Jan,
I wouldn't bother with using a synchronous motor for high break rate. By using
a universal type motor, you can vary the break rate with a simple variac.
Alternatively, you can use an induction motor. In some cases the coil
can produce a cyclic beating effect when using an induction motor. You
don't want that to happen. You can vary the RPM of an induction motor
to some degree by varying the input voltage with a variac, although induction
motors are not meant to be used that way.
Dielectric losses in the coil form are not an issue. It simply doesn't make
any difference. A possible reason to avoid paper or PVC forms is due
to possible carbon tracking which can occur due to racing sparks or
secondary strikes. Racing sparks can occur if the coil is mis-tuned or
electrically coupled too tightly to the primary.
Those sewer pipes should be excellent. It's important to apply a varnish
or polyurethane or other coating over the wire on the secondary to
prevent the wire from slipping down on the secondary form, and also
to protect the wire. This is especially important if magnet wire is used.
I'm seen many cases where the wire slipped down on the form and
the wires over-lapped due to temperature changes and it made a real
mess if the wire was not coated to hold it in place.
John
-----Original Message-----
From: Jan Ohlsson <jan@xxxxxxxx>
To: tesla <tesla@xxxxxxxxxx>
Sent: Sat, Jun 30, 2018 3:07 pm
Subject: Re: [TCML] Please review my coil plans
Thanks for your kind input!I realize now that I need a higher brake rate to use more power within a reasonable capacitor value. Perhaps I should go for six rotating electrodes and two pairs of stationary, spaced 150 degrees apart, where I could connect or disconnect one of the stationary pairs for different power levels. And perhaps a synchronous spark gap does´nt provide any benefits using a high brake rate, I could just as well use an asynchronous motor. I wonder if a variable frequency control for an asynchronous induction motor would survive in a tesla environment?I wonder about dielectric losses in the coil form. And I mixed up the materials, I was contemplating polypropylene, which is used for ground sewer pipes in my country and is easy to come by. After all a TC is a RF device, and radio transmitter folks are very conscious of inductor losses in high power applications. But perhaps the streamer losses overwhelms all other losses, so dielectric coil losses are insignificant?And I also wonder about varnishing the coil, as the dielectric varnish will give considserably more turn to turn capacitance, which the radio folks also wants to avoid due to losses. Will a secondary coil survive without varnish?I will be using JavaTC, but I like to have some adjustement possibilities in my construction, when possible. I will try to put up a temporary web site with photos of what little is ready now, the transformer is ready in the tank and the paper insulation will be dried out with heat soon, before the transformer oil is filled and the tank sealed. There will be a small opening to avoid over or underpressure, vented through silica gel to avoid water in the oil. Next I will wind and assemble the ballast inductor. And then the rotating spark gap. My plan is to start with the most difficult parts, if I dont succed there, there is no reason to spend money on the coil parts. Kind regards,Jan
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