I have a working sous-vide cooking controller project that I want to refine and put into a permanent enclosure using an arduino pro mini.
My initial prototype required 3 a/c plugs:
- A wall wart for the 5v arduino
- AC plug for the solid-state relay controlled heating element
- AC plug for a 120v pump
I want to clean this up to only need one AC plug in the new version.
I also may upgrade the current pump to a 12v DC model with higher temperature tolerances. Since this may not happen until my current pump dies, I want my power circuit to support both a 120v AC or 12v DC pump.
I'm including a first draft of my design for the power supply below. Please note that AC connection is to the left (I couldn't find the symbol in eagle).
In this design I am using an LM7805 to regulate 12v off the rectifier down to 5v for the arduino.
Here are my questions:
Should I plan on wiring all the AC components with large (12-14 guage) wiring ? I'm assuming a circuit board is not appropriate for such voltages and currents.
Where I need help the most is getting from 120v AC down to 12v DC. I've looked around at transformers and all the 120v to 12v transformers I have found are very expensive. Is there a better way to go about doing this? I've thought of finding a used 12v wall wart, opening it's case and wiring it into my project. Is this a reasonable option safety wise?
If I do use a power transformer, how wide should the traces connecting it to the incoming AC be? I'm assuming they will need to be wider than what is typically used in low voltage DC circuits.
Also, do I need C3 in the schematic? If so, should it be used by both the pump and the regulator to smooth the output from the rectifier or will the other capacitors in the standard regulator section of the circuit be sufficient?
Finally, this is something that will run unattended for hours at a time, so I would greatly appreciate suggestions for increasing safety.
Note: the DC pump I am looking at is listed as being rated for 0.46a. I don't expect the combined pump and DC circuitry to exceed about 650ma although I imagine that I will need to expect possible higher spikes when the pump starts.