Space Winding - was What to look for...

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Tesla729-at-cs-dot-com>

In a message dated 7/12/01 12:45:59 AM Central Daylight Time, 
tesla-at-pupman-dot-com writes: 


>
> . I've heard of 
> a few using fishing line between turns, but this must be a very slow task 
> to accomplish (similar to 
> handwinding a coil). If spacing is consistent, the form coating should be 
> sufficient and the coil 
> should work as good as one wound with coated wire. Spacing consistency is 
> the key to success in a coil 
> wound with bare wire. 
>
> Bart 


Hi Bart, all, 

I have used the fishing line to space wind secondary coils in the 
past, although it was still with enameled magnet wire. At that time, 
I was still under the impression that the windings would arc to 
each other unless spaced apart. I can remember my surprise 
when I close wound an 8" X 20.5" secondary for a 15/120 NST 
system w/ # 20 magnet wire and the finished coil yielded over 5 ft. 
long streamers with NO secondary coil failure! I had problems with 
exploding mylar caps and NST failure, since I was still influenced 
by the old school of air cored RF chokes at that time and was a 
little too cavalier with my SG spacing, but never secondary failure. 

BTW, when I did use nylon fishing line to space the secondary 
windings, I always just left the fishing line in place with the 
coil when complete. I'd heard of removing the fishing line when 
complete, but I found this extremely difficult to do w/out mes- 
sing up the coil. I no longer use fishing line to space the sec. coil 
as I don't find it neccessary. 

There are, of course, pros and cons to space winding secondaries. 
Some say that space winding is better due to the proximity effect 
of the neighboring windings, which is supposed to cause increased 
losses. However, the inductance density is also decreased by space 
winding and this is not a good thing. So you have to weigh the facts 
when deciding whether to space wind you secondary or not. I've 
wound my 12" X 38" long secondary for my ASYNCH rotary, 10 
kVA pole pig system close-wound with double-coated #16 magnet 
wire and I'm very satisfied with its perfromance. I did have to reduce 
the pri/sec coupling from my original design to stop turn/turn flash- 
over from the huge input powers, but once the coupling was optimized, 
I had no more problems throwing ~ 10 ft. sparks from this system 
with no secondary flashover problems or racing sparks. 

My $.02, 
David Rieben