I have a Curtis 1204 set up with traditional contactors feeding an E20 motor.  Under high load conditions climbing a hill or when the battery is 50%-70% drained I am getting a pulsation perhaps 2-5 hz.  You can feel it and see it on the load meter.  I have not had time to make diagnostic measurements yet.  Has anyone run into this before?  The consistent pulse makes me think it is the controller.  The controller is 16-20 years old and I am wondering if it may be failing.  

Any input is appreciated.

Rob Brockway