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UPS Power Draw

 
 
Louis Aslett
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      03-07-2005, 10:36 AM
First if I may give a brief background: despite having space in a data
centre with UPS, diesel generator etc etc our data centre supplier has
managed to have 3 power outages in 6 months (ironically none due to
mains power failure) and it has moved beyond ridiculous. We are
looking around alternatives, but in the mean-time I need to take
immediate action to assuage our own client's concerns.

To that end I plan to put a standard APC UPS unit into our rack. I'm
looking at the APC Smart-UPS XL Modular 3000VA 230V Rackmount
(http://www.apc.com/resource/include/...UM3000RMXLI2U),
plus extra battery, from which we should get about 30 mins runtime.
This is what the APC selector tool suggests for our exact config.

However, here's the problem: we have a 10 amp feed to the rack. The
power bar currently shows from 4 amp to 6 amp draw depending on the
server load. The APC unit above has a 16 amp IEC-320 C20 input.

My question is: can I safely use this UPS because my equipment is not
going to be drawing the unit's maximum power? The lady I phoned at
APC hinted (without saying directly) that I should be fine but stuck
to the official line which was that I should upgrade the power feed to
16A for safety. Thing is that doing so will set us back a fair bit
each month, which doesn't sit comfortably given that I'm only having
to do this to fix what is the data centre's fault!

Hoping someone with electrical/UPS experience can confirm/deny this!

Many thanks,

Louis
 
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Mike Walsh
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      03-07-2005, 03:29 PM

You can use the 10 amp feed that you have. The power requirements of the UPS are minimal; the control circuit board and trickle charger don't use much power. I am guessing that this would be around .5 amp, and much less if the battery are charged and not drawing current. Most of the power is simply passed through to your existing equipment and won't be more than you are already using.

Louis Aslett wrote:
>
>
> However, here's the problem: we have a 10 amp feed to the rack. The
> power bar currently shows from 4 amp to 6 amp draw depending on the
> server load. The APC unit above has a 16 amp IEC-320 C20 input.
>
> My question is: can I safely use this UPS because my equipment is not
> going to be drawing the unit's maximum power? The lady I phoned at
> APC hinted (without saying directly) that I should be fine but stuck
> to the official line which was that I should upgrade the power feed to
> 16A for safety. Thing is that doing so will set us back a fair bit
> each month, which doesn't sit comfortably given that I'm only having
> to do this to fix what is the data centre's fault!
>


--
Mike Walsh
West Palm Beach, Florida, U.S.A.
 
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louis@6internet.com
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      03-07-2005, 04:31 PM
Thanks so much for your response Mike. This is what my gut was telling
me, but I'm glad of the sanity check!

Just one last question ... would extra battery packs be likely to
dramatically increase the draw after an outage? Obviously the worst
thing would be for the whole lot to hum away nicely and
successfully supply power through any outage only to blow the 10 amp
circuit when power returns as it tries to draw current to recharge!

Many thanks,

Louis


Mike Walsh wrote:
> You can use the 10 amp feed that you have. The power requirements of

the UPS are minimal; the control circuit board and trickle charger
don't use much power. I am guessing that this would be around .5 amp,
and much less if the battery are charged and not drawing current. Most
of the power is simply passed through to your existing equipment and
won't be more than you are already using.
>
> Louis Aslett wrote:
> >
> >
> > However, here's the problem: we have a 10 amp feed to the rack.

The
> > power bar currently shows from 4 amp to 6 amp draw depending on the
> > server load. The APC unit above has a 16 amp IEC-320 C20 input.
> >
> > My question is: can I safely use this UPS because my equipment is

not
> > going to be drawing the unit's maximum power? The lady I phoned at
> > APC hinted (without saying directly) that I should be fine but

stuck
> > to the official line which was that I should upgrade the power feed

to
> > 16A for safety. Thing is that doing so will set us back a fair bit
> > each month, which doesn't sit comfortably given that I'm only

having
> > to do this to fix what is the data centre's fault!
> >

>
> --
> Mike Walsh
> West Palm Beach, Florida, U.S.A.


 
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Mike Walsh
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      03-07-2005, 08:11 PM

UPSs use what are essentially trickle chargers. It is assumed that the AC mains are active most of the time and the battery backup is seldom used. The power required by the charger is low. The charging current is relatively low and will not go above the designed current now matter how many batteries are connected. The drawback of this system is it might take hours to recharge batteries after a power failure of a few minutes.

(E-Mail Removed) wrote:
>
> Thanks so much for your response Mike. This is what my gut was telling
> me, but I'm glad of the sanity check!
>
> Just one last question ... would extra battery packs be likely to
> dramatically increase the draw after an outage? Obviously the worst
> thing would be for the whole lot to hum away nicely and
> successfully supply power through any outage only to blow the 10 amp
> circuit when power returns as it tries to draw current to recharge!


--
Mike Walsh
West Palm Beach, Florida, U.S.A.
 
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