So I may have accidentally blown one of my arduino boards. I'm running a mega 24/7 to monitor and control devices on an aquarium. Originally, since the Arduino advertises being able to handle 12v, I had it simply plugged into my 12v power supply. On top of that, I had all my devices running off 5v (12 channels worth of relays, a RTC, and the embedded controllers for the probes) running through the 5v on the arduino board.
Looking back, I really don't know what the h*** I was thinking... You couldn't even touch the on board step down it was so hot.
So now, I'm wising up, reading some articles, and going in for round two. I bought a proper step down to drop the 12v to 5v to power the other gadgets. The only load the Arduino needs to handle now is simply the signals to turn thing on and off and receive info. My question now is, can I run the Arduino off that 5v supply? Or should I find a higher voltage source (Just not the 12v) I know most power supplies sold online are 9v, but can I run it on less? Should I run it off that 5v supply?
I think it's more likely that the excessive current loads blew out your old unit, not the excessive voltage. I only say that because I've run a Nano on 12V for extended periods and it worked ok. It is true that the voltage regulator will run hotter, and that the "extra voltage" is "wasted" when running that way, but it shouldn't fail "just because" of that alone. So, now that you've wired your devices to run on signals with relays or whatever, the excessive current problem should be eliminated, and the excessive voltage should no longer be a problem. But, why deal with that? Eliminate both possible issues by running the Arduino on the 5V source and you have an even better solution.
I thought it might work off 5v. Just read a few things on since that is the minimum for the Arduino to run, it would be preferred to run it on 6v+. Figured I'd get some advice before I finished wiring my circuit board.
When you run an Arduino from a voltage higher than 5V, the voltage regulator on the Arduino dissipates the excess power. This power is the excess voltage times the total current draw from 5V. Your 5V relays probably take about 80mA each when powered on, so twelve of them is about 1A current draw in relays alone. So with all the relays energised, you are asking the regulator to dissipate about 7W, when it can only take about 1W.
A better approach would be to use a relay board that takes 12V power. Then the Arduino regulator isn't involved in supplying power to the relays. You can find 12V relay boards on eBay.
I think I've solved my relay issue. I have a separate step down now, away from the Arduino, so nothing is drawing power through the Arduino. The Step down I have handles up to 3A, so I should have plenty of power to spare. This also leaves less stress on the Arduino as it's only used for its signals and not any kind of power source.
You can power your Arduino with 5V, just not into the power plug (as this runs through the step down, which has a voltage drop, this is because you need >6 or 7V(?) to run it), but directly into the 5V pin. Of course, you should have proper 5V for that.