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RE: rotary spark gap; # of electrodes (fwd)

---------- Forwarded message ----------
Date: Mon, 09 Jul 2007 21:10:05 -0400
From: Scott Bogard <teslas-intern@xxxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: RE: rotary spark gap; # of electrodes (fwd)

     With an 1800 RPM motor, you need 4 electrodes, the spark gaps you are 
seeing with 2, use 3600 RPM motors, either combination will give you 120 
BPS.  Some coilers use 240, or even 480 BPS sync gaps, this is dependent on 
your capacitor size, and in part your style (more BPS technically gives 
higher losses, but can also give longer sparks (maybe) because the arcs can 
"grow" more as they do not dissipate as fast).  For your capacitor size 21.2 
nf, which is just a hair smaller than the calculated LTR sync cap value of 
25.2 nf for a 12/60, you would do best to stick with 120 BPS, higher BPS 
would lead to a cap not charging long enough to give good sparks (I wouldn't 
go out of the way to get a bigger cap either, if you go too much higher than 
25.2 tuning will become an issue, the value you have is fairly good, but if 
it is an MMC, and it would be easy to get that value, go ahead and boost it 
up to 25.2 nf).  I am building a 240 BPS gap, the reason for this is my cap 
is just about half of my calculated LTR sync, so I will get just about the 
same power out (with losses of course, but 120 BPS just ain't good enough 
for me as is, and more capacitance is expensive).  For your gap, I would 
recommend a propeller design, as they are easier to build.  See here, Terry 
Blake's site.
These designs are similar to what I use, they are good.  Once your gap is 
built, you have to phase it, which can be real easy or real hard depending 
on the type of motor you use.  If you can rotate the motor in it's mount, 
just do that to get it in phase (rotate it until it gives the longest arcs, 
and stop rotating it when your safety gaps fire (turn it back until they 
stop) if you do not have safety gaps, put them in, and set the spacing to a 
safe value for your transformer, a minimum of which is the distance, just a 
hair above that which the NST will establish an arc when turned on (you may 
be able to get away with wider since you are using a sync gap, but I do not 
know that for sure).  If you cannot rotate the motor in it's mount, you will 
either have to find a way to rotate it's mount, or build a phase adjuster, I 
wouldn't know much about that either!)  Remember, the smaller the gap 
distance the better, just don't shatter your rods.  My gaps are set too 
wide, which makes phasing easy (it will only fire in one "sweet spot") but 
if I am not mistaken, this can lead to efficiency losses, I plan on 
tightening up my next gap, and tuning with the method mentioned above.
Finally, yes, a bigger cap, meas less primary, or more top load, or a little 
of both to keep it in tune, and yes, a bigger top load will give bigger 
arcs, to a point (don't sit a Volkswagen up there and expect 100 ft arcs!  
it doesn't work that way, your top load size is limited by power input, cap 
size, and your secondary size and inductance).  I hope this helps.
Scott Bogard.

>From: "Tesla list" <tesla@xxxxxxxxxx>
>To: tesla@xxxxxxxxxx
>Subject: rotary spark gap; # of electrodes (fwd)
>Date: Mon, 9 Jul 2007 16:59:50 -0600 (MDT)
>---------- Forwarded message ----------
>Date: Mon, 09 Jul 2007 16:41:46 -0500
>From: Shaun Epp <scepp@xxxxxxx>
>To: tesla@xxxxxxxxxx
>Subject: rotary spark gap; # of electrodes
>I just got my hands on a synchronous motor, 1800 rpms.  It's an Oriental
>motor from an old teletype machine.  My question is how many electrodes do 
>need.  I've heard of coilers using a propeller gap with one rod spinning 
>four stationary electrodes.  I've also seen Johns design using the 
>motor that I have at web site www.hometown.aol.com/futuret/page6.html.  It
>seems to me that one spinning rod and two stationary electrodes would be
>enough for maximum power at minimum breaks per second, so why use four?
>I'm going to use the RSG with a 12Kv, 60mA NST powered coil that I already
>have made.  Cp = 0.0212uF.  I've read that you can increase the primary cap
>size too when running a RSG,  What is the rule of thumb for this?
>With a bigger Cp I can also use a bigger torroid.  : - )

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