First let me make sure it's clear that I am NOT trying to extend runtime by connecting two UPSs in series. That's been asked a million times on various forums, and is not what I'm trying to accomplish.
I've had 3 UPS units fail on me in the last 12-18 months, and I'm starting to wonder if it's the power flickers that are doing them in. My power rarely goes out for more than a minute or five, but before it does, it always violently flickers for a few seconds. Those flickers are hell on my unprotected equipment, and I'm wondering if that's what has caused my UPSs to die prematurely (the newest one barely lasted 5 months).
The old ones still function and still seem to do automatic voltage regulation, but none of them last more than 1-2 seconds once they switch to battery. I've tested the batteries, and they're fine; they were also all replaced about 9 months ago.
So, what I'm hoping is that the old ones can sit upstream of the new UPSs to take the brunt of any rapid brownout /surges and keep my new UPSs healthy. They're all pure sine wave and similarly rated.
Thoughts? Warnings/cautions?
I am running a UPS after a solar battery system as it doesn't switch fast enough when the power cuts (despite having a "UPS" mode) and I can tell that the lack of a proper sinewave is still a problem. It seems to work, but the real UPS makes some very strange humming noises when running that way.