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Old 03-03-2018, 01:36 PM   #5
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Join Date: Nov 2011
Posts: 1,805
Default Re: How many uf do i need to cope with the HDD inrush current

Originally Posted by evilkitty View Post
high IR would not surprise me with the way the plugs are made and the sire binging thinner than it should
a stupid high spin up current would not be hard to imagine as one of the drives i have is old, really old and had a annoying wine (sounds similar to coil wine)

when i have this be an issue is when i boot off one and plug in a second drive, it crashed windows with the drive loosing power for a moment

I figure if i remake this cable i can slap a cap at the end of each rail to handle a spike in current draw
Are you sure the first drive is having a problem and not the CPU??

If your power distribution is such that this sort of sag can be present in the power leads (esp if you've moved to a single drive per pigtail), then I'd be suspicious of the suitability of your power supply for your particular SET of loads. I see ~50W of DC load on the 12V supply and ~30W on the 5V supply. That's not counting any power you're soaking up on the motherboard or video card.

In general, you don't want to go around changing the impedance of your load (adding C) without understanding its effect on the power distribution "system" (you can send a power supply into oscillation, etc.).

If your drives stagger their spin-ups AND if your system is within the normal operating margins for the power supply (which, hopefully, doesn't have shitty caps inside), then you shouldn't see problems like this. E.g., many of my systems have 4 or more 10-15K spindles (not counting the external 15 spindle enclosures) and nothing sags during power up.

Put a DMM on the power supplies (you can do one at a time as the problem is repeatable) to see if you're really seeing a notable sag, and not "something else".

[Or, shed some load and see when the problem goes away]
Curious.George is offline   Reply With Quote