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Re: [TCML] Q

Hi Gary,
I viewed what specs I could and of course the photo's. Fr came out real close to your statement of 1500 kHz. I figured I was pretty close. For the 5 turns shown, there's also a bit of lead inductance which is somewhat considerable for small inductance primary's. I changed a few primary parameters but it was quick regardless. Basically it's easy enough to determine a near coupling and the rest is just math for the transfer rate. I think in my playing I ranged from 2.2us down to about 1.5us. So, it will be fast.
I would expect hf coils w/conventional coupling figures to be slower. But, helical primary's are just easy at this size and would be common to have a bit more coupling than what is conventional. A the high frequency also adds to transfer rate. So I expect a coil of this size to have a fast transfer rate.
For conventional turn secondary's, I view paying attention to the impedances as a good design but not a must. There is really nothing that can be done for these small coils. If there is small wire and really high frequency, well you just have to accept those losses which can be relatively high for the low power required. The fast transfer rate may help.
Even on a large scale, high turn coils are lossy and it "does" affect output. My 8.5" coil is nearly 1800 turns. Works, but I've done better. It's no surprise to me that my best coil also happened to be the coil with the highest Q and largest wire size. Of course, if someone just wants to add more power, they can of course get good sparks out of most anything.
I remember Terry's work with sec losses. In the overall scheme of things, no it's not worthy of heroic measures. But, higher Q is usually an indication of lower impedances and that's a good thing and it takes no more work than building a lossy coil (actually, building a lossy coil can be more tedious in my opinion).
I just found it interesting how fast the transfer rate was on these little coils. I think considering their size and how lossy they will be, it's probably necessary for decent output. 

Take care,
Bart


Lau, Gary wrote:

Hi Bart,

I've not yet scoped this coil to confirm your xfer time estimate.  I'm curious how you arrived at that figure, since I didn't include detailed specs for primary construction and coupling geometry parameters.  Probably just a set of good guesses based on the photo?

It wouldn't surprise me that high frequency coils with conventional coupling figures have xfer times proportionally shorter. I would guess that it all scales - could be that for coupling value X, 1st notch occurs in Y cycles regardless of frequency?  And I have no doubt that reducing the coupling to an atypically low value would reduce performance for the same reason that it would on a conventional low-frequency coil.  A lower coupling would require the gap to burn for a longer interval for each notch, resulting in higher gap losses.

I'm not convinced that secondary resistance and Q are worthy of heroic measures to improve them.  The secondary current is small and resistive losses are low.  I recall that Terry did an extensive analysis of loss components, and the secondary was not high on the list.  The primary Q however IS vital.

Regards, Gary


-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of Barton B. Anderson
Sent: Tuesday, November 27, 2007 10:19 PM
To: Tesla Coil Mailing List
Subject: [TCML] Q

Hi Gary,

I've been looking at your coil specs a tonight. I don't know if you have
equated it but the transfer rate is really fast at 1.7us! Although this
little coil is similar physically to the norm, that Mhz range really
increases the transfer rate significantly. I wonder how the coil would
work under a more typical transfer rate say in 10us or so?

The only way you can alter that is to reduce coupling. I'm kind of
curious if the high frequency and transfer rate is an area we are
overlooking with these small coils? We always seem to build them
physically the same (scaled down), but we are not accounting for the
frequency and di/dt which is associated with it.

In your case, due to the 38 awg wire size, there will be some large AC
losses. Even though transfer rate is quick, the Q is only about 144 on
this coil. This is what I was trying to explain about high frequency
coils with normal turn ratios.

I kind of doubt a reduced coupling would do better due to the Q and
secondary losses.

Take care,
Bart



--- "Lau, Gary" wrote:
Hello All,

I have finally gotten around to documenting my Bug
Zapper Transformer (BZT) powered coil on my web
site. For those interested, please see
http://www.laushaus.com/tesla/bzt_coil.htm

Regards, Gary Lau
MA, USA


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