# How to rise the secondary?

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From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent:  Thursday, July 02, 1998 1:39 AM
To:  Tesla List
Subject:  Re: How to rise the secondary?

Hi John,

> From: John H. Couture <couturejh-at-worldnet.att-dot-net>
> To: Tesla List <tesla-at-pupman-dot-com>
> Date: Wednesday, July 01, 1998 2:58 PM
> Subject: How to rise the secondary?
>
>   To Ed, Antonio, Bert, and Malcolm -
>
>   Many thanks for all the information regarding the raising of the
> secondary. It is gratifying to know that with the Internet and Tesla List it
> is possible to ask technical questions of this nature and be able to receive
> immediate replies from around the world. Coilers of only a few years ago
> were at a tremendous disadvantage without this type of resource.
>
>   As is typical with TC design, answers to a technical question sometimes
> brings up more questions.
>
>   1. Doesn't changing the coupling (K) only change the time of energy
> transfer for a tuned TC system regardless of frequency? For example with K =
> .20 the energy will transfer for all coils and operating frequency:
>    Transfer time = 1/K = 1/.20 = 5 half cycles.

Exactly. But since Fr is different for different coils, the transfer
time is accordingly different.

>   2. The total amount of energy transferred will occur when the TC system is
> in tune.
>        That is when  LpCp = LsCs
>        What are the equations relating the amount of energy transferred to
> special coupling coefficients?

There are equations in the archives (see past posts from Mark Barton)
describing the lossless case. I've found my coils generally achieve
efficiencies in the 80% range if one ignores trades going back to the
primary for a second round under no breakout conditions.

>   3. If the primary is designed with enough clearance to prevent sparkovers
> between the pri and sec coils, raising the secondary would be unnecessary?
> In other words the coupling is determined only by the sparkover clearance
> limitation. Using insulation instead of air to separate the pri/sec coils
> could be used to reduce the clearance and increase the coupling. But this
> would not change the amount of energy transfer or the length of sec term
> spark.

There is a definite voltage limitation on a secondary. The wire
usually can withstand more than the secondary as whole can - i.e.
winding length vs output voltage usually determines how far you can
push a design. Good field control can improve matters to a point.

>   4. What are the equations relating the quenching characteristics to
> coupling and output spark lengths?
>
>   5. In #1 above the number of half cycles required to transfer all of the
> energy of a tuned TC from pri to sec coils can be found. However, how many
> half cycles are required to properly charge a suitable sec terminal so there
> will be a sec output spark and quenching time is not important?

The scope shows the terminal attains its highest voltage on
completion of the first transfer.

>   6. The point of over/under coupling (critical coupling) is determined when
>        Rp = Rs  How are these two parameters calculated at the time of
> design?
>       The equation  R = Xl/Q   cannot be solved because both  R and Q  at
> high voltage operation are unknowns at time of design.

All my coils are overcoupled prior to spark production. If they were
not, transfers would never go to completion (i.e. the DSB beat
envelope would be absent). I don't think coil Q at high voltages is
substantially different from what it is at low voltages. Scope
observations bear this out in my experience.

Malcolm

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