Re: Top-load altering Q-factor of secondary cct

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Gav D <gdingley@xxxxxxxxx>

Hi Malcolm,
if I've got this right the top load can increase current flow in the 
top part of the secondary coil, resulting in a higher voltage and 
giving the appearance of a higher Q, but it's just that more current 
is flowing? Would this increased current effect manifest as a measure 
Q based on bandwidth and resonant frequency (Q = f / BW)? I thought 
there may be a trade-off due to the basic Q-factor equation.

Thanks again,

Gavin


On 10/25/05, Tesla list <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx> wrote:
Original poster: "Malcolm Watts" 
<<mailto:m.j.watts@xxxxxxxxxxxx>m.j.watts@xxxxxxxxxxxx >

On 23 Oct 2005, at 18:49, Tesla list wrote:

> Original poster: Gav D <<mailto:gdingley@xxxxxxxxx>gdingley@xxxxxxxxx>
>
> Hi all,
> I read in a book written by Richard Hull that increasing the top-load
> will increase Q-factor of a TC secondary. I assume there is a limit to
> this set by Q= 1/R sqrt(L/C). Has anyone either experienced this
> and/or know of any theory for why this happens?
>
> Thanks,
>
> Gavin

I mentioned this effect a few weeks ago. Going from no topload to a
certain amount of topload (depending of course on the secondary
design :(  increases the current flowing in the top turns of the coil
which adds to the effective inductance. Beyond a certain point, the
L/C ratio starts degrading the Q again. It happens in practice - I've
measured it many times.

Malcolm