Which UPS?

[James Knott]

Scott Allen wrote:
> AC is fed to the PC from the mains by the UPS (usually through a
> mechanical relay)

How often does that happen?  The relay will cause a brief interruption 
of power that's sufficient to reboot computers.  That sort of device 
will also not protect against short term hits, transients etc.  Many 
years ago, when I was a computer tech, one of the systems I worked on 
was for Air Canada.  That system had a huge UPS and lots of batteries.  
The UPS was run constantly to provide power to the computer sytem.  That 
building, at 151 Front St. W. also had an older generation of "UPS" 
where the incoming AC ran motor/alternator sets, with a diesel engine & 
huge, 8 ton flywheel, so that there would be no interruption to the AC 
supply.  When the power failed, a clutch connected the diesel and the 
flywheel started the it, while maintaining AC output.  The hits caused 
by switched in UPS could not be tolerated in that environment.  There 
was also stand by power in that building that was switched in on power 
failure, but computers and telecom gear were never run on it.

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