[Nut-upsdev] Re: CyberPower 685AVR and newhidups

[Charles Lepple]

On 10/31/05, Arjen de Korte <nut+devel at de-korte.org> wrote:
> It is true that if you have a power factor of one, you'll most likely
> meet the regulations. But it is not necessary to have a unity power
> factor to meet them. A synchronous induction motor will usually have a
> fairly poor power factor, but will meet the directive without doing
> anything for instance.

I was only using a motor as an example of an inductive device. I doubt
many NUT users are trying to critical motor loads with off-the-shelf
UPSes with poorly documented protocols :-)

And you're right, I don't have a good understanding of the EU
directive-- I was told that unity power factor supplies had a much
better chance of meeting the directive, and I guess I extrapolated too
far.

> > However, we only have a variable for "power", and often UPS manufacturers don't
> > distinguish between VA and apparent power.

should have been clearer here: it is hard to tell between VA and
apparent power *in the protocol stream* if the UPS manufacturer hasn't
made a distinction somehow.

> There is no way to make a conversion between (real) power (W) and
> apparent power (VA) without knowing what is limiting either of these in
> the device powering the system. In other words, there is no general
> mathematic way of calculating one from the other.

the "no conversions" idea was why I suggested separate variable names
for real and apparent power in the first place... it's a workaround
for not having proper unit support in the NUT client-server protocol.
Different numeric variable names can be assumed to be in different
units.

--
- Charles Lepple