Date: Fri, 13 Apr 2012 10:40:35 -0400
From: "Carl" <km1h@jeremy.mv.com>
Subject: Re: [Amps] Filter Capacitors
To: "Rob Atkinson" <ranchorobbo@gmail.com>, "Roger \(K8RI\)"
<k8ri@rogerhalstead.com>
Cc: amps@contesting.com
Message-ID: <06F3644C80174F748A720A59B65AA9CB@computer1>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
A choke is not a good idea unless great care is taken to eliminate/minimize
the switching spike which is present with tube and SS rectifiers. A scope is
mandatory especially if the choke and caps are not well overated for
voltage.
For decades this spike has been mostly ignored in literature and finally saw
daylight again when more boatanchor amps were being built and then the audio
types got involved and developed their own versions of reality.
I first noticed it about 10 years ago when checking ripple in a 2700V PS and
had to dig into the old handbooks and QST's and saw the "ancients" knew all
about it. I hadnt built a choke input supply since the late 50's and that
was simply using WW2 surplus from a BC-610 so obviously the design work was
already done.
Carl
## You folks are making a mountain out of a mole hill. You can easily model
all of this on Duncans PSUD. Link to it on GM3SEK’s site. The only thing
you
have to tweak is to add more diodes into each leg. Change it to 10 x 1N5408
or 6A10 and it wont crash on you. PSUD assumes the steady state load is
ALREADY connected to the output of the power supply. It also has the option
of soft start or no soft start.
## when playing with conventional choke input supplies, not the resonant types
that
henry radio used, you are in for an eye opener. When you 1st turn it on, you
get this
huge yo-yo oscillation on the P-P v waveform, that finally settles down.
what psud wont
simulate is a varying load, like ssb-cw. Once the supply is up and running,
and no more
soft start involved, is when the trbl starts up. Every time you hit the
key, you are slamming this
big load on it...and you end up toggling between full and no load. Every time
you hit the key,
that oscillation starts up, and P-P V is sky high, till it settles down. On
cw, that’s next to impossible.
## By playing around for hrs on end with psud, you can minimize the effect
some what.
Psud will handle anything from doublers to FWB to anything else. Then you can
use stuff like
L-C-L filters or C-R-C filters, or just C. Then its easy to see what the
P-P ripple voltage will
be for any given load, no rocket science here...and the software is dead on for
the most part.
You can also factor in the Z of the plate xfmr, and wiring back to main panel.
## In these 1960’s and 1970’s supplies, with the typ 8 x 200 uf caps in
series, like what was
used in a SB-220 or Drake L4B, ripple is typ 3%. Use a string of 600 uf
caps..and ripple is
down to 1%. Ripple is just inverse to C used. Rich measures still sells
his 560uf @ 450 vdc
caps. A few friends have used em in several projects. They work good too.
## back 40 yrs ago, 200 uf caps were used, cuz that’s all you could get,
that would fit inside
the typ box. Larger value lytics either did not exist, or were cost
prohibitive.
## These days, large value caps are everywhere. And no, they wont cook your
plate xfmr either.
I wired 8 x 2500uf caps in series for one of my L4B supplies, and it works
great. That’s
312 uf in total. Ripple dropped from 3% down to just .24% Dynamic
regulation is superb, it doesn’t
budge.
## BTW Roger, when you short out one of these large value lytics, it does NOT
cause the cap to explode,
why would it. Try this experiment some time. Run a pair of HV wires out to
your back yard, with the
contacts of a vac contactor wired across the leads. vac contactor also 100
feet out in your back yard.
Charge the cap up to 400 –450 vdc. Energize the coil of the vac contactor
remotely.
You will get a bang alright...and the bang will be 100 feet away..out in the
yard. Your cap
in the basement wont even break a sweat !
## put a 50 ohm 50-225 watt glitch R in series with a FAST HV fuse....and you
will never have a problem
with any high C supply. 3 kv divided by 50 ohms = 60A of fault current.
Its 60A of fault current
regardless of whether you have 25 uf or 250uf. All that happens is the
glitch R will LIMIT the fault
current to a safe value. Meanwhile the fast HV fuse will INTERRUPT the fault
current within 2 msec.
## You naysayers who keep saying High C filters cant or wont work, or are
a bomb, have yet to try it.
There are now several HV supplies built, using high C filters. And several of
the 7-10 kv no load variety
using 3900-5400 uf caps, 450 vdc type..and enough in series such that they are
only operating at
70-80% of their 450 vdc rating.
later... Jim VE7RF
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