Re: Parallel and Series LCR Circuit Qs

["Barton B. Anderson" <tesla123-at-pacbell-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Marc, 

Tesla list wrote: 

>
> Original poster: "Metlicka Marc" <mystuffs-at-orwell-dot-net> 
>
> hi john, all 
> i would like to ask another silly question, why is the 1000 to 1500 
> turn's secondary the shoot for number? what would the detrimental 
> effects of a, say 3000 turn secondary be? 
> marc




I don't think the turns is the issue, it just seems like it sometimes. The
higher the frequency of the coil, the higher the losses in the secondary (skin
effect) and the lower the Q. Lower the frequency and vice-versa. I don't
necessarily think a 3000 turn coil is a bad thing if it is wound at the right
dimensions and an eye is kept on the primary turns and resonant frequency. 

For example (h/d at 5:1): A 6 x 30 form wound with 31 awg at ~ 3000 turns, self
Fr is 62.6kHz. That's about 20 turns on the primary using a 20nF cap. Now a 10
x 50 form wound with 26 awg at 3000 turns, self Fr is 43.6kHz. Again with a
20nF cap, primary turns are 27.5. The Q's are relatively high with both coils,
and the second being the highest. 

However, try a 4 x 63 (h/d -at- 15.8:1) 24 awg at 3000 turns, self Fr is 130 kHz,
and again with a 20nF cap, primary turns are 10.5 turns. Sure it will work, but
losses will be much higher, the primary turns are less, and the Q is "much"
lower. Of course, this is extreme for example purposes, but the point I'm
trying to make is that higher turn primary's will reduce gap losses and lower
frequency's will reduce over-all losses (pri/sec). So, dimensions and frequency
play significant roles in producing optimum performance. 

Using the same wire and turns but now on a form size of 12.5 x 63, self Fr is
36.3kHz, and primary turns are 31. Q has approximately trippled and losses are
greatly reduced. (Notice the h/d is now 5:1). 

As long as you pump in power, you can always achieve spark lengths to the limit
of the coils handling of the sparks, but efficiency I think drops off when we
go to extreme dimensions without taking a look at these basic issues. I think
there is still quite a bit of room to play with, but I think it's important to
keep one eye on the primary and one on the resonant frequency to design an
efficient coil rather than worry about the number of turns (within reason). 

(BTW, the above was picked out of the air, so I'm not saying those are
necessarily efficient coils: just showing some differences). 

Take care, 
Bart