Carvin, welcome to iRV2.com. Your problem could be in any number of areas, You could have bad windings, slip rings, brushes, connections, wiring, or voltage regulator. You will need to start with a service manual and diagnose the problem. Recommend you start at the brushers and slip rings as this is the weakest link.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7