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Originally Posted by Kip Amore
Howdy fellas,
You guys will know this stuff in your sleep, but I'm the diesel newbie and I just gotta know: how exactly does the battery idiot light work in the 123? My charging system took a crap last week (stranding me roadside twice!) so I swapped the voltage regulator. BUZZZZ wrong answer. I've got an alternator on order now.
As I understand it, the charging system is like any motor - alternator spins, internally rectified to DC, regulator regulates by reading battery voltage, wiring goes from alternator to battery + (stopping at solenoid along the way). Yes, I checked for continuity from alternator to battery. Yes, the battery is new and takes a trickle charge on the charger like it should.
My question is if the car wasn't charging, why didn't the light come on? The light itself works when I crank the car. How does this light "know" to come on at low voltages?
Last question: my method of testing the charging system is to turn the wipers on and disconnect the battery with the engine running. I know not to do this on a gasser (possible surge blows out ignition system). Is there any reason why I shouldn't be doing this on the Benz?
Thanks,
Kip Amore
77 240d
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Yes
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I know not to do this on a gasser (possible surge blows out ignition system)
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Like you say, an alternator is an alternator whether it is on a Gasser or on a diesel. You can easily smoke your diodes, regulator & any other electronics (computer if fitted, CC amp, Stereo, etc)
EXPENSIVE to repair.
Just use a voltmeter.
Measure battery voltage - engine off = 12.0 - 12.6 V is normal
Measure battery voltage - engine idling = 12.6 - 14.0V is normal
Measure battery voltage - engine idling with headlights, heater on = 12.6 - 13.6V is normal
Measure battery voltage - engine at >2K RPM, regardless of load = 13.6 - 14V is normal
Note that the alternator will charge a battery to ~15V then drop the volts back to 13.6 once charged.