by peter_ » Wed Aug 28, 2013 8:52 pm
Hi Dave,
That's normal -- you definitely need a cooling fan that pushes a good amount of air over the Pololu stepper driver heatsinks as well as the MOSFET heatsinks for the heaters/heated build plates for the RAMPS controller to work. If it's not there, (1) the extruder and/or heated build plate may not be able to supply enough current to get up to temperature, (2) the steppers may not have enough current to move the axes, or especially push the filament through the extruder. Almost all the RAMPS cases I've seen include a mount for a very large fan.
best of luck!
Peter