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Re: Latest results of 12.5" coil



---------- Forwarded message ----------
Date: Sun, 19 Oct 1997 08:15:00 -0500
From: Chuck Curran <ccurran-at-execpc-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Latest results of 12.5" coil 

Hello Rodney:

Good job on getting your new 12.5" secondary coil up and making sparks.  As
you proceed with the fine tuning effort over the next few months I would
expect your sparks to grow.  Boy, I wish I knew someone that would stop by
with a big pulse discharge cap like your friend Jason did.  I do agree with
your comment about "it's time to go outside".  Your sparks could get much
too exciting to stay in a small area in the future!
I did try to calculate your systems characteristics and I'm showing
secondary resonance in the area of 82 Khz.  This figure may not be accurate,
I must mention that I used a system designed for a tight wound coil and I
really don't know the impact on inter-turn capacitance for your situation,
with the space winding.  This should still be in the ball-park.  If this is
close, the next item was to calculate the required primary inductance based
on your .15 mfd cap.  I think you would see a benefit with two more turns in
your primary.  One to use and one as extra, so to speak.  My calculations
suggest resonance would occur at 5 turns.  When I did these same
calculations for my present coil, I ended up needing about 2/3 of a turn
more than what the calculations suggested--I never really determined why.  I
believe you are already tapped at the end of your primary, so this might be
the correct path to try.   I would also start planning for a much bigger top
load.  A toroid more in the area of 8" by 40", or even bigger could make a
substantial improvement in spark output, if your power transformer can
deliver the additional power to cause breakout.  This would also lower the
resonant freq.. more and require even more primary turns for resonance.
Good luck with your coil work.

Chuck Curran


-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Saturday, October 18, 1997 12:12 PM
Subject: Latest results of 12.5" coil


>
>
>---------- Forwarded message ----------
>Date: Sat, 18 Oct 1997 21:18:10 +1000 (EST)
>From: Rodney Davies <rgd872-at-anu.edu.au>
>To: tesla-at-pupman-dot-com
>Subject: Latest results of 12.5" coil
>
>Hi All,
>
>Well, Jason Judd, Peter Electric and I got together today to try to get
>some better results from my 12.5" coil.
>
>The other day, Jason came over and showed me something we've been looking
>for, a 0.15uF 50KV capacitor... (yes R. Hull, *big* capacitors :-) )
>
>Anyhow, we hooked it up and used a microwave xformer with 100mH inductance
>as a ballast on the pole pig (11KV 5-10KVA), cranked it up and only got
>about 2 feet.
>
>Mind you, if you saw this coil, you'd probably go 'oh my, what a mess!'
>;-)
>
>It's a really messy setup, but, it works...
>
>Todays effort involved a new toroid (approx 24"x6") of alluminium duct,
>which gives probably the best topload capacitance I've had so far... it
>handles the field quite nicely too!
>
>Anyhow, by the end of the day, we'd drop the ballast down to 50mH and a
>spark length of just over 4 feet.
>
>We were using my asynchronous gap with a break rate of 288bps (12 rotating
>points with 4 stationary, basically a 4-gap rotary).
>We reduced the gap down to 4 rotating points, bringing the break rate down
>to 96 bps.
>
>A very interesting behaviour pattern followed where we could see (by the
>coil output) the phase coming in and out of sync.
>The coil would go into sync. mode, then no output, then into async mode,
>then no output, then back into sync mode... very interesting!
>
>Just before this, we hooked up Peter's sync rotary gap (110bps), which
>probably could only withstand about 2KVA of power, and ran the coil.
>Amazingly, the whole thing was in perfect sync, the streamers were nice,
>long, hot and continuous...a classic example of sync operation!
>
>But however, since we were drawing about 5KVA, the rotating electrode got
>kinda hot, and started melting the rotor disk (made from a polythene bread
>cutting board). From the centripital forces on the electrodes, they
>started melting through the disk towards its edge... rendering it useless.
>
>However, it was an awesome experience to see the distinct differences
>between sync and async operation.  Go Sync if you can!
>
>Jason and I are going to convert my 1440rpm async motor to sync this week,
>and then hook it all back up.
>
>Luckily I got the design specs right when I built mine, as in the
>electrodes stay nice and cool, and the whole thing could probably handle
>around 10KVA nicely. so far so good anyhow... :-)
>
>Currently the coil is operating in a small room with about 3 feet either
>side space between the coil and the wall, which it is striking often,
>plus the door frames, the ceiling (metal structure) and various objects
>around the room. I think it's time to take it outside!
>
>But a very successful day! It's taken me three years to get the coil
>working like this (mostly due to lack of funding and time and parts) but
>it's coming through nicely!
>
>However, before I leave, I must say, thank-you to everyone on the list
>with results from your expriences. Jason, Peter and I kept refering to the
>Tesla List for explanation and exprimental techniques used today...
>without the knowledge passed on through the list, it probably would have
>taken us longer to get to where we are today....
>
>Thank-You All!
>
>Catchya later!
>Rod
>
>Oh, here's the coil specs if someone feels like doing some maths :-)
>
>(Any get the resonant frequency? How far off tune are we?)
>
>Secondary: 12.5" 900 turns of 1mm enamel coated Cu wire, space wound at
>           21 turns/inch.
>
>Primary: 5 turns of 3/8" copper pipe, spaced at 7/8", archimedes coil.
>
>         ---( )------( )------( )---
>             ^--7/8"--^
>
>         Tapped out at approx 4 7/8" turns.
> Diameter: 24 7/16"
> Average radius: 10 9/32"
>
>Primary Capacitor: 0.152uF 50KV Pulse rated.
>
>Power Supply: 11KV 5-10KVA SWER Pole-pig.
>Power input:  240VAC, approx 16-20 amps. 50Hz
>       (Yup! out of a 10amp power outlet, luckily w/ a 20amp
>        breaker!)
>
>Current Limiting: 50mH inducive ballast.
>
>Rotary Gap: currently at 96bps, async. Will be 1500rpm 300bps soon.
>
>Top load: approx 24"x 6" toroid, situated approx 5" above top turn of
>   the sec. coil.
>
>