[Prev][Next][Index][Thread]
Re: VA vs. Watts (was Calculating VA)
"For most the term V*A is interchangeable with Watts. However,
as far as I know VA is used for devices which do not *consume*
power (like a transformer), whilst Watts are used for devices
that *consume* power (like a power drill)."
Not correct. Volt amperes are just that: the product of the voltage
and the current flowing into (or out of) a circuit. Watts are the
"real" or heating power of the circuit, and are the product of the
voltage and the "real" or in-phase component of the current. Watts are
the product of the voltage times the current times the cosine of the
phase angle between them. The "power factor" of a circuit is the cosine
of the angle between voltage and the current if expressed in per unit,
or 100 times that if expressed in percent.
Example: An induction motor can have a power factor of the order of
70%. (It is an inductive load.) If the voltage is 100 and the current
10 amperes, the motor would be "drawing" 1000 VA, but the real power
would be 10 times 100 times 70/100, or 700 watts.
Ed