On Mon, 23 Jun 2008 14:55:43 +0200, NoSp <NoSp@[EMAIL PROTECTED]
> wrote:
>Rich Webb wrote:
>> On Mon, 23 Jun 2008 12:50:11 +0200, NoSp <NoSp@[EMAIL PROTECTED]
> wrote:
>>
>>
>>> I'm planning to cut/supply power to an external SATA hard drive by
>>> having the +12V and +5V lines through a relay (dual pole), controlled
by
>>> a momentary push-button. But if the relay "wiggles" from one position
to
>>> another when activated I'm worried that this will in the long run harm
>>> the drive
>> You should be fine. You could add some capacitance to the power lines
to
>> smooth over the bounces but be aware that slowly rising power can also
>> cause some circuits to mis-behave so don't go overboard on monster
caps.
>>
>
>I haven't decided on a power supply yet, but I suppose a small switched
>type (as used with computers) is the best way to go. It'll be mounted in
>the same 1U 19" metal cabinet as the two SATA drives.
>Such a power supply must surely have the needed capacitors already to be
>able to deliver clean and stable power?
>Or should I (in addition to this) add some capacitors across the
>+12V/GND and +5V/GND lines close to each relay as well?
The power supply will be on the upstream side of the relays and won't
help to smooth the effects of any contact bounce on the load side of the
relays. But, there's probably enough capacitance on the drive's power
rails already.
The duration of the bouncing is typically around 10 msec and since it is
from "on" to "open," not "on" to "ground," the drives should be
perfectly happy. The digital ****tion will (should?) have a power-on
reset circuit that holds itself in reset long enough to wait through the
startup transients.
--
Rich Webb Norfolk, VA
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