[TCML] Q

[Barton B. Anderson]

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 at pupman.com [mailto:tesla-bounces at pupman.com] 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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