MakerFarm 8" i3v Prusa build by Printbus

[printbus]

Is something like this what you were talking about? http://www.amazon.com/LM7805-Termina.../dp/B00NCKUWE4

Yes, that's an example of a fixed regulator that could be connected to the existing 12V power supply. This is still a linear regulator and will dissipate heat. There's at least a small heatsink on the 7805 part to help with that.

The BEC/UBEC mentioned by TopJimmyCooks is a common thing in the RC hobby. BEC stands for Battery Eliminator Circuit. They are a switching type of regulator more efficient in taking just about any voltage input and providing a fixed output. FWIW, our printer application would use a BEC that can accept 3S voltage input. In RC, each "S" is nominally 4.2volts, since that's the full-charge of a LiPo cell most often used in modern RC batteries. Motors can run on up to 12S (48V) batteries, and a BEC is commonly used to power electronics that require a lower fixed voltage off that same battery, eliminating what used to be a separate battery for just the electronics.

Did you ever notice your 7805 getting hot? It could be that it was having thermal issues running without a heatsink. Linear regulators can overheat very easily. I won't bog this with the math details, but at 12V input a typical TO-220 package 7805 regulator without a heatsink will be going into thermal shutdown with just over 300mA of constant load connected to it.