Hello Everyone,
In mid-September I wrote to AMMRL regarding UPS capacity and compatibility
with buck-boost transformers. I'd like to thank David Redwine of Dow
Chemical; Josh Kurutz of U. Chicago; Jerry Hirschinger of Purdue; and
Robert Peterson of UCLA for their responses. I also talked to many other
people, and would like to summarize what I learned.
Varian said that a UPS with 6 KVA capacity would perform well for a system
like ours, and have sufficient capacity left to provide an adequate margin.
(Our Inova spectrometers have 4 channels, triple-axis gradients, and 3
waveform generators; the 600 has UltraShims (40), whereas the 500 has 28
shims.) Varian also said that their Installation and Planning Guide is
overly conservative when it comes to power requirements.
The consensus was that one should NOT have a UPS hooked up to a buck-boost
transformer. The UPS presumably sees the unequal voltages as a problem
with the power, and tries to correct it. We therefore replaced those
buck-boost transformers with Acme Isolation Transformers. These have taps,
so that the voltage output is to some extent selectable.
Our lab is on the building emergency power system. According to Liebert,
"...Networks with generator backup must have on-line UPS because only
on-line technology can protect from frequency variations common at
generator start-up..." (As opposed to off-line or line interactive UPSs.)
As it turns out, we have a pro-rated warranty on the UPS, so we opted to
have Powerware repair it. A technician was here last week, and discovered
that a battery had exploded (possibly due to over-charging). He was
worried about the possible extent of the damage, so Powerware opted to send
us a new unit instead (it should arrive next week). The new UPS will have
a 2-year warranty, and inexplicably will be cheaper than the repair, in
contradiction to what I had been told earlier.
Thanks again,
Karl Koshlap
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Karl M. Koshlap, Ph.D.
Manager, Biomolecular NMR Laboratory
Department of Biochemistry & Biophysics
Texas A&M University
College Station, TX 77843-2128
Tel: (979) 458-2272
Fax: (979) 845-9274
email: koshlap_at_tamu.edu
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Received on Fri Nov 07 2003 - 16:28:34 MST