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Re: [TCML] Newbe's First Coil
Charlie,
My TT-42 coil gives 42" sparks using a robust 12/30 NST and a synchronous
rotary spark gap, and a 4" x 13" spun toroid. You coil is about this size, so
with adequate input power you can obtain that spark length. I drive my coil
with 140volts input so this causes the NST to draw more power than one might
expect. It's probably drawing about 800 VA if I remember correctly.
When I built an OBIT powered coil, it used a smaller secondary and toroid.
The toroid was 1" x 4" if I remember correctly and it gave a 13" spark using
a static multiple gap. I think i used just 0.0015uF for the tank cap.
http://futuret.110mb.com
links to various pages on my site are at the top left of the page, some other links
also.
Cheers,
John
-----Original Message-----
From: cbroring@xxxxxxx
To: tesla@xxxxxxxxxx
Sent: Sun, Jan 31, 2010 7:02 pm
Subject: 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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>
>
>
>
>
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