Subject: Re: Inventory
From: Scott Myers <scotty-at-wesnet-dot-com>
Date: Mon, 12 Feb 1996 15:20:00 -0500
>Received: from billboard.wesnet-dot-com (billboard.wesnet-dot-com [220.127.116.11]) by uucp-1.csn-dot-net (8.6.12/8.6.12) with ESMTP id NAA07864 for <tesla-at-grendel.objinc-dot-com>; Mon, 12 Feb 1996 13:15:52 -0700
> Inventory -
> 20 X 5 torroid (from American Welding & Supply)
> 12KV transformer -at- .12A sunk in oil
> .025uf cap rated at 50KV (DC)
> Spool of #26 magnet wire
> Large 3 gang variac
> Questions -
> Secondary Coil:
> The size of the secondary is based upon the size of my torroid.
> According to the TESLAC program, I need 1800 - 4000 watts to drive
> this properly. This program assumes that I use a helix that is
> 8" - 12" in diameter. According to the TCBA article written by
> Richard Hull, that diameter is too big. My thoughts are that I should
> use a 6" diameter form that is 15" in length. Does this sound okay?
That sounds reasonable, but I would go with a little larger diameter wire and push the winding
length 4:1, about 24". Your method will work just fine. But by going to a little larger wire,
it will have a higher Q and you will be able to push it harder down the road. You might download
Richard Quick's COILBLD series from nic.funet.fi and look at the imperical data that he has
compiled on this issue of coil aspect ratio/wire diameter in classic Telsa coil systems. As far
as basing the size of the secondary on the size of the toroid, I would throw that notion right
out the window. Richard Hull, as well as many others, advocates the use of very large toroids
with very small coils. This gets into the capacitive loading of the coil. So far, no one has
come up with the limit of how big of a toroid a coil can handle. It would come back to how much
power the secondary can take without breakdown. It is not unreasonable to use a 40" (or larger)
toroid on a 6" diameter coil. It is being done by several, such as Ed Sonderman. I personally
have a 30" toroid sitting on top of my 6" coil presently. I could use an even larger one.
> Also, I have heard that gray PVC pipe is reasonable for a coil form...?
Yes, if properly sealed. PVC is very high loss at the frequency you will operate a coil at. It
must be dryed and sealed. Again, Richard Quick's COILBLD series is a good place to look for this
> Main Transformer:
> 12KV -at- .12A is approximately 1440 Watts. According to the TESLAC
> program this is not enough power for the secondary and torroid. The
> transformer is sunk in oil. I think I can push the power rating of the
> transformer to at least double for Tesla Coil operation. If I capacitively
> load the transformer to double it's rating, will this work? Or will the
> transformer core saturate and not give better performance?
Mark Graalman, the author of TESLAC, will be the first to tell you that you have plenty of power
for your coil size set-up. (See the next part on the capacitor's rating.) The table on Toroids
is just a recommendation guide. It is not intended to dictate what you can or can't use. It
just shows "typical" power levels used.
As far as can you push the transformer beyond its power rating level, I don't know. What kind of
a transformer is it. If it is a shunted style (neon) tranformer, then you could increase it
current by removing shims. But by doing this, you risk burning the transformer up prematurely.
It it is a potential type that requires a current balast, then you may be able to push it farther
intermittently. Core saturation? Again this is what a shunted style depends on to limit its
current. In a potential style, there should be a plenty heavy core to allow you to get more
power out. It all just depends on the transformer design.
> .025uf CAP:
> This is a DC cap. Will this work okay in this type of a system? Also,
> The reactance of the cap should load the 12KV transformer to around .1A
> at 60 cycles, if I do not add additional capacity will this amount of
> power drive the secondary system as stated above?
First, we need more info on the capacitor itself. What kind, what make is it? I will assume it
is some sort of a filter cap. The design of a capacitor for a Tesla tank circuit is critical,
for high efficiency and life of the capacitor. The capacitor might work ok, but then again it
might blow the first time you try it. Tell us more about the cap. If it is a doorknob type, it
will work, but keep the operation intermittent. They are inefficient at the frequencies we run
and get hot quickly. They must be allowed to cool or they will blow. The ideal capacitor for a
Tesla tank circuit is a pulse discharge capacitor, with polypropylene dielectric. These are
available, but they cost money. Since the capacitor you have has a DC rating of 50 KV, it should
work without blowing immediately. What you now need to know is what its dissipation factor is at
As far as the power input goes, you are a little light, but it will still fire the coil. You
could use a bit more current to match perfectly, but it will work.
If you would happen to have 2 of these capacitors, I would put them in series to reduce the
capacitance by 1/2 and double the voltage rating. This would also reduce the power input level
required by 1/2. It would make for a nice system.
> Spark Gap:
> I am building an 8 pole stationary gap in a brass housing that will be
> air tight. I want to quench the gap rapidly and am thinking about pulling
> a vacuum on the spark housing. Will this work? Should I be filling the
> housing with a "magic" gas, or pressurizing the housing?
A "vacuum gap's" name is a bit misleading. It is not a sealed vessel that has a hard vacuum
pulled on it. The air should be allowed to flow in from the outside by entering the housing
between the gaps. The air then travels back out of the housing via the vacuum motor (Read vacuum
cleaner motor. It is the type of motor found in canister style vacuum cleaners). I personally
prefer vacuum gaps. They provide excellent quenching with minimal cost. Brass housing? Wow!
Sounds like a monster. I have been using acrylic as my housing with copper pipe as the electrode
material. It works well and is cheap. Magic gas? Not needed. again, getting a high air
velocity directly across the gap is all that is needed. There are a few subtle details that you
will learn building a vacuum gap. But once you get the bugs out, you will like the results.