Noobian:
Tried running from the 12V directly? Also did you swap power inputs while the Arduinos were running?
Everything was powered down before swapping.
Running it off the 12v, after a quick test seems to work, in the finished design the 12v supply can vary between 11v and 15v would the higher voltage not be a problem
You can NOT power a Mega (~70mA) with ethernet shield (~160mA) directly from 12volt.
The onboard 5volt regulator will overheat and shut down (if you're lucky).
A 5volt cellphone charger (connected to the USB socket) is a good option.
But it all depends on what else you have connected.
Post a full diagram.
Leo..
Wawa:
You can NOT power a Mega (~70mA) with ethernet shield (~160mA) directly from 12volt.
The onboard 5volt regulator will overheat and shut down (if you're lucky).
That is my concern with using the 12v supply
Wawa:
A 5volt cellphone charger (connected to the USB socket) is a good option.
But it all depends on what else you have connected.
Post a full diagram.
Leo..
A USB charge is not really an option, that is why I have the 9v supply
I am guessing (lack of proper information) that you power everything (whatever that is) from a lead-acid battery.
The most efficient way (minimal heat) would be to bypass all the 5volt regulators on the Arduinos.
Use a (reliable) 5volt buck converter, and connect it's output to the 5volt pins of the Arduinos.
Leo..
Wawa:
I am guessing (lack of proper information) that you power everything (whatever that is) from a lead-acid battery.
The most efficient way (minimal heat) would be to bypass all the 5volt regulators on the Arduinos.
Use a (reliable) 5volt buck converter, and connect it's output to the 5volt pins of the Arduinos.
Leo..
The normal power supply comes from a 12v psu but has the potential to change over to a lead acid battery in the even of mains failure
KandS:
...to change over to a lead acid battery in the even of mains failure
In that case a 5volt buck converter is a better option than linear regulation.
A switching buck converter basically halves battery drain. Here is an example from Pololu. Cheaper (lower quality/specs) clones on ebay.
Leo..
Ok after getting my wires crossed and blowing up the Mega board, I have rebuilt hoping the original problem wouldn't be there but it is.
So what I have found out is the 9v causes the mega to corrupt the SD card no mater where I apply it ie Vin or the jack. 12v on the jack works ok, but this is not a long term option due to the load on the on board regulator.
5v to the vIn, so far has not caused any problems to the SD card, so this looks like the solution, I can just add a 5v buck regulator.
It would have been nice to know why the SD card was corrupting under certain power configurations but I suppose that just life
That diagram is basically it, stick 2 nanos and a mega onto the 9v, connect their I2c's together and that's it.
The regulator is an LM7809 and a 0.33uF on the input and a 0.1uF on the 9v side