[Prev][Next][Index][Thread]
Re: New Coiler: info
From: Thomas McGahee[SMTP:tom_mcgahee-at-sigmais-dot-com]
Sent: Wednesday, September 10, 1997 11:42 AM
To: Tesla List
Subject: Re: New Coiler: info
>
>
> From: Patrick J. Gustafson[SMTP:gustafpj-at-uwec.edu]
> Sent: Tuesday, September 09, 1997 4:12 AM
> To: Tesla List
> Subject: New Coiler
>
> Hello all,
>
> I have been patiently reading the list for quite some time now, but
I
> could not get my questions to post on the list. Thanks to Chip,
this
> problem has been finally resolved. Here are the concerns that I
have as
> of yet:
>
>
> 1. I have a two layer secondary coil with 28 gauge wire close
wound
> for 21.6" (both layers). The first layer is at 6" in dia. and the
> second layer is at 6.125" in dia. The calculated resonant freq's
are
> 108.71 kHz and 106.45 kHz respectively, and the calculated
inductances
> are 91.84 mH and 95.49 mH also respectively. Now since I layered
in
> parallel, can I add together the inductance values directly? ( i.e.
the
> new value would be 187.33 mH)
>
No. When the two coils are co-axial and in close proximity as yours
are, then they act like a single coil. In your case, the inductance
will be between 91 mH and 96 mH. The reason for this is that they
share the same magnetic flux, and so act as one single coil. What you
DO gain is surface area for the wire. This is very important in Tesla
Coils since the skin effect is very much at work. Also, inductances
add in series, not in parallel. In parallel they follow a 1/total =
1/first + 1/second law just like resistances do. It's easy to
remember... As you add more turns to an existing coil its inductance
increases. The new turns are effectively in series with the old
turns.
> 2. Should I be concerned with the differing resonant freq's when
> calculating the needed primary capacitance?
>
No. Effectively they will act like a single coil (for the same
reasons mentioned above). The Fres will be somewhere between 106.45
Khz and 108.71 Khz.
Others on this list have done this, and the two winding sets simply
act as if they were a single set, but made with a larger size wire.
> 3. How do you determine (a) the inductance (of chokes) needed to
stop
> the voltage spikes from reaching the NST's, and (b) what ratings
the
> parallel resistors that accompany these chokes should have?
>
Coilers on this list have reported good results with values ranging
from 1.5 mH to 10 mH. The value is not critical. The purpose of the
resistors in parallel with the inductors is to lower the Q of the
coil so that it does not ring up like a miniature Tesla coil. Good
results have been reported with values ranging from 1,000 to 10,000
ohms. The power rating of the resistors used has ranged all the way
from 5 watts to 50 watts. A good way to get the value needed is to
use five resistors in series. Thus, 5 1K ohm 5 watt resistors will
give you a 5K 25 watt resistance .
The chokes are to prevent spikes from killing the NST. The spikes
tend to be like high frequency transients, so 1-10 mH is more than
adequate. What is MOST important is that they can withstand about
30KV for a 9KV NST or about 40KV for a 12KV NST. Those are minimums,
by the way. I design for 60KV spikes using 15KV Neons. There has been
an ongoing discussion of choke designs on this List. See past posts
for the last 30 days or so for details.
> 4. What capacitance should I use for my protection cap. given the
> power supply below?
>
Most people seem to be using 500pf per terminal, grounded to the NST
case which must also be AC grounded. The voltage rating should be at
least double the NST PEAK rating. For a 12KV NST that would be 18KV
minimum. This assumes that you have safety gaps set to fire at your
NST peak rating.
> 5. For the protective spark gap for the NST's, how is the ground
> electrode incorporated into this?
>
The outer electrodes each connect to a neon transformer HV terminal.
The inner electrode (or electrodes) connect to the transformer case,
which MUST be connected to AC ground. Some people use the three
electrode version, some use a four electrode version. They are
electrically equivalent.
>
> Here are the specs. of my Tesla coil:
>
> Primary Coil - 16 turn, 1/4" soft copper tubing with 5/16" spacing.
> Inner dia. is 8" and outer dia. is approximately 25".
>
Sounds OK. The 8" diameter only allows 1" between the inside of the
primary and the base of the secondary. Many coilers have found this
to be a little too close. I recommend 1.5" to 2". An alternative is
to use a strip of polyethelene or polypropylene sheet to provide
additional HV protection at the base. An arc here is usually a POWER
ARC and can really chew up the base of the secondary.
> Secondary Coils - As stated above. Note: Went for inductance by
using
> 28 gauge wire, also to see if it can withstand the punishment.
>
> Power Supply - 15 kV -at- 90 mA NST's. ((3) 15 kV -at- 30 mA in
parallel)
>
You might want to start with just one 15KV 30 ma and then add the
others once you get the thing tuned to resonance.
> Toroid - 25" outer dia. with a 5" cross section.
>
> Spark Gap Electrodes - 3/4" thick by 2" long highly polished steel,
with
> 3/8" radius of curvature on one end.
>
Uh, steel is not really a good thing to use here, though it will
work. The heat and ozone do not make for a nice environment for most
types of steel. Steel will often turn brown on you really fast! But
try it and see what happens. Copper pipe is generally a better
material for the spark gaps. I have found that the larger the pipe
the better. Larger pipe has better thermal characteristics and thus
less flaming due to vaporized metal. A too-hot spark gap will flame
and cause great power loss and decreased output spark length. I
highly recommend forced air cooling. A vacuum quench gap is
EXCELLENT, and the only extra thing needed is a good vacuum assembly
from a vacuum cleaner.
> Spark Gap - Single static.
>
SINGLE static??? You mean ONE set of electrodes? Use at least six
sets of electrodes. Build an RQ style gap or something like it. ONE
set of gaps is going to give you really lousy results.
> Components not made yet:
>
> - Primary capacitor (Calculated to need about .0226 uF. Anyone
have
> problems with using mylar for the di-electric?)
AAAAAARGH!!!! Mylar has GREAT DC characteristics, but when it comes
to AC, it is really BAD NEWS!!! Stick to polyethelene or
polypropylene. Do NOT attempt to make a single cap rated at the
necessary voltage. Instead make four .0904 mfd capacitors each rated
at 1/4 the required voltage, and then connect them in series. For a
15KV NST the peak AC voltage is about 21KV. To allow for resonant
rise and give it a safety margin, you would want to go for about 40KV
rating. So make four .0904 mfd at 10KV poly caps and put them in
series. Skimp on the ratings and you will experience early demise of
the caps. Caps are expensive. Build them right the first time!!!
> - Protective capacitor.
See above. THESE guys can be almost any kind of cap that has the
required voltage and cap rating. In fact, a lossy cap HERE is
advantageous. Doorknob caps work well here, as well as mylar types.
> - Chokes.
See above.
>
>
> Some info:
>
> I am a Physic's major, mathematics minor at the University of
Wisconsin
> Eau Claire, so I am quite familiar with most of the terminology
involved
> in Tesla coils. This is my first Tesla coil project, which I am
> building for the Physic's Dept. (and they are funding!!) for
> demonstrations on inductance and E&M fields. I can already see
the
> limitations of these 2 coil systems, and may soon have to start
> researching into magnifiers.
>
> Any help greatly appreciated.
> Patrick Gustafson
>
Patrick,
I am glad that you have come out of lurk mode and are sharing with
the rest of us your endeavors in Tesla coiling. I hope the above
suggestions help you in some way. You will also find a wealth of info
in the archives for the Tesla List.
try one of these :
ftp://ftp.funet.fi/pub/sci/electrical/tesla
ftp://nic.funet.fi/pub/sci/electrical/tesla
http://www.funet.fi/pub/sci/electrical/tesla
They point more or less to the same site, but because of routing in
tcp/ip some may work while others don't because of servers down
between nic and YOUR site.
As a final comment : Nic can sometimes be down but not for long. The
usual
reason may be that there are already so many users in the system that
it
won't let any more - there are limits for the amount of foreign
visitors
like in all anon-ftp sites.
I have found that after I download one file that sometimes the site
tells me the URL I am asking for can't be found. I just try again and
it works.
Check out the Richard Quick (RQ) Docs especially, as they are
extremely useful in detailing the construction of spark gaps and
capacitors that were pioneered by Richard Hull of the TCBOR (Tela
Coil Builders of Richmond).
Hope this helps.
Fr. Tom McGahee