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Re: Science Fair Project
From: Adam [SMTP:absmith-at-tiac-dot-net]
Sent: Wednesday, November 12, 1997 1:00 AM
To: Tesla List
Subject: Re: Science Fair Project
Hi, this is a multi part, very lengthy (but hopefully informative)
response to several of the previous responses. Enjoy.
>> It may not be necsesarry to buy a neon transformer, you may get away
>> with a car ignition coil...Feed the coils with 12 volts square wave
>> or some hundred volts in pulsed current....
>
>I know that this is probably a bumb questions that shows my ignorance, but
>what is "12 volt square wave" . I get the idea it means just feed it
>bursts of electricity? I've read you can do this with a 555 timer- Is that
>true, I would think the voltage would be a little high for a 555 timer...
You do not feed any coil directly with the 555, the 555 only generates
the low level square wave signal, which looks like this:
+---+ +---+ +---+
| | | | | | |
+---+ +---+ +---+ etc....
This signal from the 555 is used to switch high power transistors, either
standard Bipolar like the 2N3055 & 2955 or power mosfets, like the IRF5x0
family. All are available at radio shack, I believe. Unfortunately,
unless you have a specific schematic and plans available to you (like
from a past Radio Electronics magazine) you are stuck here. Designing a
solid state TC circuit from scratch is something you do after you get
your EE degree.
I would suggest that you start with a standard sparkgap-switched coil,
and use an oil burner ignition transformer or low power neon unit for the
main supply. Oil burner units are typically 10kV -at- 23mA (current
limited) and my idea of a low power neon would be 7.5 or 9kV -at- 20-30mA.
Due to their built-in current limiting and midpoint center tap, these are
probably less dangerous than automobile spark coils, which are not
internally current limited and can pull some pretty mean flaming arcs
when given enough continuous input (i've tried this :-)
>Anyway, I think you can build a tesla coil. While it's not even necessary
>to understand much about what is going on, it will help you troubleshoot
>when things go awry. Being 13, your biggest problems will probably be
>with money.
Oh yeah, money. Here it is best for you to prepare a convincing argument
to your parents that the Telsa Coil will be a superior educational
experience. Assuming your parents are typical middle class types (not
welfare/trailer-home types), getting them to spend a couple hundred for
the raw materials should not be a problem. In the scientific research
community, this type of begging is refered to--somewhat
euphemistically--as a "grant proposal" :-)
>You'll most likely have to buy the wire for the secondary at
>the very least.
Budget: $40-$50 + shipping for about 5lb of secondary magnet wire.
Try to find a surplus dealer that will sell you a contiuous spool piece
of wire (not multiple smaller spools). I think Nebraska Surplus sales
(http://www.surplussales-dot-com/) has this, but call all the surplus dealers
on Bill Beaty's homepage lists anyways.
>The rest can probably be scrounged.
Umm, maybe not the coil form itself, the toroid, the transformer and the
other non-building material products, examples (Typical home-depot-like
prices):
Budget: $12 for a 4" diameter by 10 foot PVC pipe
$5 for a can of polyurethane and another
$4-$5 for a brush
$4 for a bottle of mineral spirits (brush cleaning)
$1-$2 for 4" PVC endcap
$9 4" by 8 foot aluminum ducting for toroid
$5 2" wide by 50 foot roll of aluminum tape for toroid
$2-$5 assorted nuts, bolts and other fasteners
$??? Wood or Plexiglas and associated costs.
Optional: $8-$12 50ft 1/4" copper refridge tubing, for a nice primary.
>You may also have
>trouble getting neon sign transformers because of sign companies being
>afraid of giving/selling a transformer to someone your age.
Most definitely a problem. I am 23 with a BSEE and 10+ years experience
working with neons, pole pigs, potential transformers, microwave units,
etc... and most neon sign places *STILL* give me a hastle. I get around
this by bringing a photo of my 8" coil throwing 5 foot sparks over my
driveway, at which point most sign builders see that I mean business.
>From what I have observed, most of them should be more worried anout
their own neon sign-making employees, who are far more non-chalant with
high voltages than I will ever be!!! The trick is looking until you find
the right neon sign guy, who understands your project and the level of
adult supervision.
>Using light bulbs as resistors, you can probably get away
>without having a variac as well.
Not really practical. Light bulbs limit the power input a bit TOO
effectively. It is OK to just let the lower voltage neons and oil burner
units run at their full rated voltage, assuming you build caps that are
robust, and the safety gaps are set to a truly safe spacing. I typically
use 0.030"/kV for my safety gaps, with smooth copper pipe electrodes.
-Adam
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Adam Smith
absmith-at-tiac-dot-net
Epoch, Inc. Digital Music Project
www.tiac-dot-net/users/absmith/ Now with MP3! Musik. Macht. Macintosh.
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