My current power setup consists of a Zero Surge 2R7.5W power filter upstream to a APC BR1000G UPS. It may seem a bit redundant, but I had the power filter before I bought the UPS, and since I live in an area with frequent lightning strikes and power spikes, decided to keep using the power filter.
Even before I hooked up the filter upstream to the UPS, I had noticed that it would intermittently emit a 60 Hz hum loud enough to be audible across the room. It would typically happen about once a week or two for a cluster of several episodes 1-5 minutes long, all within an hour or two's time. Any attached equipment would continue to operate fine. I read up on the issue, and read that it might be caused by resonant frequencies between mechanical vibration of the coils and other components, so I wrote it off as such.
Now that I have the filter connected upstream to the UPS, I can see that the output voltage of the filter drops by about 6 V during each of these episodes. Dropping the input voltage to the filter by 6V does not reproduce an episode.
Could there be an intermittent short within the filter? Any other possibilities?
Even before I hooked up the filter upstream to the UPS, I had noticed that it would intermittently emit a 60 Hz hum loud enough to be audible across the room. It would typically happen about once a week or two for a cluster of several episodes 1-5 minutes long, all within an hour or two's time. Any attached equipment would continue to operate fine. I read up on the issue, and read that it might be caused by resonant frequencies between mechanical vibration of the coils and other components, so I wrote it off as such.
Now that I have the filter connected upstream to the UPS, I can see that the output voltage of the filter drops by about 6 V during each of these episodes. Dropping the input voltage to the filter by 6V does not reproduce an episode.
Could there be an intermittent short within the filter? Any other possibilities?
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