Re: current limiting choke

>From: Kristian Ukkonen <kukkonen-at-cc.hut.fi>
>To: tesla-at-pupman-dot-com
>Subject: current limiting choke
>Hello all,
>I'm currently designing a current limiting choke to use with my pole pig.. 
>I have all things ready for construction but I'd prefer to have a reality
>check :) before making the big, heavy and expensive choke.. That thing
>will weight about 50kg when ready..

Start out smaller. It will get warm over several minutes, just let it
cool. Mine weighs about 2kg +-.

>The basic goal is to be able to both use very low powers (1kW) and higher
>powers (10kW) with the same basic choke. The easiest way to this seems to
>use a large iron I-core (10*16*30 cm, permeability 13) and wind several
>layers of coil to the form so that each layer is separate. 
My first (and only one so far) is 1000 turns of #16/1.3mm, well that
is what I started out to do! I ran out of the 1.3mm at about 400
turns, wound another 100 turns using #18/1.02mm and then finished off
with #22/.64mm wire. I used a 12"/30cm by 3"/7.62cm PVC form (plastic
water pipe, large;) I filled the form with all the I sections from
some old transformers that I haven't built yet. About 3.8cm by 3.8cm
by 18cm. The air core inductance is about 1mH, the iron core is about
9mH. I also use 10 ohms of resistive ballast in parallel.

The 0.64mm wire got very hot very fast. To hot to touch in 2 minutes
at 10A. I removed it and replaced it with bifilar #19/0.9mm SCE wire.
(the only size larger than #40(hair size) at the surplus store;)

>Is there something I am missing in the design?

	Don't forget the inductive kick from the choke when the spark
gap opens! I shorted the common mode choke in my RFI filters together
this way. Since then, I've put a 50uF 600V "motor start" cap across
the RFI filter and haven't shorted it again.

Fun things to do: place 10ohms of resistance in series, remove iron
core, place small ferrite core inside. Stand out of the way, apply
power. Watch the ferrite core "shoot" out. Or, place your iron core
half way in, apply power, watch it jump in. Soon I will get a .6m
"bolt" to use as a core, place an Al ring over it and hope it will

(chip, all of these were with the pig, gap and TC connected, the TC
formed the part of the inductive ballast;)

	Regards, and thank you for your ftp site!