Well, first let me say that I would check with an EE before I would put a
switch on the hot leg of a hard drive, as you write that you have done. I
am not so sure that a hard drive ONLY uses the yellow 12 volt leg. It might
also be using the red 5 volt.  If you kill the 12 volt side the drive
wouldn't work, but that doesn't mean the drive is fully powered off. You
would have to look a hard drive schematic. And if I were to put a switch on
a hard drive, I would kill all four wires going into the drive, not just
the hot. At least then you know that it would be a complete disconnect. And
I would never use the switch unless I was fully powered down.

I would also want to be sure that inadvertently powering off like this,
when the system is hot, could in no way damage the drive. Certainly, if you
power down when the computer is booted, then you risk making your PC
unstable, and or losing data.

The answer to your switch question is that you would hook the Supply up to
the PS side of the 12 volt yellow wire. The load would be the hard drive
side of the switch, and the Ground, which is the return for the lamp, would
be the black wire, or you could use the case, but I wouldn't.

Note: I would test the lamp without the hard drive connected to the
Load,  just to make sure the switch works correctly.

There are better ways to do this. Removable hard drive Racks for example,

http://cyberguys.com/cgi-bin/sgin0101.exe?UID=2003030310552238&GEN6=00&GEN9=5CG01&FNM=00&T1=168+0537&UREQA=1&UREQB=2&UREQC=3&UREQD=4

I always install one of something like this on my computers, so that I can
image another hard drive or move data around when a system is down. Prices
for these can range anywhere for 12 U.S dollars up to 100. If your
controller supports it, they even come hot swap able.

Of course, I would never do this with a drive where performance was a concern.

Rode
The NOSPIN Group
http://freepctech.com

At 09:14 PM 3/3/2003 +1300, you wrote:

>Because of the rather complicated setup I've got, with three hard drives
>running through a drive selector, I've added switches to the 12 volt leads
>on two of the drives, so that I can turn them off when they're not needed.
>
>These switches are simple 240v lamp switches - of the push-on, push-off
>type.  They have only two terminals, so when the 12v wire is cut, each cut
>end is screwed into a terminal socket.
>
>Here's my query:  These switches don't tell me if they are on or off, so
>I've bought some 12 volt switches with an inbuilt indicator lamp, the idea
>being that, if the switch is on, the lamp will be lit and vice versa.
>However, these switches have THREE terminals, and I can't work out how to
>set up the wiring. (duh)
>
>The terminals are labelled 'Earth', 'Load' and 'Supply'.  I guess that Load
>and Supply would be the two cut ends of the 12v wire, which currently
>connect to my simple lamp switch.
>
>But does the Earth terminal need connecting to the chassis?  Or one of the
>black neutral wires.  Or what?
>
>Ian Porter

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