Hello,
I am trying to build a project with an Arduino Mega and a 14.8V battery. Currently, I am looking for a DC-DC converter to lower my voltage to 5 V, but I figured I don't know the maximum current the Mega will draw. I will connect it through a barrel jack and i believe i will use most of the pins.
thanks ! 
Have you read and understand the FAQ section on Power?
Yes, of course, but it only discusses voltage. I didn't see any mentions of current apart from this: "3V3. A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50 mA." Am I missing anything?
what's connected and powered from the Arduino MEGA? (hopefully not a lot of current hungry devices or capacitive loads)
Best to consult the data sheet
Consult footnotes of table 31.1 (page356) for the per port current specs.
See page 354, Electrical Characteristics.
Be aware that the table lists absolute ratings. One is wise to not operate the part too close to those ratings. For instance, the recommended max per pin is 20mA.
currently its 2 pressure sensors, 2 solid state relays , a 4 inch display, a small knob , small speaker.
maybe a MOSFET to create PWM signal for proportional solenoid.
i made sure not to exceed the 20mA per pin, but my problem is not with the current drawn from the pins, but the absolute maximum current the Mega will consume without causing problems.
thanks
the MEGA itself (for computing power) won't draw more than 50mA likely
so i should take that as 50mA to operate and 20mA * 54 digital pins so that's 1.08A and 16 * 20mA for the analog pins so 1.45 A?
i read the barrel jack can only supply 1 A so in this case i will need to use 2 separate power supply options for my board? like 1 AMP from the Barrel jack and the rest from the power pins?
Barrel jack need 7 to 12V.
So why are you looking for a DC-DC to 5V
no there are other constraints on your MEGA ➜ consult the ATmega2560 datasheet, from the top of my head I think you have a max bucket limit around 200mA for all the GPIOs
No.
Each peripheral part will have signal pins (very low current) and, separate, power pins (larger currents). Power to the Mega can be provided by USB (500mA), Vin or the power jack. Vin or power jack feeds a 5V linear regulator on the Mega. The amount of current that can be supplied by the 5V regulator is limited by the input voltage. With 12V feeding the regulator, drawing more than about 100mA from the regulator can cause it to overheat and shut down,
How are you going to power your project? A schematic or wiring diagram woud be welcome.
that is an excellent point, my mistake!
i do need to look for 7 to 12V DC-DC converter. but then again, what is the current i want my dc to dc to be able to supply?
with a 14.8V 2.9A battery
What voltages are required by the project? If only 5V, get a buck converter to drop your battery to 5V, power the projct and bypass the weak on board regulator.
Water boils at 100ºC, so let's keep the onboard regulator at 75 or less.
If the ambient temperature is 27ºC, then the maximum power dissipation of the regulator will be (75-27)ºC/110ºC/W = 436mW
If Vin = 7V then the maximum current you can use is 436mW/(7-5)V = 218mA
The Mega active supply current with all peripherials is about 24mA, so that leaves 194mA for all of the IO pins and the 5V and 3.3V outputs but the Mega IC total current must not exceed 200mA
i use one buck converter to bump up the voltage to 24v to operate my solenoids and my engine.
then i planned to bump down the voltage so i will be able to operate my Arduino thought a barrel jack, maybe barrel jack is the not the optimal option, I'm quite new to this...
is that what you meant when you said "bypass the weak on board regulator"?
The on board 5V regulator has no heat sink to speak of so can dissipate little power. 1 Watt is about its limit. Over 1W and the regulator gets hot and, hopefully, shuts down. So unless the current need is small, it is best to just ignore it and provide power using a robust method like a buck converter or converters that can, gracefully, handle the project's current needs.
No Arduino board is a power supply. Get used to providing adequate external power.
so what parameters do i need for my buck converter? 5V i guess but what current rating?
Gather the data sheets for all of your peripherals. Add the supply current requirements from the data sheets plus a bit (30%) overhead. You can"t go wrong with too much current as the circuit will just use what it wants. If you need 3A and your converter is capable of 10A, no problem. Just be sure that the supply can handle worst case current load.
