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[on:]

Can I power my old (first-build, got it from SF in 2006 or 7) arduino using a car's 12v, on the 9v input? I could have swore the original arduino documentation said not to power the device with more than 9v, due to the regulator.

I am planning out the feasibility of building an MPGuino using parts I have laying around (and they are numerous!). As to why such a simple question is being asked here in the first place, I will now lament:

Upon looking for my answer on arduino's main site, I was struck with a sense of the achille's heel of open-source. I looked, and looked some more, and only found mentions of powering the arduino with USB. I searched for a good 20 minutes! I discovered that the arduino BT should never receive more than 5.5v, and that 9v batteries may drift a bit but the regulator can handle it.

But nowhere in the getting started guide nor the tutorials, was there a punctual mention of external power and its limitations. Maybe I didn't dig enough?

And that is where I find open-source's "achilles heel". Open source is a great idea and can be fruitful in innovative ways, but to someone approaching the site for the first time, useful information requires a bit of digging through disorganized ramble, and sometimes seems unattainable. The impression I get is, a whole lot of fragments cobbled together and called a product. Please, take this as constructive criticism, arduino creators, I really hope you come across this and my efforts are not wasted.

I entered the scene when arduino first came around. I couldn't imagine being a beginner now. Yes, the basics might be there, but really, some intuitive page organization would greatly reduce the amount of questions posted to the forum.

And that is why I find myself here, asking about a car battery's likelihood of frying my vintage arduino. </wall-of-text>

[Reply #1 on:]

Most regulators shutdown automatically if over-current or over-temperature, most regulators can take 25V or so on the input if it wasn't for thermal considerations, so the worst that should happen is it will shutdown after a while.  If you find the regulator's part number and google for its datasheet it will provide more definitive information.

The more current you circuitry takes the less voltage the regulator will handle without overheating note, so the answer probably depends on the external circuitry you attach to the board.  This is partly why there is no definitive answer.