Different ways to supply power

Hello all,
I have an arduino mega, and my project requires more current than it can supply (>200) but enough to be powered by usb from pc (<500).
So what i want to do is split the current before it reaches the arduino, in a somewhat similar fashion to the attached image. (I know its not mega but just flow with me…)

Problem is, in the Arduino specs it says that the input for the Vin pin should supply between 7-12 Volts (recommended), (I assume due to a voltage regulator connected to it?), and the USB only supplies 5V.
Anyway, what i wanted to ask is if it is safe to connect the PC USB directly to Vin, or must i add a bypass from the PC USB into the board’s USB connection?

thanks so much in advance,
Tim

Do not connect the USB +5vdc to the Vin pin, rather attach it to the 5V pin.

But I don’t understand your need to do this. When the arduino is cabled to the USB the 5V pin can easily supply 100ma, more likely closer to 400ma. An advantage of doing it this way is the PC USB port is protected from over current draw by a thermofuse located on the arduino board.

Lefty

yeah, but searching the web for max current supply from 5V on arduino mega doesnt bring up a definitive answer and i didnt want to repost a question that is so widely covered (even though very obscure).

some say you can only get 200mA combined, some say its 200mA from each pin so that you have 800mA (but there are only 3 5V / GND pins on the mega, wth?). I only need around 300mA at peak (when every component is transmitting), so if anyone can confirm that i may draw around a 100mA from each 5V pin at the same time, then everything is solved :slight_smile:

idantim:
yeah, but searching the web for max current supply from 5V on arduino mega doesnt bring up a definitive answer and i didnt want to repost a question that is so widely covered (even though very obscure).

some say you can only get 200mA combined, some say its 200mA from each pin so that you have 800mA (but there are only 3 5V / GND pins on the mega, wth?). I only need around 300mA at peak (when every component is transmitting), so if anyone can confirm that i may draw around a 100mA from each 5V pin at the same time, then everything is solved :slight_smile:

Well a definitive answer requires knowing if being powered via USB or external power connector, and if by external power what the specific external voltage is being used, so that is way you might find a published answers evasive.

If using USB power there is a 500 ma thermofuse that sets a maximum current limit and the board consumes around 50ma so there should be up to 450 ma or so available at the 5V pin.

If using external power then the limit is the heat dissipation by the on-board 5 volt regulator which is proportional not to just the amount of current being drawn but also the voltage drop across the regulator, that is why with a recommended external voltage of 7 to 12vdc, the closer to 7vdc input you get the cooler the regulator will run at any given current demand. With that in mind you should have no problem being able to source as much 5V pin current as you could with the USB power.

Lefty