Small tesla coil (1sq ft
From: Dale Hall [SMTP:Dale.Hall-at-trw-dot-com]
Sent: Thursday, June 18, 1998 4:25 PM
To: Tesla List
Subject: RE>Small tesla coil (1sq ft
RE>Small tesla coil (1sq ft) findings
Nice results on your small coil. Are you using a torus top load ?
As you may be aware secondary discharges up to 4X sec winding length are
reported. Achievable at optimized quench + field shaping using torus is 2-3X.
I worked with a student at the Calif State Science Fair in 1990 to achieve 2.5X
Sec height sparks from a coil only 10" high. Key to optimum performance was
submerging the PRI and SEC in mineral oil - radical, sometimes messy - but it
For less noisey dorm demos and messing around with new ideas:
For your dorm room consider using an alternate DC excitation mode. i.e.
replace the NST with a 13kV to 17kV flyback from a video monitor of TV set.
your 9kV ac rms NST = ~13kV pk
your cap rating = 12kV ac rms = ~ 17kV pk (so this is the DC level to shoot for)
Note that when you use DC the discharge rate will be slower depending on the
flyback/diode current supply capability vs Cap size, anywhere from 1 (lg C) to
50 (sml C) per sec depending on Cap size (~.1 recommended).
Note also that the Cap value when using DC may be arbitrarily increased for
longer sparks at the cost of longer charge times assuming the gap can quench
the higher peak current. I recommend .1uF to achieve longer length single
power discharge bangs (I get 9" from my Portable Battery powered (12v.04A)
6" Sec with 1.25J -at- 5kVdc & .1 & a vacuum switch (NO noise - great quench)
- mileage may vary in air, increased voltage should result in much longer
sparks J=c*v*v/2). Going to higher voltage flybacks from color monitors/TV's
allows the use of smaller Cap values and less peak current for the gap to
quench while dumping up to about 5J for really long single sparks. By the way
I've done this by sharing the flyback HV anode lead (alternate path out the top
of TV case) with the TV or monitor - nondestructively ! The CRT is just a big
glass Cap. I just unplug the filament socket to reduce HV current drain
(maximize available current for tesla cap charging.
Keep in touch from your dorm -at- UNofOK or ?
Dale, Redondo Beach, Calif
Date: 6/18/98 6:11 AM
To: Dale Hall
From: Tesla List
From: Jeff Corr [SMTP:corr-at-enid-dot-com]
Sent: Thursday, June 18, 1998 12:45 AM
To: tesla list
Subject: small tesla coil (1sq ft) findings
Hello all... in order to have a tesla coil in my college
dorm room next year :-) I had to construct a special one.
It is mounted on a 12"x12" plywood section, the secondary being only
The reason I post this here is I find it interesting this coil can produce
12" long sparks, the length of the coil itself.
Just thought that someone else might be interested in duplicating this
coil as it is small enough to carry anywhere, and still performs verywell.
Here are the specs :
power level - 9kv, 30ma 270VA
capactitor - .004uf , rated at around 12kv (physical dimensions 8" long, 3"
primary - helical, 10 turns of #20 solid copper, turns 1/8th inch apart.
secondary 1.5"x12", #32 copper enambled.
Spark gap, single gap, half an inch apart.
No safety gap, no chokes, just neon, primary, secondary, gap, and cap.
Enid, OK 73703