[AMRadio] Power factor / Capacitor engineering conciderations

Sat Apr 6 17:20:54 EST 2002

hey john,please tell me about capacitor's in modern radio's.I have a kenwood
ts-870 and icom 756pro.theese semiconductor's if kept in a stable enviroment
free of dust etc. can last at least 25 years without failure....i would
think.what is your opinoin on this john or anyone with an opinion on this
.thank you

tony k2vi
----- Original Message -----
From: "john_walker_beasley" <jbeasley at earthlink.net>
To: <amradio at mailman.qth.net>
Sent: Thursday, April 04, 2002 10:56 PM
Subject: Re: [AMRadio] Power factor / Capacitor engineering conciderations

> Thank You !
>
> WAØSTX
>
>
> ----- Original Message -----
> From: "George Pritchard" <gpritchard at comtechpst.com>
> To: <amradio at mailman.qth.net>
> Sent: Thursday, April 04, 2002 10:16 AM
> Subject: RE: [AMRadio] Power factor / Capacitor engineering conciderations
>
>
> > A short capacitor tutorial:
> > The "power factor" for capacitors is mostly an issue with "higher
> frequency"
> > due to the "ESR" (equivalent series resistance)of the capacitor at the
> > operating frequency, and to some extent the choice of dielectric. At
> 15,750
> > kHz for horizontal sweep circuits and HiFi audio, the inherent
inductance
> of
> > the capacitor degrades the expected nominal capacitance value to some
> > degree. The "ESR" of a capacitor is a very interesting science across
the
> > frequency spectrum. If the frequency is high enough, the capacitor
> > eventually becomes and inductor for two mechanical reasons. First... the
> > length of the wrap, or plates, and the diameter or width of the wrap of
> the
> > foils and dielectric is an inductance by design. This inductance is
> > partially in series and to a lesser extent, in parellel. The lead length
> and
> > thickness of the leads also adds inductance in series with the
capacitor.
> So
> > far... none of the above is a problem at 60 or 120 Hz for DC filtering
of
> > rectified AC. Even the dielectric heating at these low frequencies is
> > generally insignificant (assuming low leakage), and also depends on the
> peak
> > to peak AC amplitude apapplied to the cap and what the RMS AC current
is.
> > Leakage current is the main culprit and destructive. As the frequency
goes
> > up... all of the above play a significant roll on the effectivness of
the
> > capacitor and can lead to heating. For this thread concerning power
supply
> > filtering at 60, 120 or even 400 Hz, use what ever you have and it will
> > work, as long as the dielectric / electrolyte is is not dried out or
> > distorted. Standard electrolytics are fine for DC - 400 Hz. For
> frequencies
> > 400 - 1000 Hz use mylar, paper (not the best), metalized polyester. For
> > "audio" 1000- 20,000+, use higher "quality" types, polyester,
> polycarbonate,
> > tantalum (especially in switching power supplies). These types will also
> > have less leakage currents. For "RF" above 20,000+... use ceramic,
Teflon,
> > glass, saphire and AIR dielectrics. The ESR of capacitors finally "plays
> > into" another condition at VHF and higher RF frequencies: The resonant
> > frequency of the capacitor at some elevated frequency! It will be a
series
> > and parellel (has both) resonances at two different frequencis. It
should
> > also be noted that a voltage DE-RATING of 100% is typical for Military
> > engineering, but for power supplies in our ham stuff... 25% over rating
is
> > fine (50% if you can fit it in!). Now for temperature conciderations:
> > Aluminum electrolytics are the worst. They loose 50% of the capacity at
> cold
> > temperatures (below 0C). Tantalums are much better. Ceramics are the
best.
> > All the trade-off are physical size and dielectric when it comes to
> > temperature issues. I hope this is not to boring and is informative.
> > George (project Engineer for Militay avionics and RF microwave). Thanks
> for
> > the chance to pass on info on this most interesting subject...
CAPACITORS
> >
> > -----Original Message-----
> > From: amradio-admin at mailman.qth.net
> > [mailto:amradio-admin at mailman.qth.net]On Behalf Of John Coleman
> > Sent: Thursday, April 04, 2002 10:01 AM
> > To: amradio at mailman.qth.net
> > Subject: RE: [AMRadio] Power factor
> >
> >
> > 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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