Stefan,
Yes the gap thing has always puzzled me. Although whatever gap you do set,
the spark will have to jump that as a very minimum, the extra distance added
onto to that obviously being determined by just when it does fire.
I run a SRSG at 200 which allows a very distinctive sound when the phase is
just right, and I always know when the gaps are opening up as the sound
alters and performance drops off.
I have a weekend long event coming up this Saturday, and by the Saturday
night the gaps will need adjusting.
On a side note to anyone thinking of using some of the Tungsten / Copper
alloy rod for electrodes (I do for my statics - 3/8 inch) it ablates much
quicker than Tungsten electrode rod. It does though machine and cut like
Aluminium but is brittle if you drop out.
Be interested in your DC coil adventure, myself and a fellow UK coiler
seriously looked at a big DC coil, but without 3 phase power, the amount of
smoothing caps needed, made cost too big an issue. The reactor we had
planned on winding ourselves: purchasing suitably sized laminations.
Phil
-----Original Message-----
From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of Teslalabor
Sent: 20 October 2014 14:34
To: Tesla Coil Mailing List
Subject: Re: [TCML] Finished: New 600bps Rotary, Power Controller + Variac
for DC resonant charging TC
Hi Phil,
thanks! You are right, close gap clearances on rotary gaps seem to be
important, I observed this some years ago on a SRSG, running 200bps @
3000rpm. But always was wondering about this, because the arc ignites long
before the electrodes are coming together.
The firing voltage on my new rotary will be arround 26kV so maybe close gap
clearance will not be so important. We will see!
Yes, the experiments will show, if the brass holders for the stationary
tungsten electrodes are able to take the heat away properly. If not, it's
not a big deal to change them for massive copper pieces oder aluminum heat
sinks.
Your idea with the air movement control is pretty cool! Will have to keep
this in mind. But the air movement the disc produces @ 4000rpm is incredible
:-)
Regards,
Stefan
----- Original Message -----
From: "Phil" <pip@xxxxxxxxxxx>
To: "'Tesla Coil Mailing List'" <tesla@xxxxxxxxxx>
Sent: Monday, October 20, 2014 11:07 AM
Subject: Re: [TCML] Finished: New 600bps Rotary,Power Controller + Variac
for DC resonant charging TC
Stefan,
That's a very nice, sturdy RSG you have built, especially as it is never
easy getting an outrigger bearing to align easily, but with the revs you are
using it is a good idea! A setup like that should allow some close gap
clearances as well which I always thinks helps. (I run 10 thou clearance @ 6
- 7 Kw 3000 rpm).
If you do get overheating problems you will find a switch to copper
electrodes will have a vast difference, as the thermal conductivity of brass
is not very good (copper being about 10 times higher I think). The rotary
ones rarely get any heat to them, but the stationeries tend to ablate
mostly, presumably made worse because they are not cooled as much.
I use approx' 8 inch tall one inch diam' copper bars as terminal posts, and
recently did some experiments with smoke to find the air movement paths on
mine, and you may find a carefully sited piece of Lexan to act as a wind
shield will direct the rotor draft towards the stationary terminal posts.
(https://www.flickr.com/photos/33962508@N03/15318168107/ The black Lexan
piece slides across in front of the stationeries and directs the substantial
draft sideways)
Nice to see a motor driven variac in use, but the thought of "overkill"
comes to mind :-))
Regards
Phil Tuck
www.hvtesla.com
-----Original Message-----
From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of Teslalabor
Sent: 19 October 2014 18:53
To: tesla@xxxxxxxxxx
Subject: [TCML] Finished: New 600bps Rotary, Power Controller + Variac for
DC resonant charging TC
Hello all,
as announced some weeks ago, I now want to show you my current proceedings
with my DC resonant charging teslacoil. I just finished the rotary spark
gap, motor driven 3-phase variac which feeds the high voltage transformer
and also the power control box. Here is a video of it:
https://www.youtube.com/watch?v=wVpRE38UXqE
The rotary is made of a 450W DC Motor with a maximum speed of 12500rpm. The
speed is controlled by a variac. The disc-diameter is 25cm, equipped with 6
tungsten rods, each 6mm in diameter. The motor has a tacho generator on its
shaft, which feeds a speedometer in the control box. So this gives me an
absolutely precise measurement of both, disc speed AND bps! The meter
reading, which has a scale from 0 - 10, is just this simple:
x1000 = rpm's
x100 = bps
The rotary consists of 4 stationary electrodes, mounted to massive brass
columns, 2 on each side of the disc,
which results in a total of 4 spark gaps. I think, this in combination with
the high speed / low dwell times will have some positive effects on the
quenching properties of the gap and very low speeds will be possible without
igniting a firewheel.
In the video the rotary is accelerated up to 4000rpm (400bps) which is the
target bps for my system, where the maximum power will be processed, but
also up to 6000rpm are possible I think. Dwell time at 4000rpm is 252µs, at
6000rpm it's 168µs. But I should be aware of the following: Each electrode
weights 42,736g, so at 4000rpm it's weight rises to 86,7kg, at 6000rpm
already
195,1kg! At the moment I'm happy with 400bps, maybe I shouldn't try more
rpm's with that calculations in mind :-)))
The 3-phase motor variac can also be controlled with the control-box,
voltage can be cranked up and down automatically and stopped at every
voltage.
Regards,
Stefan
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