Max current

Forum 2005-2010 (read only) General Frequently-Asked Questions
1

Hi what is the maximum current that can be draw from the 5 volt rail
thanks in advance
Barry

2

Depends where the Arduino is being powered from.

  1. From USB - 500mA
  2. From an external DC power source - This is limited by the heating of the regulator and depends on how much voltage you are feeding into it. See:- Power Supplies
    and
    http://www.thebox.myzen.co.uk/Tutorial/Power_Examples.html
3

Thanks Mike , i read some were it was only 20 mA , 500 is fine , thanks for info
Barry

4

Its 20 mA per pin

5

40mA per pin, according to the datasheet (for the AVR chip), and the hardware reference section of the website:

6

Ok so lets say I use 14 pins does that total up to 560 mA @ 40 mA , lets say I use 4 pins and their maximum drain on each pin is going to be less than 30 mA 120 mA total , I am interested in what the regulator will deliver and it is useful to know the pin limit's too

Barry

7

14 pins does that total up to 560 mA @ 40 mA

It's a little more complex then that. While there is a 40ma per pin max current rating, there is also a processor chip package total rating (all pins combined plus internal overhead) of I think around 200ma for a 328 processor chip.

It really comes down to how much and where the power is being dissipated or consumed.

You have the on-board voltage regulator (only in play when using the Arduino external power connector), the PCs USB +5vdc limit (500ma), the AVR chips total current consumption and the individual digital output pin limits.

External components and loads can draw current from the Arduino's +5vdc and GND pins without effecting (or adding to) the current passing through the AVR chip.

A lot depends on how you are wiring your external components and loads as to which of the several limits will be reached first.

As well as current limits, the on-board voltage regulator will shutdown automatically to protect its self if it's maximum temperature is reached. This is a result of the input/output voltage drop across the regulator times the amount of current being drawn Vs the efficiency of any heatsinking for the regulator (not much on a Ardunio design).

Bottom line, don't count on more then 500ma total and some of that is board overhead, 300ma would be a more realistic project target.

Keep in mind if your utilizing the Arduino's external power input, then the Vin pin is available to supply current at what ever voltage the external power source is supplying, normally 8-12vdc. The limit here is usually the 1 amp polarity protection diode in the external power input string that feeds the on-board +5vdc regulator.

Lefty

8

The limit here is usually the 1 amp polarity protection diode

I would say the limit here is defined by the heat dissipated in the regulator and in practice is about 350mA depending on the actual voltage input.

9

Yup got it now , better safe than sorry , thanks for the advice
Barry

10

I would say the limit here is defined by the heat dissipated in the regulator and in practice is about 350mA depending on the actual voltage input.

Not if you are also pulling some current out the Vin pin for external components or loads, that was my point. Yes the on board regulator is the current limit for +5vdc usage, but there is away to consume an amp via the Arduino's external power input connector.

We've had this Vin discussion before you know.. ;D

Lefty

11

I need a sanity check...

So I want to run 2 circuit loops off the 5v out on the Arduino. The combined current draw for both of them will be about 55mA. The load resistor in each loop is 100 and 1000 ohm respectively. The Arduino should be able to handle this right?

I will be providing 12-14v (car battery) to the power plug on the Arduino.

Should I use an external 5v 1A regulator before the Arduino so it's own onboard 5V doesn't have to work as hard? Or would a 5v be too small and should use a 10v external regulator instead?

12

At 55mA there is absolutely no issue, fine just plug it in.