Re: Double humpin'

To: tesla-at-pupman-dot-com
Subject: Re: Double humpin'
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
Date: Wed, 06 Nov 1996 22:41:18 -0800
Cc: Tesla-list-subscribers-at-poodle.pupman-dot-com
Tesla List wrote:
> 
> >From hullr-at-whitlock-dot-comTue Nov  5 22:17:31 1996
> Date: Tue, 05 Nov 1996 10:37:59 -0800
> From: Richard Hull <hullr-at-whitlock-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Double humpin'
> 
> All,
> 
> I get the impression that some of our folks think that you get a double
> hump or spliting of frequencies at tight coupling.  Double humping only
> occurs in spark systems when we exceed the point known as "critical
> coupling".  critical coupling has only a little to do with
> actual inductive coupling (about 50%)
> 
> If we throw a fixed gap of a fixed dwell/quench in a system, critcal
> coupling occurs at some fixed coupling coefficient K=X.  If we have a
> variable dwell/quench gap, and a fixed tight coupling, by varying the
> dwell we can make the system go from  below critical coupling to well
> beyond.  In short, critical coupling is a sliding point based on actual
> inductive coupling and dwell/quench time of the gap's realizable
> quenching ability.  In theory we can have a single frequency output (no
> splitting) at k=.65.  This was the struggle in the early days of spark
> transmitters in the 100KW-.5MW class.
> 
> Richard Hull,TCBOR


Richard,

Excellent point Richard! Seems like every time I think I'm beginning to
understand how these things work, mother nature, or you, slap me upside
the head with a dose of reality!

A lot of coilers, myself included, have _lousy_ gaps which quench poorly
and non-repeatably. With longer-than-desired quench-times, most of us
seldom observe the phenomenon you describe! I needed to do a series of
PSPICE simulations to confirm this - I have NOT been able to confirm it
experimentally, since I don't have my high-speed rotary constructed as
yet (a Winter project...). 

The PSPICE simulation shows that, if the gap dwell-time is reduced to
the ideal time or somewhat less (i.e., the end of the first beat IF the
gap were to continue firing), the double frequency humps do, indeed,
disappear! Even if the primary is set to a somewhat lower frequency, the
secondary/toriod will ring up at its single natural frequency ONLY. 

This seems to imply that frequency splitting and secondary coil
flashover _could_ be reduced by consistently quenching quickly enough.
Previously I believed that secondary flashover was caoused by the
secondary being driven to the upper "hump" frequency, which in turn
caused the 1/4 Wave point to be lower on the coil. NOW, I'm no longer
sure that this is actually the case! Or maybe splitting only occurs
during subsequent beats (at lower energy??), but this doesn't sound
right either!! Hmmmm!! What seemed to be so simple before, turns out now
to be another layer to peel on the TC onion!

Thanks again for a very thought provoking post, Richard!

Safe coilin' to ya!

-- Bert --