Re: LC and Misc Questions

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

At 02:23 PM 7/28/2005, you wrote:

>  LC and Misc Questions
>
>   Hello list,
>
>    I have a couple of questions that have stumped me. There are too
> many postings to look through regarding these questions and I was
> unable find postings with definite conclusions or the info was way
> too scattered.
>
>   (1) I've read that secondaries should have LD ratios of 3:1, 4:1,
>       4.5:1, etc. Which one is the best? Is there any critical
>       difference?

There is no great critical difference.  The only real problem can 
arise if the secondary is so short that the streamers just keep 
hitting the primary all the time.  So the secondary needs to be 
somewhat tall with a larger top terminal to prevent secondary to primary arcs.


>   (2) Enameled wire seems to be used exclusively. Why not stranded
>       wire? It has better insulation and it is cheaper. It might
>       also help reduce unwanted capacitance, which reduces voltage
>       gain. For me, it actually worked better than magneet wire even
>       though the sec. inductance is lower.

Stranded wire can certainly be used.  The insulation is thicker so 
the number of turns is reduced but that might be fine depending on 
the other facts of the coil.


>   (3) I've read various opinions about how large primary cap and
>       inductance should be. What is the paradigm in determining
>       the best values?

Use the largest primary cap you can and still charge to full firing voltage.


>   (4) One program, TESLAN, calculates voltage gain using primary
>       and secondary capacitances. Another program, TESLAC, calculates
>       voltage gain usiing primary and secondary L's. Which one is a
>       better predictor of voltage gain?

They are both the same for all practical purposes.  L1 x C1 = L2 x C2 
so it just depends on how one writes the formulas.


>   (5) Are there adv./disadv. of using stacked primares or multiple primaries
>       wired in parallel?

In general, no.  There are a few odd situations where maybe there is 
some advantage, but 99% of the time a simple flat primary is fine.


>   About my current coil:
>
>     My philosophy is that it is much better to experiment with a trashy
> low power coil first and then move to a neatly made quality coil.

Yes.  There are a lot of things you will do different the second time ;-)


>     sec. len. - 15 in.
>     sec. dia. -  5 in.
>     sec. wire - about 260 turns of #28 stranded computer cable wire
>                 made from discontinuous pieces of 11 ft each wrapped
>                 on plastic wrapped oatmeal box forms
>
>     topload   - 2" x 6.5" made from cardboard, alu. foil, and tape
>
>     primary - 6 turns of #14 awg solid wire wrapped around cereal box
>            cardboard form measuring 5 in tall and 8 in wide. Taped at
>            2nd turn.
>
>     spark gap - L brackets or multiple screw gaps
>
>     primary cap - 3 para. Rolled caps made from foil tape and thick
>                 trash bags. Now can withstand up to  7-8kv at LOW POWER
>                 ONLY!
>
>     sec. spark len. - up to 5" snapping white with breakout
>
>     power supply - (Don't laugh) An ignition coil driven by adjustable 14uf/
>          28uf/42uf cap bank/dimmer combo with bridge rectified 
> output. I have 4 ig.
>          coils, but it's much better use one first. Higher power 
> only hastens cap death.
>
>     Except sec., setup is tightly packed in thick, small cardboard box.
>
>
>     I would gladly accept suggestions that can improve spark length.

The primary cap is the weakest point there.  An MMC that could be 
charged about 120 times per second would be best.  Your rectified 
driver could probably charge it to really high voltages, but the 
break rate is a limiter.

Cheers,

        Terry