UPS for really small load

[JHZR2]

I have a really small load that Id like to be able to keep up for a long time if my power goes out.

THe load is about 18VA, and the PF is pretty poor, like 0.5, so the wattage is not high.

So Im just curious about approach. Since some power electronics have current minimums and the efficiency of some of the devices is higher at a good amount of load, I dont want to buy too big for runtime and then eat up the stored energy by excess inefficiency in the converter, or perhaps a load that is too small to even be supported properly.

Is this a consideration? THat tiny load is across two separate plugs, FWIW.

 

[webfors]

How long is a long time?

 

[JHZR2]

ehhhh, Ill just make a handwaving argument that Id like on the order of a day or more. The typical outage is 15 minutes, not more than once a year or every other year.

But 18VA, foregetting the power factor (its dc conversion to the load), lets just say is 18W, so per day, it is 432Wh.

That starts to be a lot... like car battery size, which I dont particularly want. So probably a better value is something along the lines of a standard 7AH battery, which can give maybe 84Wh at low load.

Not optimal, but it gives a few hours...

But the question is really for that 18VA load, am I better off buying the smallest rated UPS I can, or would a bigger one, which would have a bigger battery, be OK? If the electronics go from 98% to 92% efficient due to load, say for example, that can eat a lot of stored energy...

 

[rjundi]

This http://www.apc.com/products/resource/include/techspec_index.cfm?base_sku=BX1000G

for $100 gives me 9 hrs of backup with Comcast Phone/Internet router and Cisco E3000 Router.

This setup is what I use to power my home office(laptop) for about 4-6 hours before starting my generator.