Electrical Question - Sizing a backup generator

Posted on 2011-05-05
Last Modified: 2012-05-11
I currently have an APC SmartUPS module RT6000 with four additional battery packs.  See URL below for reference.  I also currently own a Huskey 5000 watt generator.  The Huskey has a 120/240V 20 amp twist receptacle.  The APC plug has an R6-30 plug.  Assuming that the draw off of the UPS is no more than 20 amps - should there be any issue using an L6-30 to L6-20 adapter so that the generator could power the UPS in the event of a general power outage?  Thank you for any insight.
Question by:amigan_99
    LVL 116

    Accepted Solution

    Your power draw for this UPS and it's batteries is going to be at least 4,200 Watts, this is very close to 5000 Watt capacity of your generation.

    At surge potential if all batteries our flat after a power outage, i.e. the in-rush current may well exceed your generators capacity.

    It's very close.
    LVL 116

    Expert Comment

    by:Andrew Hancock (VMware vExpert / EE MVE)
    I think if it was me, I would test and check the current draw with a clamp meter to check the maximum current draw from AC.

    The potential unknown here, is the four additional battery packs.
    LVL 1

    Author Closing Comment

    Excellent.  Thank you.  I will probably go with a 10KVA model instead - only about $1,000.
    LVL 116

    Expert Comment

    by:Andrew Hancock (VMware vExpert / EE MVE)
    Yes, far better, I've seen the front panel of a diesel generator blown off, due to incorrect sizing!

    (it never recovered!, requiring a crane, to crane in the new generator, and tree's to be cut down!).

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