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Author Topic: Powering an Arduino from a car battery  (Read 1823 times)
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Northern California (by San Francisco)
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My project will use an Arduino Duemilanove on an electric car. I will power the Arduino and some other electronics (mainly headlights and signal lights) with a deep-discharge 12 Volt lead-acid battery. Can I just tap into the battery wiring to power the Arduino? Or should I regulate the voltage or drop it down to a lower voltage?
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12vdc will work OK for your Arduino. A lot depends on how much current you plan on drawing from the Arduino's +5vdc regulators output. The board itself consumes probably around 50ma, but powering external components like leds and things can increase that and of course the heat dissipation of the on board regulator. The regulator will protect itself by shutting down if it gets to hot or you try and draw too much current from it.

Lefty
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Yes, Like Lefty Said.. 12V will work.

But (There MIGHT be a But) there might be problems with noise and transient voltage spikes if you are running DC motors and stuff.

So, I would vote for using a voltage regulator and putting out about 8 or 9 volts to the Arduino Pwr In. 

And, for more confidence, I'd think about more insurance against funny voltages that may be out to get you and your Arduino:

- Have some good big common ground point on the car chassis where the motor/ controller negative and the battery negative come together. Run a separate wire from that to Arduino GND.

- Have a couple of good Bypass Capacitors right at the +12 side of your voltage regulator. Say both 1000 Microfarad 20V electrolytic and .1 uf disc. 

- Have a MOV (Metal Oxide Varistor) rated at 25 volts or less connected from the +12V supply at your arduino area, to the Arduino GND.

You circuit is not going to draw much current at 8 or 9 volts. Figure it out. Think about a small value series resistor between the vehicle +12 and the input to your regulator. This makes your bypass capacitors much more effective. If you are going to draw 1/2 amp (500ma) then a 1 ohm resistor will only drop .5 volts, but will improve the "filtering" of the bypass capacitors a lot.

I've fought these things on cars and boats, and become probably over-pessimistic about vehicle raw battery connections  smiley-roll-sweat

But do what you can, and if you have a once-in-a-while crash or misfunction with your Arduino, look at the Purity of DC...
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Regards, Terry King  ..On the Red Sea at KAUST.edu.sa
terry@yourduino.com  LEARN! DO! (Arduino Boards, Sensors, Parts @ http://yourduino.com

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Thanks for the advice, both of you. That's helpful.

My plan is not to have the Arduino run much. Just take some digital input from the USB port and send some analog signals based on the input. The analog signals will be perhaps a few milliamps. So that should not be a problem.

But I will have some DC motors (three windshield wiper type motors) and some headlights and turn signals that will also draw power from thr battery. So maybe I will run the 12V power through a switching voltage regulator and put some filtering capacitors-resistors on the power input line. If your experience with raw vehicle batteries has been dicey, that's a reason to be careful.
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