[iyonix-support] Re: UPSs and reflashing the ROM
- From: Steve Fryatt <lists@xxxxxxxxxxxxxxxxxx>
- To: iyonix-support@xxxxxxxxxxxxx
- Date: Sat, 28 Oct 2006 15:51:01 +0100
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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