Date   : Fri, 16 Jan 2004 10:00:08 GMT
From   : Pete Turnbull <pete@...>
Subject: Re: HD Powre Consumption

On Jan 16,  0:28, Richard Gellman wrote:
> Someone previously was asking about power consumption of hard drives
on
> startup.
>
> While doing a little research on Seagate's site regarding the power
> usage of a 500Mb ST1480N SCSI drive (I have one here that I planned
to
> use) it turns out said drive uses around 0.54A on the 12 and 5 volt
> lines while running, but its startup 12V current is a whopping 2.5A!
>
> Checking on the underside of my Master 128, the aux power connector
> rates 12V at 1A and 5V at 900mA. I think connecting that drive might
fry
> the PSU somehow. An external power supply is definitely going to be
> necessary.

Not necessarily (the SMPSU in the Master would just go into current
limit mode), but there's a chance it would crash the Master.

> Anyone have any quick n dirty ideas for a BBC-turns-on-PSU circuit?

When I wanted a 240V fan on one of my Beebs (couldn't get the right
size in 5V or 12V without a high price and/or current draw) I just
wired a 5V-triggered 240VAC-capable reed relay to the +5 on the Beeb.
 Such relays are easy to find, inexpensive, and very small (not much
bigger than the cassette relay in a Beeb/Master).  You can also get
"solid-state relays" which do a similar job.

You could use a triac, triggered by the 5V (or 12V) rail, but it should
be opto-isolated, which means it needs its own LV power supply, and it
won't turn off when the Master does unless you use a GTO device (which
is normally a thyristor not a triac) and some extra circuitry.

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York