[Beowulf] Re: UPS & power supply instability

[David Mathog]

RGB mentioned that "the HVAC is a nasty load".  That got me
thinking - when you increase the number of nodes running the
HVAC servicing that rack(s) is going to sense the increased
heat and compensate, presumably by running its motors more. 
So you could have an indirect problem such as: 

 increased load -> 
 increased HVAC activity ->
 UPS instability

Where the load correlates with the instability
but is not the direct cause.

Does the HVAC cooling the test rack run off the same UPS
as the rack itself??? 

If so,  it might be interesting to shut off that one HVAC, crank
up the others in the room, maybe put a few fans in (on different
circuits) to push the hot air over to them, and then try
increasing the number of nodes again.

That should at least rule out "lots of HVAC activity" as being
the (sole) source of the problem.

Regards,

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