Power supply wattage rating 'aint everything

[mdmint]

IRRC as Stanger discovered he was having issues running a bunch of HDs with a 4or500w PS. Put in a 3or350w he had and they ran fan. (don't remember the exact ratings, just know it was big to small)

I've recently had the same experience. My main workstation has been haven't intermittent issues. The latest after expanding RAID1 to 4 HD RAID5. Attempted to copy some large files to new 500G partition and drives would drop offline then come back up. (Fortunately the Promise S150 SX4 handled the weirdness without loosing data, it'd just stop and wait to see if the drive was really dead or coming back, then resume copy.) This was with a 500w rated cheapo powersupply. I pulled it and put in the 400w I pulled from my Codegen Server case when I got it. Exact same file copy works fine now. And Server is running 8 HDs on (dual redundant) 400w power supply just fine for 9 months. Lesson learned once again, cheap is CHEAP!

[stanger89]

Yup, for me it was a 400W PC Power and Cooling Silencer 400, and a Fortron FSP300-60PN.

What you need to look at when researching PSs is the actual specs. For example, I was recently looking and with supplies ranging from 300W to 510W, for most of them the only difference was the amount of current they could provide the 12V rail. The 3.3 and 5V rails had almost identical specs.

If anybody knows a good resource that lists what components use power from which rail it could be very enlightening. Or here's one I found:
http://www.pcpowerandcooling.com/maxpc/index_cases.htm

I know I've looked at WDs specs and their HDDs (contrary to what I thought) draw twice as much current of the 5V rail as they do from the 12V rail.

[mdmint]

Yeah, though unfortunately the spec's can be meaningless! The 500w cheapo that couldn't handle the load was rated 5A greater on the +12v rail than the 400w that can.

[stanger89]

The question is, what rail was causing the problem?

[mdmint]

Originally Posted by stanger89

The question is, what rail was causing the problem?

IRRC they were rated the same +5v. I've got my workstation buttoned back up and don't feel like taking the covers off to check.

I suspect the maximum output capable had nothing to do with it. I suspect it was a more matter of power not being stable.

[mdmint]

FWIW nope not the same +5v, found picture of PS inc label on NewEgg. The 500w rated 5A less than the 400w +5v rail. And I was mistaken on the +12v too, the 500w rated 9A greater.