[Prev][Next][Index][Thread]
Secondary with thin wire
----------
From: Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: Wednesday, February 18, 1998 4:06 PM
To: Tesla List
Subject: Re: Secondary with thin wire
Hi Antonio,
> 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).
I would expect the Q to come in at no more than 150 with that wire
and probably less. Skin and proximity effects mean a very great deal
when it comes to quality. I have noted the odd experience with
extreme experiments in the past, one of which should be in the
archives from last year. The coil was literally a throwaway. My
current guide for wire size:
a minimum of 3 skin depths at the lowest frequency of operation
(i.e. largest topload you will ever use) for a space wind where
spacing = wire diameter
a minimum of 5 skin depths for a closewind under the same conditions.
4 skin depths is still OK but allows no leeway for experimentation
with larger terminals and the Q starts dropping badly if you do use
them.
I base these figures on measured Q degradation using the best
techniques I have developed for measuring unloaded Q.
Malcolm