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Re: Neon XFRMR Protection


>>From scotty-at-wesnet-dot-com Thu Mar 28 09:12 MST 1996

>Hello David,
>
>>  Well, I have been following the posts concerning RF filtering and have come
>> up with a design for my resonator,.......... 
>> ..............Now for the filter. I have 8 T-250-B
>> toroids and 2 Arnald toroids from Burt. Now I plan on winding them with 50-60
>> turns of 20-22 guage single strand hookup wire rated at 600 volts and placing
>> 5 on each leg for about 3 mH (?).
>
>You don't need to use so many cores.  You are in no danger of flux saturation.
>I currently am using these same cores with approx. 115 turns in 2 layers for
>a measured value of approx. 3 mH each.  I am using 2 in series per leg.  If I
>were to use only one per leg, I would still be at less than 10% of the maximum
>flux density for these cores.  I use 24 gauge hookup wire, and that is plenty
>big for the amperage.  I am planning on winding a few more double layer units,
>but with magnet wire.  I should be able to get the value up to 6 mH a piece.
>Will they burn out with the magnet wire?  They shouldn't, but I'll let you know
>after I run them.  Save your cores.  Wind more wire per core for higher
>inductance values.  Just use plenty a dielectric between layers.  I used
>standard electrical tape.
>
Scott,
	I'm using 100 turns of #24 A.W.G. magnet wire, 2mH, and have
had no interturn arcing. I do have some arcing to the core with 2
layers of 7 mil electrical tape.

[snip]
>The resistors should dampen out the resonance nicely.  Here is something that
>many may be interested in;  I have just looked at the schematic of a commercial
>line filter recently and noticed that there was a resistor across the 2 legs of
>the filter, between the 4 chokes in the filter.  I couldn't help but wonder, is
>that filter there to eliminate/reduce resonance within the filter?  I had no
>other explaination.  There was no value indicated.  I have some 400 megaohm
>high voltage resistors that I could try in my high voltage RF filter to see if
>that works to reduce the resonance.  If it does, the power wasting 2.5 Kohm
>series filters could be eliminated.  Thoughts?
Scott,
	Are the resistors across the caps in your power line filter?
If they are, they are to discharge the caps when one unplugs the
filter from the mains.

Those 400meg resistors in series with your chokes will drop the RF
seen by the neon to about 0.1 volts:) I just ran a spice simulation on
it! Of course, you would't get a very big spark:)

If you send me your TC primary, cap, choke, bypass cap numbers, I'll
be glad to run a spice simulation for you. The 400meg resistors in
parallel with your bypass cap will not dampen the resonance.
>
>> So now if anyone can see any gaping holes in this setup please show no
>> mercy in the criticism, as so the RF does. I am looking for about 90%
>> reduction in the RF back to the neon and am willing to lose some power threw
>> the Caps. Also, if I am sigifigantly off in estimating the inductance value
>> of the chokes, please anybody who has actually measured or knows better, let
>> me know.
David,
	those toroid run 2mh/100 turns. it's a squared function, so 50
turns would give you (50/100)^2 * 2mH = 0.5mh, 200 turns would give
you (200/100)^2 * 2mh =  8mH.

[big snip]
>Richard Hull indicates that the seconday of these transformers has a very large
>inductance value.  I too have measured them with an LCR meter and it is in
>Henrys.  Since the core "disappears" (I think we can agree on that), we are
>effectively left with an air core inductor at operating frequency.  Still, with
>that many turns, we should have a high inductance, as pointed out by Richard.
1/2 winding from a 15KV 60mA neon, air core, = 8.29H Q=2.6 Rdc=27K.
note: the previous numbers don't all calculate, at least 1 is off.
[snip]

	jim