FW: Miniature Coils
Being a neophyte to the Tesla world I greatly appreciate the rhetoric
posed by the very knowledgeable people in this group! Before joining
the group I would have dismissed any claim that streamers could exceed
the secondary length as hype. The first coil I made back in the early
70's was 36" long wound with 40ga. wire (it had a few splices
were it broke during the winding phase). It never did any more than spark
up and down its length. At the time I had no knowledge of what was going on.
Now Robert has gotme! Malcolm as well, replying with 12-24" streamer lengths.
I wouldn't have expected such large numbers for such as small coil. Let me
say that my miniature coil with its ill suited parts comes nowhere near these
lengths. I would be very impressed with a 5" coil that throw of 12" arcs. :o
Before I do a SWAG on the system Robert built, described and passed on below, I would
like to pose another question. How much effect does atmospheric conditions
play on arc length? I'm looking for generalizations as to humidity, air pressure.
Here in Illinois we see quite a large range of humidity. Would I want a humid
or a dry day to measure my max arc length? If I move my miniature coil to 5000'+
altitude won't I get a long streamer? Some of you guys must have experience operating
coils in different locations.
I hope I never stop learning.
From: Robert W. Stephens[SMTP:rwstephens-at-ptbo.igs-dot-net]
Sent: Wednesday, May 01, 1996 7:13 PM
Subject: Re: Miniature Coils
>From: huffman <huffman-at-d0tokensun.fnal.gov>
>To: "'rwstephens-at-ptbo.igs-dot-net'" <rwstephens-at-ptbo.igs-dot-net>
>Cc: "'David Huffman'" <huffman-at-d0tokensun.fnal.gov>
>Subject: Miniature Coils
>Date: Wed, 1 May 1996 15:33:02 -0500
>I guess the prize could be a plate of electrons, but everyone problably
>has enough of them.
>I was just wondering who has built a small coil of resonable performance.
>I previously read that it becomes difficult since parasitics begin to overwelm
>Did the small coil you built produce 12"+ arcs? Could you describe the setup
>and how it performed?
>My coil system lacks the proper components to be a real performer, the cap
> being fairly lossy at the 3.4Mhz operating freq. is probably the weakest link.
>I simply took what I had laying around and in a few hours had a 'cute' (my wifes
>words) little coil.
>As for the 600cid mountain motor I'm sure its only lidling.
Boy you sure had some of us scrambling thinking that our ' big' coils
might have suddenly become obsoleted with a newcomer to the group
with unknown skills?
My little coil was 7 inch close wound length of #36 enamelled copper
on a section of black ABS pipe measuring an actual 1- 7/8" OD. The
topload was a hockey puck shaped brass piece with rounded edges about
the size of a smalll can of tuna (3.5 x 2 inches or so). The primary
was several turns of #14 solid copper on a 4-1/4 inch OD, ABS pipe
section as a cylindrical solenoid. I don't use ABS normally for loss
reasons. PVC is what I use mostly, it works great but easily carbon
tracks with heavy corona. The capacitor was two, 0.002 mfd ,12400
volt peak mica transmitting caps for a total of .004 mfd. Only one
half of my furnace transformer was used, therefore I had 5000 volts
available at 23 MA. The 60 Hz reactive charging current of my system cap
was 7.5 MA, which equates to just 38 watts. The spark gap was a two
series gap design blown lightly from a small fan. I don't even know,
nor did I care much what the operating freq was. Possibly around 600
This sytem was complicated by the fact that the secondary was not
placed coaxially inside the primary. It was remoted as a hand held
coil. A 10 turn #14 AWG pickup coil about 2 inches in diameter sat
within the primary, connected to an 8 foot length of RG-59 coax to an
identical 10 turn, 2 inch diameter coil around the base of the
remoted secondary. I'm sure this link introduced losses but it was
an interesting experiment which actually worked quite well.
I'm going to be a tease now and let you guess how long the output
streamers were. Gotcha!
Oh, by the way, there's no prize. Sorry.
If you'd like, I think you should forward this complete communication to
the group, I'm sure they would appreciate it's technical value, if
not its on-the-edge-of-your-seat drama! Ha, Ha.
Happy coiling!, rwstephens