Altenator plug - Page 2 - PeachParts Mercedes-Benz Forum

Masterful1 · #16 11-21-2007, 08:13 AM

no the bulb doesn't light, but I also haven't had any time to tear into the dash yet, is there another way to get at this little bugger?
also pulled the voltage regulator and it looks fine.

#17 11-21-2007, 08:25 AM

Unscrew the knee panel and push the cluster out from behind with your hand.

Stevo · #18 11-21-2007, 11:02 AM

You might be able to get to the light with out pushing out the cluster, remove the panel and take a look.

Masterful1 · #19 11-26-2007, 06:57 AM

ok so I checked the bulb all seems well there, so I guess its pull it and take it to my local rebuild shop so they can have a look at the alt.

ichbineinekrous · #20 11-26-2007, 08:23 AM

timely post. I've been dealing with my screwy alternator all this weekend, capping off the fun last night with a tow due to no headlights. I replaced the voltage regulator after having a situation where I was getting amperage from the alternator but only 10.5 V. After replacing the voltage regulator I'm getting nothing. I'm going to take it back out tonight, but I can't see how I could have mis-installed it.

Should I just buy a new alternator perhaps? And can anyone out there tell me the part number for the alternator bracket spacer? Its the one on top that the alternator adjustment bolt goes through. Car is an 83 240D. Thanks all.

Per the problem the originator of the thread is having. The last time I replaced an alternator it would do nothing until I replaced the battery with another one that had some charge left in it. Even though the original battery was connected via jumper cables to a good battery, somehow the dead battery was causing the voltage regulator to see a full charge scenario. Putting the second battery in was one of those last ditch, I don't know what else to try, type deals.

chetwesley · #21 11-26-2007, 10:25 AM

I am continuing to have a very similar problem to the original poster. I had a screw that had fallen out on the VR, which I replaced, but I am still getting nothing from the alt as far as I can tell.

I wanted to check the alt directly, to make sure it isn't a bad connection between the alt and the battery (I have been measuring from the battery and getting nothing).

Is it possible to just check the alt directly with a volt meter? Last night I took out the plug from the alt and started the car. I tried the volt meter in a couple of configurations on the alt, but got nothing off of it. I didn't know, however, which terminals on the alt to put the VM pins to.

Does anyone know how to test an alt straight from it's terminals?

ichbineinekrous · #22 11-26-2007, 11:29 AM

Quote:

Originally Posted by chetwesley

I am continuing to have a very similar problem to the original poster. I had a screw that had fallen out on the VR, which I replaced, but I am still getting nothing from the alt as far as I can tell.

I wanted to check the alt directly, to make sure it isn't a bad connection between the alt and the battery (I have been measuring from the battery and getting nothing).

Is it possible to just check the alt directly with a volt meter? Last night I took out the plug from the alt and started the car. I tried the volt meter in a couple of configurations on the alt, but got nothing off of it. I didn't know, however, which terminals on the alt to put the VM pins to.

Does anyone know how to test an alt straight from it's terminals?

U needn't test it at the alternator. It sounds as though your alternator is not primed/excited. Try swapping your battery out. And then test again, at the battery.

Masterful1 · #23 11-26-2007, 12:43 PM

Quote:

Originally Posted by chetwesley

I am continuing to have a very similar problem to the original poster. I had a screw that had fallen out on the VR, which I replaced, but I am still getting nothing from the alt as far as I can tell.

I wanted to check the alt directly, to make sure it isn't a bad connection between the alt and the battery (I have been measuring from the battery and getting nothing).

Is it possible to just check the alt directly with a volt meter? Last night I took out the plug from the alt and started the car. I tried the volt meter in a couple of configurations on the alt, but got nothing off of it. I didn't know, however, which terminals on the alt to put the VM pins to.

Does anyone know how to test an alt straight from it's terminals?

I have learned your not going to get anything without first exciting the field, so your alt needs to be plugged in to start producing power. if you would like to test the posts on your alternator you need to pop the cap off the alt plug so the terminals are exposed, then you can test across the back of the plug.

chetwesley · #24 11-26-2007, 02:37 PM

Quote:

Originally Posted by ichbineinekrous

U needn't test it at the alternator. It sounds as though your alternator is not primed/excited. Try swapping your battery out. And then test again, at the battery.

I've done this, both by charging the battery with a charger and by swapping out the battery. No rise in voltage with rise in RPM. So the alt will not produce voltage simply by turning with the engine? I guess I don't understand how an alternator works. I just thought it was like a generator which produces voltage via rotation. I'm pretty ignorant on the subject, obviously.

I've been driving my car daily by charging the battery at night every few days while I try to figure out what's up with my alt. This car gets me to work every day!

I will try on the back of the plug with the plug in the alt, as Masterful suggests.

Masterful1 · #25 11-27-2007, 05:22 AM

from my feeble understanding of how the alternator works I gather that it is not a permanent magnet generator, meaning it requires some electric current first to prime/excite the electric field meaning that it contains electromagnets. once the field is excited and it is rotating it then generates its own field using some of the electricity it is generating. the circuit that primes/excites the field of our alternators is the battery light in the dash when you turn the key to let the glow plugs cycle. if your battery light isn't coming on then you are going to have problems. you need to check the bulb and the circuit that goes to the alt, should be the smallest of the wires in the alt plug.

toomany MBZ · #26 11-27-2007, 05:54 AM

Quote:

Originally Posted by ichbineinekrous

And can anyone out there tell me the part number for the alternator bracket spacer? Its the one on top that the alternator adjustment bolt goes through. Car is an 83 240D. Thanks all.

I used a proper length of appropriate diameter pipe.

LUVMBDiesels · #27 11-27-2007, 08:16 AM

I would recommend going with a Bosch AL129X. I did it to my 300SD and the difference is immense! I got a rebuilt one for $80 on ebay. It bolts right in and really gives a lot of power even at idle. check out this thread for more information...
"Alternator" 115 Amp Bosch AL129X works in 123s!

SD Blue · #28 11-27-2007, 11:57 AM

There aren't any permanent magnets in the alternator, they are in the starter. The field on the alternator is how it controls the charging internally. It is not necessary to take anything apart to do the measuring as there is a fantastic terminal strip available on the fender for this (the alt. plug ties to it directly).

To check the alternator, connect your meter (+) to one of the large red wires and (-) to ground and 20VDC range. Start the car and you should have at least 13 or more VDC and watch as it slowly drops off, indicating charging of the battery. If less than this, switch your meter to 20VAC and the reading should be much less than 1VAC. This checks the rectifying diodes of the alternator.

If the AC voltage is too high, then you have an internal failed diode and you will need to replace/rebuild the alternator. If the AC voltage is OK but the DC voltage is too low, then the regulator is not working. There may be other factors causing this. Check for corrosion at the terminal strip, battery cables, grounding (both batt-chassis and chassis-engine), and something I found recently, voltage regulator to alternator housing.

When you disconnect the alternator plug and remove the voltage regulator, check the brushes and also check the comutator rings. If the brushes are severely worn, chances are the rings are heavily grooved. Then you are looking at strictly replacement of the alternator. If there isn't severe wear, then very likely just replacing the voltage regulator takes care of it.

The alternator doesn't really have that much to go wrong with it. Voltage Regulator, rectifying diodes, brushes and comutator rings, windings and bearings. The only time I have seen a problem with the windings was with a major bearing failure causing physical damage.

ichbineinekrous · #29 11-27-2007, 02:21 PM

I have a hypothetical for you. IF someone were to forget to disconnect the main battery leads before installing the new voltage regulator causing sparking at the alternator housing during said installation, AND IF the new regulator didn't want to go in at one point during install and after taking it back out the brushes were pushed out of their respective places and kind of hanging by the little springs, HYPOTHETICALLY is all I'm sayin'. Could something have gotten fubar'd? Before I was getting 42 amps and 1.5 volts and after this little debacle, no amps or volts. I mean, not me personally, but I mean, damn never mind,

it was me.

chetwesley · #30 11-27-2007, 02:46 PM

Quote:

Originally Posted by Masterful1

from my feeble understanding of how the alternator works I gather that it is not a permanent magnet generator, meaning it requires some electric current first to prime/excite the electric field meaning that it contains electromagnets. once the field is excited and it is rotating it then generates its own field using some of the electricity it is generating. the circuit that primes/excites the field of our alternators is the battery light in the dash when you turn the key to let the glow plugs cycle. if your battery light isn't coming on then you are going to have problems. you need to check the bulb and the circuit that goes to the alt, should be the smallest of the wires in the alt plug.

Hmmm... so are you saying a faulty battery light can cause the alternator to not do it's job?

I notice that when I glow the car before starting, my battery light and other lights on the dash (brake and brake wear indicator) sometimes come on, and other times only the glow light comes on - most of the time, only the glow light comes on.

Also, when I shut the car off, the battery light usually doesn't come on, though I think I remember in the past, that it did come on. I have seen it come on once in the past week when shutting down, but I think only that one time (though I don't watch it religiously, because I didn't know it really mattered - but I know it doesn't always come on).