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[on:]

Hello! For a project of mine I would like to incorporate an arduino controlling somewhat large loads (many 1A loads 12VDC mainly LEDs) from my arduino with the power coming from my computer PSU.   My psu is this one (http://www.newegg.com/Product/Product.aspx?Item=N82E16817121040).  It is a 1.2kW supply with 100A available on the 12V rail.  Are there any things I should know about using large amounts of power from a computer PSU?  things like power protection or any intricacies of a psu that Im not aware of?
Thank you very much for any help, I would really not like to hurt my beast of a psu and computer to boot!!

[Reply #1 on:]

nobody??

[Reply #2 on:]

still nobody??

[Reply #3 on:]

Making a workbench power supply from an atx PSU is a fairly common project. A Google search will give you numerous examples. Though I would strongly discourage 'borrowing' power from the computer, meaning- don't try to run your computer and your projects off the same unit (formula for disaster). While in theory it is possible, Murphy's law will catch up with you.

[Reply #4 on:]

yes the goal of the project was for the computer and the project to be drawing power simultaneously from the psu.  i know that this is theoretically possible because the psu is only a transformer with high current power electronics and filtering to provide very smooth power to the computer.  I was only hoping that somebody would provide me with some technical details as to why this is a bad idea.

why do you think it would be a formula for disaster?

[Reply #5 on:]

It is a formula for disaster because if you screw up ANYTHING in your circuits you stand a VERY GOOD CHANCE of screwing up your computer. If you use an external power supply and you screw up something with your arduino and added components, there is a very high probability that only your arduino will suffer.

Arduino = Cheap,  Computer = expensive

[Reply #6 on:]

beyond the incorrectly setting up of the circuit, are there any technical reasons as to why i shouldn't use the psu?
the circuit will be completely set up and tested via a test bench power supply, then final implementation done using the computer psu

[Reply #7 on:]

are there any technical reasons as to why i shouldn't...

basically we established that it is technically possible. The problem is that there really is no margin for error. If you make mistake, cross a wire, something accidentally cuts through the  wire insulation, or something completely unforseen happens( Murphy's Law),  you have 100 amps going straight to ground, (that's called welding). At best- the computer crashes, at worst- sparks, fire, and the release of very expensive magic smoke. Other dangers include dumping 12 volts unto the 5volt or 3.3volt rail (= fire, sparks, magic smoke released), or introducing nasty transients onto your computer's power rails( crashing, blue screens, and unhappy computer/magic smoke).
That said, other technical considerations include: decoupling, circuit protection, and load currents. Most PSUs either have 18awg or 16awg wire which really isn't suitable for large currents. Have you calculated your total load including what your computer components draw as well as your project?
It just makes more sense to buy a $20 15amp 12volt supply off ebay than to risk a computer that costs exponentially more.

[Reply #8 on:]

I agree.  You are flirting with danger in using the same supply to provide clean power to the PC and additionally drive potentially heavy and electrically dirty loads at the same time! Yes LEDs should be clean, but....   I wouldn't chance it.  Too much chance of a spike or transits on the supply lines.