Re: Choke Chat

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "R Heidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>

on 12/03/01 9:04 PM, Tesla list at tesla-at-pupman-dot-com wrote:

> Original poster: "Gregory Hunter by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <ghunter31014-at-yahoo-dot-com>
> 
> Dear List,
> 
> I'm not building anything new...yet. Just doing a bit
> of armchair engineering. I've recently become a fan of
> Richie Burnett's site, especially his page about DC
> power supplies and charging chokes. His explanation is
> so clear & concise, even a dimwit like me can
> visualize how the charging choke works. See:
> 
> http://www.richieburnett.co.uk/dcreschg.html
> 
> Now I'm no stranger to the HV DC power supply with
> charging reactor. I taught APN-59 Search & Weather
> radar (old, obsolete, still in service) for many years
> to Air Force apprentice avionics technicians. In the
> APN-59 power supply, a series charging choke & diode
> bumps 3600vdc up to about 6800vdc to charge a pulse
> forming network. The idea that a simple in-line choke
> could almost double the voltage was a difficult
> concept for many students, and I tried every analogy
> imaginable to get the idea across. If I ever find
> myself back in a radar classroom, I'm going to steal
> Richie's "weight on a spring" illustration--it's just
> too cool!
> 
> Pardon the ramble--let's talk about chokes. As Richie
> pointed out, a big drawback to the DC & charging
> chokes scheme is obtaining the chokes. To say that
> big, surplus HV reactors are rare is an
> understatement! One idea I've heard kicked around is
> using the secondary on a MOT as the choke. This has
> several drawbacks: 1) the bulk and weight of the MOT,
> 2) MOTs are only designed to hold off about 2kvac or
> 3kvdc--they could be subjected to considerably more
> stress in a TC power supply, 3) the closed shell,
> gapless MOT core is great for transforming, but not so
> hot for energy storage, which is what a charging
> reactor is really about.
> 
> If surplus chokes are rare, and MOTs are crappy, what
> about homebrewing? I've been eyeballing those 10 Lb
> boxes of 16 ga steel wire at Lowe's. This stuff is
> straight and cut about 16 inches long. It is meant to
> jam between 16" center-to-center studs to support
> insulation. My idea is to heat this 10 Lbs of wire red
> hot on the stovetop to anneal it, and then cut it to
> 4" lengths. Bundled together tightly, this would give
> me two short, fat, 5 Lb steel cores with a round
> cross-section. I could use easy-to-wind round bobbins.
> I would wind these with about 5000 turns each of 28AWG
> and use one choke on each leg of the DC PSU output. I
> have no idea how to estimate the inductance of such a
> choke. I'm thinking I would drive the thing with two
> series MOTs for 4kvac into a full-wave voltage
> doubler, and use the chokes to bump the resulting
> 12kvdc to roughly 20kvdc. Power control, as Richie
> pointed out, would be via a variable-speed ARSG (which
> I already have). Would my 5 Lb, 5000-turn homebrew
> chokes have enough inductance/energy storage to
> support a 2kva output power supply? If anybody has
> already explored this trail, please share.
> 
> Best Regards,
> 
> Greg
> http://hot-streamer-dot-com/greg
> 
> 
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> 
I am glad to see your posting. Whenever I suggest burned wire cores people
can't imagin that we used them 40 years ago. They worked then, they should
work now. We also used burned banding, but that is harder to use without
good shop tools.
   Robert   H