How much 5V current can I draw from an Arduino Mega 2560

Using Arduino Project Guidance
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I am using an Arduino Mega 2560 with only an Ethernet Shield. I want to power an external wireless and display device from the Mega's 5V supply.

Can anyone tell me the maximum current taken by the Arduino Mega 2560 and the Arduino Ethernet Shield. I can't find this specified anywhere. I believe that the 5V regulator is capable of delivering 800mA.

Thanks

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KineticaRT:
I am using an Arduino Mega 2560 with only an Ethernet Shield. I want to power an external wireless and display device from the Mega's 5V supply.

Can anyone tell me the maximum current taken by the Arduino Mega 2560 and the Arduino Ethernet Shield. I can't find this specified anywhere. I believe that the 5V regulator is capable of delivering 800mA.

Thanks

Well the answer depends on a lot of variables. USB power or external DC power through the external power connector?

USB power is limited by the 500ma polyfuse on the board. External power is limited by the on-board regulator's over current and over temperature automatic shutdown protection circuits. How much heat dissipation for the regulator is determined by the actual current being drawn and the voltage drop across the regulator (that is DC input voltage - 5.0 X current). So it's hard to give an exact figure and that is why there is no published Arduino spec for your question, too many variables not under total control of the arduino board.

Lefty

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If you are using the w5100 ethernet shield and USB for the power source, you probably won't have much spare power available.

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I am using a wall-wart supply and the Mega 2560's regulator. I am using an Arduino Ethernet Shield (Updated Version) http://arduino.cc/en/Main/ArduinoEthernetShield.

If I can get an idea of the typical and maximum 5V current taken by the Arduino Mega 2560 and the Arduino Ethernet Shield I can do the calculations associated with the regulator over current/over temperature, etc.

Maybe it'll be best to do an experiment: supply it from a bench 5V supply and measure the current? I'll have to check, of course, if its OK to "backfeed" the MC33269D-5.0.

Thanks for the prompt replies.

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If you're using an ethernet shield you don't want to be putting more than about 9V into the regulator, ideally less if you're running other stuff off it as well. The heatsink (what heatsink ?) isn't up to much. The ethernet shield is a greedy begger, it takes about 150mA on its own. Stick your finger on the regulator when its been running a minute or two, if you can keep it there for more than about 15 seconds you should be OK.

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I bring in my own regulated 5V power and drive +5 or VCC with it, bypassing the regulator on my promini's, which also uses the MC33269D-5.0. I have done this on 12 boxes I have had running with the first going into operation last September.

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Maybe it'll be best to do an experiment: supply it from a bench 5V supply and measure the current? I'll have to check, of course, if its OK to "backfeed" the MC33269D-5.0.

Many people power their board/project by applying a regulated +5vdc source directly to the Arduino's +5vdc and ground shield pins without problems. I don't like having the regulator's output hanging on that external applied voltage, but it seems to work fine. And that is the best way to go about your power analysis, get a actual +5vdc current draw measurement.

Lefty

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Datasheet says 1 Amp for the ams1117 regulator but it depends on the other factors stated above.

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