[iyonix-support] Re: UPSs and reflashing the ROM

On 28 Oct, Jeremy C B Nicoll wrote in message
  <4e7ce312deJeremy@xxxxxxxxxxxxxxxx>:

> So, I'm wondering if I should buy a simple UPS.  Can anyone recommend
> one?  What sort of VA rating?  One I've seen was described as having - I
> think - something like a 300W 500VA rating - how come the W figure isn't
> the same as the VA one?

Because VA and W aren't always the same thing... :-)

If you were to run a truly resistive load of the UPS, then you would
probably get 500W and 500VA out of it, as the power factor of a resistive
load is 1.00.  The problem is that even SMPS with power factor correction
don't have a truly unity PF, and the loads will still appear to be
inductive or capacitive instead of resistive.

As a result, the UPS manufacturer will derate the wattage (real power)
relative to the VA rating (apparent power).  Usually, it seems, the figure
of 60% is used.

You need to work out the required rating based on the real power in W of
the equipment that you connect.  The VA rating then takes care of itself.

-- 
Steve Fryatt - Leeds, England

http://www.stevefryatt.org.uk/

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