Re: [OT] VA=W?

[Anders Frihagen <anders.frihagen@xxxxxxx>]

At 00:12 24.05.2003 +0100, you wrote:
>So what is the difference between VA and watts, because I'd always
assumed
>they were the same. Obviously, they are both a measure of power. I
guess the
>answer lies in the fact that I'm talking about AC and the voltage is
>expressed as an RMS term or something like that.
>
>So why are transformers rated in terms of VA instead of W? And is there
any
>difference?

Watt are the unit for power, and is defined as U*I for DC and AC with a
resistive load.  However if the load are non resistive, inductive (as in a
electric motor) or capacitive (I can't really think of a capacitive load..)
the current will be out of phase with the voltage.  There are two ways of
dealing with this when it comes to calculating power, one is to use the
formula P=U*I * Cosine (of the difference in phase) you will have a really
correct answer and you will pass your EE exams.  In practice (and for low
power applications) you just say P=U*I and forget the phase question all
together, but use the unit VA to indicate that this is a simplified result.
Anders


I think I will write a book about people cloning prehistoric pigs
and call it "Jurassic Pork"