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Carrying a Full Load (fwd)
---------- Forwarded message ----------
Date: Sat, 1 Aug 1998 13:23:39 EDT
From: RWB355-at-aol-dot-com
To: lochhaas-at-computerland-dot-net, tesla-at-pupman-dot-com
Subject: Carrying a Full Load
Hi Dave,
I'm an american coiler living in Germany at the time. Although I have built
quite a few smaller Tesla coils (under 1kVa) I plan on build a bigger one
(hoping to get at least 48" to 60" sparks). Let me see if I can put some light
in to your dark. Iīll try to answer your questions with- & without using your
favorite answers.
1. I have a beefy old bug zapper that's spent the last fifteen years in the
garage in storage so it didn't suffer much when I took it apart. It has a
transformer that will draw about a quarter inch arc across a gap. Can I build
a small Tesla coil with this?
Answer:
I doubt if you could use this device.
Reasons:
1.) The device probably uses a rectifer on the secondary, so your getting DC.
DC doesnīt work all to hot in a Tesla coil circuit (although it does work).
You simply get better harmonics on AC, which is what you want for your Tesla
coil.
2.) If your unit is a DC unit and the rectifer is enclosed in the xformer,
your out of luck, because you canīt seperate it. The rectifier is a high
voltage low current unit. If you were to wire this thing up in a TC circuit
you would probably blow the diodes.
3.) The main problem is the current output of the xformer. You definitly donīt
need kilowatts of power to kill a bug. For a TC the more the better (and more
dangerous). For my purposes I wouldnīt even think of using a pole-pig for two
reasons. I canīt get one over here in germany and second these things are
really more than lethal and I do have some experience with HV/High current
stuff e.g.I build my own Tig & MIG /MAG Welders). Nothing for a beginner. Read
the safety news on the TC ring and stick to it. Donīt ever think about being
foolish in this hobby. It will be your last mistake !!! It better to be a
living guy with a small TC, than being someone with a 2-million volt TC, but
dead. Lecture over.
Now back to your xformer: I would guess this thing has an output of less than
5mA. So 18kV times 0.005A= 90VA or 90 Watts maximum. This isnīt going to get
you any sparks longer than about 2" to 3" from a well designed TC. If I were
you I would use it for what it was designed: To zap bugs, otherwise trash it.
2. The secondary of the above transformer has a red stubby cylindrical
component that is marked with: MDC 10000M Z5R 18KV. What is
this thing?
Answer:
This is probably the diode I was talking about in #1
3. I've read that spark gap arcs, like arc welding arcs, emit harmful UV.
Does a Jacobs ladder also do this? What is the physics by which UV is
produced in arcs such as these?
Answer:
All types of spark emission give off harmful UV. When my tcīs are finished I
usually enclose the spark gap in some kind of heat resistant, opaque box. The
"sparks" you are seeing are really small electronic flames. If you donīt
believe this try the following: Using a small ignition coil connected to a
spark gap (secondary) and pulse the primary with a switch & a 12v dc power
supply. Place a piece of paper between the spark gap and hit the button a
couple of times. Take a magnifying glass and have a look at the paper. You
will see tiny holes with charred outlines. If you try the same with a small AC
(connected to 110V and no switch) HV xformer -at-30mA the paper will burst into
flames. Donīt touch the paper while experimenting. (because of the higher
energy involved 10kv x 0.03A=300W.). I recently used a microwave oven xformer
rated at 2.3kv & 700mA (relativly low voltage but high current, definately
deadly!! IxU=1610 Watts peak). After the arc was started I could separate the
electrodes (using a pieces of plastic pipe about 15" long) up to two inches
before the arc cut off. After placing a candle underneath the electrodes I
could draw spark up to 3" before the arc ripped off. The candle does two
things. First of all it pre-ionizes the surrounding air and it preheats the
electrodes, so you can draw longer arcs. I used berillium-copper as electrodes
in flat form (I was demonstrating a Jacobbīs ladder to a friend). These flat
electodes are about 1.5mm thick and believe me they were red hot after I quit.
If you want to view any kind of spark demonstartion for a longer (more than
5-10 sec) length of time you should use welding goggles (for electric
welding). Gas welder goggles or even sunglasses do not provide enough
protection. Remember your eyes donīt have any kind of pain sensors built in
and you only have the two you have built in.
4. I got to examine the fluorescent tube circuitry in this bug zapper and
realized I really don't know how this works. What I've got is an iron core
inductor in one leg of the AC feed that then goes to one pin at one end of the
bulb. The other pin at the same end goes to the starter (a neon bulb and cap
in parallel) and then goes to one pin at the other end of the bulb. And the
other pin at this end goes to the other leg of the AC. What's with this
thing?
Answer:
All fluorescent circs work the same way. You have three basic parts: An
inductor, a starter and of course the bulb (no dugh ?).
What you call a neon bulb is really a bimetallic switch. When you throw the
zillion volts house current into your F- lights the following happens: 110v is
not enough to start up the lamp. Inside of the FL-tube are two filaments, one
at each end, these are wired in series with the inductor and the starter. The
current flows through the inducter, starter and filaments. The inducter surves
two purposes. First of all it limits the current flowing thru the cold
filaments (its like a bulb saver) and secondly it provides the start kick for
the FL tube to ignite (really to ionize the gas as your bulbs donīt "burn").
After the filaments heat up (the tube contains rare gases and a small amount
of mercury. In a new tube that has never been used you can actually see the
mercury drops if you look carefully.) some of the mercury vaporizes. As the
electricity also flows through the inductor it stores energy in the
windings/ironcore. The "neon bulb" switch also recieves current and the
bimetallic strip heats up. After a while the switch closes and cuts off the
current to the inductor. The stored energy is now released and placed across
the tube (from one filament to the other side, where the second filament is) I
donīt know how high the voltage is but a good guess is a couple of kVīs. This
ionizes the gas inside of your FL- tube and it conducts (excited electrons).
Presto you have light!. The rest of the mercury vaporizes and helps to keep
the gas inside conductive. This is why FL-lamps need some time to reach their
operating brightness. The high voltage is no longer necessary because the gas
can be held ionized at a much lower voltage (110v). This is why FL-lights are
called cold cathode lights or simply cold lighting (It is not the color
temperature which gives these lights the name) The capacitor inside the
starter is just there for good looks. No, really it saves the bimetallic
contacts from burning as it absorbs some of the energy of the inductor and
prevents the contacts from oxidizing. The neon gas does the same and also
s it conducts) the bimetallic strip so that it can close. (neon gas
conducts in this space at about 70-90 volts) There is usually another cap
connected directly across the mains to serve as a RF surpressor (interferance
surpressor, so your neighbors donīt get pissed off each time you throw on your
FL-lights).
Here is a small experiment you can try (to show you what energy is stored in
the inductor): Take a small relay and connect its coil terminals to a low
coltage source (5v are enough): Place your fingers across the coil and
make/break the contact to your ps. You will be surprised as to what you feel.
This experiment is not dangerous, so donīt worry. Now you know why
professional circuits have a diode connected anti-parallel to the coil of the
relay.
The common FL- circuit has some drawbacks, however. As the tube gets older, it
becomes more and more difficult to start the lamp. You notice this in the form
that your FL-lights start to flicker and take longer than usual to get
started. In really bad form they even flicker when they are running. This
means you have to renew you bulb. Modern circs have an electronic starter.
This electronic starter has more than one advantage. The electronics in the
starter can produce a much harder cut-off (of the current), so that the
induced HV is much higher, therefore quicker starting. Older lamps start
better, too. As they have no moving parts they donīt wear out as conventional
starters do. Finally they have a safety circuit in case the lamp doesnīt
start, they cut off the current until you flick the switch off & on again.
This means dying lamps wonīt bug you with their annoying flicker and it keeps
RF interference to a minimum and reduces wear and tear on the lamp (if itīs
dead who cares) and more importantly on the inductor.
Using a FL-lamp in a tc circuit or in a battery powered light works somewhat
different. These lamps usually have a HV / HF (>2kv-at-40 khz-at-low amperage)
inverter powered with a transistor oszillator and a ferrit xformer. In these
cases the gas inside gets excited (just like you when you see your tc working)
and gives off emission as the electrons fall back into their stable state. I
donīt want to get into physics right now. You can read about this in some kind
of physics book. You donīt need the filaments in this circuit. This is why you
can use your dead FL-lamp to test your tc. It just has to have a good
envelope.
One last word. If you want to build big tcīs. Start out with a small one first
and build up your experience and building skills. The FL-lamp tc test
described above should only be used on small teslaīs (<1kVA input power).
About 90% of the tc experiments described elsewhere can be done with any tc.
The bigger ones are of course more interesting, but start small. For more
information on why read the saftey FAQ from the TC-Ring.
Well, I hope I could answer your questions (maybe, yes, no donīt you get it)
bye,
Reinhard
As one of my favorite sayings go: If it doesnīt work throw another million
volts across it (or use a hammer ?)