Arduino 5V Power Input

Hello together,

i have an Arduino Mega which should operate on its own, without the USB power supply. In the project is a LiPo with 11.1V and a brushless motor. Those RC brushless motor controllers have those 3 wires, 1 is signal, 1 ground and 1 is 5V. For control, i connect the signal and GND wire to the arduino. But i thought of using those 5V for powering the arduino. unfortunately, the DC power input requires 7-12V (i dont want to use the LiPo directly because the voltage may drop under 7V). But USB usually is 5V, right? so could i solder a USB plug from the controller to power the arduino?

thank you!

If you have a regulated 5V supply you can hook it directly to the 5V pin. This bypasses the voltage regulator since you don't need it and saves some power that would be lost in the regulator.

Does the motor controller specify how much power you can draw from the 5V line?

thank you. which pin do you mean? the one named 5V? i thought this was an output :D

well you know, its purpose is: you have the battery on the motor of your RC vehicle. with this so called BEC your able to power your receiver and servos. and dont know the data but its usually around 2A, 5V.

GoingForGold: i thought this was an output :D

As long as there's no buffering or diode in the way, it works equally well in both "directions" (although voltage doesn't really have a "direction" -- current does :-)

ok thank you! i will try it this way :)

I just wondered, doesn't this 5V pin have the 40mA restriction?

GoingForGold: I just wondered, doesn't this 5V pin have the 40mA restriction?

It's not an I/O pin. It's connected to the output of the 5V regulator and USB power. If you provide power via USB or the power jack it is available at the 5V pin. If you don't, you can apply 5V to the 5V pin to power the Arduino.

The "Vin" pin is connected to the power jack and the input of the 5V regulator. If you provide power via the power jack it is available at the Vin pin. If you don't, you can apply 7-12V to the Vin pin, just like you can with the power jack, to be regulated down to 5V fr the Arduino.

thank you for this explanation, perfect!

Hi!

What if I connect an external 5V power supply to the 5V pin AND connect the USB? I assume I will connect the 5V power supply to the USB port and may damage it? Would it be recommended to cut the 5V USB line on the board for this case to be sure I never connect the external power supply to the USB port?

Thanks! Spiff

I am interested in exactly this question. I have a Raspberry Pi connected to my Arduino via USB and would like to power the Arduino from a 5v BEC. Not through the USB.

My Arduino 5v line is showing 4.8v when supplied through USB. My RPi is showing 5v on its 5v line so I assume the drop is across the USB circuitry somehow.

It may not be an issue but I would prefer to run all my 5v devices from the 5v BEC.

Similar to you my thought was connect the 5v BEC directly to both Arduino 5v lines and RPi 5v lines. What puts me off is seeing the repeated remarks about not using USB supply and connecting 5v to 5v line on Arduino.

Look at the Uno schematic.
If you apply 5V, and nothing to the barrel jack/Vin, then Vin/2 is < 3.3V, T1 is turned off and 5V cannot be reverse driven thru it and thru the PTC polyfuse to reverse power the USB connector.

Try it - power the board with 5V and USB disconnected, see if 5V appears at the USB connector.

well you know, its purpose is: you have the battery on the motor of your RC vehicle. with this so called BEC your able to power your receiver and servos. and dont know the data but its usually around 2A, 5V.

That's roughly correct. It can be as high as 3A for some BECs. You need to consult your ESC manual for the specs on the BEC. You are aware that you need to use the SERVO library to drive the ESC ?

(i dont want to use the LiPo directly because the voltage may drop under 7V

Clearly you have no experience with Lipo batteries. Each cell must NOT drop below 3.2V/PER CELL.

A 3S LIPO has a nominal voltage of 11.1 volts and a fully charged voltage of 12.54V. AT NO TIME COULD THE VOLTAGE ACROSS THIS BATTERY DROP BELOW 9.6V without PERMANENT DAMAGE to the battery AND THE RISK OF FIRE !

If you were using a 2S LIPO, which has a nominal voltage of 7.4V and a fully charged voltage of 8.4V, your concern about the battery voltage dropping below 7V would be valid, because a 2S can be discharged down to (2 x 3.2V/per cell) = 6.4V.

However, in your post you state you plan to use a 3S (11.1V) LIPO, so your concern is only valid if you plan to DESTROY your battery and start a fire when it spontaneously igninites because you discharged it below the rated 3.2V per cell.

DO YOU PLAN TO DESTROY YOUR BATTERY ?

Thank you for your response CrossRoads it is much appreciated.

From your response am I to take it that you believe USB circuitry will not have a power source to the Atmega16 UVcc pin.

Since the Arduino 5v line is showing 4.8v and is supplied through the USB what about if the USB line is cut, the Arduino side of the USB (XUSB) is supplied with the 5v from the BEC as is the 5v line on the Arduino board?

As I see it this would isolate the RPi 5v USB from the Arduino 5v USB side. It would supply 5v to either side of T1 (is that a problem?) and thus power the Atmega16 UVcc pin. Or is that over simplifying the issue?

Yes, you could lift the PTC polyfuse and connect your 5V source to that pad and isolate the USB 5V without cutting any traces.