[R129 SL] battery

[Peter Shelton]

Hi William,

I believe that Phil and Marcus have stated you on the path and it may well 
be the alternator, or the regulator section of the alternator.    The 
battery is a big 'condenser' (capacitor) and should give some immunity to 
spikes but it will not absorb all spikes in any DC system, especially when 
they are high frequency AC or AC simulated (or distorted).  I would not 
expect to see a 20 mA or even a 150 mA spike on the car current charging 
gauge, and you will require an oscilloscope or a power analyser to measure 
to these levels.  If you are using a standard meter, my guess is that it is 
not a DC spike and the meter is picking up an RF (radio frequency) style 
frequency from somewhere in the car, or it may be induced from an external 
source.

To be brief, obtain a DC clip on current meter.  Place it on the alternator 
big cable, see what current is coming from the alternator!.  If it is less 
than 30 amps or so, when the battery is 'down', then the alternator is the 
first port of call.

I use a Fluke Power Analyser and place the setting on "zero degrees" phase 
shift, and voila, you have a DC measuring device to 800 amps!  Find an 
electrical engineer, or a big electrical company and they may have one of 
these.  If you are in New Zealand, feel free to borrow mine!

Good luck and I will be interested to know how you get on!

Kind Regards, from the Deep South, Peter S.




----- Original Message ----- 
From: "william hughes" <jennianenterprises at verizon.net>
To: "SL Mailing List" <r129list at mbcoupes.com>
Sent: Saturday, April 21, 2007 6:01 AM
Subject: [R129 SL] battery



> my 1995 sl500 looses battery charge even with brand new battery.

> test shows a spike to 20 milliamps when the radio light blinks - ok

> and a random spike to around 150 milliamps evry 30 seconds or so

> almost to quick to see on the guage but shows on the recording

> any idea what might be drawing

> thanks,

> bill

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