Diy ups?

[pterfloth]

Does anyone have any plans or suggestions for a DIY UPS (uninterruptible power supply) that will provide several hours of back-up power? I have a small 400w commercial unit that only provides minutes of back-up power. All I want to do is keep my return pump running (90 watts) so that I can keep some flow going.

Every fall/winter we get power outages and I would like to get prepared. A generator will not work for me because I am often out of town.

Your expertise would be much appreciated. Googling hasn't been much help.