Hi,

I figure there's a lot of electronics gurus out there, and I need help with a quick fix for a computer system I'm fiddling with.

A PC is equipped with a 550W ATX PSU capable of delivering 12V - 20A (plenty).

It has a RAID with ten harddrives which consume a max of 1.3A during powerup and around 0.9 during idle. The disks are spun up seperately to eliminate PSU problems. This works fine, even when the drives are up in quick succession.

During activity the drives consume around 1.3A, probably with a usage spike right at the start of activity (going from idle state).

Going from idle to activity on different drives gives no problems either, neither does having all the drives running with activity, as long as they do not go from idle to activity at the same time.

If all disks go from idle to activity at the same time, some of them power off (very randomly). This will happen if I start a defragmentation run.

My guess is that the problem is that the PSU cannot quickly enough deliver the extra 4-5 (possibly more just as the drives go from idle to activity), thus making some of the drives power off as they do not get enough power.

The problem disappears if 5 drives are powered from a seperate PSU. The problem gradually disappears when less drives are connected, and worsens when more drives are connected.

Is it possible to fit a capacitor on the 12V line, giving the PSU a better chance of delivering the power that is needed?

I need to fit capacitors to two drive arrays with 5 drives, each array consuming 5A idle and around 7,5A during activity (worst case).

HOW? (Spell it out, please)

I know - "just fit another PSU", but no, I'd rather not, as the computer is stuffed, and the current PSU is capable of sustaining the load.

Feel free to email me privately, as I know this is O.T.


Thanks in advance,


Lars