# Arduino Mega current supply???

Hello,

I'm working on a project that has many sensors/servos/relays and a RGB LED and a lcd screen. I want to make sure I'm within the bounds of the onboard voltage regulators. I know that I can supply 50ma from the 3.3 v pin which should cover my sensors, and that I can supply up to 50 ma from each digital out put which will be good for my RGB led, but what is the total current limit of the 5v regulator that the Mega has. I cannot find any specs. If worst comes to worst I will just use a separate voltage regulator, but I would rather not.

Thanks,
Drew Davis

It's a linear regulator, so it depends on the voltage dropped across it... i.e It can handle more current with 7 volts in (2-volts across the regulator) than with 12V applied (7V across the regulator).

If you are going to power servos, you probably need a separate regulator.

50mA from each digital pin ? That doesn't seem okay to me. The limit is 40mA, but I would even avoid that.
You can't power a servo from the Arduino 5V pin, you just can't.
A simple small servo can draw 500mA (or even 1A) when it starts turning.
So you need a seperate voltage regulator. Since you need to power so many things, try a DC-DC converter. Use the Arduino board only to power the sensors.

I did not mean that I'm supplying power to the servos from the Mega! That would obviously be way to much current of the Arduino to handle. I'm just controlling them with the mega which can still eat up a small amount of current.

Does anybody have the data sheet to the voltage regulator so that I can calculate how much current I will be able to supply. I will be using a 7.4v battery. Thanks!

There is a very accurate and scientific way to calculate how much voltage regulator can supply. Put your finger on it, and if you can not keep your finger on it, it is too hot.

Is there a general range of current output at 7.4v? Like less then 500mA or something. I don't want to burnt the thing up!

Also, would a heat sink help?

EDIT: I added everything up and I should need less then 300 mA from the 5v pin at any given time.

No, no general range, some boards have a little better cooling of the voltage regulator.

The Arduino Mega 2560 has a copper area under it for cooling and a few vias to another copper area on the other side.

A 7.4V battery, is that a Li-ion battery. If it is charged, it is 8.4V.
(7.4-5.0) * 0.3 = 0.72 W
(8.4-5.0) * 0.3 = 1.02 W
That seems a lot to me.

The voltage regulator will reduce the current if it gets too hot. You won't burn it up.

Ok. Thanks.

From my tests, 300mA is about the limit you can get with Vin up to 12V. That runs the regulator near its rated max operating temperature. Less Vin and you can get more current/less heat.

The 50mA limit on the 3V3 line is a hold-over from when boards used the regulator of the FTDI. On boards not using the FTDI, the 3.3V regulator can actually supply up to 150mA.