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We have been having trouble making the UPS on our satellite trailer
work when run from the generator. After much investigation, the problem has now been solved and everything works fine.

I purchased a small digital line frequency meter (about $50), that just
plugs into the generator. It showed that the generator was putting out around 64 Hz. The APC UPS is overly sensitive to line Frequency and that sensivity cannot be controlled. This is unlike the APC sensitivity to line Voltage, which can be easily set in the software parameters. So we adjusted the mechanical
governor on the generator until the meter read 60 Hz (on average, since no
engine such as a generator can run at Exactly a constant speed). This
solved the problem.We have now installed the line frequency meter as a permanent part of the
trailer.

The generator governor is very good at maintaining this setting with
varying loads placed on it, so I doubt we will have to adjust this again.
It is a simple screwdriver adjustment in any case. Our generator is an
Onan RV type, which is the best available. Other types may have more
frequency variation with load.

The clear lesson from this is that anyone who is using a generator
needs to have a line frequency meter, to be sure the frequency is close to 60 Hz.

Bob

Robert S. Dixon, Ph D, PE
Chief Research Engineer
Ohio State University, Office of the CIO
and Ohio Academic Resources Network (OARNet)
Office of the CIO
Room 451 Baker Systems Engr Lab
Ohio State University
1971 Neil Ave
Columbus, OH 43210
Telephone: 614-292-1638
Fax: 614-292-7081
Email: Bob_Dixon@osu.edu

"This material is based upon work supported by the National Science Foundation under Grant No. 0073240. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation."
 
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Last Updated: October 16, 2002