In article .net,
SparkyGuy wrote:
http://apc.com/tools/ups_selector/

There seems to be 2 kinds of UPSs: those that switches to battery backup if
power drops below a minimum voltage; and those that separate the load from
the supply ("double conversion" type). This latter type is, basically, a
battery charger running an inverter it's *always" in baclup mode (c: .

It seems that the double-conversion type is truly the only kind that can
isolate equipment from "bad" power. All else relies on filtering and fast
switching from grid-supplied power to inverter power. (We pray in fast
relays!)

Am I right in thinking that a double-conversion model is the best for our
needs (our problem being dirty power, not power-fail)?

Sparky

(Double-conversion models start near $500. Ouch!)

There is a company called Best Power Technology that sells what they call
FERUPS which uses a Ferroresonant transformer to regulate the output
voltage and remove anything that is not 60HZ from the power. It will
still switch to battery when the power fails completely and produces
a sine-wave output.
--
Tom Schulz