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Thread: HELP: Severe Parasitic Battery Drain

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    HELP: Severe Parasitic Battery Drain

    I have a severe battery drain. I've narrowed it down to fuse 43. The following are on 43: central locking (which includes interior lighting), trunk light & sunroof. I removed the sunroof but the 2 connectors (switch & motor) remain dangling. I assume the sunroof circuit is the culprit. Now what??? How do I disable power going to the sunroof switch & motor? Any help or thoughts are appreciated.

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    Drain

    If you have gone so far as welding/removing your sunroof completely, just pull out the motors and switches cut the wires and tape them.

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    Quote Originally Posted by rjjablo View Post
    ...[P]ull out the motors and switches cut the wires and tape them.
    Roof replaced with sunroof delete roof. Motor & switch removed. Are there more than 1 of each?

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    There is a lot more on F43.
    Central Body Electronics is a host of circuits such as the General Module A1 which is notorious for the electrolytic capacitor failures.

    I would suggest you refer to the ETM to start your troubleshooting.
    I have attached page 0670.3-18 which has the list of systems on fuse 43.
    You will want to use an amp-meter as a fuse replacement to measure the parasitic current draw. You will most likely want to use a battery charger to keep the battery charged while you troubleshoot.
    Then go to each system that is connected to the F43 circuit and disconnect that circuit (unplug connectors that supply that module) from the fuse until you discover the system that is the culprit.
    The General Module A1 (page 6100.0-03) is supplied through the Relay Module A5 on connector/pin X253-1.
    Once you discover the system that is causing the current draw you will need to disconnect the loads and control elements connected to the modules to isolate the actual component.
    Following this method would allow you to isolate the faulty module/component without guessing and trying things that have no bearing on what is actually causing the problem.
    Best of your effort..
    Attached Files Attached Files
    Last edited by m6bigdog; 03-30-2019 at 03:27 PM.

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    What is the current drain after 16 minutes? What is the battery voltage after 16 minutes?
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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    Quote Originally Posted by Timm View Post
    What is the current drain after 16 minutes? What is the battery voltage after 16 minutes?
    Current drain 400mA; with F43 removed current drain is 40mA; battery voltage while testing 12V; however voltage drops precipitously if F43 in place. All testing done >16 minutes and with full charge. Relays K72 & 73 tested and OK.

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    12V at the batteries mean that the batteries have very little charge - or they are dead. Further info that shows the batteries are dead is that the voltage drop precipitously with F43 in place - at a current of 400mA a decent pair of batteries will maintain good voltage (above 12V) for 200 hours or so. You cannot test for battery drain with batteries that are in poor condition so I think I would start with a new pair of batteries and take it from there.

    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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    Quote Originally Posted by Timm View Post
    12V at the batteries mean that the batteries have very little charge - or they are dead. Further info that shows the batteries are dead is that the voltage drop precipitously with F43 in place - at a current of 400mA a decent pair of batteries will maintain good voltage (above 12V) for 200 hours or so. You cannot test for battery drain with batteries that are in poor condition so I think I would start with a new pair of batteries and take it from there.
    I took car to Interstate shop to buy 2 batteries. They checked the batteries and alternator and said they were fine. I believed them because it meant a revenue loss to them. Checked batteries this morning. They are >13V at 65 degrees.

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    Quote Originally Posted by radlaw View Post
    Current drain 400mA; with F43 removed current drain is 40mA; battery voltage while testing 12V; however voltage drops precipitously if F43 in place. All testing done >16 minutes and with full charge. Relays K72 & 73 tested and OK.
    Most problems with battery voltage measurement while under load/drain isn't the state of charge (SOC) it is the discharge rate.
    State of charge voltage is an open circuit 0 current drain voltage measurement.
    A fully charged (100% SOC) battery will drop below 10 volts for the seconds that the starter is engaged.
    That is when the battery is under load it is impossible to measure/infer a SOC in reference to the battery voltage.
    The typical sleeping current drain for the 850 can be as high as 50 ma.
    The 400 ma is the problem and that would drain new batteries in a day easy.

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    Sorry to disagree - but, this is a simple calculation - two batteries of 65Ah each is 130Ah total, this means that a pair of fully charged batteries can supply 1A for 130 hours to a point of zero SOC - at this point the terminal voltage will still be just below 12V (11.9V).

    A 400mA drain (0.4A) using the same method gives us 325 Hours. So, to be on the safe side, we can say from a full SOC to 50% SOC we would expect 162 hours or 6.7 days - and at this point the battery voltage will still be around 12.2V

    This isn't what the OP is seeing - his battery voltage is rapidly dropping away from 12V - and that means either the batteries were not charged, they are dead or the battery drain is much in excess of 400mA.

    I would agree that the problem is very likely to be the General Module capacitors - but it is not worth pursuing until a proper test is run as my experience of these problems are more likely be due to poor batteries than an actual electronic fault. Usually by this stage of the game the batteries have spent so long at 0% SOC that they are dead.

    More info here:

    https://www.meeknet.co.uk/e31/E31_Ba...iagnostics.htm
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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    I'll let Timm & m6bigdog (love that name) figure all that out. Too much for me. Any others feel free to chime in. Meanwhile, I'm going to get the batteries checked again and go from there.

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    How can a battery that is only 50% charged still have ~12 volts? Why does temperature also have such an effect?

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    All you could ever ask is answered on this website:

    http://www.batteryfaq.org/
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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    Quote Originally Posted by Timm View Post
    Sorry to disagree - but, this is a simple calculation - two batteries of 65Ah each is 130Ah total, this means that a pair of fully charged batteries can supply 1A for 130 hours to a point of zero SOC - at this point the terminal voltage will still be just below 12V (11.9V).

    A 400mA drain (0.4A) using the same method gives us 325 Hours. So, to be on the safe side, we can say from a full SOC to 50% SOC we would expect 162 hours or 6.7 days - and at this point the battery voltage will still be around 12.2V

    This isn't what the OP is seeing - his battery voltage is rapidly dropping away from 12V - and that means either the batteries were not charged, they are dead or the battery drain is much in excess of 400mA.

    I would agree that the problem is very likely to be the General Module capacitors - but it is not worth pursuing until a proper test is run as my experience of these problems are more likely be due to poor batteries than an actual electronic fault. Usually by this stage of the game the batteries have spent so long at 0% SOC that they are dead.

    More info here:

    https://www.meeknet.co.uk/e31/E31_Ba...iagnostics.htm
    I'm sorry you disagree also. And, it is not a simple calculation.
    The AH specification when used for battery capacity is well below 12V!! Like down to 10.5V and a starter battery is pretty useless at 10.5 volts and that is why AH is not a true starter battery performance specification.

    As I stated, the issue with starter battery isn't SOC it is discharge rate and you can do all the AH math you want but if you don't apply it to the actual battery performance, the analysis all falls apart.
    Cold Crank Ampere (CCA) and Reserve Capacity (RC) are the design specification/ratings for engine Starter Battery performance.
    Ampere Hour (AH) is the design specification/rating is for Deep Cycle Battery performance.
    Ampere Hour rating is also useful to select the charge rate.

    Can you do CCA calculations/test on a deep cycle battery and AH calculations/test on a starter battery?
    Sure! but the conditions of the test determine the results and the calculation will not follow the test results if the calculation is at the wrong end of the performance curve. Why? because the performance curve is non-linear!!

    So given 2 each 65 ah batteries in parallel is 130 ah.
    While I would believe you could drain the battery at a 5 ampere rate for maybe 20 hours (100ah) and down to 10.5 volts.

    I doubt the 130 ah with a 400 ma load would last 1/4th of your calculated 325 hours or 6.5 day.

    So here is why and you already know the answer!!
    How long will your 8's batteries last without charging before your 8 won't start? What could be a better performance test than drain the battery then test if it will reliably start the engine.
    The parasitic drain specification for the E31 is 50ma max.
    So based on your ampere hour calculation the 130ah/.05amp = 2600 HOURS or 108 DAYS or 3.6 MONTHS!! and still have 12 volts on the battery terminals!!
    BMW engineers would have loved that battery performance.
    So, how long do your batteries in you 8 last before they will not start the engine? A week, maybe 2 weeks? if you are really lucky maybe 3 weeks!!.
    THREE MONTHS!! never!!
    I would presume if you buy new batteries and leave your 8 for only 2 months, you will need to buy new batteries.

    So what happened, you ask? It is the rate of discharge that killed the ampere hour rating.
    High current draw (above 5 amps) calculates AH with some certainty (somewhat linear). But, at the low current draw (below 1 amp) the AH rating is pretty useless (non-linear) for a starter battery.
    A starter battery isn't designed to maintain a low current drain!! and if you do long term low current drain on the battery it will be damaged.
    Hence, it is a best practice to keep the battery on a charger while you troubleshoot electrical problems.
    If you don't you may discover even a new battery will be depleted and sulfate the plates in short order.

    The worst thing to do to a starter battery is to slowly discharge it for hours and hours!! Yep, 50ma for days is bad news!!
    The starter battery design is for CCA to start the engine and be on a charger until the next CCA discharge.
    The Reserve Capacity is for running the accessories for a short time until the engine is started to take the load and recharge the battery.

    FWIW,
    http://all-about-lead-acid-batteries...are-amp-hours/

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    You seem to be arguing with yourself here and have completely missed the point!

    The OP has a pair of fully charged batteries that have a precipitous voltage drop after 16 minutes with only a 500mA load.

    The answer is simple as previously stated, the batteries are dead, or the batteries were not charged, or the measurement was incorrect - it really is a simple calculation!
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    Had a similar problem which I located to the GM module, took it out and replaced the five capacitors and got down the consumption to 43mA. If you have the opportunity to borrow a GM module that you know works then try before changing.

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    Quote Originally Posted by Timm View Post
    You seem to be arguing with yourself here and have completely missed the point!

    The OP has a pair of fully charged batteries that have a precipitous voltage drop after 16 minutes with only a 500mA load.

    The answer is simple as previously stated, the batteries are dead, or the batteries were not charged, or the measurement was incorrect - it really is a simple calculation!
    Tim, I don't want to argue with you!! We have done this before.
    Neither of us are there with the OP, using our meters and can only interpret their post from the information provided.
    IMHO, "voltage drops precipitously" is not a technical explanation of the actual battery condition nor the rate of discharge.

    FWIW, I hope you read my reply as to why attempting to do "Ampere Hour" calculations is a flawed analysis and blowing that off does not help anybody.

    As I stated; again, if the battery will start the engine after 16 minutes with a 500ma load, they have enough capacity at that point to function as a "starter battery" and the batteries are not dead irrespective of the terminal voltage or SOC.
    Both you and the OP can agree on this as a valid functional test for adequate battery charge and the OP can get back to troubleshooting the cause of the 400ma parasitic current draw.
    Best Practice, put a charger on the battery while you troubleshoot the electrical problems and even if the batteries are close to dead (functionally or SOC) you can discover the source of the 500am drain which is what caused them to get that way.

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    Yes, no need to argue at all - always the problem with forums!

    I would advise something similar - switch the sidelights on for 16 minutes - if the battery voltage is still above 12V = all OK for the closed current test. If the voltage is heading below 11V then the batteries need replacing.

    With the standard bulbs fitted (unlike a lot of us that either have LED's or doubled-up bulbs) the current draw is around 1.6A - enough to get rid of the surface charge

    That should do it!
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    UPDATE: Bought new AGM batteries. Charged to 100%. Checked drain: 1 amp. Let sit overnight: 11% parasitic drain to 89%. Now what? Do I got through the fuse-by-fuse method?

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    You certainly can do - but no need to pull fuses:

    http://www.meeknet.co.uk/E64/Fuse%20...20Readings.pdf

    ...and the fuse locations:

    http://www.meeknet.co.uk/e31/Timms_B...use_Finder.htm

    It isn't as hard as it first seems as it takes seconds to test each fuse....

    It is also worth saying the 1A is more than the typical current drain if the General Module fails to go to sleep - there must be something getting hot somewhere!
    Last edited by Timm; 04-15-2019 at 03:04 PM.
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    Timm: Thank you for all your information. I reviewed the links above. After reading the "Fuse Voltage Readings To Give Current Readings", I wondered if it isn't easier to do the fuse-by-fuse method, instead of checking voltage across each fuse then remembering the fuse amps then going to a chart and looking up the correct voltage. It seemed timely to do that. your thoughts. Again thanks all for your help.

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    Most of the fuses will show absolutely no voltage across them and you can immediately discount them - it is only when you come across a fuse that actually has a voltage across it that you need to compare that with the table. So, it's pretty quick and easy. A 1A demand on a fuse will be immediately obvious.

    Although removing fuses sounds like an easy plan, when you remove one you may reset the timer in a module and you will be on a 16-minute wait until you can move on!
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