[time-nuts] Power Back-up

[Hal Murray]

> Keep in mind that the batteries are not the only thing on small cheap
> Domestic UPS's that are rated for minutes. Same goes with their
> electronics, Heatsink etc. 

If you are interested in times measured in hours, you will be running a 
typical small UPS at well below full load.

For example, if full load is 5 minutes, 2 hours will be 5%.

That's assuming time*load is linear.  From what I've lower loads load are 
more efficient. For example:
  Typical Backup Time at Half Load 15.9 minutes (250 Watts)
  Typical Backup Time at Full Load  4.6 minutes (500 Watts)

That's for an APC SUA750 from:
http://www.apc.com/products/resource/include/techspec_index.cfm?base_sku=SUA75
0&total_watts=50

Somebody pointed out that low loads are inefficient.  That doesn't match the 
numbers I'm seeing,  Maybe I'm not looking at low enough loads.  From their 
chart:

Watts * minutes
  50 * 103  = 5150
100 *  50   = 5000
250 *  15.9 = 3975
500 *   4.6 = 2300

I wonder where the knee is.  20w? 10w?

That's also from the data sheet rather than measured.  It probably assumes a 
new battery.


-- 
These are my opinions, not necessarily my employer's.  I hate spam.