[Amps] Power factor and choke vs resonant-choke input supplies

Robert Bonner rbonner at qro.com
Fri May 11 00:56:35 EDT 2007


It doesn't matter if it is tuned choke or regular choke Gary.  Without a
heavy bleeder the choke acts like a hunk of wire and the cap charges to cap
input filter voltages.

I have 100K ohms on the supply on my current amp.  It sould be 75 or 50K to
load the voltage down.

Once I key the amp and draw 300mils the voltage varies very little after
that up to full 2 amp load.  But I'm seeing 1000V drop from non-keyed to
full load.

That's another reason guys like cap input filters.  The same supply would
drop about 500 V with a 300K bleeder on cap input.

I lost two very nice oil caps a couple months ago.  The voltage was sitting
right at 4KV and the PS while in standby continued to climb.. It drifted up
to 4200 and that was that.

FYI PLASTICON CAPS have zero tolerance for over voltage.

BOB DD

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Gary Schafer
Sent: Thursday, May 10, 2007 10:26 PM
To: 'Barrie Smith'
Cc: amps at contesting.com
Subject: Re: [Amps] Power factor and choke vs resonant-choke input supplies


That is backwards. A choke without a gap will swing as the core saturates
early. Most normal chokes do have a gap to keep the core from saturating and
do not swing.
You don't want a swinging choke for a tuned choke circuit.
A tuned choke circuit requires a fairly high minimum load current to keep
the voltage from soaring.

Yes you can put a choke in the negative power supply lead just the same as
in the positive lead. But with a resonant choke circuit use a little caution
as the voltage across the resonant choke can be very high and could cause
breakdown of the transformer depending on what type of rectifier circuit you
have.

I would contact peter dahl and ask him what the minimum load current for the
tuned choke you have should be. You may "choke" (pun intended) at the amount
of minimum current required! Once you go below the minimum current the
voltage can soar quite high.

73
Gary  K4FMX


> 
> ----- Original Message -----
> From: "Harold Mandel" <hmandel at barantelecom.com>
> To: "Barrie Smith" <barrie at centric.net>; <g3rzp at g3rzp.wanadoo.co.uk>;
> "Borislav Trifonov" <bdt at shaw.ca>
> Cc: <amps at contesting.com>; <rbonner at qro.com>
> Sent: Thursday, May 10, 2007 2:18 PM
> Subject: RE: [Amps] Power factor and choke vs resonant-choke input
> supplies
> 
> 
> Dear Barrie,
> 
> Now you have a project!
> 
> First thing: See if your choke winding has a  gap. That's the big ticket
> hurdle, because without a gap, it can't swing.
> 
> Well, the choke and capacitor were purchased from Peter Dahl as a resonant
> pair, so I would assume that the 9 hy choke was proper for the job.  I
> will
> check it, none-the-less.
> 
> I was not aware that a resonant-choke was a swinging-choke.
> 
> Next, use your B&K LCR meter to measure the inductance. Can do, yes?
> 
> Yes.
> 
> Oh, well, no problem.
> 
> Build a rectifier out of some diodes and put some juice into the choke,
> but make a
> C-input filter with some small amount (2~4 uF) of capacitance and hook
> up a load resistor
> that will be more than the idle current you expect to crank.
> 
> Hook up an ammeter in the choke line. Turn the power off and put a
> capacitor across the
> choke leads. Lookit the amperage, write it down.
> 
> Start adding or substituting caps with lesser capacitance across that
> choke puppy and
> see where your jump in current occurs.
> 
> You could just hook up and do it without any juice at all, but that
> won't give you
> the dynamic performance point, which is always different than the
> calculated
> XsubC = XsubL point.
> 
> Anyway, send Tom Rauch an e-mail and ask him about testing chokes. (Har
> de Har, Har, Alice!)
> 
> I have heard that story and I'm not looking forward to this experiment.
> 
> Be careful out there. The streets are a jungle.
> 
> Not as much so as my ham-shack.
> 
> 73, Barrie, W7ALW
> 
> Hal
> 6L6GB
> 
> -----Original Message-----
> From: Barrie Smith [mailto:barrie at centric.net]
> Sent: Thursday, May 10, 2007 3:46 PM
> To: g3rzp at g3rzp.wanadoo.co.uk; Borislav Trifonov; Harold Mandel
> Cc: amps at contesting.com
> Subject: Re: [Amps] Power factor and choke vs resonant-choke input
> supplies
> 
> Peter:
> 
> Resonant-chokes may be placed in the negative lead?
> 
> Also, could you elaborate on the "close to it" resonance?
> 
> I have a largish power supply, using a Peter Dahl
> resonant-choke/capacitor combination,  that has never worked properly.
> I'd like to improve or rebuild the power supply so that it did work
> properly.
> 
> 73, Barrie, W7ALW
> 
> 
> ----- Original Message -----
> From: "Peter Chadwick" <g3rzp at g3rzp.wanadoo.co.uk>
> To: "Borislav Trifonov" <bdt at shaw.ca>; "Harold Mandel"
> <hmandel at barantelecom.com>
> Cc: <amps at contesting.com>
> Sent: Thursday, May 10, 2007 10:34 AM
> Subject: Re: [Amps] Power factor and choke vs resonant-choke input
> supplies
> 
> 
> > Why are you particularly worried abuot the power factor?
> > Some simulations a colleague did some years back suggests that in
> fact,
> the choke shouldn't be resonant, but very close to it, such that the
> choke
> looks like a very much bigger inductance rather than a straight
> resistance
> at the ripple frequency. This is done for minimum load, as the choke
> inductance will decrease somewhat as the load increases. That's how I
> very
> succesfully use tuned choke input: in addition, I filter in the negative
> lead, so you don't need to worry about the case to innards insulation n
> the
> capacitor when it's reasonable size metal cased oil cap. Incidentally,
> the
> chokes were always obtained by a process f scrounging - I've never
> bought
> one yet! That includes a massive 10H 1 Amp one set aside for a
> project....
> > I believe Tom, W8JI, has some hair raising tales about his first
> attempts
> at resonant choke input supplies....
> > 73
> > Peter G3RZP
> > _______________________________________________
> > Amps mailing list
> > Amps at contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
> 
> 
> 
> 
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