I had problems with my UPS at home when it was powered by a 15K Generac back up generator. The installers did an upgrade to the generator that is required for many high efficiency furnaces hoping it would solve the problem, however it didn't. With the generator supplying power, the UPS would not switch to it, would run down the battery, then die. Short blackouts were OK, but anything over half an hour made it useless. I talked with APC & they stated the generator produced "dirty" power that the UPS rejected. I never did come up with a solution.