Thanks for the response. Maybe I can figure out some way to limit the voltage to 48 Volts, to make sure I don't fry the controller.
UPDATE: I looked at the datasheet for the Infineon MOSFET power transistor used in the motor controller, and did not find the 50 Volt maximum voltage limitation. I did see 60 Volts as the "Drain-source breakdown voltage." I wonder where the 50 Volts comes from. Is it another part on the controller, or is it somewhere else on the datasheet for the MOSFET?