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Alternator Failure (melted) - advise wanted

14K views 30 replies 13 participants last post by  skborders 
#1 ·
My '02 540iA has 123k miles on it.

I replaced the battery in March of 2012 at approximately 115k miles with one from Autozone.

My alternator went out in August at 119k miles and I replaced it with a rebuilt from a local auto electric shop. All was fine and dandy afterwards. Voltages were in the 13.8 range on the unlocked OBC - not as high as I expected, but were varying as I'd expect so I assume everything was fine.

The alternator went out again in February at 123k miles. I felt like the car wasn't cranking as quickly the past 6-8 weeks, but its been a lot colder and there wasn't anything I could put my finger on, so I didn't really think much about it.

I finally got it back to the rebuilder to be evaluated. He was... mad at me. He initially thought a diode went bad, but it turns out the entire inside was melted and wrecked. He gave me the diode bridge to take home. Its nasty, melted and stinks.

He said something produced a massive draw, to the point of near a dead short and just dried to draw so much power through the alternator it melted.

He asked me if the car overheated - no, temps run 1deg hotter now than before (I flushed the coolant and probably don't have the mix quite exactly the same). He also asked if I have any amps in the car - I don't, its bone stock.

I found a few threads while searching, but nothing specific to my issue.

Before I rip the chassis apart inspecting every square inch of wiring looking for short or break, does anyone have any suggestions for me?

Nothing was obviously loose when I took it apart - all connections I checked (battery, alternator) were good and tight. I figure to check all the common stuff - ground points (could use some guidance on where common ones are - did find the thread about some below a vent and will check those) and the positive cable as much as I can get my hands on.)

The battery was at 11v and showing 50% charge on my charger when I got the car home. I charged it up so it would be topped off before I installed the new alternator. I intend to take it back to AZ and have them test it.

When the alternator died, like the previous one, stuff went haywire inside the car - the radio quit, the trans went into limp mode, the hvac turned off/on/off and blew on high with no display. I just attributed it to the electrical load without the alternator, but maybe that was what blew both alternators and was a cause not a symptom.

My thoughts are -
  • Bad chassis ground somewhere (I just need to figure out where they are so I can check them)
  • Shorted out jump post on the valve cover (I replaced the plastic surround when I did the VCG last summer)
  • Break in the main power wire
  • Bad Battery (no idea how/if this would show up, but I'll take it back to be tested)

The other sort of "replace it when you have odd electrical issues" thing which comes up is the key switch. I'm not sure how this would do that, but I guess I can just throw a new one at it if nothing else comes up.

Thanks for any advice/suggestions/assistance you may have.

Scott
 
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#2 ·
Hi Scott,

this is an air cooled alternator, isn't it? Make sure the cooling is sufficient, the air duct to the alternator is clean. This is the most suspicions thing for me.
All the consumers are protected with fuses, these are not the culprit. Things, that are not protected: positive wire from alternator > jumper terminal > starter > chassis entry point > battery.
It is possible to have a temporary short at the jumper terminal if something is not right there, but I doubt it. However if you have it, that would kill the battery too.
Bad battery can draw a lot's of current, that would be my second guess, but yours is fairly new. And it usually doesn't kill the alternator.
The other possibility (but less likely) is the starter, which might draw extreme high current if it's broken. Is the speed of the cranking good with a fully charged battery?

Grounding issues wouldn't melt the alternator.

Don't expect higher voltage than 13.8V with running engine. This is a regulated voltage, if it alters more than ~0.5V something is wrong.
 
#3 ·
This is the water cooled 150a Bosch.

Thank you for the thoughts on the unprotected connections. I'll start there.

I don't think the Starter would draw through the diodes or the alternator... as described to me this was a draw when running; starting I'd think it would come from the battery.

Here's the rectifier diode bridge, these are the positive diodes



Thanks also for the 13.8 confirmation. That's what I had, and I was concerned that was low (I'm used to more out of the other cars I've owned/worked on).
 
#4 · (Edited)
AFAIK the 'theory' of alternaterism, the "field" current determines the output current of the alternator.

The field current is designed to "sense" the needs of the vehicle - so that greater needs result in greater output of current.

Could it be that the field current sensing mechanism went awry?

See also:
- Why you want to clean out the air-cooled alternator air duct & cooling vents (1) (2) (3) (4)

 
#5 ·
Maybe this is a shot in the dark, but nevertheless I spit it out:
Check the front passenger door for leaky vapour barrier. If yes - go and check below the front passenger carpet for corroded connections. These are high amps fuses.
These might go hand-in-hand with the GM3 & LCM - above the glovebox, where some other relays are housed. Check if there's water ingress from the sunroof or the cabin air filter.
If you ever spilled coffee or soda on central console, open it up and clean: flasher relay, central locking button and the airbag module connectors. Car battery out prior to these.

If you have the know-how, check & test the GM3 & LCM.


As I said, I might be totally off, but I had some issues pointing to very first one I mentioned (busted vapor barrier & correded contacts), affecting the LCM & GM3, and having some weird current draw on the battery. As I write this, I slowly eliminate these.
 
#6 ·
The 540 has a water cooled alternator, there is no ducting to clog up.

Doru, thank you for the suggestions. I'll lift the carpet and have a look under there. I've never spilled anything, but who knows what happened under prior owners.

Scott
 
#7 ·
Sort of getting to whits end here with this.

I had the melted alternator rebuilt and put it in the car.
Rebuilder said my Autozone battery was to blame. Told me to replace it or he'd void my warranty. Bought the Interstate he spec'd (not from him, he doesn't sell them)
Towed the car to my Indy to have the system tested.
Indy found a bad ignition switch and said the alternator was bad, again.
Called the rebuilder who said he thought my Indy didn't know what they were doing and to try someone else.
Ran that alternator for a few days with the new ignition switch to see if that helped. It didn't. It was overvolting - 14.5 on the OBC/15 at the jump post and causing the radio and hvac to cut out.

Bought a good used alternator. Put it in the car. It lasted 45 min in my driveway testing voltages and then 3 minutes on the highway before it died. No Overvolt, just quit producing voltage.

Tore it down myself and found 2 of the negative diodes bad. Replaced all the diodes and the regulator myself. Bearings and field test fine.

That alternator worked perfectly for lasted 4 days and 75 miles. 13.8 to 14 on the OBC, nice smooth voltage, no overvolts or anything on the radio. Dropped slightly at idle, but never below 12.6. No dimming lights or dash... just perfect. But then tonight I hopped in the car to come home and is now overvolting like crazy. 14.9v on the OBC / 15.5 at the jump terminal at RPM, shows battery voltage at idle - no charge at all.

Obviously something on the car is bad causing these alternators to fail. I don't know what. I've read the charging system PDF, but I can't really find anything. Everything I've read says 14.3v is about the max I should see on the OBC. I've got 14.9 and the battery light isn't on, so I don't think the car is correctly managing the charge - but I'm not sure how this "multifunction controller" thing works as a regulator.

We've checked fuses for shorts and visually inspected the wiring everywhere. The car has no other electrical symptoms to draw on as clues. Everything works correctly.

Does anyone have any suggestions for what to check next or how to find an Indy who can help me with this? Obviously I have to buy or rebuild another alternator for them to start with... but what's the point of just feeding another alternator to this beast. I'm already $1300 into this (two alternators, two batteries, an alternator rebuild, a round of diagnostics & an ignition switch). There's a limit to my willingness to spend on this before i just part the damn thing out.

Thanks for any further suggestions you have,

Scott
 
#8 ·
Time to find a well respected auto electric shop in your area.
 
#10 · (Edited)
Mine shorted out about 4-5 years ago and seized which also caused the PS pump to be ripped off it's lower mounting brackets.
I bought one from BMW ($525) which at the time was about the only place to get one quickly, that I knew of.
The voltage regulator inside the top cover controls the output voltage, but is influenced by the DME signal from the 2 pin connector at the top front. Check to see that these wires are OK.
Pin 1 goes to F15, which should be supplying 12 volts to the alternator when the key is on.
Pin 2 goes directly to the DME, connector X60003.
You need to also check that the engine and battery grounds are good and clean. They have to be making a good connection as the alternator output voltage is referenced to ground. A bad ground connection can make the ground connection float to a voltage level above 0 volts, which is chassis ground.
Here are a few pics of what mine looked like. It was not rebuildable.
I just ordered a new regulator to fix a friends watercooled alt, should have it next Tuesday.





 
#11 ·
A voltage drop of 0.6 V (15.5 - 14.9) between the jump post and the instrument cluster appears high to me. A large voltage drop indicates high current flowing from the alternator to battery & then on to the car's circuits. Perhaps enough to be the suspected short mentioned in your initial post, especially considering your alternator may not be able to produce full current.

Checking current over ~10A with an inline ammeter will be difficult. While a clamp on DC ammeter won't be petty cash price it may be worthwhile to verify yes/no and then help trace high current to a problem. Or, an autoelectric shop with a good diagnostic technician would have one. I'll cross my fingers for you that if excess current draw is present it is not intermittent.

Regards "feeding another alternator to this beast" a suggestion off the top of my head. I don't know if this would work, but it's the best I can think of.
Find a high amp charger, with short protection if possible.
Disconnect the alternator wiring. Leave alternator on the engine.
Connect the +ve charger lead to the alternator power output cable. Connect -ve to car chassis. Wrap the clamps on +ve side to prevent any shorts to chassis or engine.
Leave the car battery in the trunk exactly as is, i.e. connected.
Start engine and trace amps and voltages to determine any shorts.
You would not be able to drive it, but would be able to duplicate vehicle operation without risking another alternator.

An alternate theory.
Any reason to suspect that coolant flow to your alternator is compromised?
If so, elevated temperature could be cooking the diodes &/or voltage regulator.

Regards finding a good autoelectric shop. If your alternator rebuilder doesn't do on car diagnosis, surely they can suggest one.
 
#12 · (Edited)
Thanks for the ideas. You're keeping me from losing my mind.

I have not inspected the trunk wiring harness. I will.
I don't suspect the coolant flow is compromised. I get good flow out of there when the key is turned on and the aux pump fires up (when the alt is removed).
I've checked and double checked the battery ground and the chassis/motor ground. I think I'll add another to the motor for good measure (have had to on other cars).
This happened on two different batteries, so I think I've ruled out the battery.

The more I look at this circuit and read the information you're sharing, the more its NOT that complicated.

12v on Pin1 to excite the field.
Pin 2 feeds a signal back to the DME to tell it what the Alt is doing - but that doesn't change the 12v on Pin 1, so it can't really impact the Alt behavior.

The alt is going to change charge based on RPM and voltage on pin 1, so either these alternators are all just bad, or what its reading on Pin 1 (across ground) is not right.
So... bad alternator(s), bad pin 1 or bad ground. That's really all this can be.

Scott
 
#13 ·
Right, it's really not that complicated. I think the rebuilds are not working correctly.
When I get the regulator next week I'll bench test the one I'm fixing for a friend. I do have a good spare one that I can compare it to.
 
#14 ·
Someone mentioned, or I read, that if the battery were out of the circuit, there wouldn't be anything to "take" the alternator output and the voltage could skyrocket.

I wonder if the explosive disconnector on the battery is intermittently failing and taking the battery out of the circuit. I sort of discount this because the car never has a start issue, which I'd expect with an intermittent battery disconnection.

Scott
 
#15 ·
There is no such thing as a negative or positive diode as far as I know. A diode has an anode and a cathode which is similar to a positive side and a negative side as diodes only pass current in one direction, but I would think you alternator guy just had bad luck. In your case since you seem to have "bad luck" with your electrical, why not buy from Autozone which has a lifetime guarantee on just about everything like this and if you lose another alternator you can replace it for nothing and will certainly have the proof that you need to look elsewhere, but I suspect that something was shorted in your alternator internally. You should not have to prove it wasn't your car if you had a warranty from this guy. You should not accept his "anger" as proof that he is "off the hook". Sounds to me his is just leading with a good offense and putting the responsibility on you to prove your car is not responsible. Give him your car to install a new one and let him find your "defect". Don't waste time with vapor barrier as alternator can handle a 50 amp load no problem and if it had one, the fuse should still blow no matter what.
 
#16 ·
You're right, a diode is a diode, but its which side is +/- - the lead or the case. On a circuit board, you just turn them around. In this situation the case presses into a plate.

I'm over the rebuilder... I agree with you, but I don't much care to address it with him.

I did suggest I'd bring him the car and let him test it - not confrontationally but just so he could see his alternator was/was not the problem. He wasn't interested.

S
 
#19 ·
I put a Lifetime warranty rebuild in it from Napa. so far, so good. 40 miles in. last few lasted 6mi and 75mi, so we should know shortly.

s
Wouldn't be the first time a suspect rebuild was the culprit. You can get a factory Bosch rebuilt 150A water cooled alternator for $400 online with free shipping and $100 core charge, refunded upon return of your old one. I think they come with a two year warranty.

I believe (but unsure) these are the same as the rebuilds sold by the BMW dealer. I had one of those installed in my car back at around 81k miles (7 years ago). It died at 192k miles a couple weeks ago. Lifetime warranty on the part/two year labor (but only if they install it). So I had it replaced, and all parts covered, including coolant, hose clamps and a few other incidentals...but they still hit me for about $450 in labor anyway (3.5 hours)

Keep us posted......
 
#20 ·
Napa's pricing varies by whether its corporate or a franchise. I'm lucky enough to live/travel by a corporate distribution center which is about 20% less than my local franchise (who I do USE, except for big ticket items like this).

There were 5 options.

$284 for a rebuilt with a Lifetime warranty built by a 3rd party (MPA). This is the one the sales guys talked me into.
$459 for a Napa rebuilt w/ a 3 year warranty
$494 for a Napa rebuilt w/ a lifetime warranty
$589 or 1029 for Bosch rebuilt w/ a 1 year warranty

They had all but the most expensive in stock. I was ready to buy the Napa w/ the lifetime warranty for $500. They talked me out of it. Said they'd sold/shipped tons of the $284 and had nearly none come back, so they saw no reason I shouldn't buy that one.

Its been in the car 220 miles now. 40mi Saturday eve and 180 today. Voltage is everything I've read on the web. Just about no charge at idle, stable 13.7 on the OBC at speed.

220mi is more than the last 3 put together.

This being the 6th or 7th time I've swapped it, I'm down to an hour, including filtering/recovering the drained coolant and refilling/burping the system. This time, in the rain, ha ha.

As far as "rebuilder just screwed up"... well I'd certainly call what I did suspect. I've never rebuilt an alternator before and I did have a hell of a time getting the diodes soldered in. I'm going to tear down the one I rebuilt (the most recent failure) and see if I see anything inside.

The one the rebuilder did? Probably has some sort of break down in the field. Probably heat related. No idea.

I suppose I could rig up a test rig and immerse the alternator in boiling water and try and reproduce it in a testable environment... but I'm not sure I'm that interested.

S
 
#29 · (Edited)
The first thing you should do when you have a Alternator or Starter problem is to have the battery tested.

Anytime you replace an alternator you should do a voltage drop test on the Charging circuit. The single biggest cause of repeat failures of alternators is voltage drop. (I work for a manufacturer) The easiest way is to check the voltage at the alternator and then the battery. Do so with the lights on and the engine at 1200-1500 RPM. The difference should be no more than .5 Volts. If it is higher, check each side of the circuit.
Positive side: red lead at the output post of the Alternator and black lead on the positive post of the battery. Record the voltage (it should be low)
Negative side: Black lead on the case and red lead on the Battery negative post. again record the voltage.
Concentrate on the side that is the highest voltage drop by checking all connections and cables. You can test each one with the volt meter by placing the leads (same operating conditions as above) on each side of a connection (for Example where the Ground cable attaches to the block put one lead on the cable terminal and one on the block near by) or at each end of a cable. Each connection should be .01V or less. Cables will depend on length.

Oh and if the system has a Field wire (a separate wire to provide voltage to the field windings) going to the regulator connection check the voltage on that wire under the same conditions, it should be within a .5V of the system voltage. If it is not the system will overwork itself because it cannot build a sufficient magnetic field around the Rotor.

Same goes for a Starter, measure the voltage at the battery and the starter while cranking. It should not be more than .5V different. If it is, do a voltage drop on both sides of the circuit using the methods cited above only between the starter positive post/case and battery during cranking.

Do not forget, the ground side is just as important as the Positive side as the current has to follow the complete path from one side of the battery (or alternator when charging) to the other. (Actually the current path is negative to positive but the automotive world favors conventional flow)

Tip: Never place a washer between two cables on the same post nor between the cable and the contact point i.e. Battery + post of a starter or alternator or cable end and engine block etc.. Most washers are zinc and will carry current initially but will build resistance quickly.
 
#30 · (Edited)
I needed a new battery as well so I put a new alternator and a new battery. I plan on a long road trip and I call myself being proactive. I got a new battery (mine was on its way out) and a new alternator because my car is at 120K miles so I didn't want the alternator failing on me on the road. To update this story, I tried an MPA alternator. It ran for less then 10 minutes then failed. I just tried a Pep Boys Alternator today. It ran 15 minutes then failed. Do I really need to get a Bosh unit at this point? Me trying to be proactive has down a car for the past few days now.

Got the Bosch unit today and it works without an issue.
 
#31 ·
This is why I don't recommend changing things like alternators at a specific mileage. (if it is not broke don't fix it) You have just as much chance of a failure of a reman unit than your original.

Anyway, have you had the ones you removed, tested after they failed? As I mentioned above, high resistance (Voltage Drop) in the circuit is the leading cause of repeat and early failures. That said, if you have a choice between an aftermarket reman and an OE reman, you should always go with the OE rebuilder. They have the Parts available without having to construct a replacement that does not copy the original.
 
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