UPS backup power

[Squiddy]

I just put new batteries in a UPS that is rated for 240Watts and tried running my Seio powerhead off of it today (with all of the snow) and had issues. As soon as the UPS went from line power to battery power, I could hear the rotor clanking around so I immediately turned it off. I can't remember but I think I have tried running my recirc pump on a UPS before and had trouble.

I'll have to play around with it because I'd love to have the tank backed up.

EDIT:

We have tried a UPS on both Fluvals and Eheims and discovered the Eheim coped well but the Fluval wouldn’t keep going. Something to do with the motor design and the fact that the power from the UPS is not an exact replica of true mains voltage, which is a sinewave shape.

This quote is from http://www.fnzas.org.nz/articles/technical/ups/. Looks like other people have tried this and had trouble. I have also read that AC motors run hotter with modified sine waves. Not sure how good this would be for the pumps...

Then again, you hear of lots of people using generators to power aquarium equipment during power outages. Generators create the same kind of modified sine wave that inverters do. I guess I need someone that uses a UPS for this purpose to come out and settle this.

I just plugged the minijet 606 in my girlfriend's 6 gal nano into my UPS and it is working fine running on battery power... mind you it is only 6 watts.