alternator dilemma

[David Anderson]

My alternator won't charge unless I goose the engine to about 1500 rpm.  then the no charge light will go out and the meter jumps to 14volts.  This is something new to my coach.  I have a Niehoff 350 amp alternator with an external voltage regulator.  I tried some different things to troubleshoot.

Engine off/key off                  key on/engine off   start up & idle                  rev to 1500rpm
R = 0 volts                             R=0                     R=1.53 volts                     R=6.3 volts  
ign = .69 volts                        ign= 5.9 volts        ign=5.9 volts                     ign= 14.2 volts  
output terminal = 13.1              13.1                     13.1                                 14.7

R is the r terminal.  ign is field terminal (I guess).  output term in the main cable strap 12v+

According to the Eagle manual the R terminal has to send voltage to a relay coil that will close a switch that sends 12v+ to the ign terminal.  When this happens the alternator puts out its rated voltage.  I noticed on my meter as I reved the engine the R terminal output would climb from 1.53 to 6.3.  As it passed 5 volts the relay wold close and the alternatorwould charge.   Every thing works fine after that even at idle.
Any ideas as to why this changed to this  way of working?

David

[Alan Baker]

Hi David,

  I think we have about the same model Eagle. Mine is an 84 model 10. I had the same problem and one of the really smart electrical guys in the club discovered that in the front ele box there is a rheostat.
He slid the contactor all the way to the connection point and instantly everything was fine and has been for several years.
He advised that if the problem were to reappear, to simply jump out the rheostat. He thought that this rheostat  might have been for use with a Delco alternator which was an option and that the Neihoff could handle full voltage. The voltage coming through this rheostat is the 12 volt exciter. Why its up front is what makes us love Eagles.

Alan Baker   

[David Anderson]

thanks Alan,

Mine is an 85 and doesn't have that option.  It has an external voltage regulator with 4 settings for output voltage.

David