Parts Catalog Accessories Catalog Tech Info Tech Forums
  Search our site:    
 Cart  | Project List | Order Status | Help    

Go Back   PeachParts Mercedes ShopForum > Technical Information and Support > Tech Help

LinkBack Thread Tools Display Modes
Old 07-24-2000, 11:19 AM
Posts: n/a

I have a 1977 280E that when I do not drive it for more then a couple of days the battery goes dead. My mechanic sayed that he was getting a reading of 9 at the alternator. I know that the regulators can be replaced. Could this be the cause of the low reading. The Alt belt is fine and the battery is new. What is the procedure for replacing the regulator?


Reply With Quote
Old 07-24-2000, 09:39 PM
Registered User
Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
I don't know what this means. We use an amperage drainage test to check the amount of current the car is consuming when not in use. If it is higher than 35MA after 5 min., you can bet there is a consumer not switching off.

Donnie Drummonds
1991 GMC Syclone
Reply With Quote
Old 07-25-2000, 11:06 PM
Registered User
Join Date: Jan 2000
Location: New Bedford, MA USA
Posts: 1,583
Does your mech mean nine volts total alternator output? If so, then start the engine and disconnect the battery and then measure the voltage at the battery terminals and see what you get. If it won't run w/o the battery connected, then your alternator is rapidly heading south (or maybe already there). The car is old enough to be entitled to a new alternator, don't you think??

Jeff Lawrence
1987 300e
1989 300e
2000 Dodge Grand Caravan SE
Reply With Quote
Old 07-25-2000, 11:33 PM
Registered User
Join Date: Apr 2000
Posts: 117
re: "...If so, then start the engine and disconnect the battery and then...."

Oh, no! Don't do that! Don't even think about that -- ever!
If you ever have an engine running and suddenly disconnect the battery, the spike will fry virtually every electronic system (radio, fuel injection processor, etc.) in your car -- instantly -- as well as destroy your alternator's diodes, so if your alternator wasn't bad before this test, it will sure to be toast after it.
You may be able to get away without damage by doing this on a lawn mower, but NEVER on a car.
I sure hope that I caught you with this warning before you tried this.
Reply With Quote
Old 07-26-2000, 12:25 AM
Registered User
Join Date: Jan 2000
Location: New Bedford, MA USA
Posts: 1,583
Well, Ken, I have to say that I've done this a number of times on many different vehicles w/o any ill effects. (including both of my 300e's, the bimmer and a couple of Jeep Cherokee's that I've owned. I realize that the battery acts as a capacitor to absorb alternator output fluctuations, but, in most cases, if the alternator is charging with no load other than a partially or fully discharged battery and maintaining at least 12 volts, there should be no inductive "spikes" generated by disconnecting the battery, especially if the alternator is not producing the minimum threshold voltage necessary to get the regulator to clamp it's output. This is not a recommended servie procedure, but it does work. When you jump start a dead or nearly dead battery, you are essentially doing the same thing. If you have a good alternator and regulator, it will clamp output voltage to avoid self destruction as it wi6ll see the dead battery as a huge load once you remove the helper from the circuit. It's the alternator that keeps things humming when your battery is dead.

Jeff Lawrence
1987 300e
1989 300e
2000 Dodge Grand Caravan SE
Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
[HELP - ELECTRICAL] tracing battery drain / ammeter usage ard Tech Help 24 01-09-2007 10:16 PM
intermitent dead battery ("+*#!) MarkM Diesel Discussion 7 12-17-2004 08:11 AM
500E Battery Drain Problem Persisting charnett Performance Paddock 6 01-15-2004 02:08 PM
2.3 16V Intermittent Battery drain when driving, Alternator OK Village Idiot Tech Help 7 02-07-2002 10:30 PM
Battery Drain RUH52 Tech Help 3 04-30-2001 11:37 PM

All times are GMT -4. The time now is 06:19 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2011 Pelican Parts - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page