Re: New Coiler
From: Mark S Graalman[SMTP:wb8jkr-at-juno-dot-com]
Sent: Wednesday, September 10, 1997 11:57 AM
Subject: Re: New Coiler
Patrick, I forgot to mention that a single static gap at this power
level simply will not perform.
I would suggest using 8-10 series gaps at about .025" each placed in a
strong air flow from a couple
of good muffin fans
On Wed, 10 Sep 1997 09:51:32 -0500 Tesla List <tesla-at-pupman-dot-com> writes:
>From: Mark S Graalman[SMTP:wb8jkr-at-juno-dot-com]
>Sent: Wednesday, September 10, 1997 7:28 AM
>Subject: Re: New Coiler
> Hi Patrick,
> Here's my 2 cents worth:
>On Tue, 9 Sep 1997 22:22:57 -0500 Tesla List <tesla-at-pupman-dot-com>
>>From: Patrick J. Gustafson[SMTP:gustafpj-at-uwec.edu]
>>Sent: Tuesday, September 09, 1997 4:12 AM
>>To: Tesla List
>>Subject: New Coiler
>>I have been patiently reading the list for quite some time now, but I
>>could not get my questions to post on the list. Thanks to Chip,
>>problem has been finally resolved. Here are the concerns that I have
>>1. I have a two layer secondary coil with 28 gauge wire close wound
>>for 21.6" (both layers). The first layer is at 6" in dia. and the
>>second layer is at 6.125" in dia. The calculated resonant freq's
>>108.71 kHz and 106.45 kHz respectively, and the calculated
>>are 91.84 mH and 95.49 mH also respectively. Now since I layered in
>>parallel, can I add together the inductance values directly? ( i.e.
>>new value would be 187.33 mH)
> No, when inductances are placed in parallel the total value goes
>and will be less than
>the least value of inductance, in this case the total inductance would
>about 46.8 mH
> Thats alot of inductance for a 21" tall coil, The concern I have at
>this point is I feel for the amount
>of power your going to run into this coil the height of the coil maybe
>>2. Should I be concerned with the differing resonant freq's when
>>calculating the needed primary capacitance?
> No, the two frequencies are close enough, you could just call it
>khz. But, in reality this
>frequency means little because the actual secondary frequency will go
>down with the addition of
>a top load such as a sphere or a torus and then drop maybe another
>khz while under sparking
>>3. How do you determine (a) the inductance (of chokes) needed to
>>the voltage spikes from reaching the NST's, and (b) what ratings the
>>parallel resistors that accompany these chokes should have?
> Here IMHO there is no need to calculate, I would shoot for about 50
>100 uH in a air wound
>choke and a few mH in a ferrite core choke. The De-Qing resistors are
>placed in parallel with
>the chokes but are placed in series with them and for a NST I would
>1 K ohm 25 watt wirewound.
>>4. What capacitance should I use for my protection cap. given the
>>power supply below?
> Two old TV style doorknobs (500 pf 20 kv) in series from each HV
>terminal to the transformer
>case work well. This value really isn't critical, I'd just try to stay
>between 100-250 pf and keep the
>leads short. What you really DON'T WANT is to have a resonate point in
>your filter (choke) system
>anywhere near the actual operating frequency of you coil.
>>5. For the protective spark gap for the NST's, how is the ground
>>electrode incorporated into this?
> The ground electrode is the center electrode and it is tied to
>transformer case which is tied to
> earth ground.
>>Here are the specs. of my Tesla coil:
>>Primary Coil - 16 turn, 1/4" soft copper tubing with 5/16" spacing.
>>Inner dia. is 8" and outer dia. is approximately 25".
>>Secondary Coils - As stated above. Note: Went for inductance by
>>28 gauge wire, also to see if it can withstand the punishment.
>>Power Supply - 15 kV -at- 90 mA NST's. ((3) 15 kV -at- 30 mA in parallel)
>>Toroid - 25" outer dia. with a 5" cross section.
>>Spark Gap Electrodes - 3/4" thick by 2" long highly polished steel,
>>3/8" radius of curvature on one end.
>>Spark Gap - Single static.
>>Components not made yet:
>> - Primary capacitor (Calculated to need about .0226 uF. Anyone
>>problems with using mylar for the di-electric?)
>> - Protective capacitor.
>> - Chokes.
> Under no circumstances use mylar for a pulse cap, it will melt at
>best! Mylar cannot tolerate HV AC
>voltages and peak currents.
>>I am a Physic's major, mathematics minor at the University of
>>Eau Claire, so I am quite familiar with most of the terminology
>>in Tesla coils. This is my first Tesla coil project, which I am
>>building for the Physic's Dept. (and they are funding!!) for
>>demonstrations on inductance and E&M fields. I can already see the
>>limitations of these 2 coil systems, and may soon have to start
>>researching into magnifiers.
>>Any help greatly appreciated.
> Mark Graalman