So a PSU 24 Volt for the head pad would power the head pad switched with a Solid State Relay controlled via the 11Amp side of the RAMPS1.4
Both the RAMPS 5Amps and 11Amps, to control the Solid State Relay and drive the 3D Printer would be powered from to 12 Volts via the buck converter stepped down from a new 24Volt PSU to 12 Volts.