Dead alternator (probably)

[runn3r]

Kinda don't wanna start a new topic for dumb questions but I had to ask..
Where do you even start when a alternator dies? I mean at least I suspect the alternator as my engine was on and lights were off and i check the voltage on the battery and it was 8.23 or something like that when i give it gas it rises a bit to 9 something but drops down to 8. Shouldn't it be like at 12v+?
Is my voltage regulator dead? Or should I just take it to a shop to refurbish it?

I was driving for approx 15kms when my dash became kinda dark then i shut off the car and start it up again an the battery light was dimmed in background and the starter hesitated to turn over the engine i turned on my high beams and my radio went dark and i got some ABS warning lights and stuff..

[danespann]

Alternator/voltage regulator seems likely, but could just as well be a dead cell in the battery.

[runn3r]

Wouldn't it still show up as 12v+ on the voltmeter while the car is on if there was a dead cell?

[chazsandiego]

Sounds like an alternator issue to me as well.

Voltage at battery with engine running should be around 14 volts. You can also double check this voltage by using test #9 on your OBC.

If the alternator has a bad diode you'll have AC voltage seeping into the battery as well which you can test for at the battery.

If you have no ac voltage at the battery and low dc voltage while running I'd replace that voltage regulator like you said.

Oh and I'd double check any applicable cables for corrosion.

http://www.bimmerboard.com/forums/posts/1094171

Good luck!



Sent from my moto e6 using Tapatalk

[shogun]

Yes, when the engine is running, it should show >12V, no matter what the battery condition is.
Could be the voltage regulator, but from my experience I assume is is a dead diode in the rectifier of the alternator = then the alternator cannot produce >12 volts and shows less, had the same on my car, battery light in cluster was always dimming, test showed 10+ volt, changed voltage regulator to new one, no change in volts, changed 2 diodes in the rectifier and the alternator works like it should now.
Here you see the rectifier http://www.3dzubehor.com/rover/boschrepair.html

[runn3r]

Sounds like an alternator issue to me as well.

Voltage at battery with engine running should be around 14 volts. You can also double check this voltage by using test #9 on your OBC.

If the alternator has a bad diode you'll have AC voltage seeping into the battery as well which you can test for at the battery.

If you have no ac voltage at the battery and low dc voltage while running I'd replace that voltage regulator like you said.

Oh and I'd double check any applicable cables for corrosion.

http://www.bimmerboard.com/forums/posts/1094171

Good luck!



Sent from my moto e6 using Tapatalk

Alright, damn. I'll check for AC voltage and see whats up. Thanks.

Yes, when the engine is running, it should show >12V, no matter what the battery condition is.
Could be the voltage regulator, but from my experience I assume is is a dead diode in the rectifier of the alternator = then the alternator cannot produce >12 volts and shows less, had the same on my car, battery light in cluster was always dimming, test showed 10+ volt, changed voltage regulator to new one, no change in volts, changed 2 diodes in the rectifier and the alternator works like it should now.
Here you see the rectifier http://www.3dzubehor.com/rover/boschrepair.html

Thanks man I'll make sure there is no AC power at the battery first cause the diode changing seems like a big undertake.

Imagine all of this happening right after dumping 100e to change plugs filters and oil kinda weird.

Thank you guys for the detailed answers I'll update this as soon as I find time to check it out.

[runn3r]

I took it to a guy and he replaced the slip rings as they were worn out, he also replaced the back bearing cost of repair was around 45 EUR cause the slip rings were hard to find for that kind of rotor.

[runn3r]

Welp sorry for bumping the topic again but i got issues again..

The battery light on the dash starts to dim on when you add gas, it kinda fades off. I checked the OBC voltage technique cause i didnt have my trusty voltmeter around and it was showing 13.8 "ub" whatever ub stands for but as i was riding to work i arrived at my job and the battery light on the dashstarted to dim out again so i checked on the obc and the voltage was 12.38 "ub". Like I said when you add gas the battery light kinda fades away but i was adding gas and checking the obc and didnt see any noticable difference it was about 0.20 "ub" difference..

A couple days ago i started my fathers car with cables and this happens to me..

And also i was driving last night and everything went crazy the abs light the handbrake light and the battery light i decided to turn off the car and turn it on again but i couldnt. Checked with the voltmeter 12.30~ volts when i crank goes to 0.0. Called a buddy of mine to start it up with cables, managed to start it up turned it off after a minute turned it on again no problem no battery lights or abs light. Decided to turn everything on inside the fog lights, rear glass heater, radio, fan, cabin lights and checked the voltage on my trusty voltmeter and it was between 13.30 and 13.80. Then the first part happened this morning as i wanted to test everything out and now I'm really confused as what this should be..

A bad battery or my alternator went to shit again?

[shogun]

UB = Betriebsspannung = supply voltage.
did you also change the voltage regulator, because you only mentioned: "I took it to a guy and he replaced the slip rings"
If the slip rings were bad = had large grooves, then a new voltage regulator is also required because that is also damaged then.
Min. length of the carbon brushes and how to measure I posted here http://www.bimmerboard.com/forums/posts/1263002/
Did you already check the ground cable from engine to chassis? Also the ground cable from battery to ground?
How old is the battery? Ever tested it with a load tester?

[runn3r]

He told me that the brushes were long enough and that they dont need changing.. Makes me wonder does running a engine without that alternator cooling duct make any difference? Cause i removed mine cause i couldnt fit that front plastic cause of led front lights..

The ground is on the engine mount right? It goes below the battery then splits in the second cable which goes to the engine mount it was fine i checked the continuity from the chassis and the negative pole on the battery. Will need to check the resistance tho.

2 years old only time it was empty was when my alternator died first time. But how does the battery empty itself and after starting it with cables and running it for a minute it could start a car two times without dieing and before i couldnt even get the engine to spin.

No I didn't, don't have a load tester.

I'll check the resistance of ground and test that out.

[shogun]

Also check the fusible link. always near the battery. E34: some have it near battery in engine bay, if battery is in trunk, then there http://www.bmwe34.net/E34main/Mainte...sible_link.htm

[runn3r]

Is the cooling duct really necessary? Maybe i fried the alternator or smth.

Ill check that too, thanks

[shogun]

well, if alternator cooling would not be necessary, they would have skipped it. In an alternator assembly there are rotor, excitation circuit and stator. As the design is compact and there are rotating part plus heavy current carrying involved, special cooling is needed. In generally simple force cooling method is utilized to cool high capacity alternator. Newer models like E38 even have water cooled alternators. Alternators, like other electrical equipment, need to be protected from heat to survive and operate efficiently. Alternators have integral fans that help with cooling but still require airflow of sufficiently low temperature for heat transfer. That is why cars have an duct which directs air from the grille down to the alternator for cooling. On my E32 750 there is a special duct in the front spoiler for alternator cooling. Everything in car design is about optimizing different attributes, choosing water cooling is expensive and complex but may provide more flexibility in where the alternator is placed on the engine and probably provides more cooling than just air, and that may enable a higher rated (power) alternator to be used. Generally the permissible temperature of rotor circuit is below 100.

[runn3r]

Welp the first guy didnt assemble it right the first time the slip rings where misaligned and ruined the carbon brushes.. Take your shit to a good mechanic/electrician folks.

Found a guy who fixed it..