S4 Alternator bearing, slip ring, and voltage regulator check & questions
12-04-2011, 04:32 PM
#16
Rennlist Member
Also stated in a previous reply, a diode trio and rectifier bridge are terms specific to GM alternators, mainly the SI series alternators.
12-04-2011, 05:20 PM
#17
Rennlist Member
An alternator has a fixed winding called a stator. The rotor is what what spins creating unrectified ac voltage. A starter and generator have fixed magnets in the case and the armature is what spins. A starter and generator will spin when voltage is applied. Remove the belt from an alternator and apply voltage. It will not spin because of the magnetic field it creates. An alternator and starter have totally different internal components.
Also stated in a previous reply, a diode trio and rectifier bridge are terms specific to GM alternators, mainly the SI series alternators.
Also stated in a previous reply, a diode trio and rectifier bridge are terms specific to GM alternators, mainly the SI series alternators.
Its not a PM rotor, because it has wires, and the commutator is connected to it, via those wires. so, its an armature, no? if it didn have a commutator, it woud be a rotor of an induction motor. but, the wires and communtator technically make it an armature. Im sure it wouldnt run like a motor with power applied to the commutator brushes, but i bet you could modify it to run.
armature definition:
2.Any moving part of an electrical machine in which a voltage is induced by a magnetic field.
so, in an alternator, since the armature doing the inducing, no being induced, so it might not be an armature.
12-04-2011, 05:25 PM
#18
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Mark, please, for the love of God, take your pedantic distractions elsewhere. I'm interested in making sure this alternator works for a hi load, low rpm street application, not underdriving it for racing, nor arguing about whether one could turn an alternator into an electric motor.
Go solve this problem, would ya?
https://rennlist.com/forums/off-topi...belt-pocb.html
Go solve this problem, would ya?
https://rennlist.com/forums/off-topi...belt-pocb.html
12-04-2011, 05:48 PM
#19
Rennlist Member
Mark, please, for the love of God, take your pedantic distractions elsewhere. I'm interested in making sure this alternator works for a hi load, low rpm street application, not underdriving it for racing, nor arguing about whether one could turn an alternator into an electric motor.
Go solve this problem, would ya?
https://rennlist.com/forums/off-topi...belt-pocb.html
Go solve this problem, would ya?
https://rennlist.com/forums/off-topi...belt-pocb.html
so,if the alternator is broke, its usually a broken winding or damaged or worn commutator on the rotor. if not, the regulator parts.
didnt mean to dirty this so clean discussion. read my first post.
12-04-2011, 11:10 PM
#20
Mark, please, for the love of God, take your pedantic distractions elsewhere. I'm interested in making sure this alternator works for a hi load, low rpm street application, not underdriving it for racing, nor arguing about whether one could turn an alternator into an electric motor.
Go solve this problem, would ya?
https://rennlist.com/forums/off-topi...belt-pocb.html
Go solve this problem, would ya?
https://rennlist.com/forums/off-topi...belt-pocb.html
12-04-2011, 11:15 PM
#21
No problem with the alternator, it's a rebuilt unit (not sure when but there's a rebuilder decal on it) that seems to be in very good shape.
The only reason I opened it up and started asking dumb questions is because it is going to go back into Dan Hebert's Turquoise '91 S4, that will go back into service in Phoenix, and will thus be subjected to headlights/A/C/carputer/stereo on while idling in traffic in 100o+ heat, so I just want to make sure it's functioning as well as possible. Dunno how well it works, as the car's been apart for 2+ years now.
Looking back through the records, Kie bought the Turquoise car in January of 2007, at which point it had front end damage and 91,000 miles. During his ownership he replaced the alternator, then sold the car to Dan in October 2009 with 99,000 miles on it.
So the 'rebuilt' alternator from Kie's ownership has no more than 8000 miles on it, which is consistent with its appearance and good-sounding and -feeling bearings. But no way did they replace the voltage regulator given how badly its brushes are worn. And that shouldn't be surprising given that a new VR is $60-70...
So I think that this alternator is fine, but the question is whether it would benefit from a new VR- I doubt it makes any performance difference (at least 'til the brushes wear away and destroy the slip rings) but hell, maybe as the brushes wear the spring pressure pushing them on the slip rings decreases and the contact isn't as solid? I have no idea, hence putting it out there in front of more-talented-than-mine eyes. I have no idea what the critical determinants of alternator current output vs. rpm are, and how the 'age' of various components in an alternator affect this. Just trying to learn.
The only reason I opened it up and started asking dumb questions is because it is going to go back into Dan Hebert's Turquoise '91 S4, that will go back into service in Phoenix, and will thus be subjected to headlights/A/C/carputer/stereo on while idling in traffic in 100o+ heat, so I just want to make sure it's functioning as well as possible. Dunno how well it works, as the car's been apart for 2+ years now.
Looking back through the records, Kie bought the Turquoise car in January of 2007, at which point it had front end damage and 91,000 miles. During his ownership he replaced the alternator, then sold the car to Dan in October 2009 with 99,000 miles on it.
So the 'rebuilt' alternator from Kie's ownership has no more than 8000 miles on it, which is consistent with its appearance and good-sounding and -feeling bearings. But no way did they replace the voltage regulator given how badly its brushes are worn. And that shouldn't be surprising given that a new VR is $60-70...
So I think that this alternator is fine, but the question is whether it would benefit from a new VR- I doubt it makes any performance difference (at least 'til the brushes wear away and destroy the slip rings) but hell, maybe as the brushes wear the spring pressure pushing them on the slip rings decreases and the contact isn't as solid? I have no idea, hence putting it out there in front of more-talented-than-mine eyes. I have no idea what the critical determinants of alternator current output vs. rpm are, and how the 'age' of various components in an alternator affect this. Just trying to learn.
12-05-2011, 03:52 PM
#22
Three Wheelin'
In 1990 Porsche changed the crank pulley P/N 928 102 139 12 (larger than the std. -11 pulley) and the alternator fan to a die cast to handle the higher RPMs.
I ordered mine from 928 Int. today. Tom said they only have one or two left. Being Porsche only did this for the 928 MY 1990, I'd say they are going to be considered rare as hens teeth
12-05-2011, 04:43 PM
#23
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Very interesting idea, but at least in PET the -11 pulley goes from 1985 up to the 1990 automatic (M28.42) engine engine 81L 51762. No idea what's on a '90 5-speed, or '91 for that matter, but it looks like all GTS engines got the -12 pulley. So hopefully they're not as rare as '90 only?
12-05-2011, 04:57 PM
#24
Three Wheelin'
From what I read it was for 1990 S4 only due to the lower idle speed than the 1990 GT. I don’t have time to look today, but check and see if the GTS idle is closer to the S4 or GT.
When doing some early research on this, I seem to remember that the PET listed both the -11 and the -12 for the GTS models.
But that was some time ago and my memory of this could be off.
When doing some early research on this, I seem to remember that the PET listed both the -11 and the -12 for the GTS models.
But that was some time ago and my memory of this could be off.
Last edited by T_MaX; 12-06-2011 at 07:21 AM.
12-05-2011, 05:58 PM
#25
Drifting
So the 'rebuilt' alternator from Kie's ownership has no more than 8000 miles on it, which is consistent with its appearance and good-sounding and -feeling bearings. But no way did they replace the voltage regulator given how badly its brushes are worn. And that shouldn't be surprising given that a new VR is $60-70...
So I think that this alternator is fine, but the question is whether it would benefit from a new VR- I doubt it makes any performance difference (at least 'til the brushes wear away and destroy the slip rings) but hell, maybe as the brushes wear the spring pressure pushing them on the slip rings decreases and the contact isn't as solid? I have no idea, hence putting it out there in front of more-talented-than-mine eyes. I have no idea what the critical determinants of alternator current output vs. rpm are, and how the 'age' of various components in an alternator affect this. Just trying to learn.
So I think that this alternator is fine, but the question is whether it would benefit from a new VR- I doubt it makes any performance difference (at least 'til the brushes wear away and destroy the slip rings) but hell, maybe as the brushes wear the spring pressure pushing them on the slip rings decreases and the contact isn't as solid? I have no idea, hence putting it out there in front of more-talented-than-mine eyes. I have no idea what the critical determinants of alternator current output vs. rpm are, and how the 'age' of various components in an alternator affect this. Just trying to learn.
Whether brand new, or heavily worn, the brushes don't put a lot of pressure on the slip rings, but the pressure does remain fairly constant regardless of brush wear. Even if they wore out completely, their retainers probably wouldn't cause a devastating amount of damage.
What I would do if I was in your position is throw in the new regulator, put it on my car, and see what it does by driving with it for a few days. A while ago, I put one of the cheap Kaehler brand regulators on my '85. It wasn't an exact fit and the voltage was all over the place. I don't know if the problem was the regulator or the alternator. I then opted to replace the alternator. I suppose the rebuilt was marginally better then the original. If that's a Bosch VR, I'd see what it does. But the only way to find out is to test it.
12-05-2011, 06:34 PM
#26
Team Owner
FWIW I would suggest to use a new VR from Bosch,
in the past swapping the less expensive brand X parts only made it necessary to then remove the rear cover and swap in a new Bosch VR.
The other option is to simply replace the brushes though they seem to be very difficult to find, you might have a good regulator with worn brushes .
This repair seems to also be a good solution
in the past swapping the less expensive brand X parts only made it necessary to then remove the rear cover and swap in a new Bosch VR.
The other option is to simply replace the brushes though they seem to be very difficult to find, you might have a good regulator with worn brushes .
This repair seems to also be a good solution
12-05-2011, 07:18 PM
#27
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Yeah, the VR I installed is a genuine Bosch VR from 928Intl (928 603 142 00). I bought one from Wagner (a W080-05, FWIW) for 19.95 but was not made warm and fuzzy by its construction. I also have a bunch of brushes from Wagner as well. (for the record they're Wagner W030-02, listed as Bosch alternator brush, 4.9 x 7.9 x 19 mm length, 60 mm LL. 12V, for 28 mm slip ring, insulated) but haven't disassembled enough to see whether the 'old' ones got replaced in the rebuild
Am working on a lead to have the alternator rewound for higher output. Not sure whether anything will come of it, will report back.
Am working on a lead to have the alternator rewound for higher output. Not sure whether anything will come of it, will report back.
01-03-2012, 02:12 AM
#29
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Another day, another voltage regulator. Here's what I think is the original VR out of my '93 GTS, 105K miles on it. Brushes are in bad shape. Somehow I was unable to get any resistance measurement across the pair of brushes.
