine under load and goes as high as 13.3-4v while coasting at speed. No concerning messages of any kind in 4 days, after approx 200miles.

    QUIETLY confident.

    Thanks as always for the support here. Greatly appreciated.

    Now if only I could get rid of the bloody vibration under braking. Swapped out discs for OEM only a couple of months ago and the dreaded shudder is starting to make its comeback.



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  • Registered Users, Registered Users 2 Posts: 3,623 ✭✭✭John.G


    Thanks for the update., very interesting. Strange that you were getting 14.4V at alternator terminal and only 12.5V at the battery terminals, normally this would indicate a very poor connection(s) or a cable breakdown, you might try this sometime again as a voltmeter gives excellent info, you might also consider putting the meter,s positive terminal at the alternator end of the connecting cable and the negative at the battery cable end, you should see practically no voltage drop if cable & connections secure, would also suggest monitoring the battery voltage fairly regularly as you don't want this battery to discharge down to 11.5V.



  • Posts: 468 ✭✭ [Deleted User]


    Good lesson for amateurs. They was really ready to replace your alternator...



  • Registered Users, Registered Users 2 Posts: 10,153 ✭✭✭✭dodzy


    Cheers, it’s got to be regulating the charge to the battery as is the case in your example, as it sees fit. Only explanation why it’s solid 14.4 at the alternator and reduced at the battery. Anyway, I’m sure if the battery was not the issue, I’d have seen something in 200miles.



  • Registered Users, Registered Users 2 Posts: 3,623 ✭✭✭John.G


    I don't think anybody suggested that, alternator testing and poor connections were suggested in at least 2 posts, post#6 "I would get the alternator checked out first." and post #9 "Obviously you have checked all connections secure".

    Can you explain how one can get 14.4V at a alternator terminal and 12.5V at the battery terminal.



  • Registered Users, Registered Users 2 Posts: 3,623 ✭✭✭John.G



    Sincerely hope your battery was the issue but I can definitely state that any car battery charging rate is governed by the alternator voltage, which in turn is controlled by the BMS system and if you measured its voltage at 14.4V then the voltage at the battery terminals should have been exactly the same, I would be a little concerned that this voltage, for whatever reason, is almost 2V less than the alternator output voltage which may result in the battery slowly losing its state of charge.



  • Registered Users, Registered Users 2 Posts: 3,623 ✭✭✭John.G


    AGM batteries are designed to require 14.6v - 14.8v when performing a full charge from a state of discharge, whereas standard lead acid batteries need 13.8v – 14.4v, hence this is what most onboard chargers are designed to deliver – not the 14.6v – 14.8v that AGM requires.



  • Registered Users, Registered Users 2 Posts: 9,619 ✭✭✭CoBo55


    Did you get the old battery tested before buying the new one? Maybe removing the old battery fixed a bad connection.



  • Registered Users, Registered Users 2 Posts: 3,623 ✭✭✭John.G


    If the old battery is still around it can be trickle charged with a ~ 5A charger, it should then take around 18 hours to reach full charge and when it reaches a open circuit terminal voltage of 12.6/12.8V then all well. However as a new battery is now installed then not really of much use as it will quickly deteriorate with no usage.



  • Registered Users, Registered Users 2 Posts: 10,153 ✭✭✭✭dodzy


    Old battery still in boot. I figured I’d hold it just in case the issue resurfaced but the more sites I viewed, and the fact that it’s a 10yr old motor, on its first battery, it’s likely the battery was the root cause. 5 days in after replacement and no issues. Fingers crossed. As John says, battery in now so Past the point of no return in effect. Plenty of reports of similar batteries not lasting as long and as earlier said, all the regular go to sites point to battery almost as a default….and rarely an incorrect call.



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  • Registered Users, Registered Users 2 Posts: 3,623 ✭✭✭John.G


    Have you any voltage readings from the voltage display both with engine running and off?.



  • Registered Users, Registered Users 2 Posts: 3,623 ✭✭✭John.G


    Don't know if this neighbour's 2011 Opel had a smart charger or not but it had something attached to the battery negative terminal so presumably had. Here is part of a posting I had (have) on here in Sept 2021. This battery had lasted 10 years, not bad?.

    "My neighbours 2011 diesel Opel Omega failed to start a few weeks ago (original 95 AH battery), the terminal volts were 11.8 so I connected in my 3.8A smart charger, after 32 minutes the battery/charger were up to 14.3V and the charger then went into trickle mode, 15 minutes after disconnecting the charger the terminal volts were 12.5 and the car started immediately and was constantly charging at 14.3V so alternator OK, next morning same story, no start, so new battery. Its amazing that my charger had only put 2AH into this battery in 32 minutes and it was then capable of starting the car even if only once, I can only explain it by the fact that while a cranking current of say 400A is required the energy (AH) required is quite small, a 3 sec crank at 400A only requires 0.33 AH."



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