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Thread: replacing Alternator's voltage regulator

  1. #1
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    Question replacing Alternator's voltage regulator

    For a week my 2000 323i was not driven and the battery got drained out completely.
    I jump started the car and drove for an hour. Then parked for few hours and the battery got drained out.
    Jump start it again. Drove for an hour and parked at home. Next morning same scenario, battery depleted.
    Got my battery charger and charged the battery over the night with "deep-cycle 2Amp mode". The battery is fully charged now and holds 12.1 Volts.
    I suspected that the alternator doesn't charge the battery.
    I tested the alternator and it shows 13.5 Volts. I think that the alternator should be over 14 Volts.
    I am guessing the brushes in the voltage regulator are worn out and it's the time to replace it.

    The question is - has anyone replaced the voltage regulator without removing the alternator out of the car?
    I saw on YouTube someone did this on a Volvo. I wonder if the same can be done on E46 ?

  2. #2
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    You have a dead battery. If you are showing 13.5volts with the car running, the alternator is working fine. A fully charged battery should show at least 12.7 volts. Load test the battery.

  3. #3
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    +1 on Battery. 13.5v is exactly what you want in these cars. The voltage regulator doesnt let these get much higher due to all the electronics.

    12.1v isnt very high for a "fresh off the charger" battery. Every battery has a bit of surface charge after charging, you need to place a load on the battery briefly before you can get a stable voltage reading. Turning your key on without starting the engine for a minute or 2 is usually enough.
    Last edited by legoman67; 11-16-2017 at 12:41 AM.
    Current:
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    - 07 335i
    - 09 335i
    - 98 M3 Eurospec

    Ex's: 1984 325e, 1988 325IX, 1992 525I, 1995 540i/6, 2002 330i, 2005 330xi, 1992 850i, 2003 330i #1, 2003 330i #2, 2002 330ci, 2004 330ci

  4. #4
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    Update:
    Today the battery test shows 11.5 Volts and the alternator test shows around 12.5 -12.7 Volts.
    I ran the test 2 times.
    When I tried to run the test for the 3rd time the battery Voltage showed up, but then when I've tried to start the car in order to test the alternator the engine couldn't start anymore.
    I turned the car completely Off and started the vehicle OK.
    Then tried for the 4th time to run the alternator test and the same scenario, the car doesn't want to start.
    Doesn't this means that the alternator is bad ?
    Last edited by Yober; 11-16-2017 at 01:16 PM.

  5. #5
    dworthy's Avatar
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    Start with replacing the battery first, then worry about the alternator second.

    I had a dead cell in my winter beaters battery, was able to jump it off and drive it home, however everything was acting funky.
    Darin
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  6. #6
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    I drove to the battery shop. They tested , all is OK with the battery. They checked the alternator with their tester, and it shows that the alternator output is 12.5 Volts.

  7. #7
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    That’s low. BMW sourced alternators frpm Bosch and from Valeo. They are not interchangeable. The first step is to determine which alternator is in the car. Remove the air filter box and the upper intake hose. Use a flashlight and a mirror to read the label on the crack of the alternator. Tre label will tell you the manufacturer and the capacity in amps. Replacing the voltage regulator in a Bosch alternator is fairly easy once you’ve removed it from the car. Basically, you remove a couple of screws at the back (make sure you use a quality screwdriver as the screws are in there tight). Then remove the crap that’s accumulated in the alternator. The voltage regulator is held in place with 2 screws (maybe small bolts). Swap the regulator and put it back together.

  8. #8
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    I've had alternators intermittently go bad (low idle and high heat) causing charging issues and rough idle issues when car was running. At high RPMs it would read 13.5v, but at low RPMs it would bounce between 13.5 and 12v. If your alternator output is 12.5v, then it is probably bad. I've never just changes the VR.

    If you replace the alternator, you can use either Valeo or Bosch, but if your new alternator doesn't come with a pully, you'll have to replace it with the same one that's already in your car, as the pullys are a different size between the two brands.

  9. #9
    dworthy's Avatar
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    Quote Originally Posted by abrittis View Post
    I've had alternators intermittently go bad (low idle and high heat) causing charging issues and rough idle issues when car was running. At high RPMs it would read 13.5v, but at low RPMs it would bounce between 13.5 and 12v. If your alternator output is 12.5v, then it is probably bad. I've never just changes the VR.

    If you replace the alternator, you can use either Valeo or Bosch, but if your new alternator doesn't come with a pully, you'll have to replace it with the same one that's already in your car, as the pullys are a different size between the two brands.
    Please note what Marc said above about non-interchange alternators.
    Darin
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    05 M3 Imolarot II(405)/Gray(N5TT) ZCW, ZPP 6sp Manual C.F. Lip, CSL diffuser, Euro Infra-Rot front windshield and a trunk liner! Mr. Go_Fast Stored for the Winter
    Past:
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    82 528i euro Saphire Blue Met/Blue Leather RIP
    79 525 euro Green/Green RIP
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  10. #10
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    I've tried to start the car in order to test the alternator the engine couldn't start anymore.
    I turned the car completely Off and started the vehicle OK.
    did you do something in between like charge up the battery?

    How is your engine ground cable? this is starting to sound like a bad connection issue.

    Also a battery at 11.5v with no load on it is dead.
    Current:
    - 07 328CI
    - 07 335i
    - 09 335i
    - 98 M3 Eurospec

    Ex's: 1984 325e, 1988 325IX, 1992 525I, 1995 540i/6, 2002 330i, 2005 330xi, 1992 850i, 2003 330i #1, 2003 330i #2, 2002 330ci, 2004 330ci

  11. #11
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    It's possible that your alternator has a bad diode, but that's an uncommon spontaneous failure with modern alternators. Generally that only happens when the battery is connected in reverse.

    At this age, it's much more common that the brushes are worn down and barely making contact.

    To verify it's easiest to remove the alternator. Perhaps someone that does this task daily can remove the regulator by feel and inspect with a mirror, but you won't be able to. A Bosch alternator has a plastic back cover held in place by two terminal nuts, and perhaps a screw. Once removed, clean out the accumulated leaf bits and litter to reveal the regulator/brush assembly. This is held in place by two screws, usually with #2 Pozi-Drive heads. Do *not* use a regular #2 bit on these, as it will cam out and round the screw head.

    I'm uncertain of the modern specs, but older Bosch alternators had new brushes that extended 13mm, and 5mm was the wear limit. Much like brake pads, there needs to be plenty of material to provide thermal insulation from the hot contact surface.

    When reassembling, tighten the fasteners only to snug or carefully follow the factory torque specs. The terminal nuts are soft plated copper and can't handle the torque that their size suggests.

  12. #12
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    I finally received my borescope and used it to see the alternator's label without removing the filter box. I have Bosh 0123515022.
    Now I know which type of voltage regulator is required. https://www.ebay.ca/itm/REGULATOR-fo...53.m1438.l2649
    My original question: is there possibility to replace the voltage regulator without taking the alternator out of the car?
    Also , has anyone tried to replace just the brushes ? I wonder if these brushes are suitable ? https://www.ebay.ca/itm/BOSCH-ALTERN...53.m1438.l2649
    Last edited by Yober; 04-06-2018 at 11:58 PM.

  13. #13
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    Don’t buy the VR from eBay as you can get a counterfeit part. Go to fcpeuro for the part.

    Yes, you have to pull the alternator from the car to change the VR.

    Im still betting the battery is toast. Why? Lead acid batteries don’t tolerate a total discharge. The chemistry permanently damaged the lead plates, thus reducing the battery’s capacity. Plan on a new battery before next winter.

  14. #14
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    Healthy alternators with BAD batteries...........5 year batteries is often the time to replace them. Yes some live again as much time..but rarely. As batteries become older they develop resistance..gradually. An older battery 4 to 6 years, develops resistance to charging from your alternator. When this happens, your alternator begins to work harder. Alternators in our BMW cars are quite expensive to replace. In my opinion, switch-out the $150 battery for a new one in 5 years...or sooner..

  15. #15
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    As batteries grow older, the internal resistance increases. That *decreases* the charge acceptance / recharge current. The alternator doesn't have to work as hard to recharge them, although it does have to work longer.

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    Yes, you are correct. Alternators put out dc voltage based upon their command (via regulator) A really bad and or old battery with a most resistance will demand max from attention from the alternator...thus shortening the alternators work life.

  17. #17
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    A battery with a shorted cell will result in the alternator putting out its maximum current, which could possibly shorten its life.

    An old battery without a shorted cell will result in the alternator putting out lower current, which puts less stress on it.

    But what type of failure are you worried about? The bearings? A heavy electrical load puts more mechanical stress on the whole alternator, but the bearings are significantly oversized for the load. They usually fail when the rubber seals leak, which is more dependent on heat and environmental conditions.

    The brushes? They usually fail from wear. They last a very long time if everything goes well, and only wear quickly if grit gets into their semi-sealed enclosure. The control current goes through a thick continuous copper ring, and has a trivial impact on the brush life.

    The regulator? There isn't any significant load-based wear mechanism. (Thermally driven diffusion in the semiconductors is so minor that it can be ignored.)

    The diodes? That's a tougher one to call. High current output increases the heat the semiconductor junction. Thermal diffusion could be an issue. Thermal cracking could be an issue. Diodes are really robust, but it's tough environment. It's not often that diodes fail in their regular environment, but they can fail with a shorted battery cell or a momentary reversed jump start. And they can fail in a way that a rebuilder won't catch. I wouldn't expect diode failure to happen out of the blue, but it's one of the top things to suspect in a recently installed rebuilt alternator.

  18. #18
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    Today after charging the battery for 24 hours I've tested it with the Fluke multi-meter and it showes 12.2V.

    I connected my Fluke multi-meter and pushed the min/max button in order to record the minimum and maximum reading after I would start the car (i.e. to load test the battery and to check the alternator's output). The minimum reading after the car start was 10.0V (indication for the battery load test) and the maximum reading was 12.2V (alternator test indication).

    Then I ran on-board test (holding the left button on the odometer for few seconds, then clicking till it will get me to #19 , then wait for a second, then click till it will get to #9) and it showed me following: the battery 11.7 V . I immediately checked the battery with Fluke meter and it showed 12.2V .
    I drove for about 15 minutes with the on-board tester On and
    the alternator was fluctuating between12.7V to 13.1 V.

    Looks like the battery doesn't take full charge (as I understand it should of been minimum 12.6V) , however the battery output under the load is 10V (as I understand it should be minimum 9.6V).
    Looks like the alternator's maximum output is 13.1V but my battery doesn't take more then 12.2V.

    Do I still need to change the battery or the current battery is sufficient with 10V output when loaded ?

  19. #19
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    Quote Originally Posted by MarcoZandrini View Post
    Don’t buy the VR from eBay as you can get a counterfeit part. Go to fcpeuro for the part.
    I contacted the sales rep of FCP Euro and it appears that they do not sell voltage regulators for Bosh alternator model 0123515022

  20. #20
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    If you charge for a few hours and the voltage is still under 12V, you have a dead cell in the battery.

    Your 12.2V is an over-charged battery at 14.6V with only 5 of the 6 cells working.

  21. #21
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    12.2 is super low for a fresh off the charger battery.

    The voltage regulator on these alternators is not serviceable separately.
    Current:
    - 07 328CI
    - 07 335i
    - 09 335i
    - 98 M3 Eurospec

    Ex's: 1984 325e, 1988 325IX, 1992 525I, 1995 540i/6, 2002 330i, 2005 330xi, 1992 850i, 2003 330i #1, 2003 330i #2, 2002 330ci, 2004 330ci

  22. #22
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    Legoman67, Iím confused by your statement about VR.
    In the 7th post above MarcoZandrini advised that VR for Bosh alternators is easy to replace.

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