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Secondary Coil Turns
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From: Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: Monday, June 08, 1998 12:37 AM
To: Tesla List
Subject: Re: Secondary Coil Turns
Hi Steve,
> From: Steve Young [SMTP:youngs-at-konnections-dot-com]
> Sent: Saturday, June 06, 1998 10:45 PM
> To: Tesla List
> Subject: Secondary Coil Turns
>
> To all,
>
> In many postings I have read, the general advise is to not exceed about
> 1,000 turns on the secondary of disruptive TCs. For example, Bert Pool's
> excellent "Building Conventional Tesla Coils" states secondary coils should
> be at least 400 turns, but no more than 1,000 turns.
>
> Question: If the length to diameter ratio is kept within reason (3-5:1),
> why not use 1,200 or 1,500 turns? At least this would lower the operating
> frequency which is advantageous, even if secondary voltage doesn't increase
> much. Has someone done experiments which indicate about 1,000 turns is the
> point of diminishing returns?
Yes. It isn't a sudden thing but affects output as noticeably as it
is progressive. For example, an 1800 turn coil wound with that H/D is
a total loser. The reason is that copper losses due to small wire
size become very significant as you cram more turns in. The effect is
noticable on small and large coils. I could have done a lot better
Q-wise had I wound my 17" coil with just 500 turns of thick wire or
500 turns of thinner wire (spaced of course). H/D wasn't much over 2.
I stuck nearly 1000 turns on (closewound) and ended up with a
resonator whose wire losses get a lot worse as a large topload is
added. I may wind it again someday. The problem is that frequency
drops as inductance increases but at the same time, the wire size
which *needs* to increase as skin depth becomes greater is also
decreasing. Knowing what I now do, I would use 1000 turns max. for an
H/D of 5 and proportionately fewer for lower H/Ds.
Malcolm