Date : Fri, 16 Jan 2004 23:35:44 +0000
From : Richard Gellman <splodge@...>
Subject: Re: HD Powre Consumption
Mike Tomlinson wrote:
>In article <4c7195f21dinfo@...>, Sprow <info@...> writes
>
>
>
>>In article <4007301B.4040806@...>,
>> Richard Gellman <splodge@...> wrote:
>>
>>
>>>Someone previously was asking about power consumption of hard drives on
>>>startup.
>>>
>>>
>>Me. And I'm glad someone believed me enough to look independently.
>>
>>
>
>Richard's talking about a 3.5" drive, not the 2.5" drives I was
>referring to in my posts.
>
>
This is true. The drive in question is a rather antiquated 3.5" full
height drive (wide as a 3.5" floppy, hight as a 5.25" floppy). I decided
this was reasonably relevant given the size of the beast. I figure if a
SCSI drive is to be chosen, its unlikely to be a 72GB hot swap. And of
course, the smaller the drive, the older it is (generally speaking).
>Example: from Seagate's website for the current-model ST92011A 20Gb
>2.5" 5400rpm drive.
>
>"Power Requirements +5 VDC +/-5%
>
>Power Management (watts)
>Seek 2.4
>Read/Write 2.87
>Idle 0.97
>Standby 0.36"
>
>So that's 480mA when seeking, 574mA reading/writing, 194mA idling, and
>72mA in standby.
>
>The .pdf datasheet says the maximum current is 1.2A. Presumably this is
>when the drive is spinning up (it doesn't say.)
>
>
>I see no problem running this drive off a Beeb's PSU.
>
>
>
A BBC B PSU maybe. The B's had a slightly sturdier PSU than the Master's
did. The standard Master 128 PSU can't chuck out more than 1A (according
to the PSU itself, I'd bet that it could take a little more). Putting
1.2A on that could be taking a chance, and it certainly doesn't leave
any room for anything else (I had planned to connect the floppy there,
and start CopyFiles doing its thing).
I favour the Master 128 because the ADFS ROM is more native in the
Master. While the ADFS ROM will work in the BBC B, hooking up the ADFS
AND a hard drive is more of a hack-upgrade than a anticpated one. Plus
the BBC B will suffer memory strains as the ADFS attempts to keep the
current catalogue and free space map (7 sectors, raising page to &1500
before sequential I/O buffers and any other workspace).
A point of note regarding spin-up currents: Its not so much the current
it draws as how it draws it. Gradually increasing current tends more to
make the components warm up for a moment. Its the sudden drawing of
current on start-up that causes the power surge that causes components
to fail. I would still favour an external PSU for a hard drive, unless
the HD can guarantee it doesn't draw more than 900mA on startup.
-- Richard Gellman