Alternator rebuild? - Page 2 - PeachParts Mercedes-Benz Forum

cirrusman · #16 09-06-2010, 04:17 PM

Oh, I've got one of those although I don't know how to use it except to check whether an AA battery is good or not... It's got a needle instead of an LCD but it's the same thing, I'll go ahead and check then. What should be the setting on the multimeter and what should my readings be? Also, wouldn't I blow the little thing if I plug it directly to the battery?
By the way, thank you so very much for your input...

Diesel911 · #17 09-06-2010, 04:20 PM

Quote:

Originally Posted by cirrusman

I don't know if it's not outputting any voltage to the battery at all, I'd have to go to checkers to have them check it I guess, but with the engine in idle I can tell that the electrical stuff like windows, wipers and such are drawing power from the already discharged battery and not from the alternator as they work very slowly. I followed the 2 green bolts and they go to the battery, so I guess the red would go to the starter... With the battery plugged, the 2 green screws light up the tester light, the blue and the red don't; with the battery disconnected all of them light the tester light; can't really make anything of this except maybe a bad ground somewhere? I'm not all that good with electrical stuff. The alternator light in the dashboard works fine (the bulb that is) but still does not comes on when I turn the key...

What type of tester are you using? If you are using one that has a several light on it to indicate if the Alternator is working or not you will need to consult the instructions that came with it. If you do not have the instructions some companies that make stuff have them on their web site.

Many of the members use a digital Volt/Ohm Meter (Multimeter) that sells for less than $5 at Harbor Freight.
With it you can check the Voltage when charging and read what it is.

JamesDean · #18 09-06-2010, 04:21 PM

Analog multimeters usually have a 20 volt DC range on them, I think. Depends on model. You should set it for DC volts, you want it to be within a range what will include 10-15volts

Typically, you'd like to see:
battery - no engine = 12.4-12.6 (this is for a fully charged battery)
battery - @ idle after rev = 13+ (somewhere in the neighborhood of 13-14v or so)

The others vary wildly from car to car however ideally you want the system to be above 12.8v especially under load. If your system should dip under 12 while loaded then your not charging the battery and you have a problem somewhere

For example, my 190E is equipped with a 143amp alternator and you'll be hard pressed to load it to the point where it drops below 13. The SD however is a 65amp can can be easily overwhelmed with too many items running.

cirrusman · #19 09-06-2010, 04:26 PM

I'll go get to work on it now and I'll post my results... thank you guys so much!

cirrusman · #20 09-06-2010, 08:48 PM

Alright, so I charged the battery and tested the alt. No charge. I read the same 13V whether the car was running or not, declining slowly as I started the car several times. I figure a new alternator will be the end of my electrical woes...?

cirrusman · #21 09-06-2010, 09:50 PM

Quote:

Originally Posted by Diesel911

You did not say if your Battery/Charging Light on the Instrument Cluster was glowing Red (indicating not charging) or not.
If that Lignt Bulb is burned out your Alternator will not charge as it need the little bite of current flow caused by the Light Bulb to charge.
To test it turn you Ignition Key to the first position and you should see it glow Red. After your Engine is running the Red Light should turn off when it starts to charge.

I got this from another post... My alt light is NOT coming on at all... I just replaced the bulb but it's still not lighting up. Does it fail totally when the alternator fails too? Or is there something else along the line that can fail too? I checked the wiring that goes to the cluster. On the center rectangular bunch in the center the #7 hole carries current, and that one only. On the round bunch on the left #7 and #12 carry current. I don't know if this is relevant or not or if I should get me a new alternator... I just don't want to spend all that money to find out later that it was something else...

Diesel911 · #22 09-07-2010, 12:42 AM

Quote:

Originally Posted by cirrusman

I got this from another post... My alt light is NOT coming on at all... I just replaced the bulb but it's still not lighting up. Does it fail totally when the alternator fails too? Or is there something else along the line that can fail too? I checked the wiring that goes to the cluster. On the center rectangular bunch in the center the #7 hole carries current, and that one only. On the round bunch on the left #7 and #12 carry current. I don't know if this is relevant or not or if I should get me a new alternator... I just don't want to spend all that money to find out later that it was something else...

I have only investigated the Voltage at the Alternator Connectorwhen the connector is disconnected.
The 2 large slots that the Red Wires go to should have the same Voltage as the Battery at all times.
The Smaller Slot has a thin Blue Wire on it atd that goes to the Battery/No Charging Light. With the Key in the Off position there is no voltage.
With the Key on there is voltabe but slightly less than Battery Voltage. If the Key is on and you are not getting any Voltage or voltage is very low you have issue in that circuit.
2 of the things in that Circuit are the Bulb and the Ignition Switch itself. From what I have read the Bulb needs to be 3 watts; the wattage is on the package somewhere if you buy them at Autozone or a similar parts store.

Some members who have had one of more Brushes on the Voltage Regulator worn out have said their Batterly/No Charging Light did not come on and there Battery died on them.

I do not know enough about how the Diodes work in the Alternator to know if they could cause no or low charging but at the same time have no Battery/No Charging Light lighting up.

The Autozone type places do not have this type of equipment but the places that have the Diagnostic Engine Analyzers can hook your Alternator up and project a wave form on the Screen and they can see if a Diode is no good by looking at the wave form.

About 1/2 a dozen times in some of the Alternator/Charging threads I posted pics of an Alternator Test cord I made. That tells you real quick of it is your Alternator or the wiring.
Right now I cannot repost those pics as I am having some computer issues. My old photo software will not work on my new 64 bit computer.

Diesel911 · #23 09-07-2010, 12:50 AM

No one likes to spend money and find out that they replaced something and they still have the problem they had to begin with.
All you can do is try to learn enough so you can make an educated guess.

funola · #24 09-07-2010, 08:11 AM

If your alt light is not coming on, it will not charge! The light provides excitation to the alternator and is required for it to charge. Since you changed the bulb, the problem is elsewhere than the bulb. As a test, hook up a light bulb to 12V + and the other end of the bulb to the alternator excitation terminal and see if it charges.

cirrusman · #25 09-07-2010, 04:24 PM

I finally got a hold of my repair CD and with the schematics I was able to check the whole charging system. It's the alternator. Whew! Now I know...

mak · #26 09-07-2010, 08:21 PM

Rebuild the alternator with new bearings ,regulator and cleaned the brush commutators . Its operationally fine but the original problem still exists . The charging voltage drops to 12.8V after some running ,cold the unit gives 13.8V

mak
300

whunter · #27 08-22-2011, 07:46 PM

for new members

tobybul · #28 08-22-2011, 08:24 PM

Thanks Roy. My eBay-bought 80a alternator conked out recently after almost 4 years of use. I kept it thinking I'd replace the voltage reg and see if that fixes it. Well it didn't. I brought it to AZ to have them test it after I put a new Bosch reg and the tester indicated "FAIL". So I am wondering what else is inside the unit that would cause it to "fail" when tested. I thought I might take it apart and learn something. Thats why I'm asking the experts in the forum who might have done one.....

Diesel911 · #29 08-22-2011, 08:34 PM

Is the 80amp alternator the one that outside looks like the Stock Alternator and uses the same connector?

If you take the Alternator to a Privately owned Alternator/Starter Shop that has test equipment with an Oscilloscope they can tell you if the Diodes are no good and maybe some other info from the wave form on the screen.
I have only been inside of mine enough to change the Bearings. But, I found the Harbor Freight 12volt Impact Wrenches that are made for the Lug Bolts/Nuts worked well to snatch off and tighten the Alternator Shaft Nut (with Blue Loctite on the threads).

Over the years I have used the 12 Volt Impact wrench for nearly everything that a Pneumatic one will do. I have one in each of my Cars to speed up Flat Changing or Tire Rotation.

I do not know how much of the .pdf file will be helpful.