I've just acquired an older 1.4 kVa BEST Micro Ferrups UPS, the one with the huge and heavy ferro-resonant transformer.
I changed the battery, plugged it in, and it works great. Runtime is excellent for home use. Just one thing though: It hums and buzzes like an old neon sign ballast. Almost unbearable. I may not be able to use it for home because of the noise. It's quite a buzz.
Is there anything I can do to eliminate or minimize this noise?
Probably not... Ferror-resonant transformers are inherently noisy, especially those of several years ago. You might try opening the unit so that you can get to the big transformer. ( Remove battery connections first!!!) See if tightening the assembly bolts in the transformer offers any relief. If that doesn't fix it, there's probably one thing left to do... consider building a small housing for it and mount it outside the house. Run a wire from house wiring to the UPS, and another back into house to feed equipment. ==============
Dave M
Never take a laxative and a sleeping pill at the same time!!
I'm assuming that when you say "...excellent for home use." that you may not have a 1kw load on the UPS.
It's possible that the ferro-resonant transformer needs a minimum load to go into regulation without all that buzzing and humming.
Try adding a 100 or 200 watt incandescent lamp on the output to see if that helps.
If it does then wire a lamp to the ferro-resonant transformer output before it goes to the UPS circuit. This will keep it happy when the mains are up and will not be an additional load when the UPS kicks in.
Check the cap to the transformer. Make sure that all bolts are VERY tight. The only time you should hear anything is possibly when the UPS inverter is running (i.e., no A.C. input), and then not much. I have a dozen of these things (1's, 1.4's, 1.5's, and some 5 kva) here, and they are all silent, except for the fan(s).
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