RE: [TCML] All of my tesla coil questions (for now)

["Lau, Gary" <Gary.Lau@xxxxxx>]

Hi Nicholas,

Welcome to the TCML.  My answers and comments interspersed.  Bear in mind that opinions differ between individuals on this List, and not everything you read is correct.  In building Tesla coils, there are a few things that are cast in stone (like you can't use electrolytic caps, you can't use solid state transformers), but then there's a lot of things that have a great deal of latitude in choosing, like NST ratings.

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Nicholas J. Goble
> Sent: Wednesday, June 11, 2008 8:47 PM
> To: tesla@xxxxxxxxxx
> Subject: [TCML] All of my tesla coil questions (for now)
>
> I figure I should introduce myself.  I'm a sophomore in college,
> studying business.  I have only a basic college level physics course
> under my belt, but I've read a lot about Tesla coils on the Internet.
> I've always enjoyed building things and impressing people with them.  I
> think the most fun is building them though.  My plan is to build a
> small to medium coil over the summer.
>
> Instead of filling the archives and your inboxes with multiple
> questions that are unknown to me but second nature to everyone else,
> I'll just clump them all in one big message.  Here are all my
> questions; hopefully someone can answer them:
>
> 1) Do I NEED a Terry filter?  I know they protect the transformer, but
> I don't know how they work and what happens if I don't use one.

A Terry filter, to a large degree, protects you from yourself.  Very often beginners open their gaps too wide, or things aren't built or hooked up properly, and the gap is effectively not connected.  Either scenario will cause the voltage on the NST and cap to climb to destructive levels.  The MOV's and safety gaps in the Terry filter protect against this.  In lieu of a Terry filter, a simple PROPERLY SET safety gap alone will be 95% as good as a complete Terry filter.  Ask about how to set the gap, it's a whole other topic.

> 2) Do I NEED a saftey gap?  Again, I know they protect the transformer,
> but I'm in the dark as to how they work and what will happen if I don't
> use one.

See above.

> 3) How much should I plan on spending on a transformer (approx 10KV,
> 30mA)?  I don't want overpay because of inexperience.

One can often get a free NST from a sign shop if you show up in person, speak gently and display competence without sounding cocky.  Any core and coil (as opposed to solid state) NST can be used.  I've build a very satisfying coil using a 4kv/20mA NST (see http://www.laushaus.com/tesla/minicoil.htm), so don't get hung up on finding a particular voltage unit, and don't believe those that say you need at least X kV to work.


> 4) How do I construct an MMC?  What type of circuitry do I use?  I
> can't find any concrete information on MMC's.

There is no real circuitry beyond the capacitors, and it's generally considered a good idea to place a 10M 1/2W bleeder across each cap.  It's not true that bleeders are only if you're using DC.  An AC powered coil can still leave a charge on the cap if certain failure modes occur.

There are a zillion types of capacitors, and very very few of them are suitable for use in Tesla coils, so let me simplify things.  Use Cornell-Dubilier 942C20P15K-F caps.  These are 0.15uF@2000V each.  Use enough in series to give the correct voltage.


> 5) Instead of building an MMC, whould it be cheaper and/or more
> effective to build a plate capacitor out of just window glass and some
> other metal?

Cheaper, maybe, but it will perform poorly, and will be huge and heavy.

> 6) This was my plan for a spark gap: Have 2 rods (preferably Tungsten)
> form a gap inside a PVC pipe and have a fan or blower at one or both
> ends.  Will this be sufficient?  Would a rotary gap be better?  I just
> don't want to be replacing the rods every time I fire this thing up.

A rotary might be best, but is much, much more complex to build and requires special consideration for the cap value, and all in all, is not recommended for a beginner.

A static gap, using parallel copper pipes, with a small fan blowing on it (you don't need a leaf blower!), is the best place to start.  I have a variety of static gaps described on my web site http://www.laushaus.com/tesla

> 7) Should I use insulated, magnetic wire on the secondary coil?

The correct term is just "magnet wire", but yes, any magnet wire you come across, typically in the range of 22-32 gauge is fine.  The goal is to wind a secondary with 800-1600 turns, so the gauge should be chosen per the coil form size.  More of the sequence of determining sizes in http://www.laushaus.com/tesla/howtodesign.htm

> My biggest fear is that my coil doesn't work after all the time and
> effort I invest into it.  My second biggest fear is that it dies
> shortly after I put it together.  My third biggest fear is that I die
> from it.  I'm pretty sure I can be safe around electricity.  Just don't
> touch the thing when the cap is charged or it's plugged in, right?
>
> These are all my questions for now.  I appreciate all of your past and
> future answers.  This has been an extremley helpful listserve.  Thanks
>
> Nicholas Goble

One often sees unremarkable results on the first try, myself included.  If it were easy and everyone got the same results, it wouldn't be nearly so fun.  Enjoy!

Regards, Gary Lau
MA, USA
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