From: Daniel47@teranews.com
On 04/01/14 00:21, Uncle Peter wrote:
> On Fri, 03 Jan 2014 12:52:45 -0000, Uncle Peter wrote:
>
>> I was wondering why this 2nd hand UPS I bought says 1500VA, 980W. Are
>> they assuming you don't have decent PFC on your computers? When did
>> they start putting decent PFC in computers?
>>
>> I tested (with one of those plug in energy meters) a computer running
>> a good graphics card and CPU flat out with a cheap power supply (CIT)
>> with "passive power factor correction" (along with a stereo playing
>> loud and two old LCD screens), as this is where the UPS will be used.
>> The meter indicated a PF of 0.71. I then tried a computer with a
>> Corsair power supply with "active power factor correction", running a
>> dual chip graphics card flat out, and got a PF of 0.98.
>
> This answer from Yahoo answers seems correct:
>
> "This is of the specification written by UPS manufacturers is widely
> misunderstood by users.
> The actual load that can be supported can be up to 1500 VA OR 980W.
> These figures MUST NOT be exceeded. Power factor is irrelevant.
> Thus with a PF of 0.98 the load can be 980W/1000VA (both figures are
> within the limits above, limited by W)
> With a PF of 0.5 the load can be 1500VA/750W (limited by VA)
> Battery standby time is determined by the W (watts) of the load. Thus
> if it will give 5 mins at 980W you can approximate that it will give 10
> mins at 490W."
>
> Presumably the invertor has a wattage limit and the transformer has a VA
> limit.
The transformer consists of two, inter-wound, inductors, one of which is
connected to a resistive-capacitive-inductive load. So the phase shift,
reflected back from the secondary winding into the primary winding will,
almost certainly, not be 1, i.e. purely resistive.
HTH
Daniel
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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