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Re: Got a few questions
From: Rick Holland[SMTP:rickh-at-ghg-dot-net]
Sent: Saturday, September 13, 1997 5:15 PM
To: Tesla List
Subject: Re: Got a few questions
Tesla List wrote:
>
> From: Kevin Radtke[SMTP:umradtke-at-cc.UManitoba.CA]
> Sent: Friday, September 12, 1997 5:00 AM
> To: Tesla List
> Subject: Got a few questions
>
> Hello Everyone,
> I posted a fairly long description of my Tesla coil last week
> hoping for suggestions on improvements, but I guess the mailing was a bit
> long for anyone to read through so I'll just be a wee bit more breef this
> time. I've just got a couple of questions.
>
> 1. Which set up is better.
>
> A) _________Cap______________
> I I
> spark gap xsfrmr
> I________Cap_____________I
>
> B)
> Primary____________Cap__________
> I
> xsfrmr
> Primary__________spark gap_____I
>
> Are the two caps in parrallel the same equivalent capacitence as
> the one in B)
>
The "two caps in parallel" are actually in series. When the spark gap
fires it creates a type of short circuit or path of low impedance. This
means the caps are effectively in series with each other and the primary
winding. I have heard on this list that this is a preferred method as it
divides the voltage and discharge strain over two caps instead of one.
Of course, they should be matched as well as possible to divide the load
equally. The "b" circuit should definitely *not* be used as it makes the
secondary of the supply transformer an integral part of the high
frequency/high voltage circuit. This will destroy the supply transformer
in a very short time.
> 2. After burning out two 5kV transformers we read up on protection and
> installed a safety gap and two chokes like this.
>
> 100 turns of 28awg around 1/2" wooden dowel
> ///////////|________
> | |
> 15kV 30mA transformer
> | |
> ///////////|________|
>
> the gap has enough clearance so that 15kV just won't arc over.
> During operation of the coil this gap fires quit often and is really
> hurting performance of the coil. Directing a small fan at the gap reduced
> the number of times it will fire but has not eliminated it. What's going
> on and how do I fix it?
>
> Thanks in advance for any help you could give me.
>
> Kevin Radtke
The chokes should probably be a little bigger, since the gap is firing
so much. You said that 15Kv "just won't arc over". Try widening the gap
a tiny bit. The transformer should be able to handle a couple of hundred
volts over voltage rating. Also, you might add some high voltage
"doorknob" (try 500 pf at 25 Kv)type caps from each transformer lead to
the RF ground. Do not use the transformer ground since it is probably a
part of the house wiring and is not designed to dissipate voltage at the
frequencies of a TC tank circuit. Using the house ground means you're
injecting high voltage spikes into the house wiring system with almost
surely disastrous effects on your tv, stereo, computer, and possibly
other hardier appliances.
Hope this helps. Good luck and be safe.
--
Rick Holland
The Answer is 42