[Beowulf] UPS & power supply instability

Jim Lux James.P.Lux at jpl.nasa.gov
Wed Sep 28 10:53:54 PDT 2005

At 09:54 AM 9/28/2005, David Mathog wrote:
>David Kewley <kewley at gps.caltech.edu> wrote:
> >
> > The problem is this: We can fire up our cluster to about 40% of maximum
> > load and everything is fine.  But if we go over some threshold right
> > around 40% of max, the output currents from the PDUs go unstable.
>It might be a useful diagnostic to place a purely resistive load
>on one of the UPS units and see if the Liebert is also
>unstable with that.  Unless you happen to have access to a
>lot of desk lamps you can construct a test rig without
>spending _too_ much money by wiring a large number of
>incandescent bulb sockets onto some sort of heat resistant
>frame, each set of 5 100W bulbs (wired in parallel) with its
>own cord.  100 W bulbs, sockets, and cords are all farly cheap.

300W halogen shop lights are also cheap, and you'll need fewer of them.

BUT... a 1000W - 1500W space heater or tabletop hot plate or toaster or 
hair dryer is even better. And cheaper.  You can boil water to absorb the 
heat (and simultaneously give your AC a workout removing the heat of 

For that matter, Home Depot is selling room airconditioners for <$70 that 
would make a dandy load (and have other uses), but are not resistive.

If you need a bad PF load that looks like a computer power supply, there 
are some fairly easy ways to do it, but nothing you can just inexpensively 
buy off the shelf. (Diode bridge, suitable big capacitor, and suitable 
resistive load)

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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