Are there Bosch alternator rebuild kit/which ones do you recommend?
 

I have a W116 alternator that I want to rebuild, and I'm curious if there are any kits for me to do so with/which ones are of a good quality.

If the slip rings are in decent shape, all you probably need are the front/rear bearings and a new regulator. If the slip rings need attention, you might be able to take the rotor to an auto electric shop and get them machined or replaced.

Forgive my ignorance, but are the brushes located in the regulator*? Also, where would I get the bearings? The dealer?

A big part of the reason that I'm rebuilding an alternator is to find out how it works :).

Yes.


They are very common bearings. Don't get them from a dealer.

The front bearing is a 6303, rear is 6201. Both double sealed.

Sweet! Thanks.

Note: Stretch did a write up on rebuilding an alternator a while back.

Here is how it works:
The shell of the alternator is wound with three circuits of copper wire spaced 120 degrees apart. This is called the stator.

If you were to take a bar magnet and rotate it inside the three coils of wire, then an electrical current would be produced in each of the three coils. Each coil produces a ac voltage 120 degrees offset from the others. As one reaches its positive peak, another is heading negative towards its negative peak and the third has passed its negative peak and becoming more positive.

You may ask why the three coils, that is because it is the most efficient.
And you may ask why are we making ac when we need dc for the battery, the answer is there are diodes that turn the three ac waveforms into one dc output. Using the three coils results in a much smoother output, (closer approximation to pure dc) than trying to convert one ac coil to dc.

Well now we have a voltage but no way to control it. So instead of a bar magnet we use a coil of wire on the rotating part, called the rotor. By varying the current through the rotor coil we can adjust the strength of the magnetic field and thus the output voltage at the stator.

This is where the regulator comes in. There are 3 connections on the regulator. The first two are the brushes, which touch the slip rings on the rotor coil. Slip rings allow the current for the rotor coil to transfer onto the rotating coil from the stationary regulator. The third connection on the regulator is battery voltage. It goes from the battery through the alternator light bulb to the regulator. This is the small wire in the 3 wire alternator harness, the two fat wires go to the battery and carry the output from the armature. (There are two thinner output wires instead of one fat wire since that absorbs the flexing better between the engine and the body.)

The regulator takes the voltage from the battery and does two things. First it measures the voltage level on the thin wire to know where to set the output voltage so it will correctly charge the battery (and not fry the electronics on board). Second it takes that battery voltage and uses it to create a controlled amount of current to excite the rotor coil. The amount of current sent from the regulator, through the brushes and slip rings, into the rotor coil, is directly proportional to the desired output voltage.

If the alternator is not charging then a voltage difference exists across the charge warning bulb so it glows. Once the alternator is charging, the voltage is equal on both sides of the bulb so the bulb does not glow.

Once the alternator gets up to speed there is an auxiliary stator winding and another set of diodes that is used to feed the regulator in addition to the battery feed through the charge warning bulb. That is why the alternator can produce power at high rpms but not at idle if the charge lamp is missing or burnt out.

I play with huge ones at work, the big boys work just like the one in your car except:
- we have a honking 60 L, 16-cylinder, quad turbo Diesel engine for a prime mover, the typical electrical output is 2.5 MegaWatts, your house uses less than 5 kiloWatts on average. The typical data center has no less than two, and sometimes up to 16 or more, of these generators.
- the engine typically burns 150 gal/hr at full load
- we don't use diodes, we want to stay with a 3 phase ac output (usually 480 V but sometimes 4160 or 13800 V)
- and I can assure you that if the regulator does not excite the rotor, we get no electricity...

My 124's alternator had bad bearings. Took it to a local motor shop and they were able to replace the bearings and the regulator since the brushes were almost gone, and it was about $50.

Final thought, if your brushes are wearing down, replace the regulator before the brush holders dig into the slip rings. If those get damaged severely, the alternator can become scrap metal...

You did not say if your Alternator was not charging or if it was just an issue with the Bearings.
If it was not Charging and it was not the Voltage Regulator of Brushes it could be an issue with the Diodes or some of the other parts. They would need a more step by step trouble shooting process.

commutator? Another term for it is the slip ring. Some where in the repair Links someone posted on getting a new Slip Ring and over 4 years ago it was about $6.

When I replaced the Bearings on mine I got them from eBay. The Bearing Numbers are often imprinted on the Bearing Shields on small bearings and some times in tiny Letters and Number on the Bearing itself.

Somewhere in the Repair Links people have brought Brushes from ACE Hardware and used them. With Carbon Brushes you can lay Sandpaper on a flat surface and easily sand Carbon Brushes to shape.

DIY Repair Links
DIY Links by Parts Category - PeachParts Mercedes ShopForum

PeachPartsWiki: Do It Yourself Articles - Mercedes Vehicles

Alternator part links from My notes; don't know if they all apply or not.

Wagner Alternators and Supplies, Inc. Alternator Parts in Chino CA

has some bosch stuff expensive
Alternator Parts, REGULATORS, RECTIFIERS, PULLEYS, BEARINGS, REPAIR KITS, NATIONS AUTO ELECTRIC

Mercedes Bosch Starter Parts alternator parts
New Alternators and Starters from Fleet Alternator Starter

general
#1 High Output Alternator,200-250-300-350,High Amp Alternators, Starters and more

How exactly does the reg know its target voltage and how does it physically adjust the field current? Is there a transistor under that black cap?

Correct me if I am wrong, but I think you have them backwards. The field should be the windings in the shell, and the armature should be the rotating part?

As far as I know, these are the parts of an alternator

http://www.peachparts.com/shopforum/...1&d=1361945436

I believe that "commutator" and "armature" are components of a generator.

Yes there are electronics under that black cap. That is how it knows the target voltage.

As to the naming convention that is how I remember from school. When I get home I will have to pull out my rotating machines class book (I still have it) and review...

I will be seeing the service guys from a gen manufacturer today at the site I am on, I will ask them what they call the windings if I get a chance. (I don't work for the gen manufacturer, I am on the power switchgear side of the system.)

Edit 28-Feb-2013: the terms the manufacturer guys use are "rotor" and "stator". I went back and pulled out my book from my rotating machines class, and it uses "armature" and "field" even for ac machines. Further research leads me to believe "rotor" and "stator" are indeed the correct terms. I updated original post above.

Yeah, that's what inspired me... I want to take one apart myself :). Thank you very much for taking the time to write that alternator write-up! I enjoyed it.
Whoa. And I thought that the 7.3L Ford diesel was big...
Righto.
I'm getting Squiggledog's core, so I have no idea. I'll see if he does.
All right. I have a multimeter (three, actually), so I can use Strech's diagnosis guide...
Okay. I may try to find that thread...
I may be buying a set of SKF alternator bearings from qwerty, but otherwise I'll look to eBay or the helpful links you provided. Thank you!

The bearings of the alternator seemed to be fine, but the alternator was no longer charging the battery. I replaced the voltage regulator with a new Bosch one, but it still wouldn't put out a charge. It had a lot of grease and dirt at the mounting points, so maybe it was just not grounded well enough anymore. But, I decided I wanted to upgrade to an 80 amp alternator, so it was worth replacing anyway. The slip rings seem to have a good amount of wear.