Alternator

[thsupernge]

Engine running rough and dies after a few minutes. I am testing the alternator at the battery and only getting 10.8 volts pretty sure that's a dead alternator. What are the recommendations here? A rebuilt alternator from the host? What are people's thoughts?
Thanks in advance for the help.

[PeteKz]

More info: What year car? Internal or external voltage regulator?

If you only have 10.8 volts at the battery, that indicates a bad battery. Even with the alternator dead, you should have battery voltage at 12 volts. How old is it the battery? Is it fully charged? Have you removed, cleaned, and reinstalled the terminals to the battery?

[thsupernge]

Yeah sorry. It's an 88 so internal voltage regulator. The battery is less than a year old. Yeah fully charged. And yeah everything is spotless.

[john walker's workshop]

Does the alternator light come on with the key on/engine not running? Then go off when running?

[PeteKz]

Good question on the alternator light.

Disconnect, clean, grease, and reinstall the battery terminal connections. If the battery is charged and you don't have 12v there, something is wrong with the battery.

[wazzz]

Not necessarily a dead battery. If testing 10.8V at the battery when engine is running, since the alternator and/or the voltage regulator are not working at all, the engine electronics and ignition are all running and relying on the battery as the only voltage source. That might explain this low battery voltage.

[john walker's workshop]

Originally Posted by john walker's workshop

Does the alternator light come on with the key on/engine not running? Then go off when running?

The alternator won't charge if the bulb is burned out.

[Schulisco]

Check the voltage at various places in the car to make sure not chasing a defectove alternator or voltage regulator instead of bad ground and contacts ...

[GH85Carrera]

As suggested above, remove the battery cables, clean them and the posts, and measure the battery while disconnected. It should be just over 12 volts. If not, hook up the battery charger.

With a charged battery, and the car running, check the alternator light.

If you can find a local alternator-starter repair shop, have the old one rebuilt. Rebuild shops are hard to find, like radiator repair shops, and engine machine shops, they are fading away. A new Valeo alternator is plug and play. It is a real challenge getting the wires hooked up with the air diverter in the way.



I had my tachometer modified and got rid of the dumb shift light, and had a volt meter added. It sure is comforting to see the alternator charging when driving.

[thsupernge]

No battery light on start at all. I can check to see if its burned out. Battery is fully charged and I will check the terminals again. Thanks for all the help here guys!

[thsupernge]

After charging the battery is at 12.9 and is now at 11.5v after running for 20 min.

[wazzz]

So it sounds like what I said above, battery is good but charging system is bad and when running the engine, only the battery is used, hence the voltage drop after some time.
It could be as simple as a dead bulb in the gauge. If that bulb is blown or missing, the alternator does not "boot" (can't find the word for it but it needs this bulb and some current flow through it, otherwise it does not supply voltage).

[thsupernge]

Cool I'll give it a shot and see what I find.

[ian c2]

It’s very exciting !!!
I can hardly resist looking

[Schulisco]

Originally Posted by wazzz

So it sounds like what I said above, battery is good but charging system is bad and when running the engine, only the battery is used, hence the voltage drop after some time.
It could be as simple as a dead bulb in the gauge. If that bulb is blown or missing, the alternator does not "boot" (can't find the word for it but it needs this bulb and some current flow through it, otherwise it does not supply voltage).

^^^ This! ^^^

That little current going through that bulb drives the excitement of the alternator. Without that current the excitement won't work and therefore the alternator won't produce any or only little electrical energy. That's also why an LED as replacement for the alternator control bulb won't work too as the current is much lower through that LED.

https://www.hella.com/techworld/uk/technical/car-electronics-and-electrics/starting-and-charging-system/checking-the-alternator/#in--2041489067

Section 5.4 and

https://forums.pelicanparts.com/bmw-6-7-8-series-technical-forum/550712-alternator-idiot-light.html

Thomas

[thsupernge]

Bulb is good but changed it anyway. Now it lights up with key on power. Maybe that was it?

[thsupernge]

Getting 13.6v at the battery while running now...

[thsupernge]

Originally Posted by ian c2

It’s very exciting !!!
I can hardly resist looking

Good one!

[famoroso]

Spread the good word...

Always check to see that the alternator warning light lights up when the ignition is turned on (i.e. ignition switch position 1).

Many owners miss this.

[pmax]

Can't get charged up without a little excitement !