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[on:]

I have a board with an Arduino Mega on it and I'd like to know if I can supply 5V externally (via an on-board regulator on the board the Mega plugs into) without damaging the Arduino?

I have also laid out my "motherboard" to accept the new chipKIT Mega board which has a jumper that basically connects "normally" (i.e., Vin goes to the onboard 5V regulator) or bypasses the regulator and goes directly to the 5V bus.  The output of their regulator is still connected to the 5V bus but it's not the same one that's on the Arduino board so I don't know if I can supply a regulated 5V from OFF the Arduino to the 5V pin and keep everybody happy.

Also, what would happen if I use the external supply to 5V (assuming it won't go backwards through the regulator) and then connect up the USB port to download code or get something out of the Arduino?  I can't find anything in the data sheets for the regulators that the Arduino uses that say I CAN'T do this but I wanted to make sure before I plug it in.

Thanks,

len

[Reply #1 on:]

I have a board with an Arduino Mega on it and I'd like to know if I can supply 5V externally (via an on-board regulator on the board the Mega plugs into) without damaging the Arduino?

I suspect there is. However the wording of your question is a little hard to nail down what you actually want to do. So you have a on-board regulator, but your not talking about the mega board which also has a on-board 5vdc regulator? Care to try and reword or better discribe what you have and what you need to do?

[Reply #2 on:]

It sounded vague to me and I WROTE the OP!  :-)

You got the jist of what I want to do.  This project will always have either a +12 (solar) or +24 power supply available.  I'm using one of Murata's 24/12 -> 5V switching regulators on my "motherboard" so that gives me a source of +5 (which I need elsewhere so the Arduino regulator is not going to supply enough current).

I'd like to supply +5 to the Arduino (instead of an unregulated voltage, because +24 is going to make the regulator too hot) and I'd rather not use ANOTHER regulator to plug into the normal power jack on the Mega.  If I can just put +5 INTO the Arduino without damaging the (Arduino's) on board regulator, I'm happy.

Is that a little clearer? It still sounds vague but between the two posts, maybe it's clear enough.

Thanks,

len

[Reply #3 on:]

Clear enough. You can take the external regulated +5vdc and wire it directly to the +5v pin on the arduino board, many do this. My only caution about doing that is that I would recommending removing the external +5vdc when you are using the USB link on the mega board, as if not you would effectivly wiring two active +5vdc sources together, never a good engineering point as the two voltages are bound to be a little different in level and current may flow where it shouldn't. Other then that there is no problem powering an arduino board via it's 5V pin, assuming it's a stable and regulated source.

Lefty

[Reply #4 on:]

All
Let me share my experience with powering the 5V pin.

I have done this with a Arduino duemilnova and 3 megamoto shields powered by a 12V lead battery. I used a switching regulator and a capacity to get 5V.
All worked fine during test (no power on the power lines of the megamoto) but with power on the powerlines and motors running the Arduino died after a while (about 15 minutes).
Trying to connect my PC to the USB resulted in the com port being recognized but not being functional. With a 9V battery on the power connector the USB and Arduino worked.
A couple of days later the Arduino worked normally again. 
I never really understood what the problem was.
It may be related to powerspikes on the gnd
it may be related to the megamoto (but I have had no issue at all I relate to the megamoto).
I'm sure it was not a coincidence because it happened to 3 different Arduino's. All the exact same scenario.

I switched to powering the Arduino via power plug and a 9v battery as a workaround but I still need a decent solution. As I have plenty of (power consuming) shields I do not want to put 12 V on the power plug.
The shields I have are 3 megamoto's 1 ethernet and 1 GPS shield (and I also power a RC receiver).
I am considering to "cut" the power to the shields and power the shields separate from the Arduino. I would however prefer to understand what was going on and have a nicer solution.

Can anyone make sense of these weird behaviors?

Best regards
Jantje