I’m jumping on the heated platform bandwagon:
With 4 x 1 Ohm power resistors the output is around 36 Watts. Testing has shown that it will hold 60 C at at 70% duty cycle (178 pwm) — too hot to touch for more than an instant.
I’m driving it with my Arduino Pro Mini-based temperature controller, shown here:
This board provides two channels of thermistor based PID temperature control. The sensor and driver circuits are borrowed from the RepRap extruder controller. The controller will run stand-alone using pre-set temperatures, or will respond to Gen3 protocol commands over RS485.
It includes a standard PC power connector (molex) for easy RepRap use, and jumper selectable RS485 termination.
When I complete the move to a stepper driven extruder this board will control both the extruder and platform heaters.