{Chrysler 300} mechanical alternator V regulator

[John Grady <jkg@xxxxxxxxxxxxxxxxx>]

Hi 
I have recently had a succession of these that have been messed with; lots of hassle . 

 I once  had a Chrysler publication called “ The New Alternator”  or something like that from ? 60-61 that I believe had the air gap and point specs for the single coil mechanical VR . I can’t find it of course  , nor can I find this info in any of the FSM . The info for the three coil one is common and not the same . 

if anyone has that , maybe post it or send copy to me ? 

I have found out a lot about it - in this aggravating journey , thought I might share it . Some surmising on my part , but pretty sure about it . 

The upper points set are normally closed will open to begin regulating field magnet down at about 13..8 to 14 v . Opening adds the ten ohm resistor under the VR into the field .  The other 40 ohm resistor  is directly  across the field I think to suppress arcing and burning when opening the field current  

so most of the time it is rapidly cutting the ten ohms in and out ,  vibrating  . That holds 14 by varying output current to match the need and thus hold 14 or so .  Some slight swinging around of gauge is inherent and normal . 

But on a sunny day with no load , even ten ohms is too much charge , and It will show 4-5 A charge (not needed ) for a while . As the battery volts then rises too high , maybe 14.5 + , the VR arm moves down more , and soon touches the lower grounded contact which shorts out the field to ground . The field is connected to the moving arm. That  Kills all output. ( the 10 ohms limits ignition circuit current ) and it probably vibrates there the same way to prevent overcharge . 

So  failures :
1) the two contacts are set by a jig at factory (?) then held there by a 1/4 hex clamp screw through a plastic block . This comes loose (?plastic  shrinks?) the contacts slid or moved closer together resulting in a dead short between all three . That shorts your hot ignition lead to ground ( top 12 v contact touches bottom ) can burn up your harness . In my case a wire inside the VR blew itself open ( whew!) .I have seen advocating a 10 a fuse on the ignition lead into this VR —- might be smart and be sure that block clamp screw is tight .  
2) the 10 ohm resistor opens . So then the minute the points open first time at 14 v typically after a normal  start , a big arc happens ( no shunt to divert current across points) and soon , after some wild full scale on off swings , — the arc welds the contact , You get huge charge current , so volts  go to 16 or more , boils battery , can destroy radio and electronic ignition , (?why they say not to use this vr with EI?) . 
but root cause is crud and corrosion on the ends of the larger 10 ohm resistor , —I now add small crimps on the resistor clamp sleeve . the connection is simply a  squeeze on the end of the resistor winding    (!)  . Don’t like that...  time ruins it . 
Sometimes this is intermittent , and in one case , there was soon no or small charge after max charge as weld residue apparently held points electrically open .. 

So you can generally fix some of this or prevent it , but one is still  left with question what are factory gaps ? I think they were all the same gap and final trim of ?14 volts is by bending the spring holder tab on VR , more tension is higher volts .  

Note the air gap to magnetic post is even more important for correct operation than the contact gap ( added for those with gold screwdrivers who bend contacts , ruining all three gaps)  . I mean literally millions of them were made and ran fine . 

DONT mess with any of this , and “experts “ will for sure make it worse. It comes correct . 

But once messed with—- as three of mine were ( disturbed gasket)   — it sure  would be helpful to know factory gaps . 

I reset the 14 v initial opening using electrical methods ,  but I do not know the correct gap to the lower overcharge contact . 

While on this the NAPA electronic replacement for this part — silver with a red wire hanging out , are utter Chinese junk , they fail in months by shorting to full charge . 

Solution ? proactively replace with high end Echelin /Standard new mechanical one !   Rock Auto . 

or easy conversion to a 2 field wire alternator and later 2 wire VR , used from about 70 up . Mid seventies dodge 100 truck parts are good.  But then non stock .
Millions of darts etc used this mechanical device they are good , but they get old like the rest of us...  Both problems here are due to time , basic unit is still ok if you think about it . Maybe replace resistor with better quality .  

thanks ,
John G 

Sent from my iPhone not by choice 

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