Hi, Tim.
The Volt-Amps drawn will be greater than the Watts on the nameplate,
but without knowing the power factor or harmonic content of the draw,
it's a crapshoot what exactly the factor will be. The 0.707 is only
the ratio of peak voltage (or current) for a pure sinewave to the RMS
value.
HTH,
Donald.
> Date: Tue, 25 Feb 2003 10:43:57 -0500
> From: <Tim.Mullen@trw.com>
>
> Richard Welty [mailto:rwelty@suespammers.org] wrote:
> >
> > actually, for any really serious installation, i generally
> > advise my clients to hire a professional engineering consultant
> > who does generator/UPS setups for a living. it's way too easy
> > to undersize these things and screw yourself.
> >
> > richard
> > ("you mean we have to have power for the lights and the A/C too?")
>
>
> I've done the really big UPSs for large computer installations - you
> know, the ones where the UPS sits in four full size cabinets and is
> powered by 480 Volt 3 phase. In those cases, the Voltage, Amps, Watts,
> and BTU requirements were easy to determine (the manufacturers all
> readily provided the info).
>
> For this case, I'm trying to size the smaller rack mount type of UPS
> to power a rack of 8 small servers. The problem is that the UPSs are
> rated by VoltAmps, and the only info I can get on the servers is Watts.
> I'm going to need several of the rack mounted UPSs to spread the load
> as there is no room in the facility for a separate large UPS. I also
> need to make the set up "redundant" to power the redundant power supplies
> in the servers (each of a server's two power supply connected to a
> different UPS). It's not that much of a problem except that I also
> have to power things from standard 120V-20Amp power circuits because
> the cost of running additional power circuits is excessive (and a long
> lead time task).
>
> I'm trying to get hold of the vendors technical people to determine
> the actual Amps (or VA) requirements - in the mean time, I think that
> it's the .707 factor (for the RMS) that I was looking for...
>
> As for the lights and A/C - been there, done that. The lights
> are usually provided by the facilities, but they always seem to
> forget the emergency lighting...
>
> The one other thing that usually gets forgotten is the "Emergency
> Off" circuits. I've had the pros outfit the computer room with
> fire detection systems that kill all power to the room. However,
> they usually seem to forgot to provide a method to shut down the
> UPS along with the other power - power TO the UPS, yes; power
> FROM the UPS, no...
>
> Thanks for all the input...
>
> Tim Mullen
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