Yes, its possible you could see 50 volts there.. trying to remember the pinouts.. all of my service manuals are in my cabinet at work.. grr.. trying to go off of memory. Interestingly though that you're losing any DC voltage there.. that voltage is delivered directly from the rotor, slip rings and brushes and passes through no electronic equipment. Can you see the brush holder at the end of the rotor/stator assembly? With the unit off pull the brush wires and measure ohms across them. If memory serves me correctly, you should see 28-30ohms between the two leads, 0 ohms between either lead to ground. You can always pull the brush block and inspect the brushes for length and wear and visually inspect the slip rings that they both ride against. Unless one of the wires on the brushes is broken or very loose I cannot see how you can lose DC for such a long time occasionally.... keep me posted on what you find, I'll have access to my manuals in the morning.
94-Newmar Kountry Star 40-KSDP
Spartan/Cummins 8.3C-300HP/Allison 3060 WTEC-II/25yr RV Tech RVIA Certified/Onan-Cummins Certified