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I've had a VDO voltmeter on my 73's dashboard for many years, and regardless of engine speed, it's always read about 12.6 +/- volts.  It's never run my battery down (the last one lasted 9 years) and always provided sufficient voltage to keep the battery charged and things working in the electric department.   So I thought the voltmeter was simply reading a little low.  It's connected to the" ignition on" terminal on the starter switch so it doesn't read all the time. 

 

Just for the heck of it today I put a voltmeter across the battery terminals while the engine was running about 1200-1300 rpm and was kinda surprised to see the voltmeter reading 12.64 volts, regardless of engine speed.  I know it should be more like 13.65 volts.  I don't have a way to check amperage (it's a 45 amp unit) but again, it doesn't run the battery down.  Here's what I know:

  • both alternator and voltage regulator are original, never rebuilt
  • ground wire from alternator to block is clean, good and tight
  • plug in terminals at both the alternator and voltage regulator end are both clean and tight.  The wire bail is even in place on the alternator end.
  • battery terminals are nice and clean--and the battery is brand new.
  • new urethane alternator bushings, and the belt is tight and not slipping
  • No odd noises emanating from the alternator. 

 

Anything I overlooked to test?  And what might be the most likely culprits?  Diode pack?  Slip rings? 

I know I could replace it with a later, higher capacity unit, but want to stick with the original alternator/external voltage regulator.  

 

Suggestions cheerfully accepted, and outcome will be shared.    

 

TIA

 

mike

 

PS--still looking for anecdotal stories about your trip to, during and from Vintage this year.  PM me.

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If it's an original external voltage regulator,  then it's doing well having regulated for 50 years....chances are the regulator has drifted. 

If you pull the plug off the regulator and put 12V on the DF wire then the alternator will run at maximum output, likely 16V at battery with engine at 1500rpm. If you get that then it confirms the alternator is good and the regulator is the culprit. 

There are modern electronic replacements available, some discussion here on adjustment of old electromechanical type: 

https://www.benzworld.org/threads/early-external-voltage-regulator.3006437/

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4 hours ago, Buckeye said:

carbon brushes worn out and Slip ring diameter is below 31.5mm. When was the last time that you had these items replaced?

Never.  Except for the mounting bushings, the alternator is as it left the factory in December 1972.  But it's been showing the indicated 12.6 volts--verified between the voltmeter and my multimeter--since I installed the voltmeter back in 1987.

 

mike

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19 hours ago, dlacey said:

If it's an original external voltage regulator,  then it's doing well having regulated for 50 years....chances are the regulator has drifted. 

If you pull the plug off the regulator and put 12V on the DF wire then the alternator will run at maximum output, likely 16V at battery with engine at 1500rpm. If you get that then it confirms the alternator is good and the regulator is the culprit. 

There are modern electronic replacements available, some discussion here on adjustment of old electromechanical type: 

https://www.benzworld.org/threads/early-external-voltage-regulator.3006437/

Mike, try this if you haven't yet: ccs-32029-0-19975600-1433442629_thumb.pn

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This is a go/no go kind of situation, right? As long as the brushes are making contact, with the slip rings, you get output. I guess anything increasing resistance in that circuit (e.g., dirty slip rings) might reduce output. Being shown are of course brushes with voltage regulator, not the external V/R used in the factory 02 alternators.

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