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RE: Advice on Secondary

Original poster: "Medina, Benjamin Alejandro (UMR-Student)" <bamxbb@xxxxxxx>


Hey. How are you? Thanks for your reply and suggestions. Sorry I took
this long to reply but I have been busy with school stuff.

Ok, well we're done with the secondary. 4"x30" PVC with 1" free on both
ends wounded with 22 AWG wire, about 1050-1100 turns.

For the capacitance in our series resonant circuit (LC) we will most
probably buy aluminum duct and use that as the toroid (not sure of the
dimensions yet). Should it be glued or just connected with an aluminum
or steel strap (to tighten both ends of the duct)?

We are shooting for our first trial on the 2nd week of February.
Depending on how that goes, we will go with a 6" diameter PVC and/or MMC
caps. We'll see how it goes. Thanks for your comments.

Our goals are to get the longest sparks. There is another Tesla Coil
Group in our senior design class, so we are competing vs each to see
gets optimum performance...

I forgot to tell you that we have a $400 student budget so we rather
spend the money purchasing other components than buying another AWG

We are thinking about a rotary spark gap (RSPG). We have a 1/6 hp motor
and will follow our design from the following link


Any other suggestions as to the spark gap? As the # of stationary
electrodes increase, will that improve our TESLA COIL performance??

As far as the overall casing goes, do you know of any websites where we
can get ideas or find cheap materials to build it?

Where can I find LDPE or HDPE for the primary? Can the base be made of
wood, or does it have to be some type of plastic (polyethylene)? What
material do you recommend to separate the copper spiral turns?

Lets say our needed capacitance is 5.3nF, calculated from
(C=1/(2xpixRxf)), and if we have a total capacitance of 15nF. Is that
OK? In other words, having more capacitance than what is needed is ok??

Thanks again man!!!!

Ben Medina

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

Icky... glass is quite lossy, and glass plate caps are a pain.  If you
cheap, use beer bottles in a bucket with salt water.

Or, spend a few bucks and make yourself an MMC (search the list archives
google for it).  String together 10-15 suitable polypropylene caps in
series, each cap is 2000V, 0.15 uF.  That will give you 10-15 nF.
Each cap is around $3, so you're looking at 30-40 bucks in caps.  Not
any old cap will do... you need ones suited to carrying the neccessary
current, but the folks on the list have spent years researching this,
the archives contain all you need to know about which part numbers to

If you're wanting more turns, why not just wind with 24 AWG or 26 AWG

But... spark length is mostly a function of input power, not absolute
number of turns.

What are you going to use as a spark gap? (I'd start with three pieces
copper pipe a couple inches long arranged in parallel).. rig up a muffin

fan to blow over it.

What are you going to use as a topload?  A toroid made from aluminum
duct and pie pans work well.