Re: OLTC update - Poor seconadry Q

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

Hi Terry,

Yeah, I figured that was too easy! :^)

After reading some of the later posts, I "plugged in" your secondary's
parameters into a spreadsheet I use for coil design. The impact of skin
effect and coil resistance drops the loaded Q to about 90. Assuming that
proximity effects for your closewound coil are of the same magnitude as
for skin effect, the Q would drop down to the mid 40's (even assuming a
"perfect" ground to the base of the resonator). Throw in a bit ground
impedance and add some more losses from the Sonotube, and the measured
value is certainly in the right ballpark. Bummer! 

Sounds like you'll need a significantly larger diameter coilform wound
with larger diameter magnet wire to get Q up to a decent level. For
example, using a 30" x 6.5" toroid atop a 20" coilform wound with 35" of
#22 AWG (~1230 turns relatively closewound) should give you about the
same Fo of 38 kHz. However, Q should be closer to ~70 - 80. Like the car
ad says, wider is [probably] better.. :^)

However, a 30 pound system it ain't (any more...).

Best regards,

-- Bert --  
-- 
Bert Hickman
Stoneridge Engineering
"Electromagically" (TM) Shrunken Coins!
http://www.teslamania-dot-com

Tesla list wrote:
> 
> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> 
> Hi Bert,
> 
> First thing I tried.  It made no difference.  Apparently the low Q is
> something with just the secondary/toroid.  I will take off the toroid and
> investigate more...
> 
> Cheers,
> 
>         Terry
> 
> At 07:49 AM 8/31/2002 -0500, you wrote:
> >Hi Terry,
> >
> >I'd bet if you remove the secondary from the primary and re-measure it
> >you'll see a Q more like 200. The primary "gap" is conducting on
> >alternate half cycles, sapping energy from your secondary and lowering
> >the effective Q.
> >
> >Best regards,
> >
> >-- Bert --
> >--
> >Bert Hickman
> >Stoneridge Engineering
> >"Electromagically" (TM) Shrunken Coins!
> >http://www.teslamania-dot-com
> >
> >Tesla list wrote:
> >>
> >> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> >>
> >> Hi All,
> >>
> >> I have adjusted my coil as best I can but the output still seems
"weak".  I
> >> think I now know why.  My secondary Q is only 36.  That works out to a
> >> secondary AC resistance of about 3300 ohms!!  R = 2 x pi x F x L / Q
> >>
> ><SNIP>
> >>
> >>         Terry
> >