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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.