We recently got an inline generator installed at our facility that backs up our IT room. It detects the outage and kicks on within about 20 seconds of an outage. For those 20 seconds between the time of the outage and when the generator takes the load over, the equipment is running on battery power supplied by our current line-interactive UPSes. Unfortunately, the power delivered by the generator has a large enough variance in voltage that the UPSes alternate between battery and generator power several times per minute. I know this can be mitigated by double-conversion / online UPS systems, but I'm wondering if the current setup will suffice (aside from the screeching of the current UPSes).
My thought is that the only way to tell will be to run off of the generator for an extended period of time and monitor to see if the UPSes are running on generator power enough of the time that they can keep their batteries charged up. There's no doubt that the screeching will be annoying to anyone in the vicinity, but employee workstations will have crapped out within 5 minutes of any real outage anyway so it's not as though they'll have much work to get done. Our basic need is simply to keep servers, networking equipment, and phones up and running indefinitely in an outage.