Re: Larger secondary more efficiency?

[Terry Fritz <twftesla-at-uswest-dot-net>]

Hi Alan,

At 04:31 PM 10/9/2000 +1300, you wrote:
>Hello all,
>
>I need some advice on materials.
>(Living in New Zealand, materials are difficult to find.)
>
>My power supply is 15kV -at-120mA, and
>I have a large amounts of 24AWG magnet wire 
>and 3/16 inch copper refridgeration tubing.  

Perfect!!

>
>I would like an 8" or larger secondary, to increase efficiency,
>but over 6 inches PVC pipe becomes too expensive for me.
>I asked around about cardboard tubes equivalent to sonotube, 
>(for forming concrete columns) but all I can obtain 
>is 300mm OD tube, (that's 11.8 inches). - BTW this is cheap.

I have PVC and Sonotube coils and I like the PVC better.  The Sonotube is
really strong but it does get frayed at the edges a little and basically
looks like "cardboard".  We also suspect that the Sonotube is very lossy
(if that makes a difference).  The PVC coils are rock stable and looks good.

However, larger diameter secondaries have higher coupling.  In this case it
is about .12 with the 6 inch and 0.2 with the 12 inch secondary.

>
>With 120 mA of current, can I use that large a secondary?
>(It's all I can get )
>I have heard that larger coils are more efficient, but surely
>there is a cut off point where efficiency starts to drop as coil forms
>get larger?

15kV at 120mA implies a 1.8kVA coil which should put out streamers about 72
inches long.  So a 30 to 36 inch secondary would be fine.  I like longer
secondaries to reduce racing arcs and primary strikes.  I would think the 6
inch dia. would be good but you may want a conical primary to help
coupling.  The 12 inch may have to be rasied a bit if racing arcs appear.
If you close wind, count on having about 15-20 primary turns but run the
numbers through one of the programs to check on all that.

cheers,
	
	Terry


>
>Thanks in advance,
>
>Alan Williams
>