On Tue, 14 Aug 2007 00:36:28 -0700, SparkyGuy
wrote:

These units cost a lot more than the normal line interactive UPS.

Why? These and the other types have:
1) battery charge circuit
2) inverter that generates AC output to the load
3) some kind of power-fail switch-over (the double-conversion type
may
eliminate this altogether)
4) line filter

Please enlighten me. Why should the double-conversion UPS be so much
more
costly?

Sparky

There are several reasons.

1) the D/C UPS must constantly supply power to the load often at
maximum rating. It therefore has to be reliable over a long period of
time at higher operating temperature - thus better design and higher
quality and better heat dispersion. A line interactive backup UPS is
only ever called upon to supply DC-AC converter power on rare
occasions and then only for short periods - thus cheaper design and
construction.

2) It has to regulate both voltage and frequency thus more complex
design. It will also employ a true sine wave DC-AC converter in order
to keep waveform distortion below about 3%.

3) It must incorporate power factor correction to maximise converter
efficiency and minimise operation temp whereas LIUPS does not usually
incorporate this feature.

4) Up to 3 times the number of components compared to a LIUPS.