[Beowulf] Re: UPS & power supply instability

David Mathog mathog at mendel.bio.caltech.edu
Fri Sep 30 11:16:50 PDT 2005

David Kewley wrote:

> Maybe I wasn't clear enough.  We have two UPSes, one for computers
only, and 
> one for HVAC only.  Here is more detail of the feeds into the room:
> substation A -> panel A --> UPS B -> HVAC control, fan, condensate pumps
>                         \-> HVAC heaters, humidifiers
> substation C -> UPS A --> PDU1 --(45 whips)--> 15 racks
>                       \-> PDU2 --(48 whips)--> 16 racks

> I think it's unlikely that there's significant feedback between the
power to 
> the HVAC and the power to the computers


Since they are on separate loops you can even test this.  

1.  Shut off all the computers.
2.  Cool the room a bit more than usual with the HVAC.
3.  Shut off the HVAC
4.  Shut off UPS B.
5.  (QUICKLY) spin up enough nodes to trigger the power
    instability, see if it occurs.

Then before you or the machines heat stroke

6.  Turn UPS B back on
7.  Turn the HVAC back on.

We all pretty expect that the result of this experiment
will be that you see instability at the same point.  If so,
you can definitively rule out the HVAC circuits as a
component in the problem.


David Mathog
mathog at caltech.edu
Manager, Sequence Analysis Facility, Biology Division, Caltech

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