UPS question

Erik Trulsson ertr1013 at
Wed Aug 11 21:59:01 UTC 2010

On Wed, Aug 11, 2010 at 11:20:42PM +0200, Oliver Fromme wrote:
> Ryan Coleman <ryan.coleman at> wrote:
>  > He thinks that at 500W needed it would give me about 12 minutes on
>  > a 1400VA.
> That W and VA numbers of the UPS are pretty much irrelevant,
> because they tell nothing about the capacity of the battery.
> Those numbers only give an upper limit on the power that
> the UPS can handle (i.e. you cannot connect devices totalling
> 800 W to a 500 W UPS, for example).
> In order to be able to estimate how long the UPS can power
> wattage, you need to know the capacity of the battery.
> The capacity is usually given in Ah units (Ampere hours).

Technically correct, but in practice you can often make a good guess
based on the W and VA numbers.  When you look at the specifications of
various UPSs one will find that a great many of them are specified to
be able to provide power for about 5 min when running at max load, and
proportionally longer when under lower load.
So for an UPS rated 1000W with a load of 500W it will probably be able
to power that load for about 10 min.
(There are of course UPSs that behave differently, but I believe they
are a minority.)

<Insert your favourite quote here.>
Erik Trulsson
ertr1013 at

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