On Aug 14, 3:36 am, SparkyGuy wrote:
Please enlighten me. Why should the double-conversion UPS be so
much more costly?

To add to what Ross Herbert has posted: a standard computer grade
UPS has a power supply to charge the battery about the size of a power
brick (wall wart). The double conversions UPS must have same supply
that is significantly larger than a computer power supply. It must
both recharge battery and to run the output inverter - another power
supply. Whereas a simple battery backup (standby) supply only has a
an output inverter, the double conversion must have a big output
inverter AND have an even bigger power supply to power that output
inverter and to recharge battery.

Then double conversion design gets more complex - more things that
app note did not discuss. Standard UPS may output extremely dirty
electricity - as made obvious in specs and by numbers I posted
previously with a spike of up to 270 volts. It is a double conversion
UPS. Its power supplies - especially ouput inverter - must be far
more complex to have a cleaner output. Therefore efficiencies are
lost. Now its battery and input power supply must be bigger. More
expense.

Double conversion UPS may be $500+. Better UPSes - building wide
solutions - are even more expensive since design must be even better,
battery must last much longer than 3 years, and it actually contain
effective surge protection (meaning it is properly earthed).