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UPS Power Draw

Discussion in 'Hardware' started by Louis Aslett, Mar 7, 2005.

  1. Louis Aslett

    Louis Aslett Guest

    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/techspec_index.cfm?base_sku=SUM3000RMXLI2U),
    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
    Louis Aslett, Mar 7, 2005
    #1
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  2. Louis Aslett

    Mike Walsh Guest

    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.
    Mike Walsh, Mar 7, 2005
    #2
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  3. Louis Aslett

    Guest

    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.
    , Mar 7, 2005
    #3
  4. Louis Aslett

    Mike Walsh Guest

    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.

    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.
    Mike Walsh, Mar 7, 2005
    #4
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