Looking for an UPS Expert

I can't say for sure, but it is probably because the power supplied by the UPS or generator isn't a pure sine wave that the second UPS is expecting on it's input. It all depends on the quality of the UPS output.

 

JIM, you are right because on all mine they all say NOT to do that. The original poster should not try that as they or his equipment will be damaged. Don't have time to explain the technical end of it now.

 

The short version - Never chain UPS's like you're trying to do - it's bad. It's specifically documented as "Don't Do it!" by all UPS manufacturers. And for some manufacturers, it will void the warranty.

The long version is twofold. (It's documented at length in several APC knowledgebase articles which I cannot find right now as APC's web site is not cooperating).

A) The downstream UPS may not recognize the artificial power of the upstream UPS, and go on battery - just as you're experiencing. If the SmartUPS creates a standard sine wave, it may make the downstream UPS happy. If the BackUPS creates a modified square wave, the downstream ups may not like it.

B) Even if the downstream UPS is happy, unless the upstream UPS is creating a 100% perfect regulated sine wave, the downstream ups may spend all it's time attempting to correct minute flaws in the upstream UPS's output. It's power stabilization circuitry may be constantly alternating between correcting for undervoltages, overvoltages, wave distortions, frequency shifts, etc... from the artificially generated power. This is *extremely* hard on a UPS, and can lead to premature death.

Of course given a perfect setup, it could work without incident. But the general rule is - Don't do it. If you do do it, don't be terribly surprised if your UPS's wear out far sooner than they should - and not in a way where replacing the battery will bring them back to life.

-Ken

 

I have some experience with trying to use electronics off a generator, and it appears that the quality of the power can vary widely, and the power can also fluctuate in ways that don't affect normal appliances, but do affect UPS's. When I tried to use mine off a generator, it kept switching back and forth, on and off battery, and it really made me nervous to watch. I also blew a surge protector that I have a small television plugged into while using the generator. So, I stopped trying to run anything delicate I cared about. It ran the fridge, well pump, furnace, lights, microwave, etc., all without problems.

Unfortunately, I decided that the safest thing is to not use delicate electronics such as computers or Tivos while the generator is on line.

It may be that some of the higher-end generators, such as Hondas, may work better in such situations.

 

Alot of it has to do with the quality of the UPS. The cheaper ones aren't able to "boost" or "trim" the power without goin on battery fully. The better UPS's (I.E. APC's Smart UPS line) are able to compensate for this. Running all our HT equipment (and RPLCD) off a SU1400 at the lake works fine. Even ran it during the ice storm where we were without power for 6 days. The generator is a midrange one (9000) and they all have swings in their power output so.... Neighbors came over to watch HD programming (extra bodies made cheap heaters in the house since it was 20degrees outside )