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Re: First Coil Design (fwd)



---------- Forwarded message ----------
Date: Sun, 29 Mar 1998 14:07:24 -0600
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: First Coil Design (fwd)

Tesla List wrote:
> 
> ---------- Forwarded message ----------
> Date: Sat, 28 Mar 1998 06:31:18 -0800
> From: djQuecke <djQuecke-at-worldnet.att-dot-net>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: First Coil Design
> 
> Well, I've spent a couple of months collecting most of what I need for my
> first coil.  I've tried several of the Tesla programs (and generally come
> close to the same answers <g>).  I thought I'd float my plans (and
> questions) for this first coil and see if I'm close.
> 
> I have one 15k, 30ma, 115v, 60hz neon transformer and intend to add a second
> soon.
> 
> With one tranny, I'll need .0053uf and with two, .0106uf for the tank
> capacitors?  I'll try saltwater, poly/flash in oil and I'm working on an
> experimental design (aren't they all <g>) using a product called ALPOLIC
> I've mentioned on the list several months ago.

Capacitance sounds ok - make sure you run identical caps in series to
withstand the voltages you'll be developing. 

> 
> Secondary is approx. 4.2" diameter and I'm figuring 21" tall (5 to 1).  I
> haven't wrapped it yet, though I've built a crude motorized "lathe" (PVC
> <g>) and have started sanding on a 36" PVC pipe.  I've got 1000' of 22 gauge
> magnet wire and a gallon of oil based polyurethane.  I'm figuring about 790
> turns of wire at 37.5 turns an inch and about 840' of wire used.

Sounds good! Because you'll probably not be able to get the tightest
turn-turn spacing, you'll probably get more like 750 turns. With no
topload, you'll be at about 520 kHz or so.

> 
> Primary is 1/4" copper fridge tubing, inverted saucer, 1/4" spacing, 15
> turns (or however far 50' gets me <g>).  I'm not certain about lateral
> spacing of primary and secondary.  I'm taking a shot at 5/8" space between
> secondary and inner coil of primary??  Inductance figures don't seem to add
> up??  Best spot to start tap?

You'll need to add more clearance to prevent primary:secondary
flashovers. Plan on at least 1.5" minimum since you're running off a 15
kv source. Assuming a 30 degree inverse conical primary with the
innermost diameter of 7" and a center-center turn spacing of 0.625"
(3/8" air space between turns to permit tapping), you should be able to
make a 12-turn primary with 50 feet of material. This would give you
about 30 - 56 uH from turn 9 thru 12. With a 0.0106 uF tank cap this
will give you between to 320 - 440 kHz on your primary.

> 
> Secondary base is easily adjusted vertically to optimize coupling.
> 
> I've built a safety gap using 3/4" x 1.5" brass rod on 3/8" threaded brass
> rod in a nylon base.
> 
> I've built a similar spark gap with attached airblast for main spark gap.
> I'll also try a couple of 6" RQ cylinder gaps.  I've acquired a motor, (a
> 1/2hp Dayton with a variable speed drive, 705-4230rpm), bearings, etc for a
> rotating sparkgap but have had trouble locating the G-10 (same as GAROLITE?)
> material for a disk.  The locals don't have a clue so far.  I've seen it in
> McMaster's.  Any other (cheaper) mail-order sources for a 10" - 12" disk or
> a 10" x 10" - 12" x 12" sheet?  Best thickness??

Garolite is a similar, but higher temperature version. Either will work.
Typical rotor thickness is 0.375 to 0.5". However, I'd also suggest
defering any rotary construction until you've built the RQ or a vacuum
gap. These tend to perform better for neons and are MUCH less difficult
(and expensive) to construct.

> 
> Toroid constructed from 4" aluminum flex, pizza pans and aluminum tape.  I
> have yet figured diameter.  Would seem that the goal for me would be to try
> to get secondary freq. down from approx. 515kHz range to the 250kHz area??

Unless you're williong to go with more turns on the primary, or go for a
bigger power source and larger tank capacitance, you should shoot for
around 350 kHz. Using a couple of 6" piepans and 4" dryer duct will get
you right in the ballpark at about 12 pF:

     .                        . 
  .     .\                /.     .
          \--------------/     Dryer Duct  
  .     . /-----____-----\ .     .  
     .   /     ||  ||     \   .
                |  |  
                |  | 2" PVC pipe (for adjustment)             
                |  | 
               ||__||
           |------------| 
           |            |
           |            | 
             Secondary    
               Coil         
> 
> I have a 5a STACO variable transformer. (Large enough?)  I have access to a
> 10a if necessary.
> 

Since you're sizing the primary cap for 60 Hz resonance, you'll
definately need that 10A variac when you add the second transformer. 

> Four 8' ground rods.  Any problem with cutting them in half and going with
> eight 4' rods?? (Hardpan about 5' below surface)

No. This may actually provide a better distributed ground anyway.

> 
> I still need to figure PFC??  Seems to be contrasting arguments over the
> need for this?

Not necessary if you're driving your coil off a 15A circuit. 
PFC's can help reduce overall current draw fron the mains plus they'll
add a bit more "pulse snarfing" (protection for HV kickbacks and
transients from getting back into your 120 volt supply mains)... 

> 
> I need to build chokes.  I saw a thread on using the cores from flybacks.  I
> have several such cores at 4" square by 1/2" diameter.  Is this viable?
> 
Should be as long as you use well insulated wire. Single-layer air core
chokes also work fine.

> What changes will be necessary when going from 30ma to 60ma with a second
> (or third) tranny? (Besides capacitance of the tank circuit...)

You may need to beef up your sparkgap a bit. 
> 
> Cheap source for high voltage wire?

Check some of the surplus houses. Also, Joe Cassata (Coax Connection -
630-420-0342) used to have 20 kV polyethylene insulated wire that was
only about 1/8" in diameter. Neon sign shops also carry GTO HV hookup
wire, but this tends to be about 1/4" to 5/16" in diameter. If you go
with single-layer closewound air chokes, you can use magnet wire. 

> 
> Sorry this is so long but I tried to include all necessary info (as well as
> fish for some answers <g>).
> 
> As my first coil, I want to try as many different methods in constructing
> each part, hence the different capacitor types, spark gaps etc.  My thought
> is to try and keep as many parameters as possible variable for optimization
> later (variable speed motor, secondary height, primary length, etc).
> 
> Anything obvious I'm missing here?
> 
> Thanks for your time,
> 
> dj

Good luck, and safe coilin' to you DJ!

-- Bert --