[TCML] MOT supply

[Barton B. Anderson]

Hi Ben,

The small coil causes a few strait forward problems. First, it's obvious 
the frequency is high. By itself, about 1.4 Mhz. This affects 
penetration depth to 2.73 mils (under 3 thousands of an inch of the wire 
is conducting the majority of the current). This results in AC losses 
near 80 ohms.

Second, the small diameter results in a very small inductance about 
2.2mH. The inductance stores energy charging your top terminal to some 
capacity. The top terminal is small and can only store a feeble charge 
and the secondary is just not capable of charging a large top load. So a 
small coil is limited and also has higher AC losses due to the 
frequency. In the end, you get about a 2" or 3" spark (or maybe slightly 
more if you figure out how to optimize the coil).

A larger secondary can store more energy and thus transfer a greater 
charge to a larger top load storing more energy available at the point 
of breakout. What DC said is true. I hope this helps explain why. The 
most I've got out of a 2" coil is about 4". It started at 2" in which I 
increased toroid size to about 2" x 8". Just like any other coil, the 
larger the top load, the longer the sparks, but there is of course a 
limit of both time to charge and charge voltage (this is true for any coil).

Due to difficulty at guessing at toroid sizes, we often use dimensions 
we "think" is good and do the best we can with it. Top terminal sizing 
can be difficult to find the "best" size for the situation. There are 
numerous dimensions and we can't build them all. Think of it: the same 
tube size, but increase the horizontal dimensions. Or, keep the 
horizontal dimension and change the tube size. Or, do both. After all of 
that, change the height of the top terminal above the secondary. In 
otherwords, the number of possibilities and it's relationship with the 
application are endless. Toroids are difficult to make and expensive to 
buy. And so I say again, we do the best we can with determining a good 
toroid size for our coil and hopefully it will perform well. This is one 
area where experience helps, but experience is not vast simply due to 
the number of possibilities. However, there are some obvious limitations 
that help put a window around the possibilities.

Take care,
Bart

Ben Sneath wrote:
>> The 1.75 inch dia sec is going to severely limit your
>> output spark.  My  estimate is 3-4 inches max.  Going to a
>> larger dia sec will improve output.
>>
>> Resonance Research Corp.
>> www.resonanceresearch.com
>>     
>
> Exactly how does this small diameter prevent long sparks?
> does it not have enough inductance? would you please explain
> how diameter limits spark length...
>
> it is wound with 434 turns of 30 gauge wire from a
> degaussing coil from a computer moniter, winding length = 6"
> toped with a 1.5x4.7" toroid
>
> Ben
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