[Amps] The power of an oversized electrolytic capacitor /howmuch PS filter C is enough?

Thu May 10 09:35:08 PDT 2012

I suppose we could argue technicalities all day. To me damping is something
that reduces oscillations. Mechanical, a shock absorber. Electrical, lower
the Q of the circuit.

A power supply that is said to have "good regulation" does not have to have
feedback. 
Regulation in a power supply is holding the voltage within a certain range
when a load is changed a certain amount.

 All of the factors discussed will determine how close the voltage is held
as the load is changed. Resistance of the transformer, size of the
capacitors etc.

A ferro-resonant transformer or a tuned choke can supply excellent
regulation in a power supply over a certain load range with no feedback
involved.

73
Gary  K4FMX

> -----Original Message-----
> From: Al Kozakiewicz [mailto:akozak at hourglass.com]
> Sent: Thursday, May 10, 2012 11:46 AM
> To: garyschafer at comcast.net; amps at contesting.com
> Cc: ham_amplifiers at yahoogroups.com
> Subject: RE: [Amps] The power of an oversized electrolytic capacitor
> /howmuch PS filter C is enough?
> 
> To continue the physical analogy, you're describing damping, not
> regulation.  Adding mass to increase inertia may mimic the results of
> regulation, but only if the time interval of the measurement is
> relatively short.
> 
> For the purpose of the amplifier power supply discussion, I get the
> point.  But regulation is an active process, not passive, and requires
> feedback.
> 
> Al
> AB2ZY
> 
> ________________________________________
> From: Gary Schafer [garyschafer at comcast.net]
> Sent: Thursday, May 10, 2012 11:21 AM
> To: Al Kozakiewicz; amps at contesting.com
> Cc: ham_amplifiers at yahoogroups.com
> Subject: RE: [Amps] The power of an oversized electrolytic capacitor
> /how       much PS filter C is enough?
> 
> Think about this: if you place a resistor between the transformer and
> the
> filter capacitor your dynamic regulation will deteriorate. Thus the need
> for
> low resistance transformer windings and heavy primary lines. This is
> just as
> much "regulation" as is an active regulator, although not with the same
> precision.
> 
> A flywheel on an engine does provide dynamic regulation as well. It
> keeps
> sudden loads from dragging the rpm down instantaneously as well as
> smoothing
> the "ripple" of the firing cylinders.
> 
> 73
> Gary  K4FMX
> 
> > -----Original Message-----
> > From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]
> > On Behalf Of Al Kozakiewicz
> > Sent: Thursday, May 10, 2012 9:29 AM
> > To: amps at contesting.com
> > Cc: ham_amplifiers at yahoogroups.com
> > Subject: Re: [Amps] The power of an oversized electrolytic capacitor
> > /how much PS filter C is enough?
> >
> > Although I understand the point being made, filter capacitors, no
> matter
> > how large, do not provide "regulation" any more than a big flywheel
> > takes the place of a governor on an engine.  Regulation requires
> active
> > circuitry and feedback.
> >
> > OK, back to nuclear weapons design.
> >
> > Al
> > AB2ZY
> >
> > ________________________________________
> > From: amps-bounces at contesting.com [amps-bounces at contesting.com] On
> > Behalf Of Leigh Turner [invertech at frontierisp.net.au]
> > Sent: Thursday, May 10, 2012 7:19 AM
> > To: 'Jim Thomson'; amps at contesting.com
> > Cc: ham_amplifiers at yahoogroups.com
> > Subject: Re: [Amps] The power of an oversized electrolytic capacitor /
> > how      much PS filter C is enough?
> >
> > Hi Jim,
> >
> > There are two aspects to consider here; the static and dynamic voltage
> > regulation, and the amount of ripple on the B+ plate supply.
> >
> > In CW and SSB amplifier service the keyed and syllabic fluctuation of
> > load
> > defines the requisite dynamic regulation capability of the HV power
> > supply.
> > Achieving static and dynamic regulation under 5 percent would be good
> > design
> > practice. As for rms ripple voltage, a target of less than 2 to 5
> > percent of
> > the DC supply voltage under full load current would be considered good
> > engineering practice.
> >
> > A large energy storage capacitance on the HV rail makes sense from the
> > point
> > of view the amplifier load current requirements have a large peak-to-
> > average
> > ratio in SSB service. A stiff B+ voltage also helps with minimising
> IMD.
> >
> > For common 3 kV @ 1A amplifier power supplies, i.e. a load resistance
> of
> > circa 3000 Ohms, a reservoir capacitance of about 60 uF would be
> > sufficient
> > to yield the above respectable regulation and ripple objectives. One
> > might
> > double the filter capacitance to circa 100 uF for good measure; but
> > going
> > beyond that amount of capacitance would be a futile exercise in
> > diminished
> > returns.
> >
> > Now your 7 kV B+ supply corresponds to a PS load resistance of circa
> > 7000
> > Ohms, so there is an associated relaxation in the capacitance required
> > to
> > meet a given percentage ripple voltage objective.
> >
> > The tolerable ripple level superimposed on the HV plate supply above
> > which
> > incidental AM hum sidebands appear on the radiated signal is an
> > interesting
> > question; the anecdotal experience of Rich's friend with only 2 uF of
> > filter
> > capacitance suggests there's a large tolerance to ripple on the plate
> > supply
> > with the tube and tank circuit exhibiting a good PSRR.
> >
> > We can note the amplifier in question here uses a 4-1000 tetrode, and
> > that
> > such tubes exhibit a plate current virtually independent of plate
> > voltage,
> > i.e. tetrodes are a constant current device. Such a characteristic
> would
> > make it more immune to ripple and noise on the B+ plate supply.
> >
> > Leigh
> > VK5KLT
> >
> >
> > -----Original Message-----
> > From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]
> > On
> > Behalf Of Jim Thomson
> > Sent: Tuesday, 8 May 2012 5:19 PM
> > To: amps at contesting.com
> > Subject: [Amps] The power of an oversized electrolytic capacitor /
> >
> > Date: Sat, 5 May 2012 20:59:29 +0930
> > From: "Leigh Turner" <invertech at frontierisp.net.au>
> > Subject: Re: [Amps] The power of an oversized electrolytic capacitor /
> > overkill
> >
> >
> > I agree Rob; a fraction of that massive HV PS capacitance would create
> > an
> > unperceivable difference in the Tx performance and signal at a distant
> > Rx
> > station :-)
> >
> > Leigh
> > VK5KLT
> >
> > ### Leigh, how many uF in your opinion, do you suggest I use on a 7.7
> kv
> > No
> > load B+ supply.
> > What is the bare minimum I could get away with. I'm being serious
> here.
> > Rich Measures has a friend with a 4-1000 amp...and he only uses 2 uf
> for
> > a
> > filter cap...and No choke anywhere. Nobody hears any hum.
> >
> > On a similar note, a friend was on one night, toggling between his SB-
> > 220
> > and his Alpha 9500.  Nobody could tell the difference between the
> 1200w
> > of
> > the SB-220.....and the 1500w of the Alpha 9500.
> >
> >
> > -----Original Message-----
> > From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]
> > On
> > Behalf Of Rob Atkinson
> > Sent: Saturday, 5 May 2012 8:53 PM
> > To: Jim Thomson
> > Cc: amps at contesting.com
> > Subject: Re: [Amps] The power of an oversized electrolytic capacitor
> >
> > 832 uF at 7.7 KV.  No offense, but that's a waste of capacitors.
> >
> > Rob
> > K5UJ
> >
> > On Fri, May 4, 2012 at 9:28 AM, Jim Thomson <jim.thom at telus.net>
> wrote:
> >
> > > ###  BTW, My latest creation uses 24 x 10,000 uf @ 450 vdc caps, all
> > in
> > > series... and charged up to 7700 vdc. That's one bank.  I built a
> 2nd
> > > identical bank of 24, and parallel the 2 x banks together... onto a
> > common
> > > buss....
> >
> > ###  I got them for dirt cheap.  There is No way I would build
> something
> > like this by paying full price for new caps. I wouldn't buy a brand
> new
> > vac
> > cap from Jenning's either, they are cost prohibitive.  But I have
> > managed to
> > buy surplus, nib, sealed in the box, Jennings ceramic vac caps.   They
> > come
> > encased in a metal foil bag which has been vac sealed.  You poke a pen
> > knife
> > into it, and whoosh, the air rushes into the bag.  Once bag is
> removed,
> > then
> > you unseal the box...and the new vac cap is inside a box, lined with
> > foam
> > rubber on all 6 x sides.
> >
> > later... Jim  VE7RF
> >
> >
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