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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Sun, Oct-28-2012, 02:35:43 AM   #41
Pnick
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Default Re: Alternator and Battery question :)

Alternators use DC brushes and copper commutator bars that get worn out in time. A remanufactured alternator just gets cleaned and new brushes installed but the commutator bars are just polished clean but but are still worn. It'll last a while but I won't expect 20K-30K miles out of them.

A good 12V battery should put out at least 14V when checked with a voltmeter without a load. When a load is placed on the battery such as a headlight/engaging starter, voltage should not drop below 12V. If it does, then the battery is kaput.

When a battery is disconnected while the engine is running, the alternator can go into a surge and possibly damage electronic equipments such as the ECU.
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Old Sun, Oct-28-2012, 04:10:43 AM   #42
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Default Re: Alternator and Battery question :)

I disagree.
Depending on the level of wear of a commutator, and how well it is reconditioned, and most importantly the quality of the springs behind the brushes, they can often last another 50-80k miles, largely dependent on if a quality rebuild is done, including bearings if needed, as well as other electrical components such as the regulator and the AC to DC bridge (diodes).

I agree, however, and unfortunately, that your characteristic of what is done during rebuilds, especially if done overseas as most from "big box" auto stores are - regardless of warranty, is correct and wholly inadequate.

You are way better off if you can find a local auto/electric shop that can do their own testing - where they may learn the stator is shot and a rebuild is un-economical, a rare condition, source and repair all needed parts, including bearings, which may require the skill to epoxy in a new bearing if wear there is extreme, and support their finished product since they are a local business with a reputation. It is harder and harder for these shops to survive because Autozone and the like have a "lifetime" warranty that is next to meaningless if one has to replace the same part 2 and 3 times or more, as we've seen on this board many times.

By the way, alternators produce AC current, not DC. Not sure the brushes are different one way or the other, but to call them "DC brushes" is a bit odd, since they flow AC; the voltage gets converted to DC through the diode bridge after the fact. Not a bid deal, just sayin...

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Originally Posted by Pnick View Post
Alternators use DC brushes and copper commutator bars that get worn out in time. A remanufactured alternator just gets cleaned and new brushes installed but the commutator bars are just polished clean but but are still worn. It'll last a while but I won't expect 20K-30K miles out of them.

A good 12V battery should put out at least 14V when checked with a voltmeter without a load. When a load is placed on the battery such as a headlight/engaging starter, voltage should not drop below 12V. If it does, then the battery is kaput.

When a battery is disconnected while the engine is running, the alternator can go into a surge and possibly damage electronic equipments such as the ECU.
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Last edited by RedM3/4; Sun, Oct-28-2012 at 04:13:49 AM. Reason: AC vs DC
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Old Sun, Oct-28-2012, 06:19:34 AM   #43
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Default Re: Alternator and Battery question :)

Couple of issues here between Pnick and REdM3/4:

1: Commutator bars in the rotor are made new very thick. Part of the reman procedure is to polish the copper and undercut the resin they are set into. If they don't do this, the brushes will ride on the resin and not touch the commutator as soon as they start to wear, leading to a no charge condition that usually starts at high rpm and gets lower as the commutator wears.

2: The brushes carry the field current, not the output. Pnick is correct that the brushes carry DC. The stator outputs the AC that goes to the diode bridge.


And yes, disconnecting the battery while the engine is running went out as a valid test procedure in the mid-70s with electronic ignition modules. You'll cook shit that way...
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Last edited by brichter; Sun, Oct-28-2012 at 06:22:51 AM.
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Old Sun, Oct-28-2012, 11:36:27 PM   #44
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Default Re: Alternator and Battery question :)

Good point, I stand corrected.
With the frequent failure of rebuilds, I've often wondered what kind of job they do (or don't do) on the commutator.
In the old days, and I expect still in some shops, the commutators were turned on a lathe to clean them up. I especially wonder if they leave out the resin undercut step, since the rebuilds often seem to run for a short while before failing.

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Originally Posted by brichter View Post
Couple of issues here between Pnick and REdM3/4:

1: Commutator bars in the rotor are made new very thick. Part of the reman procedure is to polish the copper and undercut the resin they are set into. If they don't do this, the brushes will ride on the resin and not touch the commutator as soon as they start to wear, leading to a no charge condition that usually starts at high rpm and gets lower as the commutator wears.

2: The brushes carry the field current, not the output. Pnick is correct that the brushes carry DC. The stator outputs the AC that goes to the diode bridge.


And yes, disconnecting the battery while the engine is running went out as a valid test procedure in the mid-70s with electronic ignition modules. You'll cook shit that way...
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Old Tue, Aug-30-2016, 09:51:20 AM   #45
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Default Re: Alternator and Battery question :)

Is the commutator too far gone?




or can I just replace the voltage regulator?


Last edited by Guam135i; Tue, Aug-30-2016 at 10:52:14 PM.
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Old Tue, Aug-30-2016, 09:59:07 AM   #46
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Default Re: Alternator and Battery question :)

What do you use to turn the tensioner pulley to get the belt out? The upper alt bolt also holds an idler pulley. The regular 3 series does not have this?

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Old Wed, Aug-31-2016, 03:50:31 PM   #47
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Default Re: Alternator and Battery question :)

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Originally Posted by Guam135i View Post
Is the commutator too far gone?




or can I just replace the voltage regulator?

The lower one looks like it's worn pretty deep.
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Old Thu, Sep-01-2016, 12:43:21 AM   #48
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Default Re: Alternator and Battery question :)

Quote:
Originally Posted by brichter View Post
The lower one looks like it's worn pretty deep.
Yes it is, I think
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Discussing Alternator and Battery question :) in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)