OT: How many internal IDE drives maximum off of an ATX power supply?

[Madison Kelly]

Salman Ahmed wrote:
> What's the maximum number of IDE (UltraDMA 100/133) drives that I can
> safely power from a ATX power supply (assuming that you have enough
> IDE/UDMA connectors of course)?
> 
> I have an old PIII system (Abit BH6) in an ATX case that currently has
> 3 UltraDMA 100/133 hard drives connected to a Promise UltraDMA 133
> controller card. And I am wondering if it's OK to add a 4th such HD in
> there without running into any power supply issues.
> 
> I am not sure what the wattage is of the power supply in the case but
> it is an ATX case. This system does not have an optical drive and the 3
> HDs connected to the Promise controller card are only ones in there
> presently.
> 
> Thanks.
> 
> 
> Salman Ahmed

Look up the max volt-amps drawn by each drive for the 5vDC and 12vDC 
rails. Then look at the maximum amps available on each rail (5vDC and 
12vDC). I really doubt it, but you may have multiple 12vDC rails which 
will have their own max draw plus a combined max draw across all rails.

Lastly, you will need to determine how much amperage draw the rest of 
your system draws on the 5vDC and 12vDC rails, and make sure those plus 
the combined draw of your HDDs doesn't exceed the max draw of your PSU.

Lastly, it is important to realize that switching PSUs have a curve of 
efficiency. *Generally*, PSUs are most efficient around the 75%-85% 
range. Most better PSU companies will show you an efficiency graph.

One thing to understand, that *many* people miss, is that "wattage" on 
PSUs is often *very* deceptive and often flat out misleading. I've seen 
500w cheap PSUs fail long before a well built 350w PSU. Shady PSU makers 
love to play fast and loose with their wattage by doing things like 
saying 500w PSU!!! (*max 350w on the 12vDC and 5vDC rails).

So long answer short; it depends on the quality of your PSU and the max 
amperage available on the 12vDC rail mainly, with the 5vDC rail being 
important but much less so.

Madi
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