Alternator Test Quick Question - Page 2 - PeachParts Mercedes-Benz Forum

JamesDean · #16 01-07-2010, 10:40 PM

Quote:

Originally Posted by layback40

Not coping with loads is a sign of the charge circuit not being up to spec. Until you have the output voltage at the back of the alt, you cant tell what is the cause.

Those measurement were conducted at the back of the alternator.

layback40 · #17 01-07-2010, 10:59 PM

Sorry James, didnt see that.
looks like alt or reg has a problem. I would first take the reg out, 2 screws (Battery disconnected when doing this) & check the brushes, if they are good, not wonky or warn down to nearly nothing, then its the reg or the alt. You could try the reg out of your other car. If it still gives readings like these, then the alt should be replaced, you will probably get a new reg with the replacement alt.

Diesel911 · #18 01-07-2010, 11:01 PM

Quote:

Originally Posted by JamesDean

Results of tests round #2 measured from alternator output:

Battery - Car Off - 12.28v
Key On - Car Off - 11.50v - No GP Light On
Glow Plugs verified to be running, voltage @ GP #1 ~11.05
Cranking Voltage - 10.4v
Started Idling - 13.14v -
Started Revving - 13.70v peak
Only Blower High @ Idle - 12.55v
Only Blower High @ Rev - 13.42v
Blower High + Lights @ Idle - 12.13v
Blower High + Lights @ Rev - 13.33v
Blower High + Lights + Rear Defrost @ Idle - 11.87v
Blower High + Lights + Rear Defrost @ Rev - 12.68v
Blower High + High Beams + Rear Defrost @ Idle - 11.69v
Blower High + High Beams + Rear Defrost @ Rev - 12.36v

It does not seem to cope well with loads. Not sure if thats an indicator of the battery or the alternator.

I have another SD, its battery is currently on trickle charge, it has not been driven since snow hit. (not a winter car)

When the Key is On and No Glow Plug light is on I would be curious to know if you are getting Voltage to the Glow Plugs? In the Glow positoin there should be no other current drawn but the Glow Plugs and the Clock.

Since the Battery voltage drops to 11.50 Volts it appeas that something; if not the Glow Plugs is drawing the current.

And, you said that the Glow Plug Light works sometimes and sometimes not. This makes me think that the Ignition Switch might be haveing a problem. However, I know of know way to test the switch.

JamesDean · #19 01-07-2010, 11:08 PM

Quote:

Originally Posted by Diesel911

When the Key is On and No Glow Plug light is on I would be curious to know if you are getting Voltage to the Glow Plugs? In the Glow positoin there should be no other current drawn but the Glow Plugs and the Clock.

Since the Battery voltage drops to 11.50 Volts it appeas that something; if not the Glow Plugs is drawing the current.

And, you said that the Glow Plug Light works sometimes and sometimes not. This makes me think that the Ignition Switch might be haveing a problem. However, I know of know way to test the switch.

Diesel911 see the line right below the one you highlighted in blue. I verified that the plugs were running, I also heard the relay click.

JamesDean · #20 01-07-2010, 11:13 PM

Quote:

Originally Posted by layback40

Sorry James, didnt see that.
looks like alt or reg has a problem. I would first take the reg out, 2 screws (Battery disconnected when doing this) & check the brushes, if they are good, not wonky or warn down to nearly nothing, then its the reg or the alt. You could try the reg out of your other car. If it still gives readings like these, then the alt should be replaced, you will probably get a new reg with the replacement alt.

I've never taken the regulator out of one of these before, is it difficult? I assume it can be done on the car.

Should look something like this:

http://imgur.com/pZYdJ.jpg

maybe not as filed down as those are...

layback40 · #21 01-07-2010, 11:13 PM

James, If you end up having to get another alt, chances are you can get a higher amp one. If you just need a reg, you may be able to get a higher amp one as well, as long as it fits. There is no difference with the alt's the higher amps come from different internal setting in the reg.

JamesDean · #22 01-07-2010, 11:15 PM

I'll go pull the one SD's regulator and snap a picture for you guys to see...

layback40 · #23 01-07-2010, 11:20 PM

cant look at that link.
There are 2 screws holding the reg in. When you remove them, careful you dont drop them! PITA !!!
When you come to putting it back in, it can be a little fiddly, you need to put the reg in the space & then move it towards the middle of the alt to line the holes up for the screws, again its a PITA and screws can fall out. Or maybe my fingers are not as nimble as they used to be!
I will be away for the next 45 min.

JamesDean · #24 01-07-2010, 11:28 PM

Photos:

http://i98.photobucket.com/albums/l250/MafiaNicky/IMG_9423.jpg

http://i98.photobucket.com/albums/l250/MafiaNicky/IMG_9425.jpg

from a 1982 300SD (Green)

Removal was trivial.

I can only hope re-install is as decent.

I'll leave it out until I hear back from you. The car isnt going anywhere anytime soon.

layback40 · #25 01-07-2010, 11:37 PM

havent gone out yet!
That reg's brushes look ok, the ones in my cars are a lot more warn. I think you may need to try the reg from your other car, if it doesnt improve things, another alt is required.

JamesDean · #26 01-07-2010, 11:43 PM

Alright so I should pull the regulator from my other SD and install it in the broken down one?

I'll try to repeat the tests and post back.

barry123400 · #27 01-08-2010, 12:32 AM

Quote:

Originally Posted by layback40

James, If you end up having to get another alt, chances are you can get a higher amp one. If you just need a reg, you may be able to get a higher amp one as well, as long as it fits. There is no difference with the alt's the higher amps come from different internal setting in the reg.

Higher amps are not a function of the voltage regulator exactly. The regulator adjusts the output voltage of the alternator in comparison with the variable output currrent. . I think I have this right.

The ability or lack of ability to deliver the current is more a function of the other components of the alternator.

One thing I did notice was an underpreforming alternator is suspected. I would first bring the cars battery up to a sitting static voltage of at least 12.5 volts by charging it first. Twelve point two eight volts is too low.

Otherwise the indicated voltage drop you see may be the alternator voltage sagging a little to bring up that semi depleted or defective battery. As the alternator is trying to deliver its maximum output it just may sag voltage wise a little in the process.

Remember you are now asking it to increase the charge substantially into the battery and at the same time deal with a fairly heavy drain. You may be demanding too much output as some of these alternators are just 55 amps.

Now if the battery cannot be charged up to at least 12.5 volts under static test after an external battery charge the battery is shot. That will drag the alternator down and can destroy it over time.

JamesDean · #28 01-08-2010, 12:39 AM

uhm...

well I kinda locked myself out of my house. Its cold outside. I went out to get a drink and check the battery charger on my SD in the garage. Then I went back in to get the light to do the work...and the door was locked..as well as every window and other door around my house.

Furthermore, the doorbell is useless, as is holding down the van's horn. I had an ingenious plan though: I was able to start up the one SD that I am working on...I was going to drive to my grandma's (about 1 mile away) and phone home..(my cell was in the basement) and tell my parents to unlock the door. However this plan was a failure as I couldn't figure out how to bypass the steering lock out. I was proud that I got the engine to run though.

What fun. Also, there is about a pound of oranges and grapefruit on my roof.

Needless to say I'll resume work on the SD tomorrow. I have a few other things to reconnect up (switch off vac line namely)

I ended up banging on the ceiling (my parents room is above the garage) with a 4 foot lead pipe. Impressively enough, I manage to break a wire for the garage door opener clean in half with the blunt end of the pipe (i had a coupler on it)....

JamesDean · #29 01-08-2010, 12:41 AM

Quote:

Originally Posted by barry123400

One thing I did notice was an underpreforming alternator is suspected. I would first bring the cars battery up to a sitting static voltage of at least 12.5 volts by charging it first. Twelve point two eight volts is too low.

Otherwise the indicated voltage drop you see may be the alternator voltage sagging a little to bring up that semi depleted or defective battery. As the alternator is trying to deliver its maximum output it just may sag voltage wise a little in the process.

This was one of my original thoughts. I was thinking about putting it on a 2-amp charge overnight... Would that be permissible? Or is that too long?

Must repair broken wire on garage door.

layback40 · #30 01-08-2010, 12:48 AM

Barry,
The voltage regulator monitors the output voltage of the alt and attempts to keep it at a preset voltage. It does this by adjusting the voltage across the rotor coils. The difference with high amp regs is they are just able to give a higher voltage across the rotor coil. The low amp ones just reach a certain voltage and then flat line. The higher the primary voltage ( rotor coil) the higher the output of the alt.