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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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