Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Vintage Mercedes Forum

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 12-17-2007, 10:11 AM
Registered User
 
Join Date: Jun 2006
Location: Austin, TX
Posts: 201
Low voltage - battery drain

I've had a slightly strange problem develop on my 79 280SE. The battery is slowly being discharged during my stop-and-go commute, especially with headlights/heater/wipers on. I have to put it on the charger every few days otherwise it loses enough juice to be unable to start the car.

Voltage with the car idling and no load (at both battery posts and clamps) is 12.3 V which is kind of low - it's always been up around 13.5 or so. With everything on it doesn't change much, 12.1 is the lowest I saw. I replaced the alternator a couple of years ago (maybe 15k miles) with a Bosch rebuilt unit. The charging light on the dash doesn't normally come on (and I know it works because the belt broke a few weeks ago). It does however come on when I start the car, and I have to rev the engine a tad to make it go out, then it stays off.

I guess it's possible the alternator brushes need to be replaced already, but does anyone have any ideas on what else could be going on? I don't think it's the battery.
Thanks!

__________________
kalpol
79 280SE
82 Fiat Spider 2000
81 Fiat Brava
04 BMW R1150RT
96 Jeep Grand Cherokee
Reply With Quote
  #2  
Old 12-17-2007, 06:31 PM
Registered User
 
Join Date: Jan 2006
Location: Tucson, AZ
Posts: 5,358
It could still be the battery. If you are charging high amps the voltage will be low, hence the 12.3 volts reading. It's the old flowing water analogy. A shallow river flows fast (voltage) whereas a deep river (charging amps) flows slower.

Load test the battery. If it tests okay then re-check your alternator. If you have an induction ammeter you can check for running amps. You should be showing 13.5 V and about 2 to 20 amps at idle with no accessories on after the battery has recharged the starting amps draw.

Last edited by Mike D; 12-18-2007 at 09:14 AM.
Reply With Quote
  #3  
Old 12-18-2007, 10:32 AM
Registered User
 
Join Date: Jun 2006
Location: Austin, TX
Posts: 201
Excellent, thanks. So I have a multimeter with an ammeter - 10 amps I think it will handle...I've never used it, should I be able to test the charging amps with this?
__________________
kalpol
79 280SE
82 Fiat Spider 2000
81 Fiat Brava
04 BMW R1150RT
96 Jeep Grand Cherokee
Reply With Quote
  #4  
Old 12-18-2007, 12:40 PM
Registered User
 
Join Date: Sep 2004
Location: Dublin, Ireland
Posts: 385
Quote:
Originally Posted by kalpol View Post
Excellent, thanks. So I have a multimeter with an ammeter - 10 amps I think it will handle...I've never used it, should I be able to test the charging amps with this?
Be careful if its a regular multimeter and your putting it in series with the battery, the current drawn by the starter will probably blow its internal fuse.
Mike suggested an "Induction" ammeter which measure the current flow indirectly.
Reply With Quote
  #5  
Old 12-18-2007, 12:43 PM
Registered User
 
Join Date: Jan 2006
Location: Tucson, AZ
Posts: 5,358
Nope! You'll toast the ammeter when you try to crank it. If you pull the alternator wire and put the meter in-line you'll fry it when the alternator "spikes" as it receives voltage. Inductive or high amperage in-line is the only way to check (high amperage in-line must be able to handle the cranking amps). Inductive aren't as accurate but you're just looking for a charge indication.
Reply With Quote
  #6  
Old 12-18-2007, 02:27 PM
Registered User
 
Join Date: Aug 2004
Posts: 232
A climate control servo that won't "park" will drain the battery. I went through a couple of batteries before I figured this out.
Reply With Quote
  #7  
Old 12-18-2007, 06:49 PM
Registered User
 
Join Date: Jun 2006
Location: Austin, TX
Posts: 201
Quote:
Originally Posted by oxymoron View Post
A climate control servo that won't "park" will drain the battery. I went through a couple of batteries before I figured this out.
It's a Euro model with manual climate control. (I loves it). But good point anyway.

__________________
kalpol
79 280SE
82 Fiat Spider 2000
81 Fiat Brava
04 BMW R1150RT
96 Jeep Grand Cherokee
Reply With Quote
Reply

Bookmarks

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 On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 04:05 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2024 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page