UPS Recommendations

Michael Torrie torriem at
Thu Aug 26 21:40:00 MDT 2010

On 08/26/2010 01:24 PM, Corey Edwards wrote:
> A generator won't solve your problem without a UPS. It takes up to a
> couple minutes for the generator to kick on and switch over. During that
> time you need a UPS to carry the load. There's really just no way around
> it. Preventative maintenance is your best bet.

Generators bring some interesting things to the mix.  As you say you
can't have a generator without a UPS.  But the UPS has to be pretty
smart when switching back and forth between line, battery, and
generator.  Not only does the UPS have to carry the load while the
generator gets up to speed, it also has to match phase with the
generator.  This doesn't take very long, but you have to have a pretty
expensive UPS to do this.  Then when line power returns, the UPS has to
carry the load again while it adjusts the phase to match the line phase.
 We have a nice big, in-line UPS at work that does all this.  Works well
if you have the resources.

The reason that some cheap (and very expensive) UPS's kill the load when
the battery dies is that to avoid all this phase-matching nonsense, some
of them just run the power through the batteries at all time.  In other
words you're running AC->DC->Battery->Inverter->Load.

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