From: @.   
      
   On 5/10/2023 12:55 AM, Xeno wrote:   
   > On 10/5/2023 3:05 am, 😎 Mighty Wannabe ✅ wrote:   
   >> On 5/9/2023 10:39 AM, Xeno wrote:   
   >>> On 9/5/2023 11:34 pm, 😎 Mighty Wannabe ✅ wrote:   
   >>>> On 5/8/2023 11:58 PM, Ivan Vegvary wrote:   
   >>>>> 1948 Pontiac, 12V battery, one wire alternator (was working when   
   >>>>> parked 12 years ago).   
   >>>>> No amperage reading even at 2000 rpm.  Battery voltage 12.6V.   
   >>>>> Battery voltage with car running 13.8V, however amp meter only   
   >>>>> reads 0 or negative with headlights on.  Placed an after market   
   >>>>> ammeter between the alternator and the battery.  Same reading as   
   >>>>> ammeter in the dash.   
   >>>>> How could this be?  Alternator supplies voltage but no current.   
   >>>>> After idle for 12 years maybe residual magnetism is gone. Needs to   
   >>>>> be excited.  Can't find a YouTube that shows me which terminals to   
   >>>>> zap.   
   >>>>> All help is appreciated.  I can certainly buy a new unit, but   
   >>>>> possibly have other problems.   
   >>>>>   
   >>>>> Thank you   
   >>>>   
   >>>> If you get 13.8V when the car is running, that means the alternator   
   >>>> is providing output.   
   >>>>   
   >>>> The alternator output is AC. You need to use AC ammeter to measure   
   >>>> the AC current output from the alternator.   
   >>>>   
   >>> Correction, the alternator output is DC. The 6 internal power diodes   
   >>> provide the necessary rectification. The 3 exciter diodes are meant   
   >>> to excite the field coils and set the generation process into gear.   
   >>>   
   >>   
   >>   
   >> Are you sure that's true for 1948 Pontiac?   
   >>   
   >> Maybe that alternator had been modified to use external rectifiers   
   >> and regulator.   
   >>   
   > Then it wouldn't be a single wire alternator, would it? Think about   
   > that for a moment. Alternators are, typically, 3 phase. That means 3   
   > +ve power diodes, 3 -ve power diodes and 3 exciter diodes. If there is   
   > only one output wire, then all *rectification* and control has to be   
   > on-board.   
   >   
      
   If the alternator really has DC output, then the car's ammeter and   
   external ammeter should register DC current.   
      
   I believe somehow the alternator burnt the internal diodes, and the   
   owner rewired it as single phase output and used external rectifier   
   after the car's dashboard ammeter. That means the dashboard ammeter has   
   not been working properly ever since. A germanium diode was used so some   
   reverse current is flowing back into the alternator when the engine is   
   not running but the key is on auxiliary. That's when and why the   
   dashboard ammeter registers negative.   
      
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