[Beowulf] Re: Emergency Power Off

Jim Lux James.P.Lux at jpl.nasa.gov
Mon Mar 19 20:09:40 EDT 2007

At 04:20 PM 3/19/2007, David Mathog wrote:
>"Robert G. Brown" <rgb at phy.duke.edu> wrote
> > APC has a button -- it is spec'd somewhat in the pdf Jim and I passed
> > back and forth and you can look it up on their site.  There are some
> > other companies that sell them as well.
>Found this one:
>Pricegrabber shows that it's around $550.
> >
> > They don't look terribly easy to wire up, though, and say that they are
> > only to be installed by "professionals".
>I think that's for the ones that both shut off the main breakers and
>the UPS boxes at the same time.  The panel part of that is definitely
>professionals only.  I don't think that's necessarily so for the
>UPS parts.  The Tripp-Lite UPS units we have either have a separate EPO
>port (whose specs I'm still waiting for, there's nothing in the
>manual), or for the ones that can be controlled by a serial port, there
>is a sort of hybrid serial port/EPO cable.
>Most of the Tripp-Lites that have serial line control have an inverter
>kill circuit that only requires a ground wire and 12V (or less)
>positive voltage applied through a 10K resistor.  This is how
>they can make the Y cable: just hook another 10K resistor to
>the pin and bring that line out separately.  Logical OR via separate
>pull up resistors.
>In any case, the current and dc voltage on these Tripp-Lite EPO
>lines isn't very high.  I'm thinking for the few that we have
>in our computer room this circuit would probably due the trick
>(sorry about the ASCII art):
>   +-[9V+]-[9V+]---SWITCH -+  (<--switch is normally open)
>   |                       +-10K-- UPS1 -------+
>   |                       +-10K-- UPS2 -------+
>   |                       +-10K-- UPS3 -------+
>   |                       +-10K-- UPS4 -------+
>   |                       +-10K-- UPS5 -------+
>   |                       |                   |
>   +-----------------------+                   |
>   |                                           |
>   +-common ground ----------------------------+
>The pair of 9V batteries should last for the shelf life of the
>batteries (5 years?) since there is no load except for the one time
>the switch is used.  The 10K resistors might not be quite
>the right value, I'll have to get the actual specs and see what
>the needed voltage and current are.

That would probably work, and I'll bet the resistance isn't 
critical.  It probably is putting a few milliamps through an opto 
isolator or similar, and your 12V +10K is simulating a Data Terminal 
Ready line or something.

>Possibly the switch needs to be closed for a couple of seconds, but
>that could be handled mechanically in the kill switch (separate
>mechanism to release it back to the open state, so one slap will
>turn off the inverters.)

The standard E-stop red mushroom head switch has a push to actuate, 
with maintained contact, until you twist to release.

>Clearly this wouldn't work for the Compaq EPO I cited earlier.
>Caveat emptor, your mileage may vary, etc.
>David Mathog
>mathog at caltech.edu
>Manager, Sequence Analysis Facility, Biology Division, Caltech
>Beowulf mailing list, Beowulf at beowulf.org
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James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875 

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