Battery light, cooked the alternator?

[Schreier]

This morning I made a mistake while driving the Z3 on the highway; down-shifted when I really shouldn't have and revved the engine quite high.

The battery light came on, stayed on for maybe 5-10 seconds, then went off. Then came on again for about the same period, then went off.

When I got down to surface road speeds, the light came on again and didn't turn off.

After I parked the car, I ran a quick scan with the Torque app while it was idling (even though there was no CEL), but found nothing. Turned the car off, turned it back on and started it, and the battery light remained.

Battery cables are in fine condition and are firmly attached to the battery. What are the odds that I cooked the alternator during this mistake? Are there other things I should look into, first?

[rf900rkw]

You had Torque plugged in, and didn't check the battery voltage?

[Schreier]

You had Torque plugged in, and didn't check the battery voltage?

d'oh. Nope. That would have been the smart thing to do.

What voltage am I supposed to be looking for under normal running conditions with no accessories on?

[rf900rkw]

13.5-14.5. I like closer to 13.5. But anyway, the high rev likely put the end to a brush that was just about to pack it in anyway.

[BimmerBreaker]

13.8 is what I looked for

Can an over-rev cause a spike in the voltage system to pass the voltage regulator?

[khammack]

... Can an over-rev cause a spike in the voltage system to pass the voltage regulator?

Isn't that what a voltage regulator should do?

The voltage regulator will allow the alternator to make enough power to maintain proper voltage level, but not allow system voltage to rise to a harmful level. With regulators for the alternator system, voltage limiting is the means of controlling output.

[Schreier]

I'm getting a fairly steady 14.2v at the OBD port with the Torque app.

Light is somewhat intermittent, much more on than off. No apparent reason for it to be on or turn off
(independent of revs, road bumpiness, whatever).

[BimmerBreaker]

Isn't that what a voltage regulator should do?

Yes and thats why I was just asking... maybe an over-rev (which would put components outside of their design parameters) caused the alternator to briefly output more voltage than the regulator was designed for.
Not suggesting it did happen, just wondering if it could

[Mr Bingley]

Well, if you made a money shift and all it costs you is an alternator, you're doing just fine.

[Schreier]

Well, if you made a money shift and all it costs you is an alternator, you're doing just fine.

That I know of... knock on wood.

Still very curious why it's tripping the charge light when it's producing a healthy, steady 14 volts.

[328 Power 04]

The little 2.5L can take up to 7500 before valve float, just for your info.

That doesn't mean these are words to go (shift) by, but glad you didn't have any bent valves.

[Schreier]

Folks, I think I have solved the problem. I changed out the voltage regulator, and the charge light has disappeared.

The alternator on this car is a Bosch AL0735X, an 80 amp unit which was purchased and installed only about a year (and less than 5,000 miles) ago. Removed the air box, released the tension on the belt, took out the two bolts (17mm drive, I believe), and took her to a couple of places to test.

The original plan was to have the alternator rebuilt by someone else. The first place I visited was an old-school alternator rebuild shop. The guy had a old-style alternator bench tester, which only connected to the alternator via the positive connector and the ground chassis of the alternator. The rebuilder said showed the Bosh unit putting out 100 amps. Well, OK, I thought, but that didn't tell me anything I didn't already know. The alternator was putting out what I thought was good power, and hadn't killed the battery in the past 100 miles. "It could be anything," the rebuilder said. "Must be one of those computers."

Ah, sure thing.

Second place I took the alternator was the AutoZone up the road, which actually had a digital machine that plugged into the alternator's 335 plug. I don't know if the test was actually any good, because the service rep seemed to have an extra lead just hanging out, but the alternator did not pass according to the machine. The car's battery was tested, too, and checked out just fine. Good enough to try some surgery on the alternator, I thought.

I got to work taking the thing apart. First came off the black plastic cover, the one with the hole that connects to the air duct on the car. The voltage regulator was easy to find and photograph.

20170808_214547.jpg

Some research led me to believe that what I actually needed was called a "voltage regulator and brush holder." Which makes sense, because the brushes, brushes holder, and the voltage regulator are all combined into one modular unit. Handy, because you don't have to troubleshoot or repair each item individually if you don't want to. For the AL0735X alternator, the part number for the brushes holder and voltage regulator was 1 197 311 536.

I found a replacement on Ebay for around $30, which was manufactured by "Transpo." The replacement item was very similar to the original, with just slight differences here and there. There was no obvious cosmetic signs that the original part was damaged -- though the new part had brushes that seemed to be 1/3 longer than on the original part. I've no idea how long brushes are supposed to wear, but it's entirely possible the alternator already had some mileage on it.

Anyhow, taking the original part out was a snap. It's just two phillips head screws holding the thing in. It's probably the easiest thing to service on the alternator, which is great, because it looks like anything else would take a ton of time and energy to do anything else to it properly. It would be better to get a whole new alternator, I think, if it were anything but the brushes and regulator.

2017-08-14 21.22.21.jpg

Manhandling the alternator back in was a bit of a pain, too. I didn't remember that the top bolt was the longer one, and the bottom bolt was supposed to be the smaller one. So I spent a lot of time trying and failing to get the bottom bolt secure when it wasn't going to happen. Don't be me. Keep track of which bolt went where; they're not interchangeable.

Put everything back on proper, and she fired right up! No more charge warning light. Here's my readout from the Torque app.

Screenshot_2017-08-14-20-31-03.jpg

It looks like the old regulator was actually down a few tenths of a volt, which could have triggered the light. Earlier, the voltage was drifting between 14.2-3 volts, but now it was more in the range of 14.4-5. Noted for later.

Now, on to the next issue. I've replaced all the shocks and struts with Koni Sports, and put in new shock mounts and reinforcements on all corners, but I've still got a nasty little rattle in the rear that I suspect is the fuel tank straps.