[AMRadio] Power factor

[John Coleman]

	The power factor of capacitors is never quite perfect that is if the
waveform across the capcitor is compaired to the wave form across the
resistive only load they will not be exactly 90deg difference.  This is due
to internal series resistance (not reactance) of the capacitor and the
internal shunt resistance of the capacitor (accumulative leakage and
dialectric loss). Electrolitics or notorios for poor power factor especialy
as the frequency increases.  Special capacitors are often used in coupling
the defection power to the coils of a deflection yoke on a CRT because some
capacitors will get hot and consume the power and also change the shape of
the defection current passing through the yoke causing nonlinear sweep.
This is also true of HIFI amplifiers where the speakers or connected in
series with a coupling capacitors.  It's been a long time since I fooled
with the math on this but servicing this stuff I have found that you can't
just replace a bad electrolitic with any thing that matches the value.  I
have also found that a lot of manufactures made monitors with a poor choice
of coupling caps to the deflection yokes.  Sometimes in order to get the
repair out and not have to worry about it I would replace a 1uf/400v
electrolitic with a 1uf/600v mylar.  Much larger and hard to get in but no
more trouble.

73, John, WA5BXO



-----Original Message-----
From: amradio-admin at mailman.qth.net
[mailto:amradio-admin at mailman.qth.net]On Behalf Of Donald Chester
Sent: Thursday, April 04, 2002 8:24 AM
To: billsmith at ispwest.com
Cc: amradio at mailman.qth.net
Subject: [AMRadio] Power factor






>From: "Bill Smith" <billsmith at ispwest.com>

>If the cap shows high leakage, or a high power factor, it is probably
> >spent, but if it acts as a new capacitor you have saved a good part.

What exactly do you mean by a capacitor's power factor?  How do you measure
it and exactly what are you measuring?  I am familiar with the concept when
talking about transformers, but what about capacitors?  I would assume the
power factor of a good capacitor standing alone would be zero, since the
(ac) current would lead the voltage by 90 degrees.

Don K4KYV

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