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Secondary with thin wire


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From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent:  Wednesday, February 18, 1998 4:32 PM
To:  tesla-at-pupman-dot-com
Subject:  Re: Secondary with thin wire

Hi Antonio,
             There is a second consideration worth noting also:

> From:  Antonio Carlos M. de Queiroz [SMTP:acmq-at-compuland-dot-com.br]
> Sent:  Tuesday, February 17, 1998 1:47 AM
> To:  Tesla List
> Subject:  Secondary with thin wire
> 
> Hi:
> 
> I was looking what I have around to build a small capacitor-discharge
> Tesla coil. I found a PVC tube with 8.8 cm (3.5") of diameter (more 
> than enough, about 2m) and many spools of 32 AWG magnet wire (relay
> coils). By my initial calculations, I think that I can build an 
> acceptable secondary with this rather thin wire, with 1500 turns, what
> results in a winding measuring 30 cm (I don't want sparks longer than
> about this for awhile).
> The inductance would be 20.8 mH, the self-capacitance 10.4 pF,
> with resonance without top terminal at 305 kHz. Considering only the 
> DC resistance of the wire (223 Ohms), the Q reaches 435 (I didn't 
> compute the skin effect and other losses yet). I will have to use 
> five of the spools to complete the required wire length.
> Some advice on how to make this work? Is the thin wire a so serious
> problem? An it is really necessary to dry and coat the PVC tube with
> polyurethane varnish before the winding? (saves a day).

Using the C ratio formula to calculate peak Vout and a guide of 
3'/MV, make sure the instantaneous primary energy you will be using 
can't exceed that figure or you will have sparks tracking along the 
outside of the coil at quite modest k's. I assume a lossless transfer 
when using that guide (i.e. losses are not factored into the 
equation) or the 3'/MV figure should be pushed out to around 4'/MV. 
It is a small matter of making allowances. 

**N.B.  JHC and others - I am *NOT* saying the transfer is lossless. 
However, I have measurably achieved a figure well in excess of 80% 
in a small coil.

Malcolm