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Re: power supply options

Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Scott,
It is good that you have a three terminal safety gap (two gaps, one for each of the outside MOTs and center terminal connected to the center tap of the MOT stack). The fact that they dont fire with a SRSG but do fire with a static gap suggest to me that they are not set correctly for a static gap. With a SRSG (120bps), timed optimally after peak, and using a capacitance of around 2.7-2.8 * Cres, the operating voltage will be higher than with a static main gap set to fire at the peak open circuit voltage of the MOT stack. If you ever do go back to a static gap, set the safety gaps to just barely not fire when the MOT is driving a no load (TC tank cap and main gap removed). Once set, never be tempted to change the safety gap setting. You can also set the main gap this way but set it so it just fires with this no load condition. If the safeties are set correctly, the main gap setting should not be an issue as the safeties will do the protection if the main is set too wide.
With a SRSG, the safety gap needs to be set a little wider since if it fires just once, it will screw up the SRSG timing and make the coil run rough for that moment. If the safety needs to be set too wide to keep them from firing, one may need to increase the tank cap some. I use 15KV NSTs where the peak no load voltage is about 21KV. With my SRSG, the peak operating voltage is 24500 V and the firing voltage (after peak) is 24KV. If I time it for peak, the firing voltage would be around 21KV. 

Gerry R.

Original poster: "Scott Bogard" <teslas-intern@xxxxxxxxxxx>

Yes I have safety gaps, they never fire since I
got my SRSG (although they may have the other
night when it died, it only ran for a second
before I saw burning mots).  I use the same
arrangement you do, but the gaps are on the
"tank" side of a filter circuit (which I will
remove, for testing sake, once I tested that my
urethaned MOTs are working) and I use 1/4 in
bolts (which should not make a difference in a
safety gap).  I still have to float the cores,
then after a second coat of polyurethane, I'll test them.
Scott



From: "Tesla list" <tesla@xxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Re: power supply options
Date: Sun, 29 Apr 2007 22:56:01 -0600

Original poster: "Hydrogen18" <hydrogen18@xxxxxxxxxxxxx>
Are you running a safety gap on your 4 pack? I have one on mine. It's 3/8ths carriage bolts mounted in a piece of 3 inch pvc pipe. One is connected to the center tap of the transformer arragngement, the other two have about 1/4 inch spacing from the center element. Whenever I was first coiling it would fire alot as things went a stray. Polyurethane will probably work just as well as epoxy, at least for the insulation value. Putting it all over might inhibit the heat disspation a bit, but I've notice MOTs main way of heat dissapation is through the iron core to begin with. 

Eric

----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Saturday, April 28, 2007 8:01 PM
Subject: Re: power supply options


Original poster: "Scott Bogard" <teslas-intern@xxxxxxxxxxx>

Eric,
I will try removing the filter, and increasing
the ballast.  I'll of course put a simple low
pass filter in my control box to try and prevent
voltage spikes in my breaker box (the FCC
requires a filter of some kind).  My spark gap
was just a synchronous rotary (spacing set at
about 1/16 inch each side), but now it is a
rotary with a static in series (the static was
set at about 1/4 in.).  The reason I switched, is
because I just recently put a heavier gauge wire
in my tank circuit, and I started having
quenching problems.  I turned it on, and almost
immediately my outer 2 mots died, the spacing was
obviously way too big (lousy arcs while it
lasted, for like a second) (it was also very,
very humid, so that probably did not help).  As I
am starting to run really, really low on MOTs I
am taking a stab at fixing these.  I removed the
carbon trails with a toothbrush and some
turpentine, and I put a thick coat of
polyurethane all over, especially in the cracks
(more coats to follow!  I did not use epoxy, as
polyurethane is much cheaper, and it will flow
better into the cracks (methinks).).  My tank
capacitor is rated to 40 kV DC (tested to 45 kV),
so I could (in theory) put 28.28 kV into it (MOTs
can't do that easily).  I'll let you guys know how it goes.
Scott



From: "Tesla list" <tesla@xxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Re: power supply options
Date: Sat, 28 Apr 2007 16:45:14 -0600

Original poster: "Hydrogen18" <hydrogen18@xxxxxxxxxxxxx>
I don't run mine with any filter whatsoever. If you keep killing them, I suggest trying to run it without it. Out of curiosity what spark gap lengths are you using(if you are using a static gap) for the 6 pack and 4 pack setup? I've never used much over 2/10ths of an inch total. I think the switching to 4 pack was a good idea since it should be more reliable, still have enough voltage to reliably fire a gap, and will stress the outer MOTs less. The only advantage to the 6 pack would be if you had a very high voltage rated primary cap and had similiarly designed small conductor for the primary. 

Eric
----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Friday, April 27, 2007 9:55 PM
Subject: Re: power supply options


Original poster: "Scott Bogard" <teslas-intern@xxxxxxxxxxx>

Ok,
    I sent a reply to this message, but never
received it in my inbox, so I'll resend it.  My
MOTs are dying, and I have no clue why.  I use
mineral oil, and I float the cores on the outer
MOTs (I have been using 6, but I had so many
problems, I backed off to 4, and that worked fine
until earlier tonight.  The too biggest problems
I think it might be, is insufficient filtering,
or the fact that the transformers are just a foot
and a half away from the primary coil (and may be
having feedback induced in them).  I have safety
gaps, which don't fire since I installed my SRSG,
and the filter consists of two 50 ohm ohmite
resistors, filled with welding rods to add
"inductance".  There are also 3 strings of
ceramic capacitors, 150pf from hot to hot (in
front of the resistors) and 300pf from hot to
ground (on both sides).  I don't know if it
actually does anything, and it may be the
culprit.  I don't know, but any input would be appreciated.
Scott Bogard



From: "Tesla list" <tesla@xxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Re: power supply options
Date: Mon, 23 Apr 2007 13:26:43 -0600

Original poster: "Jonathan Peakall" <jpeakall@xxxxxxxxxxxx>

Scott,

Why not attack the problem from a different angle? Why are your MOTs dying?
What can you do to stop it? Maybe you could tell us what you are doing that
kills MOTs and maybe the kind folks on this list can help you find a way to
use them in a manner that does what you want and doesn't wind up frying the
MOTs.

Jonathan
www.madlabs.info

----------------------------------------------------------------------
Some people are like a Slinky .. not really good for anything,
but you still can't help but smile when you shove them down the stairs.
----------------------------------------------------------------------
----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Sunday, April 22, 2007 7:32 PM
Subject: power supply options


Original poster: "Scott Bogard" <teslas-intern@xxxxxxxxxxx>

Greetings all,
     Ok, I am on a students budget, so for now, a
pig is not an option (not even one of Dr.
Resonance's $125 pigs, I am chronically poor,
until I graduate, and get an engineering
job).  Right now I am using MOTs, which are free
(which is very good), and they put out lots of
power (which is also good) but they do indeed
occasionally burn out, and my supply is dwindling
faster than it is growing.  Can anybody give me
another (very cheap) option for a nice and beefy
HV power supply, in case I run out of MOTs before
I graduate in 2 yrs.  I suppose there probably is
no easy answer, but maybe somebody out there can
tell me something to look for (or where to look).
Thank ye kindly.
Scott Bogard.
P.S.  I have considered building a transformer,
but I think it is a little beyond my skill level
(and patience, winding stuff by hand for hours on
end drives me absolutely crazy).  Plus I don't
believe there is any good scrap yards near me, so
I would have to order wire and cores and stuff,
which I think would end up not saving me any
money in the long run.  Thanks again.

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