Re: Big Coil, small transformer Blues....

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Pyrotrons-at-aol-dot-com>

Hi Carlo and All.

-- snip
> It's a 15.5'' x 50" secondary with 537 turns and a .09uF / ~5 turn 
> primary. The thing is that I've tried to run it with a 15Kv 150ma NST 
> and was shocked at how wimpy the sparks that came out of it were.
-- unsnip

You have to run a LOT of power into a big coil before your system starts 
getting efficient. It's a very popular misconception that a bigger secondary 
will result in longer sparks. This is true ONLY when there is enough power to 
drive the secondary. Otherwise, your sparks get shorter. That's been my 
experience.

Here's something for you: this Sunday, we are testing a new coil that's 
strikingly (pun intended) similar to yours. 

15" secondary wound with #12 magnet wire (700 turns)
1/2" copper primary, 1/2" t-t spacing
.1uF tank capacitor
SRSG, 120 or 240BPS, whichever works better.
Radical topload!!!

We plan to run it at 12kVA for tests, if it works good we up the power to 
20kVA and play.

15 - 25kVA is good for a 15" diameter secondary, although good results may be 
gotten far from this range. But I'm afraid 150mA is way too little. Try a 6" 
or 8" coil, you will be pleased.

You might be able to tune it perfectly, get the gap to quench perfect, and 
make everything seem right, but somewhere ----- somehow, efficiency goes way 
the heck down!

An explanation, anyone?? Here's the question:

For a given Tesla coil system that is efficient with a given secondary coil, 
why does the sparklength not increase when a larger secondary is dropped in 
place of the original one?! I'm thinking the answer will go into some nice 
neck-deep theory, but maybe not.

We'll let everyone know how it goes with the 15" -at- high power.

Later on,

Justin Hays
KC5PNP
G-3 #1150
Email: pyrotrons-at-aol-dot-com
Website: www.hvguy-dot-com