I originally said " electrodes will have a vast difference, as the thermal
conductivity of brass is not very good (copper being about 10 times higher I
think)"
TEN times - really? I looked up that on the web, but clearly read the wrong
column in the data table!
So mea culpa - big time, as it's actually around THREE times more
efficient. Figures vary depending on the brass mixture being used; even pure
copper seems to vary depending on which source you look at.
Phil
-----Original Message-----
From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of Phil
Sent: 20 October 2014 10:08
To: 'Tesla Coil Mailing List'
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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