Re: Perfecting my final design...

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

Hi Paul, all,
               This post is directed mainly at beginners and others
wanting to get a first coil going on a shoestring.

     My very first working coil used a couple of old oil/paper
dielectric (non-PCB!) capacitors which had previously seen service as
smoothing caps in a transmitter power supply. The units were
individually rated at 12kV with a capacitance of 0.25uF. I used them
in series for a total capacitance of 0.125uF. They were big grey
bricks. The coil ran at a rather high frequency (about 300kHz if I
recall) and the primary coil was a single turn of copper tube which
was partially made up of the caps - they were arranged to connect
into the primary without adding any extra tube. Performance by
today's standards was truly abysmal (I much later scored over 5 feet
with the same transformer and extended foil home-rolled caps vs.
around 15") but the coil worked! and gave me my first taste of what
was to come.

     I have no doubt that anyone wanting to violate the Freau power
vs. sparklength limit with microwave oven caps would be seriously out
of luck but there is no reason why a working coil could not be built.
It might not last all that long and long runtimes would be out of the
question but short runs while allowing cooling in between would be on
in my opinion.

     Those oil/paper caps eventually carked it due to the thin
internal connecting wires melting and the dielectric showed numberous
punctures but what did that matter having allowed me around 10 years
of experimenting and delighting friends.

Malcolm

On 16 Jun 2005, at 11:03, Tesla list wrote:

> Original poster: "Paul B. Brodie" <pbbrodie@xxxxxxxxxxxxx>
>
> Christopher,
> A while back, there was a post from a young guy in Israel. I think his
> name is Nir. He used a bank of microwave caps on his coil. Maybe he
> will see this and reply. If I remember correctly, he even had some
> pics on his web site. I'm sorry I can't remember any more than this.
> Does anyone else remember his posts about the coil he was building?
>
> Where did you get those caps? I hate to tell you this but microwaves
> are there for the asking at appliance repair centers, at least they
> have been for me. In fact, thee owners I have dealt with have been
> very anxious to get rid of them They are easily disassembled and the
> transformers, HV diodes, and caps are almost always in good condition.
> Out of the 12 I have taken apart so far, I have only run across one
> bad cap. The repair guys tell me that the control boards are almost
> always the source of failure in microwave ovens and they cost too much
> to replace vs. buying a new microwave. So when this happens, people
> just leave their microwaves at the repair center and they are stuck
> with them. For some reason, junk dealers don't want them. Look on the
> 4HV forum and I'm sure you can find dozens of projects you can do with
> these caps. I feel sure that it won't be a total loss, by any means.
>
> If you have any trouble with microwaves, locating them, identifying
> parts, or whatever, let me know and I'll try to help or point you in
> the right direction. Regards. Paul Think Positive
>
> ----- Original Message -----
> From: "Tesla list" <tesla@xxxxxxxxxx>
> To: <tesla@xxxxxxxxxx>
> Sent: Tuesday, June 14, 2005 7:07 PM
> Subject: Re: Perfecting my final design...
>
>  > Original poster: "Chris Rutherford" <chris1@xxxxxxxxxxxxxxxxxxx> >
>  > I can't answer your question, but I'm slowly building/designing my
>  first > Tesla coil, unfortunately I *may* have just waited about $200
>  on some > capacitors that may be useless.  I purchased 10 * 2500V
>  1.3uF microwave > capacitors, they charge up nicely and produce a
>  nice crack when discharged, > except when thinking about their make
>  up (liquid filled) and their 50Hz > frequency rating, when I start to
>  pulse them in the Khz range they may > start to heat up due to losses
>  etc.  Can anyone advise?  If they're no good > as high voltage pulse
>  capacitors would they be any good in a voltage > multiplier circuit
>  to drive a pulse capacitor? Or should I just use 4 * 4KV >
>  transformers with secondary in series??  Any ideas what I can do with
>  10 * > 2500V 1.3uF 50Hz capacitors in relation to making a Tesla
>  coil?? > > Thanks > > Christopher > > ----- Original Message -----
>  From: "Tesla list" <tesla@xxxxxxxxxx> > To: <tesla@xxxxxxxxxx> >
>  Sent: Tuesday, June 14, 2005 7:02 PM > Subject: Re: Perfecting my
>  final design... > > >>Original poster: "Adam R."
>  <arabraxas@xxxxxxxxxxx> >> >> >>I'd like to go with a large cap but I
>  just expanded it! I am using the CD >>caps (2000v .15uF) and have two
>  strings of 15 for a .02uF cap bank >>total...it does not look like I
>  can easily get some more of those caps >>(cheaply). >> >>Here are the
>  results of the spread sheet, the inductance is much higher >>than I
>  thought. >> >>Diameter of tubing 0.25 >>separation of turns 0.25
>  >>Number of turns per spiral 10 >>Radius inner turn 4 >>Separation of
>  spirals 2 >>length     TOTAL 2.5 >>n            TOTAL 100 >>L
>     TOTAL 3003.5 >> >>Also, shouldn't the two spirals be wound in
>  opposite directions so the >>magnetic field matches? >> >>I'm worried
>  working with the acrylic: I don't have special bits to drill >>with
>  it or saw it so I hope when drilling it won't crack and its only 1/4"
>  >>thick. To hold the copper tubing in I'm using PE cutting board
>  strips. How >>can I bolt the PE down? I'm guessing just extand 1/8"
>  nylon bolts on the >>strips. >> >>The distances btw the two coils
>  will be adjustable so I can experiment >>differing setups. >> >>Even
>  just using two layers of 5 turns (6 or even 6.5"dia center) of .25"
>  >>Cu tubing spaced .25" apart (hopefully enough room to put 1/8"
>  bolts?) >>sounds like it'd work (with the .02uF cap). I'm just
>  worried about using >>thin bolts (1/8") but then that'd lower the
>  risk of fracturing the >>acrylic. (However, the center holes for the
>  secondary are 1/4")....so >>should I shoot for 5 turns? I might even
>  be able to make a crappy mock >>setup and test it with my L meter. >>
>  >> > > >
>
>
>