E60I

Hey guys,

My car is ten years old (bought in 2005) and I think the alternator is about to go out. Yesterday, I went to Autozone and had the battery and alternator tested "from under the hood". Their reading stated the "diode" for the alternator is bad and so is the battery.

Since the battery is 4 years old, I went ahead and replaced it with the Duralast Gold 95R-DLG ($176). After fully charging it at home with my slow charger, I have been getting around 12.6 volts (fully charged) with engine and all accessories off.

With the engine "idling", radio and all lights on, I am getting around 14.20 reading; occasionally, it drops around 13.84 volts. Is my alternator going bad?

Autozone is selling a remanufactured Duralast alternator (180 Amp) for $153. Huskerparts.com is selling it for $453 (185 Amp). Since an alternator's job is "to maintain" the battery (and I have just installed a new one yesterday) and not charge the battery, is the difference in "5 amps" going to cause any problem for my car?

Given that the charging system (IBS) adjusts accordingly (charge more for old battery, charge less for new one) due to the age of the battery, I have not registered the battery yet. Without registering the battery, I want to test to see if the voltage will go above 15.5 volts at 1500 RPM. If it goes above 15.5 volt @ 1500 RPM, then I know the IBS myth is a proven fact. In theory, if it goes above 15.5 volts at 1500 RPM on a "new battery", then it is overcharging the battery because it is thinking I still have "the old one".

Thank you for reading this. :-)

All suggestions and feedbacks are appreciated!!! :-)

Have a great day, guys.

abe76247

14.20 and then dropping to 13.84 is normal.

The test you propose is not going to tell you anything.

Registration when the same battery type is used is not nearly as big of a deal.

To see if registration makes a difference you'd have to place the same loads on the same battery so the IBS can measure the current draw and then the system will measure the rest voltage of battery and vary charge. Then run the engine the same speed with the same load and monitor the charging. It is even more complicated than this as the system will lower charge rate on heavy acceleration for briefer period for a low battery and run charge rate at a high rate on coast for longer for low battery also.
The registration and the way complex charge regulation is about long term care of the battery so it can last 6-8 years in a car with a lot of loads that is tough on a battery. If the battery is charged according to an aging profile then it can last longer if charged in little different ways that fits its age.
The system is adaptive so a good battery not registered is still cared for well. The biggy is telling the system the battery type as AGM and FLA batteries need different care.

audiophool

I put a new battery in my '08 535xi last week after getting tired of limping along with one that seemed on its last legs. Judging by the date code on one terminal, the old one was ORIGINAL (7 years of severe use - low temperature winters) and the car has racked up 166,000kms (~100,000 miles). For the last year or so, the clock would reset every few days, presumably due to load during cranking, and needed to be charged every week or so (C-Tek charger). I'd picked up a voltmeter that plugs into the lighter (LED readout) and before changing the battery I'd frequently see voltage over 15.2. Since changing the battery (not yet registered), I've not seen the voltage exceed about 14.6.

txag_530i

If you decide to replace the alternator then I wouldn't buy anything except an alternator remanufactured by Bosch.

E60I

I went to another Autozone today to get my battery and alternator tested again. The guy tested the battery from the posts under the hood and showed me that my battery is bad. I then opened the trunk, showed him the new battery and told him I bought it from them yesterday. Hence, he corrected the setting on his tester, tested it again and showed that it is good. With that said, if you ever want to get your battery tested while it's still in the car, BE SURE THAT THEY SET THEIR TESTER TO THE RIGHT "CRANK SETTING" BEFORE YOU ACCEPT THE RESULT AND BUY ANOTHER BATTERY!!!

There after, the guy tested my alternator about four times with the tester. The first test showed a FAIL. The second test showed a PASS. The third test showed a PASS and the fourth test showed PASS. Can anyone explain that? Do you think only the "voltage regulator" is bad?Thx
http://www.realoem.com/bmw/showparts...45&hg=12&fg=22

turboawd

what is the problem? are you wanting to change the alternator just because its old?

E60I

Sorry for the late reply! The engine was struggling to start last week for the first time within 8 months. It took me more than four times (it cranked each time) to finally get it running. The guy at Autozone Auto Parts Shop said my battery and alternators (their tester indicates bad diode) are bad. After replacing the battery, another guy from Autozone tested the alternator and gave me mixed signals. Other than that last bad start (before I bought the new battery), there appears to be not signs of weak battery before nor after the battery was changed. I don't want to change the alternator unless I get some real compelling reasons to. Thx

turboawd

alternator does not start your car. it charges the battery and provides power while the car is on. it doesnt sound like you ever had a low or dead battery, so i would not worry about the alternator.
why the car didnt start is another issue it seems.

E60I

Here's my understanding: A car needs a sufficiently charged battery to crank and get the engine running. If the battery is bad, the alternator will work harder than it needs to! An over worked alternator will eventually burn out because a bad battery is not holding the charge. Inversely, a bad alternator that does not work sufficiently can't or may not be able to maintain the sufficient charge for the battery to crank and get the engine running.

Update: After the battery replacement, the car continues to accept one crank to get the engine running. I am also not convinced that the old battery was bad.


QUOTE=turboawd;1562126]alternator does not start your car. it charges the battery and provides power while the car is on. it doesnt sound like you ever had a low or dead battery, so i would not worry about the alternator.
why the car didnt start is another issue it seems.[/QUOTE]

pcy

Dan, if you have an auto electrical repair place around where you are, you can take the alternator to them and have them bench test it; they have equipment to load test it. While it's there, they can check the bearings, brushes, and the voltage regulator.

I personally prefer to keep/have the original alternator rebuilt, rather than install any of the aftermarket alternators.