charging system problems 93 300E - PeachParts Mercedes-Benz Forum

Bryan · #1 03-07-2006, 06:47 PM

I was driving along and the radio went dead. The ABS SRS ARS lamps came on. I pulled over and shut the car off to see what was wrong. When I tried to start the car, it was dead. I had someone jump me off and I was able to drive 7 miles to my house. The car idled fine but when the head lights, ac, and stereo was on those same lamps came on again. I never got a battery warning lamp. Any information would be helpful.

#2 03-07-2006, 07:01 PM

You need a DC Voltmeter. Measure the voltage across the battery without engine running. It should be right at 12 volts within a couple of tenths. Then start the car even if you have to jump it. The voltage across the battery with engine running should be about 13.8. If it is less than 13 then use your voltmeter for a voltage drop test. Measure from negative battery post to alternator case and it should be less than .1V or so. Then measure from the output connector on the alternator to the positive battery post and it should be less than about a tenth. If it is more on either of these you have a bad connection, find it and fix it.

If the voltage drop is okay but the voltage across the battery with engine running is bad, then kill the engine and remove the voltage regulator on the back of the alternator and inspect the brushes. If worn to a nub or near a nub, click on fastlane above and buy one of their $15 voltage regulators and that will in all likelihood fix it.

BTW, a search would have found dozens of posts like this with the same instructions which would have prevented me from keying them in again.

Good luck,

Bryan · #3 03-07-2006, 07:08 PM

Sorry for not doing a search. I am new to this forum. Thanks for the information!! Bryan

dave_rose69 · #4 03-07-2006, 08:09 PM

Check your serpentine belt for excessive looseness, or perhaps a major oil leak that might have caused it to slip on the alternator. After you do that, clean your battery posts and terminals nice and shinny with a combo wire brush cleaning tool for batteries, and conduct all of Larry's tests.... BTW, changing the brush holder- Voltage regulator module might bide you some time instead of a RB or new alternator, but those brushes ride a commutator disc thats part of the armature. if the commutator is shot, its time for another unit.....

Dave....

Bryan · #5 03-07-2006, 08:21 PM

How hard is it, to change the whole unit? Any special tools needed?

glenmore · #6 03-07-2006, 08:30 PM

Quote:

Originally Posted by Bryan

How hard is it, to change the whole unit? Any special tools needed?

If it is similar to the regulator on a 91 300CE, it is just plug and play. Take a look at the part at Fastlane to get an idea, I think it is just two screws.

glenmore
1991 300CE
2000 C280
1990 LS400