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I wanted to use the cigarette lighter receptacle of a car as the power supply for the Arduino Mega. From 12 V, I will convert it to a 7 V supply, but my problem is, what must be the minimum current or electrical power to be fed into the Arduino Mega?

And are there any things I have to do to the Arduino Mega 2560 for it to function well in supplying it a 7 volts supply from a car?

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The Arduino's voltage regulator is rated for a suggested input range of 7 to 12 volts. Automobile power will range from slightly below 12 volts to over 13 volts, so stepping it down to 7 volts is a good idea.

Looking at the data sheet it doesn't say how much current it draws. Since it uses a linear power supply it will likely draw the same amount of current regardless of the input voltage, and simply waste the power from a higher input voltage as heat.

The power from a car cigarette lighter should have plenty of current, so your proposed setup should work just fine. Is your 7 volt supply regulated?

Note that you could also use a "buck" style switching power supply to feed 5 volts directly into the 5V line. There are several buck style power supplies on the market for less than $10 US that will provide up to 3A of regulated 5 volts.

  • Recommended voltage is 7-12V, maximum is 6-20V. So 13V would still be fine (though wasteful). – Gerben Sep 20 '14 at 20:59
  • Is stepping down the 12V to 7V and limiting it to 2Amperese already sufficient for the Arduino Mega 2560? Can it run 4 different UARTS, where these 4 different shield also get its power sources from the 5 V of the Arduino? – weyhei Sep 24 '14 at 11:54
  • @Gerben - automotive power is not limited to 13v. In fact it's notoriously variable (lower and much higher) and electrically grungy, for example when the engine is running (or worse, starting). – Chris Stratton Oct 21 '14 at 15:46
  • The input filter caps are rated for 16V, so putting an Arduino on the automotive supply directly is a very bad idea. – Ignacio Vazquez-Abrams Dec 19 '14 at 23:01

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