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Re: [TCML] Newbe's First Coil
Thanks for the suggestions.
I just removed the pizza plate and wrapped the cookie tin with a length
of 4" aluminum dryer duct. This made a rather stable 18" diameter
toroid. Re tuned by one tap on the primary and it acts a little
different. No more sparks coming off the top load at all unless I
bring a grounded probe near it. Then I get about a 8-9 inch arc to the
probe. If i lay a screw driver on the toroid to make a sharp point
(no, I'm not holding it in my hand) I do get some discharge off the
tip 3-4 inches long. The arc to ground is about the same length as
before i re-did the top load but more intense now, so that's a step in
the right direction.
All connections in the 10kv wiring are made with sheet metal screws
directly into wood. Guess i need to fix that. I have some 1/4 nylon
or delrin sheet I can cut up for insulators.
The spark gap was the last thing I did so it was rather hastily built.
I'm amazed it hasn't caught the wood on fire yet! There are several
poor high resistance connections that probably raise the Q of the
primary circuit. The gap was set by making it as wide as I could and
still have it start with the primary capacitor disconnected. It looks
like a ball of fire in operation. I can make something heavier and
better insulated with a fan on it.
The primary windings are supported with wood rods. They are loosely
close wound and rely on air and the plastic jacket for insulation. The
wire says 600V insulation, rms I guess. With two layers of insulation
between each pair of conductors I am right around the maximum rating of
the insulation. This doesn't take into account leakage, but no signs
of shorting between turns yet. Anyone else use close spaced pvc
insulated Home Depot house wire for the primary inductor?
I just ran the thing for a few minuets with the new toroid top load
and couldn't detect any capacitor heating this time, but I'm leery of
putting any more power in the system with those capacitors and this
spark gap. I've been reading the list archives about capacitors.
Any Idea how much input wattage a coil of this size can take?
Charlie
-----Original Message-----
From: Lau, Gary <Gary.Lau@xxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Sun, Jan 31, 2010 4:16 pm
Subject: RE: [TCML] Newbe's First Coil
Hi Charlie,
I agree with all that Matt suggested.
Additionally, I suspect that your caps may be a problem. Ceramic caps
have a
very high temperature coefficient, meaning that their capacitance will
vary as a
function of temperature. So the primary tuning will rapidly drift as
it runs,
and won't be in tune with the secondary. I'm not sure that blowing air
on the
caps will help; if the exterior is getting warm, the interior will be
MUCH
warmer. Funny that only one gets warm though!
I don't see a problem now but this is something that may need to be
said. It
may appear that performance increases as you increase the gap spacing.
You must
resist the temptation to do this, as having it too wide will allow
voltages in
excess of what the OBIT can endure to develop.
Regards, Gary Lau
MA, USA
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of mddeming@xxxxxxx
Sent: Sunday, January 31, 2010 3:36 PM
To: tesla@xxxxxxxxxx
Subject: Re: [TCML] Newbe's First Coil
Welcome Charlie,
ANY coil that works on the first try IS a success!
Here are a few simple suggestions that might improve your results:
1) The pizza pan/ cookie tin combo is a problem. The thin edge of
the pan,
and the
sharp edges of the tin allow charge to bleed off, reducing peak
voltage. The
fatter
and more rounded edge of a toroid allows more charge build-up. A
piece of
aluminum dryer duct or foil-covered Styrofoam doughnut will serve you
much
better.
2) Your spark-gap definitely has heating problems. If you are not yet
going to
use a
multi-gap, then at least do the following:
(a) Use heavier, brass, round-headed bolts or threaded rods with
brass balls.
Brass
conducts heat and electricity better than steel, and larger terminals
mean
better
heat dissipation. Rounded terminals mean less corona loss.
(b) Put a fan or other blower on the gap. Hot, ionized air in and
around the
gap
causes it to fire sooner preventing full charge build-up.
(c) Slightly reduce your gap width. 5-6 mm (1/5 to 1/4 in.) will
prevent a
misfire from
overvolting your transformer and your caps.
3) Make sure that none of your OBIT HV connections are mounted
directly into
wood. Even at only a few thousand volts, wood starts to become
progressively
conductive becoming both a power drain AND a fire hazard. Use ceramic
or HDPE
insulators to support the gap and all HV wiring.
4) Blow air onto your caps also. As they warm up, they change value
and spoil
the
tuning, even if the heat doesn't damage them.
5) It is not clear how or what you are using to keep your primary
turns
properly
spaced. Also, make sure your tapping clips are not touching / arcing
to the
turn
below.
These should be relatively inexpensive and quick improvements without
having
to
rebuild everything. Let us know your progress.
Matt D
-----Original Message-----
From: cbroring@xxxxxxx
To: tesla@xxxxxxxxxx
Sent: Sun, Jan 31, 2010 1:21 pm
Subject: [TCML] Newbe's First Coil
Hello to the members of this list. For no particular reason I built a
Tesla
Coil this
winter. Just got it running, more or less. So (hopefully) here are a
couple of
photo's
of what I put together.
http://img651.imageshack.us/img651/5567/1000420.jpg
http://img683.imageshack.us/img683/5931/1000424e.jpg
http://img651.imageshack.us/img651/5043/1000425.jpg
http://img651.imageshack.us/img651/5164/1000427.jpg
The transformer is a 10kv 23mA oil burner trans. Primary is about 12
turns #
14
sold house wire 10" diameter with a couple extra taps available.
Secondary is
1300
turns #27 on 3.5 inch pvc. Spark gap is 2 nails spaced about 5/16"
Capacitor
is two
6000pF 30kv hokey puck ceramics, and one shows a slight temperature
rise with
use. Top load is a cookie tin and bent pizza pan. The ground is the
house
wiring
tied in to an extensive ham radio/ lightening ground system.
It really doesn't work that great. I removed a coupe turns and moved
the tap
around
to get the best coupling I could. I get a ring of 2 inch sparks of
the pizza
plate. I put
a screwdriver on top and get 3-4 inch sparks off that. I haven't
tried
bringing a
grounded probe to the top load yet. Anyway, I read that the ceramic
capacitors
are
not really durable and one of mine shows some heating after a minuet
or so of
on
time to. I think I need to work on that next. I expected a little
more out of
it even with
the 250 watt power transformer.
I need to figure out how to ground the thing. I need a better
capacitor. I
have lots of
big transformers and DC power supplies to play with once I get the
coil
working a
bit better.
Any suggestions are much appreciated.
Charlie
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