i have this mobo with atom 330 wich i know has a tdp of 22.5 W, a a-data vitesta ddr2 and a seagate 80 GB ata hdd
Q: how much does it need to power on?
I am afraid of some info on the internet that hdd's can eat up to 30 W on start-up.
I have a pico 80W psu and in my home country i could only find this 3A 12 V DC russian delta c power adapter (at home in Romania). This is a test PC so i could just test it when it's ready, but no harm in asking. It's case is hand-made (7.1 inch * 7.5 * 3.5) from an older one and the pourpose of the test is to have only copper heat-sinks and no air holes in the case and keep the PC running. After this one passes the test i will try a low power high end buit again without ventilation.
At power up, the CPU and the GPU basically are idle. To decrease power requirements, a laptop hard disk could be used. I agree that a 36W power adapter is rather weak, particularly when using a 3.5" drive.
Unless Atom motherboards work differently than every other computer motherboard, the first hurdle isn't whether the PSU can sustain idle wattage, it is the test that comes 1 second after the power button is hit where everything tries to max draw at once to make sure the PSU can handle the max load.
The hard disk will probably generate more heat than the rest of the components. Will your hard disk be mounted directly to the case to maximize heat dissipation? Is the case without active ventilation or is it completely closed?
That check is why computers turn on and turn right back off if they don't have a good enough PSU attached, if I am not mistaken. Other things cause this too, but in an otherwise good computer with a PSU that would handle only idling load and no more, it won't start.
Also why a computer will cold start OK when it can't handle the computer's max draw during a sustained load scenario (like when gaming). The PSU doesn't have tons of heat when a cold start happens, but gaming for long periods of time does cause heat to increase in the PSU which reduces its max wattage below what it was at during the POST checks.