UPS question

Oliver Fromme olli at
Wed Aug 11 21:21:02 UTC 2010

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).

For example, a battery with 10 Ah capacity can deliver
10 Ampere for 1 hour, or 20 Ampere for 30 minutes, or
30 Ampere for 20 Minutes ...  and so on.
At a typical battery voltage of 12 V, 30 A would be 360 W.

So, theoretically a 10 Ah battery would be able to hold
devices that use 360 W for about 20 Minutes.  In practice
it will be less because no UPS has 100% efficiency.

Best regards

Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M.
Handelsregister: Registergericht Muenchen, HRA 74606,  Geschäftsfuehrung:
secnetix Verwaltungsgesellsch. mbH, Handelsregister: Registergericht Mün-
chen, HRB 125758,  Geschäftsführer: Maik Bachmann, Olaf Erb, Ralf Gebhart

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