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Highest Q coils ?

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dex

Wed Jan 01 2014, 10:33AM

Registered Member #2566 Joined: Wed Dec 23 2009, 05:52PM
Location:
Posts: 147

Hi All,
What is the highest possible quality factor (Q) range for tesla coil secondary coil?
I'd like to know both about actual msms examples and theoretical analysis dealing with maximum Qs attainable.

Dr. Dark Current

Thu Jan 02 2014, 12:54PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Hi,
I'm not sure what do you want this for, but usually the highest unloaded Q have coils with fewer turns of thicker wire and a topload. If you could get a thick Litz wire and make a coil with a hundred turns or so (or less) with a large topload, the unloaded Q could probably approach 1000.

However, I think what matters the most (and has an effect on efficiency) is the ratio of unloaded and loaded Q.

dex

Thu Jan 02 2014, 03:34PM

Registered Member #2566 Joined: Wed Dec 23 2009, 05:52PM
Location:
Posts: 147

Yes, I'm interested in circumstances where the unloaded Q of secondary is maximized. Frequency range of interest 10-100 kHz. Why do you think capacitive top load must be very large? That doesn't sound right to me. Speaking of numbers, I've never heard of measured Q > 500, for tesla coil secondary.

Sulaiman

Thu Jan 02 2014, 06:41PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

in my opinion;

Tesla Coil secondaries are not optimised for unloaded 'Q' because they are intended for
A) Power Broadcasting per N.Tesla's dream
or
B) Sparks/Arcs for entertainment

in either case the loaded 'Q' is of interrest.

We make our TC secondaries long and thin (typical H/D = 3 to 5) to give space between earth/ground or the primary, and the topload, to allow for long arcs.
For a single layer solenoidal winding optimum 'Q' is when H/D is about 0.4 to 0.5,
leaving little distance from topload to surroundings.

For a given required inductance, unloaded 'Q' will increase with increasing wire diameter,
and at 10 to 100 kHz 'Litz' wire does make a significant improvement,
but there is no requirement for high unloaded 'Q' so the extra expense gives little improvement.

So if you want really high unloaded 'Q' use 660/46 "Litz' wire, (e.g.

)
with H/D = 0.5, a styrene former, and leave about one wire diameter between turns
.... unloaded 'Q' will be >500.

Dr. Dark Current

Thu Jan 02 2014, 08:00PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Yes. Another point, for a given frequency, the larger the coil the higher unloaded Q. Use Litz wire.

dex

Fri Jan 03 2014, 08:34AM

Registered Member #2566 Joined: Wed Dec 23 2009, 05:52PM
Location:
Posts: 147

Sulaiman wrote ...

in my opinion;

Tesla Coil secondaries are not optimised for unloaded 'Q' because they are intended for
A) Power Broadcasting per N.Tesla's dream
or
B) Sparks/Arcs for entertainment

in either case the loaded 'Q' is of interrest.

We make our TC secondaries long and thin (typical H/D = 3 to 5) to give space between earth/ground or the primary, and the topload, to allow for long arcs.
For a single layer solenoidal winding optimum 'Q' is when H/D is about 0.4 to 0.5,
leaving little distance from topload to surroundings.

For a given required inductance, unloaded 'Q' will increase with increasing wire diameter,
and at 10 to 100 kHz 'Litz' wire does make a significant improvement,
but there is no requirement for high unloaded 'Q' so the extra expense gives little improvement.

So if you want really high unloaded 'Q' use 660/46 "Litz' wire, (e.g.

)
with H/D = 0.5, a styrene former, and leave about one wire diameter between turns
.... unloaded 'Q' will be >500.

Thanks!
By unloaded Q I meant spark uloaded. I didn't know about H/D ~ 0.5 condition... No wonder unloaded Q of usual TC secondary is below 500 since it is made H/D>>0.5 and without Litz wire.

Uspring

Fri Jan 03 2014, 12:04PM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
Location:
Posts: 711

Q for secondaries without arc load is given by
Q = sqrt(L/C) / R
omitting some other smaller effects. R is the resistance of the secondary winding. A large L and a small C will increase Q, as well as a thicker winding, which will reduce R. A larger L means more windings, and thus a bigger R, so adding more turns might not change much wrt Q. JavaTC calculates these values.
For TCs, the loaded Q plays a much bigger role. A litz wire winding doesn't increase loaded Q to any reasonable extent.

dillon

Sat Aug 08 2015, 05:22PM

Registered Member #54416 Joined: Wed Feb 04 2015, 01:30AM
Location:
Posts: 13

until the spark does break out, its the unloaded q that develops the voltage rise. same for a spark gap coil. put a large toroid to keep the coil to develop a high hv breakout ,but its the q that causes resonant rise until breakout

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