Choke Chat

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

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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