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Discussion Starter · #1 ·
Drove my car one day parked it in the garage, the next morning trying to start, all I hear are loud clicks and it would not turn over the engine. Jumped the battery and my car started. I charged my battery manually with a charger in my garage then drove it to get tested. Everything tests OK, my battery is good but one thing about my alternator is that when I initially start the car it will only give 12.1 v output and within 10-15 sec it will go to 14.2. One tech said that it should be at 14.2 at the beginning and that I should replace it but an alternator shop told me that this is normal and it is called something like “delayed charging alternator” common in BMWs where it is designed to start lower and go to 14.x shortly after.
The puzzle is, why it happened when all components are testing OK now. It was a colder night but nothing special, we had few even colder nights a week before that and I had no issues. What does your alternators output at the start, is it 14.x from the beginning?
Thanks
 

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The running UB (in your cluster) should be between 13.6 and 13.8. Seeing the amount of wiring, .4V drop isnt out of the question when comparing direct readout from the alternator and from the cluster.

To answer your question, I think it's normal (the voltage regulator takes care of this). If the battery keeps dying, you might have an issue with your alternator (or a dead battery)
 

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Discussion Starter · #3 ·
I agree it is either the battery or alternator but they both check OK for now, providing that my alternator reachign 14.x withing 15 sec is indeed OK??.., and that is what I am trying to find out?
 

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I agree it is either the battery or alternator but they both check OK for now, providing that my alternator reachign 14.x withing 15 sec is indeed OK??.., and that is what I am trying to find out?


Who is doing the checking? How did they measure output? Also, what brand/how old/what size is the battery?

Independent battery shop diagnostics dont necessarily work well (most had issues with my 89 Merc 300E). You'll need to see what the output to the cluster is at idle and we'll go from there.
 

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Discussion Starter · #5 ·
Who is doing the checking? How did they measure output? Also, what brand/how old/what size is the battery?

Independent battery shop diagnostics dont necessarily work well (most had issues with my 89 Merc 300E). You'll need to see what the output to the cluster is at idle and we'll go from there.

Well, I did at 3 diffrent shops, Schucks Auto Parts, Patteries Plus, and another Schucks.. , They all used diffrent but very similary testing equipment, the one that is the size 5x12 inches and has a digital display showing how the battery, starter and alternator work. They all sowhed the same resulsts whichs is: my alternator start at 12.1 and reaches 14.2 withing 10-15 sec, the question is: "is this normal" one shop said yes anohter one said replace the alternator?? Thanks
 

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Well, I did at 3 diffrent shops, Schucks Auto Parts, Patteries Plus, and another Schucks.. , They all used diffrent but very similary testing equipment, the one that is the size 5x12 inches and has a digital display showing how the battery, starter and alternator work. They all sowhed the same resulsts whichs is: my alternator start at 12.1 and reaches 14.2 withing 10-15 sec, the question is: "is this normal" one shop said yes anohter one said replace the alternator?? Thanks
And Im going to keep telling you that testing equipment is only as good as the guy using it. Either way, alternator output is measured in amperes...the only time you look at voltage is to see if the voltage regulator has failed. There are 3 different parts of these alternators that can fail. If the voltage regulator were bad, you'd go above 14.2 when the engine is revved and the voltage would be all over the place at idle. Have you ever accessed the secret menu and looked at the battery voltage in there while the car is running? That's where you'd notice if it were a dead/dying battery or an alternator.

Humor me and go check. Also, the battery size/brand/age would be infinitely helpful to know.
 

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Discussion Starter · #7 · (Edited)
Yes, I know that techs can miss-interpret readings, but 3 different techs reported the same finding with 3 different tools and based on that I think the information about my alternator is fairly accurate. I don't know how old my battery is (I wish) and I have not looked into the hidden menu (I will). Before I change batteries I want to make sure my alternator is behaving as designed so that I don’t ruin a new battery if my Alternator is bad.
 

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Yes, I know that techs can miss-interpret readings, but 3 different techs reported the same finding with 3 different tools and based on that I think the information about my alternator is fairly accurate. I don't know how old my battery is (I wish) and I have not looked into the hidden menu (I will). Before I change batteries I want to make sure my alternator is behaving as designed so that I don’t ruin a new battery if my Alternator is bad.

That's well and good. The electrical system on our cars is a bit more complex than most...so I dont trust those tests. The battery age is usually indicated on the sticker thats on the battery. Either printed mm/yy, or with dots missing on the corresponding month and year for an OEM BMW/Douglas battery. The secret menu will give us battery voltage whilst the car is running, and paint a clear picture as to what's doing what.
 

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Discussion Starter · #9 · (Edited)
I have looked for a sticker but can't find one, I will tonight again to make sure I am not missing it. My battery is OEM BMW battery...
Also..., my battry light is not "ON" up on the dash, whichs is what happend when my alaternator died on my old e39 540i.
 

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Discussion Starter · #11 ·
The indicator Dot is black (not enough charge) but I was told that those dotes are not an accurate way of reading the state of the battery...?? How old is "too old" for a battery?
 

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Discussion Starter · #13 ·
I can further test the battery and look for dates on it, but even if I look into the hidden menu and see some amp numbers, I still dont' know if upon start of the vehicle when my alternator gives 12.1 amp and later reaches 14.x amp, is this good or bad??, I don't have a baseline of what normal is
 

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Your alt volts are wrong. Sign of a failed diode. The field (windings) are live and drawing power from your battery. It is trying to be a motor, which it cannot be because the brushes are not configured for that. The other thing that could do that is a surface charged Battery. Which reads right by all tests but has no reserve. If you turn on the radio for 15 mins your battery will not have enough to turn over your car. In this case the battery sucks all the amps the alt can produce so the volts are low just after start.

Sorry this really does not give you an answer, but I have a test for you that should tell you. First with key on and motor off run the stereo for 15min then try and start the car. No start- still no answer could be either. Charge the battery with a charger and do the test again. If it is still no start then bad battery, but if it was better then alt also.

Likely both are bad. if the diode fails there is really no signs until the battery is effected which can take months. Likely both are bad in your car. Alt is bad and killed your battery. It charges but it also discharges. Another good simple test is start the car and turn on everything you can. Listen to the fan and watch the lights. you may not have full amps at idle but it should only take you raising the rpm by 100 to have the fan at full speed and the lights at full bright. My car has full power at idle not all do though.
 

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BMW has installed "soft switching" alternators in our cars (and all others since), so showing 12v for a while before rising to 14v is completely normal. I'm not saying there's nothing wrong with your alternator, only that your observation of voltage is normal.

As for your battery, look on the negative post and there should be two pairs of numbers stamped into it. The upper one is the week of manufacture, the bottom the year. Factory batteries typically last from three to five years depending on how they've been treated, number of discharges, etc.

It sounds like you have a draw which has flattened your new battery. The correct way to find this is with an ammeter and a device which will enable you to condition the car as if you were to have driven it (start the engine, work some electricals like windows,sunroof, etc. then shut off, get out and lock. Make sure the trunk is open and latched), then without breaking the circuit, place your ammeter in series with the battery and wait for 16+ minutes til it falls asleep. Set the meter to min/max and record for an hour or so and if the closed circuit current is more than 40 milliamps at anytime, you should do more investigating. Maximum average draw for our cars is about 25 milliamps. More than 40 is abnormal.

Let us know the results.
 

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Good lord.

15 seconds is nothing in the life of your car. I have no idea if my car goes to 14V immediately or 15 seconds after start, nor do I care, and neither should you since it isn't relevant. If your alternator gets to 14V after 15 seconds then look elsewhere for the problem.

Most likely culprit is a failing FSU, which, incidentally, is also almost impossible to diagnose. In the meantime, if your vehicle doesn't die again I wouldn't worry about. If it does, I'd replace the FSU. If it still dies after that then I'd do more detailed diagnostics. I've written very detailed steps that describe what Lardog88 suggested above - find them and follow them and your problem will go away.

d-
 

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Discussion Starter · #17 ·
OK, had to pull the battery out to see the date sticker, it says" shipped July 2007", the numbers on the negative terminal says 04 07. So my battery is not new but not super old, a?? One thing i know about my car is that after I open the trunk and close it I can hear for a while the Nav CD system going on with souds like you just put a CD in it and is trying to adjust it. I have evern heard it other times as I walk by my car so I am not sure if it may be doing it on and off all night, however this is nothing new it has been going on for years. Do your cars have the same noises coming out from the Nav CD player in the trunk?
 

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+1 on probable FSU

Get a multimeter and test the voltage at the battery. With car off should be in the 12v range (assuming it isn't already dead). With engine running you should see something in the 14v range (I have no idea if it takes a min or two to get there). IF you see the voltage fluctuating rapidly with the engine running it is likely your voltage regulator is bad.

If the charging volts look correct, go ahead and disconnect the FSU (there are a number of threads on the board) and then run the car normally to charge up the battery. If it doesn't drain then you should replace the FSU (very simple, but helps to have small hands). Its a $50-60 part and 10 min of your time.
 

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I'll respectfully disagree and say that a 3.5 year old battery should still have at least a couple more years in it, even if it you discharged it once (the fact that you got clicks, even though it would start, means that it wasn't fully discharged, it just didn't have enough amperage to spin the starter).

You could replace the battery - that is an alternative, but could also lead to replacing your battery yet again if you do have an undiagnosed current leak. A better option, in my opinion anyway, is to get a trickle charger and use it to fully recharge your battery, then work on diagnosing the real issue. Chargers are relatively inexpensive (mine was $30) and can be purchased at many locations.

d-
 
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