How would I go about taking this 12VDC 3A input and reducing it down to around 9VDC for the Arduino Uno R3 to handle more comfortably?
I would take the 12V down to 5V and feed the Arduino with that on the 5V pin.I would use a buck converter to get the 5V. Lots on line to choose from.
I was hoping to also power my Arduino off the same power supply using the Vin. I read that it supports 7-12V input and that 12V is not recommended as it will make the voltage regulator on the Arduino very hot if not burn up overtime.
The drop is only about 1/4 watts wasted with only the Arduino.
I tested my 12VDC 3A power supply on Vin in hopes of not releasing the magical smoke inside, and everything works fine but the voltage regular does get extremely hot; well enough to burn my finger.
You can decrease power dissipation in the on-board regulator by connecting any external circuitry to the Arduino power pins.
Given that the power pins are driven by the onboard regulator how does this help?
Would it be possible to take a LN7805 for example and feed that directly into the 5v on the Arduino? I don't think that would be as efficient as a buck converter, but it would be much smaller and I could soldier that to a custom PCB with the transistor for the door strike.
It's hard for me to judge by looking at pictures of how big these buck converters are, do they make them small enough to fit into a single/double gang box for example?
My main concern with all of this is really stability, this is going into a crawl space near a door and I don't want it to implode and catch fire for example.
If you don't draw any power from the Arduino for any other circuitry, it may be okay.