----- Original Message -----
From: "Larry Benko" <xxw0qe@comcast.net>
To: <amps@contesting.com>
Sent: Friday, March 08, 2013 6:02 PM
Subject: Re: [Amps] Freescale LDMOS devices
There are 2 type of power factor calculations.
For linear loads PF = true power / apparent power = cos(theta) where theta
is the angle between the voltage and current entering the device. Think
"motor" here for an example. This power factor CAN be corrected by a
shunt capacitor across the line.
For non-linear loads (like ALL power supplies linear or switching) the
calculation is considerably harder BUT after more math than anyone here is
interested in we get PF = cos(theta) * ( 1 / sqrt( 1 + THD^2) ) where
theta is the angle between the fundamental (60Hz or 50Hz) voltage and the
the fundamental current. The other term accounts for all the harmonics
that are generated and THD is the total power in all the harmonics as a
fraction of the total power. This case can NOT be fixed by a shunt
capacitor. Looking at any capacitor input filter shows the fundamental
voltage and current are very close to being exactly in phase unless the
power xfmr has a lot of leakage inductance. If I remember correctly even
with an inductor input filter where the inductor current never falls to
zero you can not totally fix the PF issue especially since most chokes
used for this purpose are swinging chokes which are non-linear. In the
case of a high frequency switching power supply the harmonic issues can be
filtered out restoring good PF but for linear power supplies removing the
120 and 180 etc. Hz harmonics while passing the 60Hz is not easy to do.
** Henry and others did it with a tuned choke and it worked well until the
cap started getting leaky and the C changed. BANG!
Carl
KM1H
In this country we pay for real power and not reactive power. The
electric meters I have played with (20 years ago) did a very good job of
only responding to real power. I loaded some down with large capacitive
loads which did not appreciably change the measured power consumption.
Larry, W0QE
On 3/8/2013 2:51 PM, Carl wrote:
So install a power factor correction cap at the mains panel.
Carl
KM1H
----- Original Message ----- From: "Roger" <sub1@rogerhalstead.com>
To: <amps@contesting.com>
Sent: Friday, March 08, 2013 11:23 AM
Subject: Re: [Amps] Freescale LDMOS devices
Curiosity, as this is something most hams are unaware of, or concerned
about power factor.
In practical terms just what does that mean to a QRO operator? Yes, I
know it makes the load appear larger than it actually is and if you draw
enough load it can be noticed by the power company. Still, no one here
in the states complains whether you draw 1 KW, or 15 with your station.
I've never heard of a commercial ham amp with power factor correction.
Do they exist?
So other than a bit of unneeded increase in your bill, what is the
problem where the single station is concerned "here in the states"?
73
Roger (K8RI)
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