[TCML] largest secondary coil you'd drive with an NST

Sat Dec 15 18:34:21 MST 2007

Hi David and Jared,

I'm not saying less wire is better and I'm not saying more wire wire is 
better. There is a reason helical air coils favor a 4:1 or 5:1 range for 
spark production and it has everything to do with optimizing the 
impedances of the system as stated previously.

I'm not saying Jared's 12"x48" coil won't do well. It is on the edge of 
starting to get lossy to the point of affecting output and in this case 
I think it would do better with a higher gauge wire size in the 18 to 20 
awg range (for the reasons stated previously). In reading Jared's post, 
a coiler might think "more wire is better, hey, I'll wind 5000 turns of 
30 awg". Because I disagree with that, I am compelled to state my thoughts.

My 13" diameter coil was first wound with an h/d a little over 3:1. 
Experienced coilers on the TCML recommended 5:1. I didn't listen (had 
that PI ratio theory in my head). Well, it worked fine, but only about 3 
to 4 foot leaders. I broke down and added over a foot to the coil 
(something that can be done with sonotube). It did much better with 5 to 
6 foot leaders now with over a 4:1 h/d. I then upgraded the spark gap 
and hit that 9 foot range. For that coil, those were the two major 
improvements (and they were night and day).

I then got on the kick of higher turn coils. And again, going against 
the TCML recommendations (800 to 1500 turns), I wound a high turn coil 
about 1800 turns (I learn the hard way like everyone else I guess). At 
first I thought the coil was doing well (it worked fine), but after 
enough run time I started paying closer attention to power input and 
realized how inefficient the coil was. It was drawing too much power for 
the spark output, even using a very efficient G10/tungsten rotary. The 
problem was the high turn coil was lossy and a poor impedance match.

It took me a while, but I started to realize the experienced coilers on 
the TCML really do know what their talking about. Theory is always up 
for debate, but their experience is priceless. These days, I pay far 
more attention to their recommendations.

Take care,
Bart

David Rieben wrote:
> Hi Jared,
>
> I don't believe Bart was trying to make a "blanket statement"
> by saying that the less wire you use, the better. He WAS
> stating that you need to MATCH your coil's specs with the
> power source. It would be rather foolish to build an Electrum
> sized coil and run it with an OBIT and a 5 nFd primary C
> as it would  be to build small 2" x 10" secondary coil w/ #32
> AWG and try running it with a 25 kVA pig and a 200 nFd
> primary C! Can you say "meltdown" ;^)
>
> David
>
> ----- Original Message ----- From: "Jared Dwarshuis" 
> <jdwarshuis at gmail.com>
> To: "Tesla Coil Mailing List" <tesla at pupman.com>
> Sent: Saturday, December 15, 2007 4:31 AM
> Subject: Re: [TCML] largest secondary coil you'd drive with an NST
>
>
>> Hi Bart:
>>
>> You don't make coils better by using less wire. A coil with no wire 
>> at all
>> would be the best coil using this line of reasoning.
>>
>> Small inductors are more portable but do not yield better performance.
>>
>>
>> Jared Dwarshuis
>> On Dec 14, 2007 9:40 PM, Barton B. Anderson <bartb at classictesla.com> 
>> wrote:
>>
>>> Hi Jared,
>>>
>>> There is of course a max inductance for an h/d ratio for a given wire
>>> length. I did a personal study of this sometime back.
>>> http://www.classictesla.com/download/max_L_table.pdf
>>>
>>> What not everyone realizes is there is that max inductance is not the
>>> same for resonant and low frequency inductance.
>>>
>>> Your 22g 12"x48" coil would yield 1720 turns. Consider the toroid and
>>> primary in place and your nearing about 54kHz, so the frequency "is"
>>> low. But due to the high turns, the proximity losses increases as does
>>> the dc resistance. DCR is about 86 ohms and ACR is about 177 ohms. This
>>> does add up to a lossy coil in the end. I know from experience because
>>> I've built one similar except using 24g. I even ran it on pole pig
>>> power. Sure it will perform if enough power is put to it, but it does
>>> take more power.
>>>
>>> The common h/d recommendation of the 5:1 range is not only considering
>>> the h/d ratio, but the wire size that fits into that ratio and how that
>>> wire size electrically affects impedance.
>>>
>>> A coil should be sized for the energy across the gap and the time
>>> involved. The transformer of course has to be sized to accommodate the
>>> power needed for the cap size and charge rate. The later is far easier.
>>>
>>> Take care,
>>> Bart
>>>
>>> Jared Dwarshuis wrote:
>>> > For a given length of wire your inductance will be greatest with an
>>> inductor
>>> > that has a large diameter and a short height. However if you make 
>>> your
>>> coil
>>> > to short you can get problems with flashover from end to end.
>>> >
>>> > Wire is reasonably cheap compared to capacitors and NST. Using a 
>>> lot of
>>> wire
>>> > is the easiest and cheapest way to increase spark length. I  would
>>> recommend
>>> > using 22 gauge on a 12 inch by 4 ft concrete form.This will give a 
>>> nice
>>> low
>>> > frequency and if (when) you upgrade to using more NST (or a pole pig)
>>> you
>>> > will be all set. Finer wire also works and I would not be 
>>> surprised if
>>> one
>>> > could drop down to as fine as 28 gauge for a pole pig powered 
>>> coil. But
>>> fine
>>> > wire does not seem to survive strikes very well so we use the thicker
>>> stuff
>>> > as insurance.  (tiny wires are hard to wind, they get crossovers > 
>>> easily)
>>> > Jared Dwarshuis
>>> > On Dec 14, 2007 12:47 AM, Tim Meehan <btmeehan at gmail.com> wrote:
>>> >
>>> >
>>> >> I hate to ask this too - but what is the optimum aspect ratio for a
>>> >> secondary?  I've run JAVATC, and have built a feeble (but pretty)
>>> classic
>>> >> tesla before ... and have read but probably poorly understood a few
>>> >> papers.
>>> >> I think that I'm ready to build version two of the static-gap,
>>> >> NST-powered,
>>> >> properly filtered and protected coil.  I just want to make sure 
>>> that I
>>> >> learn
>>> >> as much as possible before I start purchasing things that probably
>>> won't
>>> >> suit my needs.
>>> >>
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>>>
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